HO NG GRAFT & HYDROFOIL

THE INTERNATIONAL REVIEW OF AIR CUSHION VEHICLES AND HYDROFOILS

KALERGWI PUBLICATIONS Steadying wings that skim through turbulent water

Four of the six major U. S, hydrofoil projects now under way are using stabilizing equipment designed and manufactured by Hamilton Standard. They are tho U. S. Navy's PCH (Patrol Craft, Hydrofoil), the Maritime Com- mission's Denison, the Marine Corps' 35-knot Amphibi- ous Assault Hydrofoil, and also the 300-ton, 220-foot AG(EH) now being built for the U. 5. Navy. Hamilton Standard's capabilities in the hydrofoil field are backed by years of success in designing stabilization equipment for helicopters. If the stabilization of hydro. foil "wings" is your problem. write the United Aircraft !nternational representative listed below. '.I

Sole overseas represeiltative for Pratt & Whitney Aircraft . Hamilton Standard . Sikorsky ~ircraft. Nof'den United Technology Centre . United Aircraft of Canada Limited. REPRESENTATIVE FOR HAMILTON STANDARD PROU~JCTSIN ENGLAND: UNITED AIRCRAFT INTERNATIONAL, SARL, 39 AVENUE PIERRE lev de SERBIE, PARIS 8e, FRANCE The new Westlal~dSR.NS hovercraft comrnerzced its initial 'als or1 the Solent on April Iltlz. Capable oJ carryirzg up to 1961 FOUNDED QCTQBEW elzty pcissengecr or 2 torzs of jreight, it has been designed rtse as 11 short rrrrzge pclsserzger ferry or for fire fighting First Hovering Craft ;& Hydrofoil Monthly in the Worl well rrs a search urici rescue craft

NAVAL ARCH TECTS D SCUSS HOVERCRAFT AND HYDROFO r 1WO interesting papers were presented in London on March congratulation for its sincerity. ?'he author's film portrayed 25th I964 at the meeting of the Royal Institute of Naval a hovercraft behaving rather poorly, a fact which the author Architects, and are reproduced in full in the pages of this used to some advantage in presenting the major of the many publication. problems still facing hovercraft designers. The paper entitled "A Progress Report on Hydrofoil Ships" It is interesting to note that the Cinited Kingdom Cont~'ollirrg by Mr E. Ralph Lacey, Assistaut 'rechnical Director, Preliminary Authorities class the hovercraft as an airplane, while Mr Bing- Design Branch, Ship Design Division, Bureau of Ships, Depart- ham considers "seaworthiness" to be the most important ment of the Navy, aclequately met the aims of the author in characteristic. presenting a progress statement on United States Navy hydro- During the discussion which followed the paper, Mr Bing- foil craft. It is regrettable in many ways, although understand- ham expressed his disapproval of the suggestion that hovercraft able, that Mr Lacey was unable for security reasons to give might use a submerged foil arrangement where auxiliary lift more precise details concerning the performance of the USS and improved directional stability and control are required, "High Point". 'I'he paper successfully emphasizes the urgent having indicated in his paper that the hovercraft relies upon need for much theoretical and experimental work in the fields the surface for its support but endeavours to remain detached of seaworthiness (ability of a craft to operate on rough seas from it. at speed with maximum comfort and controllability) and One fact is certain, however, that hovercraft and hydrofoil hydroelastic stability. designs and applications must be complementary. The hydro- The paper of Mr A. 8. Uirrgham, Chief Designer I.iovercraft foil designer need be no more reluctant to use an air cushion Division. Vickers-Armslrongs (Engineers) Ltd, entitled "'The than a hovercraft designer need be to use a foil, should such a tiovercraft Ferry", must earn him unanimous approval and fusion of principles improve craft design and performance.

IN THIS ISSUE ------

People and Pr~jects 4 Editor: Hovercraft Grand Prix 6 JUANITA KAIERGHZ

The Hovercraft Ferry 8 HOVERING CRAFT AND HYDROFOIL is prodrrced by Kolerghi I'irblications, 53-55 Beak Street, London W1. l'eleplior?e: CERrard 5895. Printed in Great Britain by Aquavion's Aquastroll 18 Vi1lier.s Publications, London, NW5, Annzral srrb- scriptiorl : Five Guineas UK and equivalent overseas. A Progress Report on Hydrofoil Ships; 22 USA arid Carrudu $15. There are twelve Is.sues

Contents of this issire are the copyright of Kalerghr Publications. Permission lo reproduce pictures and text can be granted only under written agreement. Extracts or comments ,nay be made with dne acknowledgernenl to Hovering Craft rrnd Hydrofoil. (4 forty-seat A yuclstroll 40-P. ~~rrlherdetails of this 'craft trppecir oil page 18 Ilzterior of the wheelhouse the Aqmuvio/t Aquu~troll40-P

A new company, Scandinavian Hovercraft, Lid, has lust A inodel of a new British hydrofoil has been tested at speed been formed In Norway, and may, later on extend its activities in rough water. The craft, dcsig~~edby Mr Philip Castle and to othel Scandinavran Countrrcs. The company has already Major Michael Trasenter Incorporates a Delta aerodynamic been In contact with groups Interested in starting regular hull of shallow "V" section and narrow sharply swept fuiiy hovercraft passenger services in Western Norway, pa~tlcularly submerged main foils. Great stability is achieved duc to a new with vessels carrying twenty passengers at a speed of 62.5 to simple incidence control system in the bows and the wide 75 mph. beam aft. The craft can be easily beached, berthcd or used for landing alongside. A large manned model is in the process of being burlt.

Sir Eric Mensforth, chairman of Westland Aircraft, has re- turned from a visit to Japan where he had talks with Mitsu- bishi concerning the manufacture under licence of Westland An increasing number of overseas buyers are showing intcr- hovercraft by Mitsubishi plus a general interchange of tech- est in the Aquavit 30 knot hydrofoil manufactured by Inter- national Aqi~aviotiof London. An agency has becn formed nology on hovercraft. to cover the Argentine and Uruguay The firm, called Tracia SA of Buenos Aires, has taken one of the craft for operating a passenger ferry service on the River Plate. Another agency has been formed in Bombay entitled AFCO The technical licence agreement concluded nearly a year ago Ltd, an association of Duncan Macneill and Co. A number of by Mitsoi Zosen with co-licensors Vickers Armstrongs (Engin- Aquavits are in service, on order, and on demonstration In eers) and Hovercraft Development Ltd, regarding the manu- Borneo, Malaysia and Pak~stan. facture of air cushion vehicles has now been formally approved by the Japanese Government. Under the agreement Mitsui has the exclusive right to sell Vickers Armstrongs hovercraft in Japan, South Korea, Taiwan, Okinawa and the Philippines, The first hydrofoil passenger ship designed as an English and can also export vehiclcs to any other country on a non- Channel ferry is maklng its maiden crossing. T11e craft, an exclusive basis subject to the licensor's consent. lnten~atio~~alAquavion Aquastroll 40-E' wbs built at a ship- Hovercraft models to be manufactured under licence are yard in Papendrecht, Holland. Development has cost about VA-1 (experimental); VA-2 (five to ten passengers); VA-3 260,000. The craft will go to the Orkney Isles for one month's (twenty-six passengers); VA-3B (100 passengers); VA-4 (140 trials with tho Orkney Island Shipping Company, and if the cj tons, can carry thirty-two cars plus 130 passengers); VA-5 (300 trials are satisfactory it will be used for passenger services tons); VA-6 (33f tons, for military use); VA-7 (230 passengers). there. Pull details of the craft are given on page 18. LENGTHY and detailed article on "The Next Steps in A River Shipbuilding" printed in the February number of IPyechawy Transport, monthly journal of the Ministry of the River Fleet of the Russian Union of .Federated Socialist Re- publics, contains some interesting inforlnation on Soviet in- tentions in relation to hovercraft and hydrofoils for the cur- rent year. During 1963 experiments were carried out with a new type of hydrofoil, the "Chaika", designed and developed by the Krasnoye Sormovo shipyard. This vessel with a draught on foils of 1.1 metres (3 ft 7 in) carries thirty passengers at a speed of 86 kmh (nearly 50 knots). Its distinctive features are high powcr/passcnger ratio (30 bhp per passenger) and the sub- stitution of water-jet propulsion for propellers, the latter rendering thc vesscl less vulnerable to damage when cruising in shallow waters. Trials carried out with this vesscl on the river Oka showed, however, that a craft with such small foil- immersion and such high speed is unsuitable for use on shallow rivers because it is incapable of negotiating at full speed the numerous sharp turns which are a normal feature of such rivers, and because the consequent frequent reductions of speed (often to the point where the craft becornes a displacement Tlze new Dritish hydrofoil model described on the opposite vessel) imposes intolerable strain on the diesel engines. Another puge disadvantage for a vessel with such small foil immersion is that when it encouriters even small waves such as those set up by vessels passing in .the opposite direction, the shock experi- enccd is intolerable for the comfort. of passengers and crew. It was therefore decided not to proceed with the project of putting the "Chaika" type vessels into serial production. As a result of this experience, it is intended during 1964 to concentrate on tile development oT hydrofoil vessels of the Rakcta type for fast passenger service on shallow rivers. These craft (which were described in detail in the October 1962 issue of Hoveritlg Craft urzd Hydrofoil) will be modified to have a In the rneant~me the Leilingrad Experirnc~ltal Shipyard is foil immcrsion of only 1.2 metres (4 ft) with a consequent re- developing a small hovercraft carrylng only ten passengers on a duction of their speed from 40 knots to 31 knots, and of their totally different prlnc~plcfrom both mcntloncd above. It will passenger carrying capacity from sixty-six to a lower number have a moderate speed ol only 50 kml~(31 knots). IE experi- not yet stated. ments wrth this prove at all enconraglng, the project will be Experience has shown however that if is impracticable-- pursued further. for the present at any rate to use hydrofoil vessels i11 depths of watcr less than 1.2 metres (4 it), so work was carried out during 1963 with an alternative type of vessel, a serni-hydro- plane type which had been developed at Leningrad by the naval constructor Oskolsky. This vesscl has an all-welded hull of aluminium---manganese alloy and draws only 0.4 metres Pravdu of March 26111 announces the production by the (1 ft 4 in) when under way carrying sixty-threc passengers, and Krasnoye Sonnovo Shipyard at Gorki, on the river Volga, of when powered by an M-50F diesel engine of 900 bhp will a new type of hydrofoil vessel, claimed to be the fastest river- develop a speed of 42-45 kmh (26-28 knots). The prototype, vessel in the world with a speed of 110 kmh (68.35 knots). The though not scheduled for completion until 1964, was speeded new vessel has been designed by I<. E. Alekseyev who designed up on account of the unsatisfactory experience with the the first USSR built hydrofoil, and looks much the same as "Chaika", and was, in Eact, completed by the auturnn of 1963. Lhose of the Meteor type. It has a streamlined rocket shaped This opened up the prospect of having fast carriage for hull and carries 150 passengers. Wherc it differs fundamentally passengers, i.e. at speeds of at least 40 kmh (24.8 knots) on from the Meteor, however, and from all other types ol hydro- rivers with depths as little as 0.5 metres (1 ft 7 in). Work has foil hitherto produced in the USSR, is in having gas turbines been proceeding during the past winter on the perfection of instead of diesel engines, and water jets instead of propellers. [his prototype and the correction of defects discovered in the The gas turbines were designed and bu~ltespecially for the course of trials. Final specifications will be drawn up and the purpose in the USSR. The hull is made of all-weldcd light type will be put in serial production to meet a very urgent metal, and more extensive use has been made of synthetic need. materials in the finish and furnishings. The vessel is air-con- The chief advantages concerning hovercraft in the USSR ditioned throughout, and her communications system has bcerr are that thcy can be rised over the shallowest watcr and, per- improved, as compared with that of preceding types by the haps more important, over water on which ice has been provision of a radio-telephone set for communication with formed. An experimental vesscl of the sidewall type was de- passlng vessels. veloped by the Experimental Shipyard at Leningrad in 1962 but 'The new vcssel is thc s~xthto be produced by the Krasnoye was found ~~nsr~itablefor passenger transport on account, Sormovo Shipyard, and special credits for her construction mainly, of her propelling unit, an aircraft engine aerial pro- have been given to the young designers, Vlad~mirIgnatlev, peller. Thc project has not been abandoned however, and Lyudmila Korotkova, Calina Lepilova, Yuriy Garanov and further work will be done on it using other means of pro- Rimma Zhirnova; as well as to the platers, Valeriy Krymov pulsion. More success was achieved with a ground effect and Yuriy Levin; the carpenters, 'Taisiya Pottoratskaya and machine developed by the Krasnoye So~movoshipyard with a Marlya Korostylyeva; and the assembly teams of N. S. Yakov- somewhat original hull-form. This craft is powered by an air- lycva and A. M, Dolgova. It is interesting to note that a large craft type gas turbine and has developed speeds of up to 150 proportion of thc above-named are women. kmh (74.5 knots) carrying fifty passengers. It is intended for The "Delfin" (as the vessel will be christened) is now ready use on the major rivers of the USSR, and the current economic for launching and will carry out trials on the Volga as soon plan prescribes the completion of a prototype for trial in as the river is ice free and safe for ~lavigationin April or actual service by the third quarter of this year. May. She will be ill regular service this summer. The flag goes dowt~on the world's first /?overcraft race, on Lake Nurley Grifin, Canberra, Austrc~lia.Thr stnrtrr's vehicle i~ itself rc~zuscial -- (11% urnplzibious car by Bryan Cooper

A MAJOR factor in the development of automobile design and a special pr~zewent to a craft which made the fastest rut1 ha7 been motor racing. While primarily organised as a -"-45 "ph. The race was not without incident. Most of the entrants sport, the experience which manufacturers have gained in pro- found steering to be a problem, causing many of the spectators ducing high compressiorl engines for racing cars, streamlined to be splashed with water and dust. When engine of me body designs, suspension units, brakes, high performance tYres, craft failed, the craft and driver disappeared beneath the sur- ctc, has led to many improvements in the ordinary productiorr face of the lake. 'rhe driver was rescued. car. And so the world's first hovercraft race has been run. But The question has been asked might it not be possible to race the question remains - who should organise such events? in Ilovercraft In the same way. Not the large, passenger carrying Australia, it seeins likely that bcfore long hovercraft clubs will craft of course, but small craft such as the Hoverbout and be formed. In the UK however, apart from a few isolatecl in- Dynacraft, and others nhich will undoubtedly follow as the stances the idea of home-made hovercraft has not caught on public becomes accustomed to the Idea of buying a hovercraft to the same extent, and in the initial stages it would need some as an alternative to a motor boat or yacht. Racing such craft effort by the lnanufacturers to launch the idea of hovercraft would certainly provide a public spectacle and add to the racing. snterest In hovercraft, and for manufacturers who produced It was to look into such possibilities that Stirling Moss, at speclal racing craft, the knowledge gained might well be a onc time the world's leading racing driver, paid a visit recently way of "improving the breed". to the makers of the [-loverbout to see their machine. Fle ex- The first hovercraft race has in fact already been staged, on pressed considerable interest in the idea, but fclt that a good Lake Rurley Criflin in Canberra, Australia, earlser this year. deal of thought is necessary to work out the regulattons which Organ~sedby the Canberra branch of the Royal Aeronautical would have to be imposed. Minimum hover heights would Soc~ety,the main "efficiency" lace took place over a triangular have to be established, aird if it proved that power units If miles course with competitors handicapped according to ranged greatly in sile, separate classes would have to be de- power, tlrne, and hovcr height. vised, as in motor racing. Stcer~rlgwas shown in Australia to be a problem, and the course would have to be wide enough "Do-it-yourself" hovercraft building has already become an to permit safe overtaking. On the corners, Moss felt that a enthusiastic hobby in Australia, and all the ten machir~es special technique would have to be learned of drifting the which took part-there would have been eleven but one craft in a similar way to a racing car, with additional problems engine failed to start - were built in garages and backyard if two craft entered a corner at the same time. workshops all over Australia. They varied considerably in The construction of the course itself opens up some interest- design and performance, with shapes ranging from darts to a ing posstbilities. It could include water as well as areas of combination of three conical chambers joined togetl~erby a concrete and grass, and low obstacles could erisure that all the tubular framework. Some had as many as three engines-- craft were capable of maintaining the given minimum hover others just one. The mosl popular choice of power unit was height. the two-stroke lawn mower engine. Hover heights ranged from It is of course early days to think about hovercraft racing half an inch to four inches. as a serious sport, but there is no doubt that if the public take Over 10,000 spectators watched the race, which is an Cndi- to buying small craft, as well as building craft themselves, cation of the kind of public interest which can be aroused. there will come a time when owners will want to pit their The winner was one of the smaller craft, powered by a single skill against each other. Useful technical knowledge could be 8 hp motor set at an angle so lhat it provided forward drive as gathered by manufaclurers who decided to build racing hover- well as lift. It reached a top speed of 30 mph. Other prizes craft, and perhaps, one day, the champion drivers of such a were awarded for manoeuvrability and novel design features, sport will achieve the fame of present-day racing drivers. The first hovercraft race in the world has now taken place and has aroused considerable interest and discussion about this new fomof sport. These are some of the cmft which made history. ..

Enfered by the Amberley Hovercroft Group of No 3 Aircraft Depot, Amberley, Quecr~sland,this craft won first prize in the "'l~zgent~ity"contest

Nr Roy Iiuynzond won (1 speciczl prize for driving the fustesf The winning craft was driven by Mr Allen Flawkins, of New craft in the rnain "Eficiency" race. He reached a toy speed of South Wales. It weighed 300 lb (with driver) ond was powerecl 45 mph by un 8 hp motor

@ MI K M.Mcleod's craft, weighing 600 lb (with driver) was This 12 hp crcift, driven by Mr A. L. Ellis, won first prize for I~~wercdby lulvrl mower engines totalling 10 ltp. It cnme second "Manoetrvrobility" and wcls third in the main race in the main race, was highly commended in the "lngen~lity" colltest, (ind was sc>cond irr "Mu~zoeuvrubility" " Figure 1. Colztilzenfal ferry routes

A. E. Bingham Chief Designer (Hovercraft Division), Vickers-Armstrongs (Engineers) bid

Introduction The principle of the hydrofoil was first used towards the end FOI,LOWING a relatively short period of development, of the last century. A number of patents were taken out in the hovering craft, or air-cushion vehicles to give them tl-teir early years of this century and in 1919 a craft capable of 60 generic term, have demonstrated an ability to operate in knots was built and tested by Dr Alexander Graham Bell and moderate sea conditions around our coasts and have become Frederick Walter Baldwin. It was not until after the Second sufficiently well engineered to carry fare-paying passengers. World War that hydrofoils became a commercial proposition, At present the hovercraft is by no means an all-weather and at present these craft have an operational cruising speed vehicle; there are limitations on Lhe height of the waves in of approximately 40 knots. which it call operate comfortably, and seas with regular wave By comparison, progress with the hovercraft has been charac- shapes can present a handling problem. Experience is filling terised by a long period during which tentative ideas for air- in the pattern of the behaviour of this revolutionary craft which lubricated ships (e.g. De.Laval patent, 1883) and air supported relies upon the surface for its support but endeavours to re- land vehicles were proposed, but wlth little practical result. main detached from it. 'The realisation in 1953 of a practical means of containing This paper investigates the aleas in which the hovercraft is the air-cushion has, together with the deep-cushion concept, l~kelyto show a commercial return to an operator, and dis- made the operational hovercraft feasrble.(l) The ten years which cusses certain oC Lhe design problems which require solution to followed encompassed the development of substantial theoreti- corlstruct a satisfactory craft. The paper is based upon studies cal work on the subject, the building in the UK of at least six carried out by Vickers-Alrnstrongs (Engineers) L~rnitedin as- experimental ovenvater hoverclaft, and others overseas, and sociation w~thHovercraft Development Ldmiled. the successful completion of passenger carrying services in A brief reference should be made to the development of coastal waters. This latter achievement is particularly satisfying high. speed over-water craft. In view of the stringent standards required by the controlling Planing hulls made their first appearance in 1870 when the authorities in the TJK where for the moment the hovercraft is Rev. C. M. Ramus built a model which, however, did not pro- officially described as an aeroplane. gress any further for no suitable power unit became available The hovercraft has yet to be accepted as a practical com- until after his death. The first full-size craft was manufactured mercial ferry vehicle. The passenger services carried out to date in 1905. have been experimental and operating reliability has not been . This paper was lead at the Meeting of the Royal Instit~rtionof Naval Archit ccts, London, nn March 25th, 1964 Figure 2. Scat~dirlcrvianferry rolrtcs and the forecasts for l~~t~~retraflic have been exceeded by a small margin.(" Forecasts for the Scandinavian routes show similar growth up to the 1980's. It is not the purpose of this good. Poor serviceability of engines, damage by the sea and paper to discuss the traffic, or the accuracy of the published itoating debris, coupled with the limited wave capability of the lorecasts, but the great and increasing demand for travel can craft used, have caused services to be suspended for short only encourage the introduction of new facilities. periods. However, over 10,000 fare-paying passengers have been Overall trafic figures do not give a realistic picture of daily carried without injury or serious incident, and the general pub- circumstances. On all the routes investigated 75% of the annual lic l-ras shown great enthusiasm for a journey by hovercraft traffic occurs within the period of the five months May to wherever the opportunity occurred. September, and on Inany routes weekend traMc is appreciably To become established the hovercraft must meet three broad higher than week.day traffic. requirements : -- - Current fares charged for air and ship ferries show an (1) Have acceptable economics. interesting pattern. Pig. 4 shows single Sares where passengers (2) Display satisfactory operating characteristics, with sea- are either second class or one class (berths are extra on the worthiness coming top of the lis';. night ferries), and the car fare is that charged for a length of (3) Offer a realistic engineering concept a primary aim l4i ft. A constant fare irrespective of distance is indicative of being a low maintenance requirement. the working of a particular fares policy and due account of [his These three objectives became the subject headings for the must be taken when making comparisons with the calculated first three parts of this paper; the human need for faster over- operating cost of a competitive vel~icle. water travel is assumed to be incontestable.(') Bv reason ol' the heavv and increasing trafic and the current Ipasrt 1 - Econon~icAspect fare' levels, domestic an2 UK to ~or~yirrerrtroutes offer the most attractive area for introducing a new, and as will be The fast hovercraft as at present conceived has a low overall shown, a fairly expensive craft. eficiency, the installed power being in the range 100 to 150 shp Hovercraft economics cavour a low density high value cargo. per ton displacement for a speed of around 80 knots in still air Passengers and motor cars come into this category with mean conditions; when using gas turbine power these figures indicate values as follows : a fuel consumption such as to rule out transoceanic journeys by reason of the inability of a craft to carry sufEcierit fuel. 'The I~overcraftis suited to the shorter sea routes; it shows up to partic~ilaradvantage, in comparison with converrtional ships, where the journey time can be cut by taking a direct route regardless of tides and shallow water; also its ability to load and unload on land enables a saving in turn round time to be made. The short ferry routes in Northern Europe are shown in Figs 1 and 2. Also shown is the projected rail link between Clearly then in terms of revenue per lb weight carried or France and the UK -- the Channel Tunnel; the presence of this per sq H deck area occupied, the passenger gives the greater link completely alters the forecast traffic pattern for the years return. However, conditions may exist where a car-carrying 1972 onwards, the earliest possible date for the opening of capacity is required and the optimum hovercraft Lo accom- the tunnel. modate the same load would be larger than the passenger A remarkable growth of passenger and car traffic over the equivalent and could lead lo radical changes in design as will last decade has been evident on all the short sea routes. Fig. 3, be discussed later. V. W $ hw I cc JT~ where W = disnlacement weight;- h = wave height; W V = craft saeed relative to the water: I :-wavelength. W Waves may contact the cral't at any point over the bottom, inducing vertical and often rotational accelerations to the craft. Far more severe to the local structure and to the detriment of passenger comfort are impacts on the bow and beam area. I,oads incurred when floating on the water with no air cushion are less than impact loads on high-speed craft. A background of manufacturing experience on flying boats and sea planes enables the constructors to contemplate using ESTIMATED CHANNEL aircraft type structures and materials for hovercraft, but the TUNNEL TRAFFIC W high-stress levels permitted in these structures make it necessary to expend considerable design effort to check each component of the structure. Common sense reasoning was used to produce loading cases on the first generation of craft which operated with generally satisfactory results. Impact pressure measurements have not so far been entirely satisfactory, and the development of this technique is essential. At present, much useful data is obtained from measurement of craft accelerations when impacting waves, and from an cxamination of the dents in the craft.

A U.K.- CONTINENT (AIR) U.K.-CONTINENT (SEA)

SCANDINAVIA (SEA1 V)W IL 2

0: W 0 zW V) V) 40"

>. g WLL.

A

Figrrre 3. Trafic from UK to Contirterzt

Part 2 Operational Cl~aractesistics Part 1 arrived at the conclusion that the English Channel routes were likely to be an attractive commercial proposition for hovercraft. In this Part the performance required of the hovercraft is described against the background conditions of U) wind and sea encountered in the area. A similar analytical W 0: procedure to that to be described would be carried out for any 2 other routes; the Scandinavian routes, for example, would (1: certainly prove less arduous. 4 The construction of present-day hovercraft Iias provoked U some expression of doubt from conventional shipbuilders. The r (I: one sidewall type operating is constructed principally of glass- (I: fibre reinforced polyester resin with a marine plywood pas- U-W senger deck. The other amphibious high-speed types are built up from 18 swg or thinner high strength aluminium alloy. The light weight, low inertia and flexible make-up, of the craft results in low impact loadings and permits the use of thin B plating. St~ucluralloading conditions arise in the main from high- speed impact with the sea; the impact load I increases according STAGE LENGTH (NAUTICAL MILES) to the relationship Figure 4. Ferry fare rates NORTH SEA ENGLISH CHANNEL

$1 AVERAGE ROUGH SEA I S CftERbl

I.-C----,------~~--10 20 -- 77--- 200 500 -"700n WAVE LENGTH (FEET) Figure 5. Wave churncteristics

In the interests of passenger comfort, and of n~ini~nuniresis- tance, it is desirable to prevent the llull making any contact with the water. The early concept of hovering craft and the first working models relied upon the hovergap, or daylight beneath the craft, to avoid impact. If craft rolling and pitching, etc., is INCREMENTS OF 50 FEET ignored the mean hovergap requires to be approximately half the wave height, crest to trough, to just avoid contact. In OVER 350 FEET keeping power requirements to a manageable level, project de- signs for craft to operate over waves in excess of 4 ft became OVER 250 FEET larger than the square/cube law of structure sizeiweight would permit in practical terms. This state of afrairs was cliarlged /?igure 7. Wave letlgtll prohability completely by the demonstration that prooled fabr~cextensions fitted to the air curtain nozzles in the metal hull could be made b sulllc~entlyflexible a, deflect readily when mcountering waves From personal obse~vatiorlit is clear that succeeding waves and yet have a sufficient "life" to be an engineering proposi- in a sea have varying heights arid that occasionally waves con- tion. lhe important contribution made by the flexible nozzle siderably higher than the average do arise. Tl~eordinate scale extension, or "skirts", to improving hovercraft wave riding displays units of significant wave height; for a given sample of capability cannot be over-emphasised. On the debit side, skirt recordil~gsthe highest one-third are taken and the average of contact wlth the waler when negotiating waves creates adcli- this batch is ~eferredto as the significant wave height. The tional drag and the permanent increase irr craft frontal area numerical value so derived is a good indication of a wave increases alr resistance. height f~equentlyenco~~nterecl but certainly higher waves must Irrespective of whether flexible skirts are fitted, a hovercraft be anticipated. aligns itself with the mean water surface slope. It follows that The followrng table will be of interest. the hovercraft designer requires some knowledge of wave shape, height, length, and velocity and the contribution of wind speed, fetch, and topographical factors. lielatiotlship with Percentage Fig. 5 shows the wave shape envelope of height and length significant wave occurrence ol' derived using expressions developed by Darbyshire@) for wind Wave height parameter height smaller waves generated waves. 13 f or 1-Isig ...... 1.0 87 H 1 / 10 (1 in 10 average) ... 1.27 96 H max (1 00 waves)...... 1.6 99 1-1 1 / 100 (1 in 100 average) 1.67 99.5 z %I NORTH SEA Fl max (long periods) ... 2.4 99.999

It is important to realise the limitations of the data derived from the method referred .to above. No account has been taken of waves arising from distant storms, ir~creasedheight of waves due to wind against tide or l'rom refraction of waves from estuarial banks or from steepening in shallow water, nor of waves generated by passing ships. Nevertheless it is considered that the techniques now available can be very useful in the initial assessment of wave characteristics. Perhaps more than 011 any olher seagoing cralt, the hover- craft is likely to be affected by topographical influences; the amphibious hovercraft inevitably passes through regions of very shallow water and possibly surl'. Both these circumstances pro- duce steeper and often higher waves than winds generate. Therefore it soon beconies most desirable that the actual con- WAVE HEIGHT (FCFT) ditions on a proposed route arc sampled over a reasorlable Figure 6. Wave height probability period of years. NORTH SEA A wave shape envelope based upon visual observations at sea('>)d~ffers considerably in form from the envelope now pro- posed, Frg. 5, and confirms suspic~onsregarding the tendency BEAM SEAS --- for the human observer to exaggerate wave heights In the seas OVER-WAT6.R SPEED normally encountered. HEAD SEAS - Vk =30 KNOTS The weather ships and borne hght vessels now regularly @ r -1 ."/ measure sea condit~ons Information on the short sea routes, r-i 1 '1- !I Fig 1, 1s available rrom the Brrtish, Dutch, and German statrons.(4) In terms ol wave he~ghtand length some data is shown In F1g.s 6 arid 7.

E NCOUNIERED PERIOD Before decrsions can be taken about the necessary height of (SECONDS) the "hard" structure above the calm water to avo~dimpact in the wave he~ghtsassessed or measured, the response of the I craft to waves requlrcs some attention In much the same way that the freeboard of a displacement ship may be related to wave he~ght and pitch and roll amplitude. Resonance and KNOTS burld-up of amplitude occurs in a certain band width about arr encountered wave period, where the encountered wave period is dersved from the wavelength In the directron of motion div~dedby craft speed. For the short sea routes Figs 8(u) and 8(6) show the fre- quency of occurrence of waves of glven encountered period; by the nature of the definition the faster the craft the shorter the tlme between wave crests in head seas but beam Feas show no apparent shortening. Natural oscillalio~ldata for the present-day family of hover- craft with cushion pressures (or base loading, a measure of

VkS90 KNOTS structural density) of up to 60 Ib/sq ft are illustrated by Frg. 9. I I The ordinate scale of stiffness has units "percentage centre of (lift) pressure shift per degree". Stiffness is calculated from the applied moment required to roll or pitch the craft, i.e. M 0 per cent CP shiftldegree -- X 100 2 4 a 8 (SECONDS) = WX, ligure 8(u). Prcqtiertcy of ertcounters -- North ,Secl where M is moment t,o tilt craft througli 1 degree in roll or pitch; W is craft displacement weight; L is cushior~dimensions either beam or lengthwise. Unless special al.rangements are made a stiffness of 2+"/,n pitch and 14% in roll may be expected. A period of 3 to 4 seconds about both axes will be exhibited by a craft of 150 tons displacement weight. C] ENGLISH CHANNEL Assuming a band width of excessive response to waves HEAD SEAS--- +-p second about the critical region, a craft maintaining 60 BEAM SEAS --- knots cruise speed should meet beam seas which for 6% of the time introduce roll amplitudes greater than the wave anipli- z lo T -r-i QVER-WATER SPEED 3 tude; in head sea conditions there is less likelihood of meeting - .------r-1 Vk :30 KNOTS a - I resonant conditions, about 3 % of occasions in the North Sea W R area and 1 % on the Dover-Calais route. - WO Naturally the well-known ship techniques OF changing course 2 4 fi 8 10 12 Z ENCOUNTERED PERIOD (SECONDS) or speed to avoid excessive pitch or roll oscillations are avail- W able to the hovercraft captain. Quite marked changes of course are required and speed reduction is likely to make matters worse for these routes, the driver may be reluctant or unable to increase speed to move away from this uncomfortable con- dition. ----.. The alternative course of action to changing the encountered Ill frequency is to modulate the craCt characteristics artifically so Vk :60 KNOTS ---A I I Cm7 that in effect the natural period of oscillation is remote from I I the wave period encountered. Most cross-channel ferry ships are stabilised in roll and it may be essential to fit at least roll stabilisation in a cross-channel hovercraft. Elovercraft operating at the time of writing do not have artificial stabilisation although Hovercraft Development Limited (HDL) have conducted some trials at sea of an experi~nerital nature. liesonant oscillations have bee11 encountered, but tl~c non-regular make-up oT succeeding waves has usually prevented this effect becoming objectionable. An exceptional case occurs r--r-1 Vk = 90 KNOTS when meeting on calm waters the lateral wave train of a passing ship in which case a build up of pitch amplitude is frequently experienced. A further operational feature possibly unique Lo hovercraft, 0 -n- 2 4 6 8 10 12 although planing craft might exhibit it to some extent, is evi- (SECONDS dent when operating in bearxi seas. The free-of-the-surface Figure 8(b). Freql~encyof encouitters - - Bizglisll Charzncl hovercraft is constrained only by gravity to accelerate down I3

Comfort Boundary I

PEAK VTRIICAL ACCELERATIONS

'0'

PERIODIC TIME (SECONDS) Figitre 9. Pitch cind roll response

any incline over which it might be hovering, this is true whether the incline is a sloping beach or the side of a wave. Conseque~ltlya hovercraft operating in a beam sea will quite readily operate along the crest or trough of a wave, but should it find itself on the sloping side it will pick up speed sideways remarkably quickly and slide towards the trough and, if cir- FREQUENCY (CVCLES/ SECOND) cumstances are favourable, up the side of the next wave. Row- Figure 10. Comfort Dor~tzdctry ever, this is an r~ncontrolledmanczuvre and technique rnust be sought to avoid it or to render it innoc~~ous. Wind conditio~rsin themselves, apart from the wind-induced waves, considerably affect hovercraft performance. A 20 knot In addition to vibration generated by machinery on board, headwind reduces by a similar amount the speed of a craft an oscillating longitudinal acceleration can occur when operat- capable of cruising at a maximum speed of 80 knots; this repre- ing through head seas. Fig. 11 indicates this condition which sents a considerable increase in journey time or alternatively a diners from calm water in that the normal lo the water surface reduction in range for a given fuel load. Annual distribution upon which the cushion pressure reacts has a rearward com- of winds in the Channel area is : ponent; a half-wave later this has become a forward com- ponent. For a hovercraft 100 tt long travelling in a 5 ft sea the mean wave slope can apply to the craft a deceleration of 0.05 g (1.6 ftlsec2) followed by an acceleration of a similar value as wave crests and troughs deflect first the front skirt and then the rear skirt. At 60 knots this maximum amplitude of oscillation would occur with a frequency of 0.5 cycles/sec. The n~agnitudeof this vibration increases as the mean water slope 10.- 20 increases, so that larger acceleration forces may be expected 20 -- 30 when a shorter craft operates over steep waves; however, for Over 30 the ferry hovercraft which is in excess of 100 St long, waves 5 it high would produce a perceptible deceleration and the 10 ft high waves would border on the unpleasant. In a manner Summarising the position, the craft must be expected to similar to that tor the pitching movements, this vibration may operate regularly in 5 ft waves and headwinds of 20 knots; a be reduced by changing course. statement of the performance in these conditions represents In consideration of the rapid deceleration which may occur actual circumstances better than still air, calnr sea data. if the craft impacts a wave or alights on the water followi~~g The wave and wind conditions have been discussed for a an engine failure, one experimental craft was fitted with rear- desirable route area and have shown the order of problems ward facing seats; in another some seats faced forward and they present. In addition to making the crossing safely, despite others aft, but the evidence is inconcl~~siveas to whether Sor- wind and waves, the hovercraft must give a reasonable pas- ward or alt-facing seating is desirable. senger comfort level. Vehicle noise is now a rnatter of much debate and the government committee report on the subject(') recornmends that hovercraft noise levels be controlled by legis- lation at this early stage in development. Noise, defined as unwanted sound, is inevitable on a high- powered machine such as the hovercraft. External noise eman- ates principally from the air propellers and noise levels are reduced if the tip speed and blade loading is not allowed to cxceed well-understood levels; however, such measures are accon~parried by some thrust loss. To the passengers, gearbox and transmission noise is generally the most noticeable; the science of gear design does encompass vibration and noise and although good gear design practice is well established the behaviour of an assembly comprising gearbox, transmissior~ shafting, and a thin plate structure cannot be predicted at all accurately. At the lower frequencies, 0.1 to 50 cycles per second, vibra- tion gives rise to body discomfort through the human frame itself. Fig 10 shows a criterion for bodily comfort,(^) Analysis Y>*. of comrnents In reply to a questionnaire during the Rhyl- Wallasey experimental hovercraft service in 1962, coupled with vibration measurements on the craft itself, fits well on the diagram. Figure II. Action of the flexible skirt Figure 13. Power rc~qrtiremcrlts

OVER-WATER SPEED (KNOTS) I.'iglirc 12. Wave cal~ability

The sea areas under review, the English CharrneX and ( urrent n~lesfor right of way are contained in the Permit Southern North Sea carry a large volume of traffic; this con- to Fly ~ssuedto the operator of the hovercraft. 'rhi~states that gestion of vessels across the route of a hovercraft ferry service the craft should comply with the various international regula- requires prior consideration. tions regarding collisions for seaplanes on the water, and further that "the 'aircraft' shall keep out of the way of other Sample radar counts obtained by Decca(" show that on the vessels". Dover-Calais route there were seven vessels within 5 miles 'Three aspects of the operational problem have been sur- each side of the direct route at the time the scan was made veyed; wave and wind conditions, passenger comfort in terms on May 23, 1956, and nine vessels in a similar area astride the of noise and vibration, and collision avoidance. However, many Hook-Harwich route; most of the vessels were travelling across other problems may arise, for example difficulties in operating the routes considered. across a shore line, the nuisalzce in the terminal area from The captain of the hovercraft travelling at 60-80 k~lotshas machinery noise and the spray generated by tlie air-cushion, the problem of observing the shipping in this vicinity and or thirdly reco~icilinga lzovercrafl with ?hipping rules in res- Identifying those vessels for which he rn~tst take avoiding pect of lights, safety equipment, and procedure. action. To be able to maintain speed with visibility less than 5 miles it is essential that radar aids are available; probably Part 3 Desigr~Consideratiorrs the best solution for a short journey of up to 80 niiles would No attempt is made to give simple rules lor the des~gnof a be to maintain surveillance from ground stations each end of hovercraft, but overall aspects ol perfo~mallce are examined the ferry route and advise the captain by radio communications and some suggestitrns lor nip roving the behaviour or the craft English Channel sea traffic is concentrated in clearly defined III waves are described. tracks, ships hugglng either the English or French coasts. Fig. 6, concerning sea state in the Channel, shows that waves Ref. (9) defines the route which most ships use and on which of slgnlficant height in excess of 10 ft occur 2% of the time almost all collisions occur; if this area should not he well w~tha wavelength not sholter than 200 ft. Thew waves arising surveyed by the ground radar, ferryborne radar would be re- from winds with a long fetch and blowing up-channel become quired. The problem has become similar to that of air traffic beam seas for the Channel-crossing craft control, but whereas a State, by reason of ownership, controls A llovercraft with a flexible ski11 at present state of design the airspace above it, the three-mile territorial limit restricts recluires a sklrt of vertical height about 8 ft to cope with 10 ft the jurisdiction of France and England to a relatively small waves, and the rema~ning2 ft is made up by cushion-air and portion of the Channel. However, since thirty-SIXcollisions noz7le-air curtain at tlie bottom of a wave trough; at otlrer occurred in the Channel in 1961 and thirty-five in 1962, somc points the skirt is in contact with the water. If the craft re- form of overall control would appear to be desirable. lf an splonds excess~velyto the wave shape, longer skirts would be ~~utlioritywere introduced, the control of ship and hovercraft req lured ferries could be readily integrated. 70 ensure that a craft is stable in side winds and able to accept modest CC; movements arising from fuel usage and Complementary to observing an obstacle the hovercraft cap- passenger and frelght load out-of-trim, the minimum dimen- taln must be able to manceuvre the craft to avoid it. 'Turning rlons of the craft should be at least five tirnes the depth of the radlus on present-day craft ol IF to 25 tons is about 500 yards air cushio~l flexlblc extension plus hovergap. at 45 knots; the larger craft for a more open-water route will Thus the beam will he 50 It with 60 ft more desirable, and an take a radius of about 1,100 yards, since with increasing size average length to beam ratio of 24 gives a length of 125 to the weight of the craft rises more rapidly than the elements 150 ft. which can generate a side force, e.g. propeller thrust or craft Excessive toll osc~llationis l~kelyto be encountered on about side area. For comparison a frigate at 33 knots turns at 475 10% of all trips undertaken and roll stabilisation would be yards radius(l0) and a crow-channel ferry 500 yards at 19 knots. most desirable. Where air-curtains contain the cushion in Above all the hovercral't has an excellent emergency braking depth, e.g. large hovergap, control rnay be applied by operating feature, by reducing lift power and trailing flexible skirts in the airflow valves iri the ducting. Where flexible skirts are used the water a progressively increasing resistance can be secured; liovergap will be small and flow control valves are illeffective ultimately, to avoid an imminent collision by putting the craft 111 producing roll or pitch rotation; an effective method would dowt~on the water, deceleration of 1 g (32ft/secz) is readily be to adjust the length of the skirt below the 111111 as illustrated available, although some distress to passengers could result. in Fig. 11. PRINCIPAL LOADING CASES FROM WAVE IMPACT. SPEED 65 KNOTS WAVES 5 FEET

AMIDSHIPS DIAGONAL CORNERS

I 1 I CRAFT SPEED (KNOTS) I 45 35 65 75 (I -r---i- -4++...4 '--+ I,# I5 1.6 10 12 I1 16 11 I 3'0 4 '0 5 0 6'0 ;0 LOAD racron -!. WATER IMPACT PRESSURE(LBIIN~) DISPLACEMENT WEIGHT (LIIJ/FT') cusnloiv AREA

Stridcture weight

The roll stabilisatioxi installation would lift LIP the slrt, impact load of 1.5 times displacement weight is currently along the length of the craft, on the side tending to rise in applied to ensure adequate strength in large craft. response to a signal from a co~rtrolcircuit using a gyroscope Hull plating pressures increase with craft speed; the effect as a reference for lrorizontal datum. on structilre weight is shown in Fig. 15. The water pressures Waves are not so c~niformthat contact between the actuated qi~otedare distributed pressures, the assumptio~ibeing made skirt and the water would be avoided and similarly in travelling that locally sustained pressures may reach 1.4 times the dis- across waves the skirt will be deflected as waves pass under the tributed value. hull. The energy expended in deflecting the skirts appears as Published data on bottom pressures on planing boats at an additional drag on the hovercraft, increasing with craft sea(11) and aircraft nlodels during ditching trials(l2) give local speed and the extent of skirt deflection, as shown in Fig. 12. pressures considerably in excess of the mean shown here. The latter reference draws attention to the fact that pressure trans- @ The craft speed is ~lniforrnfor waves zero to 2ft high, a ducers placed in the centre of skin panels indicate lower pres- result of operating with an effective hovergap of I ft and as- sures than transducers mounted on rigid frame positions, clearly suming no craf't response. the result ol flexibility of the transducer mounting. 'This prob- For routes across the English Channel, waves in excess of ably gives the clue why hovercraft designed using data similar 5 ft occur for less than 17% of tlie time; as a reasonable choice to that in Fig. 15 have operated successfully without plating for nominal design conditions this wave height is used in damage. Not only does the detail design result in local fexi- defining craft speed. bility, folded thin sheet frames, etc, but the whole structure Power is required to lift, stabilise and propel the hovercraft; is relatively flexible; if the design is based upon rigid body these components of the total power requirement are shown in analysis considerable alleviation results from the flexible nature Fig. 13. ol the structure. Shallow water, tliat is locations where the water depth is 'I'he smaller the dimension the lower will be the manufac- less than 50% of craft length, increases the magnitude of the turing cost ol the cral't. A high-speed passenger-carrying hover- wave-making resistance at the hump speed (Ftr --. 0.65). craft will have installed power of about 100 slip/ton and, to It is important to note that the magnitude of wave making minirtrise size, a cushion pressure as high as "hump" drag con- drag at the "hump" increases as weight2 and that the total siderations allow, say 60-85 Ib/ft"for craft 160fl long. As far power required to ensure tliat hump drag can be overcome is as accommodation is co~~cerxiedthe craft will be space limited sufficient to give the hovercraft a speed of 75 knots in calm and in the larger sizes where motor cars may be carried, a conditions. Increased weight in itself increases the lift power twin deck craft may be worth while. The area of deck available requirement but the increase in wave-making drag with weight Tor accommodation on present-day craft is shown in Fig. 16. is far more serious and may become the basic design considera- Drawing upon the various aspects reviewed it is possible to tion in a moderate speed hovercraft. set up a picture of the hovercraft ferry. An eflicient hovercraft Turning to the craft structure, the efrect of size is shown in is the smallest craft, and hence the cheapest product, which will Fig. 14. The term cushion pressure (displacement weight/ carry the load and perform as desired. Since headwinds and cushion plan area) is an inverse measure of craft size through waves have a niarked effect on hovercraft speed and range it is the constant weight lines; the combined efyect of increasing size essential to take the performance in the average sea condition. is to induce a rapid increase in the moments applied to the If water is shallow over significant parts of the route, engi~ie structure from wave impact and conseqi~ently the weight of power may have to be increased and there could be a mini- material built into it. Thus at a given weight the proportion mum size or maximum c~~shionpressure to permit the craft to talcen up by tlie structure increases at the expense of payload. accelerate satisfactorily. Three loading cases define the overall bending arid torsional Fig. 17 illustrates the trend ol' costs with increasing cusliion resistance requirements. As discussed in Part 2 the load applied pressure for a single deck craft of I50 toris displacement to the bottom plating Prom water impact increases with craft weight. @ speed and weight The formulae currently used give impact Data refer to a passenger ferry carrying about 500 passen- loads of two or three times tlie displaceme~ilweight in the case gers and their luggage and capable of maintain~ng65 knots in of small high-speed cral't, but the analysis is considered in- 5 ft waves. If it is to carry a large proportion oC cars, 28 cars appropriate for large cralt since it indicates loads less than and 140 passengers for instance, the craft must be larger to those encountered when floating on tlie water. A mininiurn accommodate the motor cars, and thus the cushion pressuxe 1s 7----11-- IT- 2500 4000 6000 8000 tolooa PAYLOAO x CRUISING SPEED (TON KNOTS) Figure 18. Work capacity * 5 0 '100 150 200 DISPLACEMENT WEIGHT (TONS) Figure 16. LrJective deck ureu willing to pay a little more than the miuimum lor a sbo~teror more comfortable journey. lower. For minimum operating cost this is not necessarily a Fig. 20, showing traffic on sorrle northern Europe slzort-sea disadvantage. routes, enables the routes likely lo prove attractive to kc Hovercraft first costs, Pig. 18, are high compared wit11 ferry picked out. boats and series production aircraft in terms of work capacity, An illustration of a practical layout follows rn Fig. 21. FOP payload and cruising speed.(l3) 'This state of affairs may be control, the driver adjusts the propeller blade angle to obtain expected to change with technical development and the estab- differential thrust, and over hard ground retractable wheels are lishment of a design from which a number of substantially lowered to prevent side drift. The craft shown here can be similar craft may he built; however, at the moment the first bu~ltusing information available now; however, th13 is hardly cost makes a considerable contribution to hourly operating big enough tor all-the-year opcrat~onon the Channel routes. costs by way of interest on capital, depreciation, and insurance. 'The development foreseen in Fig. 19, shows a larger craft can The method of costing is similar to that used for aircraft since be available in the next year or two. 'This will have substanti- no suitable formulae are available for ship costing. Mainten- ally better economics; the ship and ailcraft ferry operators ance costs are, oC course, less than for aircralt since the struc- have a formidable contestant standing in the wing?. tural and mechanical components are less sophisticated. Cor~clusions Using this procedure, D~rectOperating Costs oC two to three sh~ll~rigsper ton mile are obtained for short journeys, e.g. ferry Practical overwater hovercraft have operated since 1959, but @ stage length of 50 miles, which limits utilisation to about in sp~teof the short period of development, experimetltal sum- 1,500 hours. mer servlces have shown that hovelcraft are seawo~thyand Operating costs are marked up by a factor of 2.5 to give a have public appeal. Increased slze 15 required to enable hover- realistic fare alter paying for the establishment to operate, craft to operate in the waves encountered on the yhort-sea publicise, and profit from the ferry operation, and allowing for routes tn no~thernEurope; the layout and opcratlng features or a real~sticdesign are discussed a load factor. These fa~elevels lie between those currently /I charged by ship and air ferries, Fig. 19. Fares are shown per unit weight based on five passengers and one car. In terms of a fare stage of 25 miles the fares are The author wicihes to thank the management of Vickers- £5 10s Od per car and &1 18s Od per passenger. 'These fares Armstrongs (Eng~neers)1-imited and Elovercraft Development can be maintained ~f 60% of the overall capacity throughout L.im~ted for permission to pul~lislithis paper, which is based the year is mainta~ned,and with seasonal trafic variations this upon the work carried out by then staff, and wishes to express may be a d~fficultposition to hold. Clearly, hovercraft should his appreciation of the considerable help rcceived from col- be introduced on a route with a high traffic volume, anticipat- leagues in the preparation. ing that there will always be a section of the travellixig public

100 4 PRESENT STATE?&.IIO I ENGLISH CHAMNLI SHlP FERRY FARES FARE RATE

E SHlP FERRY FARES

DISPLACEMENT WEIGHT E CUSHION PRESSURE CUSHION AREA Figure 17. Economic size Figure 19. Novercrufl economics LEQPOLBO RODRIQUEZ SHIPYARD MESSINA - ITALY

Licensed by Supramar A.G. Zug-Switzerland The Greatest Experience in Hydrofoil Boat Building

I-lydrofoil Boats Across The World's Seas 0 20 40 60 8a 100

STACE LENGTH (NAUTICAL MILES1 in 15 Countries (C Figure 20. Truflie vmlrinie - References (I) C'OCKEKLLL,C. S.: "Notes on the Design of High Speed Surface Craft", Hovercral't Limited Report No 1/ 57. (2) GABRIELLI,G., and KARMAN,'TII. VON: "What Price Speed?" Meclianiccll hngineeriizg, October, 1960. (3) 'The Channel Tunnel Study Group Report (1960). (4) ROLL,DR H. U. : Drr11scIz~r Wetterdier~st Seewafterami (1956). (5) DARBYSHIRE,M. : "Forecasting of Wind Generated Waves," Enginecrirtg, April Sth, 1963. (6) BARNABY,K. C. : Btrsie Naval Arclzitectrlre. (7) WII.SON, SIR ALAN:'lhe Government Committee Report on the Problem ol Noise. (8) SINGI.ETON,W. 7'. : "Ride and 1-landling --The Ergono- mics Approach", A~ntomotiveIlesign Engineering, July, 1963. (9) Collision in the English CI~nrinel1955-1961. Decca Radar Limited. (10) LAMB,P. M. : "Hovercralt Navigation --.The Operational Problem", The Jour~zal of the I~zstituie of Navigatiorl, October, 1960. (1 1) Du-CANE'.,P. : TIZC IJlanirzg Perforrncmce. Pressures arzd Stresses in a Nigh Speed 1,aunch. (12) "Some Hydrodynamic and Structural Aspects of Design for the Ditching of Landplanes", RAE l'ech. Note No Aero. 1848 SME 380 (November, 1946). (13) TRII.LO, R. L.: "What Price Hovercraft?" Flight Inter- national Air Cushion Vehicles Supplerneri/, August 22nd and September 26th, 1963. ANY KIND of SHIP REPAIRS The Aquastroll 40-P is the second geizeratioil craft followii~g upon the Aquavit which was descr;bed ill this p~bliccltio~tirt lunuury 1962

Length ... ..+ 12,16m---39ft 11 in Extreme breadth ... 5,66m-18ft 7in Depth at step ... 1,301~--4ft 3in Draught at anchor i. 2,30 m --- 7 ft 7 in Draught at speed . . . 2 1,15m-3ft 9in Load capacity .. . 40 passengers Number of crew . .. 2-3 Engines ...... 2 Boeing Turbo-Mar~negas turbines, type 502-10 MA 270 hp each Speed ...... * 32 knots - 37 mph - 60 kmh Range ...... t 180 naut mlles -- -C 210 st miles - It_ 330 km Fuel ...... D~esel oil, 380 IJS gall- 320 Imp gall - 1.450 1 Fuel consumption ~brox65 IJS gall/h -- 55 Imp gall/h -- 250 l/h

THE HYDROFOILS The Aquastroll 40-P has a main hydrofoil, two front foils and a stabilizer. This combination of foils maintains the craft's stability under all conditions. Even sharp S-turns can be made at full speed without danger of the craft overturning. The foils do not protrude sideways from below the hull and this enables easy mooring and allows the craft to come alongside other craft without special precautions. The foils are rigidlv fixed to the hull by bolts, aad they are not adjustable, ?heesystem bcing autostabilizing. The front foils are suspended in rubber blocks which absorb vibrations and damp possible shocks. Generally driftwood does not damage the foils or the propellers which are adequately protected. In the rare case of hitting a rock at full speed, the foils will break off without damaging the hull.

The twin-lead 24 volt system is insulated from the hull. 'She batteries have a total capacity of approximately 300 Ah. The installation comprises a complete set of navigation lights, anchor light, two search lights, two head lights in the how, cabin, engine room and wheelhouse lighting and an inspection light. The wheelhouse contains the engine instruments and warning lights, a compass, chart table light, stabilizer position indicator, windscreen wipers and air horn. It can be equipped with wireless and loudspeaker, and a VHF transmitter can be installed in the pantry. The main foil, tog ther with the two compensating bow foils and a stern stabiliser the patented Aquavion foil system auto-stability under all sea conditions. Giving a high manoeuvrability, the foils are also non-protruding, allowing simple mooring alongside quays or other craft. Add to this low passenger cost per mile, 40150 seat capacity and gas turbine engines giving speeds up to 30 knots, and you have . . .

the first British Hydrofoi designed specif ica economics sea transport with speed and safety. 8 INTERNATIONAL AQUAVlON (CB) LTD

40 ST MARY AXE * LONDON EC3 Telephone : AVEnue 651 11 PROPUISION the batteries are carefully separated from the rest of the craft The craft will be powered by two Roeing 502-10 MA Turbo and provided with independent ventilatiorl, like the fuel tanks. Marine gas turbines of 270 hp each and will attain a speed The hull is made of non-corroding seawater-resisting light of ri-- 32 knots. The propeller shafts are made of stainless steel alloy. and arc supported by cutless rubber bearings. The engines are The passenger cabin has two lavatories and a paritry in the also flexibly mounted, to eliminate vibrations and sound trans- forward part, and two side entrances just aft of these. There mission to the hull. The turbine intake and exhaust ducts are is an emergency exit in the aft wall of the superstructure. The irlsulated acoustically and, where necessary, thermally. flooring will be covered with boucl6 and coco mats near the entrances. The cabin is thermally insulated, and is provided with THE HULL luggage racks. It contains one bench for seven passengers aft, The Aquastroll 40-P is built according to the rules of Bureau ten benches for three passengers and four folding chairs with Veritas and Lloyd's Register of Shipping. The hull is divided back rests, situated against the forward wall. The seat& are into three main watertight compartments by two transverse made of foam rubber, the backs of Wairlock, antl they are bulkheads: fore peak and engine room, passenger cabin and covered with Saran cloth. 'l'he benches are provided with arm aft peak. The fore peak is separated from the engine room rests. The cabin will be provided with forced ventilation, and by an airtight partition. Longitud~nal watertight bulkheads may be heated with hot alr. form lateral compartments at the sides of the passenger cabin, 'The wheelhouse has one door on each side and contai~~stwo engine room and the fore peak. All compartments can be bilged adjustable seats for pilot and navigator with a chart table ancl by a hand bilge pump. The aft peak 1s used to carry luggage. space for a w~relessset in between, antl a folding clrair against The hull is protected by rubber fenders. and for safety's sake, the aft wall. HOVERCRAFT LEADERSHIP

Only four years have passed since Westland's Saunders-Roe Division designed and built Britain's first hovercraft, the experimental SR.NI. Yet to-day, the Company is offering the most advanced range of high-speed, amphibious hovercraft available anywhere. Sizes range from 7 to 374 tons, and load-carrying capacities from 20 to 150 passengers. In development trials, during which it has to-date covered allnost 100,000 passenger miles, the 27-ton, 70-passenger SR.N2 has given the firs.t demonstration by a large hovercraft in Canada, and operated highly-successful experimental passenger services between Southern England and the Isle of Wight, and across the Bristol Channel. The world's largest hovercraft, the SR.N3 (illustrated), has started its proving trials, prior to delivery to the British lnterservice Hovercraft Trials Unit for evaluation in a number of over-water and amphibious operational roles. Confident in future prospects for this revolutionary transport vehicle, Westland already has the 170-ton, 600-passenger SR.N4 in the advanced project stage. This craft will be able to operate fast, all-the-year-round ferry services for passengers and cars across the English Channel.

high riding H 0 V E R C R A F T

WESTLAND AIRCRAFT LIMITED YEOVIL SOMERSET ENGLAND - by E. Ralph Lacey Assistant Technical Dirwtor, Preliminary Design Branch, Ship Design Division, Bureau of Ships, Department of the Navy, Washington, DC

Introduction and Backgrotrnd to demonstrate the practicability of the concepts. This ship, the It is six years since P. R. Crewe presented before this Institu- HS Denisorz (Pig. I), was designed and built by Gmn~manand tion his paper entitled "The Hydrofoil Boat: Its History and is now engaged in a programme of demonstrating its capa- Future Prospectsw.(') During that period, the United States bility at several Atlantic and Gulf ports. Government has intensified its interest in craft supported by Passenger Ship Prototype, EX$ "Denison" hydrofoils. Therefore, this paper will be a progress statement Description from the United States. The Denison is an 80-ton, 60-knot ship with surface piercing Emphasis on Ocean Goirlg Crafl main foils and a submerged tail foil. Reference to the three The principal impetus to hydrofoil development in the United view drawing Fig. 2 shows that the main foils are a develop- States from 1947 to the present has been the US Navy Depart- ment of the William Carl runabout design. The single tail strut ment's research and development programme. About four supports the submerged tail foil and encloses the power shaft- years ago, the Navy accelerated its programme of hydrofoil ing to a single pod which carries a supercavitating propeller. development. The reasons for this increased emphasis are re- All foils and struts retract by rotation so that all parts can be lated to the desire to increase the speed of surface units to keep lifted clear of the water for cleaning and maintenance. The pace with the ever-increasing speed of other forms ol weapons, main power is provided by a General Electric MS240 gas but particularly with the hope that hydrofoil craft would pro- turbine rated at 14,000 continuous hp. In its present configura- vide a more effective platform for coping with the high speed, tion, the Uenisolz requires about 10,000 hp to operate at 60 continuously submerged nuclear submarine. knots. 'The hull and transmission is designed to permit later Therefore, the emphasis in the Navy has shirted to hydrofoil conversion to an 80-knot foil system it" this appears desirable. I) craft which are able to perform in the open sea and to increas- Sea Stute Capability ing the speeds of hydrofoils beyond the conventional limit of The Denison has a stability augmentation system, which approximately 60 knots. The statement was made in Ref. (I) actuates flaps on the main foils and changes incidence of the that operational hydrofoil boats were likely to remain below stern foil. According to early reports, the ship has been able 100 tons for sorne time to come. This seemed to be a most to remain foilborne in very short steep waves up to 8 ft in logical statement based on the evidence at hand. We now find height with this system operating. The control system is criti- ourselves, however, making a maximum effort to prove that cally necessary in order to remain foilborne in long following hydrofoil ships of several hundred tons are practical and can seas. In rough water, the ride is quite comfortable with the have a useful role in naval planning. most noticeable motion being the lateral accelerations. Peak Maritime Admirzistratiorz Programme accelerations which have been measured are 0.45 g vertically At about the same time as the Navy accelerated its pro- and 0.40 g laterally in seas which were estimated to be 7 Et in gramme, the US Maritime Administration, encouraged by the height Fig. 3 indicates approximately the type of wave con- results of Navy research, decided to vigorously explore the ditions in which Deni~onhas operated foilborne and the cor- possibility of increasing the speed of ocean transport through responding speeds of operation. Reduced speeds in waves over the use of hydrofoil ships. Ref. (2) is a study made by the 2 ft high are necessary to avoid cavitation on the foils. At Grumlnan Aircraft Engineering Corporation for the Maritime wave heights over 5 it, rurther speed reductions are considered Administration. Based on this study, the Maritime Administra- tion decided to build an experimental prototype hydrofoil ship m

Figure I. NS "Denison" foil-borne on builder's trictls Figure 2. Three-view drawing oJ HS "Derlisolz" This paper was vead at the Meeting of the Royal Institrrtion of Naval Avchirects, Lorzdorz, on March 2.5111, 1964 ---" GYRO IMPUT ----- ROLL IMPUT "a*.- HEAVE IYPUT

AFT ACCELEROMETER WE SE

Figure 5. Diagram of a typical submerged foil control system

which should restore the designed efficiency. Figure 3. Speed versus wave height experience with 'The principal data on Denison are given in 'Table I. "Denison" Hydrofoil Patrol Boat Prototype, US9 "Big11 Point" to be necessary to avoid excessive motiorls and bull impact with In 1958, the Bureau of Ships began the design of the first the waves. US Navy operational. hydrofoil patrol boat, USS High Point, The testing of the sea state capability of Denison is con- PC(H)-1. This ship is to perfonn inshore anti-submarine duties tinuing. Therefore, the data shown in Fig. 3 should be con- and in addit~outo its capability lo go at high speed in rough sidered to be very approximate pending the accumulation of water on its foils, it is required to have a fairly long range more experience in rough weather. and excellent seakeeping ability in the hull-borne mode of Propeller Difficulties operation. In the first few months of operation, Denison was plagued Selectio~zof Foil System by Fatigue failures of its supercavitating propeller blades. This A surlace piercing foil system, with automatic controls, and difficulty has been reduced by new propellers with thickened a submerged foil system, were studied and debated for this blade sections. This has cost some propulsive efficiency, how- ship. However, the foil-borne sea state requirements were so ever. The Navy, the Maritime Administration and Grumman stringent for a craft oC the size conte~nplatedthat it was deci- have co-operated to obtain a titanium propeller for the Denisorz ded that only a submerged foil syste~nwith automatic controls could meet the performance requirement. This decision was reinforced by the very successful performance of one of the Navy's tcst craft, Sea Legs (Fig. 4). This 5 ton craft with a sub- ENISON merged foil system in canard arrangement had been demon- strating sea-going performance in excess of any other craft its Draught(hul1) ...... 6.2l"t Span over foils ...... 45.0 ft Draught hull-borne - foils down ...... 15.4 ft Designed displacement ...... 80 tons Designed speed foil-borne ...... 60 knots Designed hull clearance foil-borne ...... Foil-borne power-one MS240 gas turbine 14,000 hp continuous 20,000 bp take-off Take-off speed ...... 27 knots Designed speed hull-borne ...... 10 knots

Figure 4. US Navy submerged foil test craft, "Sea Legs" Figure 6. Artist's concept of "High Point" muin foil Strucr~rreand Matrrials The hull of PC(H)-I is built of an aluminium with superior resistance to salt water corrosion and is all-wcIded. Integral plate-stiliener extrusions were extensively used For decks and portions of the sides and bottom not having escessivc curva- ..I ture. Fig. 7 shows the contiguration of the extrusions. The foils and struts are built up with ribs, spars and pliiting similar to aircraft wing construction. The material oC the foils and struts is a structural steel of 80,000 psi yield which is weld- able. It is not corrosion resistant and must, therefore, be coated For protection. An extensive investigation and test programme of possiblc foil coatings was carried out to select a coating which would provide no entry of salt water and would adhere under severe conditions of cavitation and high velocity flow. Figure 7. Extr~idedaluminium plate and stiffener The coating selected was oC the neoprene type. This coating has so far been unsatisfactory. It did not adhere to the Coils even under static conditions of salt water immersion. It has not size. The foil system designed Tor PC(H)-1, therefore, is as yet been determined why service experience does not match nearly as practicable, a scaled-up version of that tested on Sea the laboratory results. It is possible that surface preparation of the steel or the method of curing after application is at Legs. fault. It' the conditiolis of application are too exacting for the The struts in the foil system retract vertically into the hull, average shipbudder, another coating may have to be sought. thus reducing draught for hull-borne operations. Inspection, cleaning or other maintenance of the foils and struts can only Propeller Di~ctrlrics be done by divers or by drydocking. PC(H)-I in early trials has been experiencing difficulty with the after propellers. After very lew hours of operation the Arrtorncttic Controls blades have pitted and cracked. An intensive investigation is, The Automatic control system for PC(H)-I receives craft therefore, under way to improve the wake conditions in way of motion input Crom a sonic height sensor at the bow and from the after propellers and to redesign these propellers for greater roll and pitch gyros and vertical accelerometers. (See Fig. 5.) strength and better adaption to the wake conditions. The computer portion of the control system then transmits High Point has successlully completed her preliminary accep- signals to control the hydraulic actuators which move the flaps tance trials (Fig. 8). She exceeded her designed Coil-borne speed on the forward and after foils to maintain height, pitch and roll on trials using somewhat less than estimated power. These attitudes within very close limits. The control system also limits trials did not require opera ti or^ in rough water. In the early the vertical accelerations and orders contouring of waves too part of 1964, High Poitlt will complete extensive special trials high to avoid hull contact. It also permits banking in turns to for the Bureau of Ships to determine how well she meets her reduce side loads on the struts. performance goals in rough water. ll~rllForrn Table I1 gives data on High Point which can be released at The hull form oC PC(H)-I does not make any particular con- this time. PI cession to its marriage with hydroloils. Two characteristics, long hull-borne range and excellent hull-borne sea-keeping, re- Conudirrtl Hydrofoil Ship Prototype Another programme to adapt large hydrofoil craft to naval quired selection of a hull with low resistance at a speed-length use is under way in Canada. The Royal Canadian Navy has ratio of 1.00 to 1.20 and a hull with proven ability to operate recently decided to proceed with design and construction of as a boat in very rough weather. Models were studied with a a 180 ton anti-submarine hydrofoil ship prototype. This ship chine aft and with a moderate step amidships. These features will employ a Coil system which is entirely surlace piercing and made a very slight improvement at take-off speed but were ol canard configuration. This programme is being watched with harmful to endurance at lower speed. Therefore, a hull form interest in the United States because the novel approach may resulted which had no step and carried a round bilge all the very possibly develop into a more economical type to construct way to the transom. Proptclsion System Powering ol PC(H)-1 on the foils is by two Bristol-Siddeley Proteus gas turbines rated at 3,100 hp each for continuous operation. Gas turbines were chosen principally because of their very high power to weight ratio compared to any other type of prime mover. At the time of the design, the Proteus engines were the only thoroughly marine adapted gas turbines in their power range. The turbines are located aft, taking air down the trunks used to house the retracted struts and discharging exhaust directly aft through the transom. The power shafts lead forward to right anglc bcvcl gears at the top of each strut, in a propulsion pod and then to counter-rotating propellers at each end of the propulsion pod. Counter-rotating propellers were selected to reduce the gear size and hence the pod diameter. The smal!er diameter propellers also increase the range of foil depths that can be utilized without propeller broaching. Fig. 6 gives an impression of the power transmission and main foils. To meet the hull-borne endurance requirement, it would not be feasible to use the gas turbines lor propulsion. Their fuel rate at low power is far too great. Therefore, lightweight diesels are employed for the hull-borne mode of operation. The engine installed is a Curtiss-Wright (lomerly Packard) rated at 600 hp lor continuous operation. This engine is connected to an out- board drive on the transom. The outboard drive is steerable through 360". It also rotates about the axis of the horizontal shaFt for retraction prior to take-OR. Figrtre 8. "High Poitrt" foi!-borttc, on brtildrr's ~rials The total foil area is about 500 sq ft and the three foils are I TABLE 11 geometrically similar with an aspect ratio of 3. The plan- US"HIGH POINT," PC(H)l --DIMENSIONS AND DATA iorm has considerable sweep and taper. The sweep is desirable Length overall (hull) ...... 115 ft 9 in to delay cavitation and to facilitate shedding of debris. It also Maximum breadth (hull) ...... 31 ft 1 in reduces impact due to re-entry from a bkoached condition. The Draught (hull) ...... 3CL9in foil section is a modified NASA series 16. The modification Draught hull-borne, (oils down ...... 15 ft 4 in consists ol a minor thinning forward to facilitate foil fabrica- Draught foil-borne ...... 6 ft 7 in tion. Displacement, full load ...... 108 tons Lift of the toils is varied by incidence control rather than by Designed speed ...... Over 40 knots Raps. Two considerations led to this choice. Torsional dellec- Foil-borne power, contirl~~ous...... 6,200 bhp tion caused by flaps tends to reduce the flap effectiveness. Hull-borne power, continuous ...... 600 bhp Added stiffening to take care of this deflection would lead to a weight disadvantage. In addition the limited space in the trail- ing edges makes it difficult to install controls. Although the conlrol power lor incidence controlled Foils is high, there is a saving in drag lor equivalent changes in lift. and yet retain satisfactory sea-keeping performance without The autopilot is similar in principle to that on High Point. need of automatic controls. Fig. 9 is an artist's conception of In this ship the sea state requirement is greater than that of the Canadian design. High Point and the limiting vertical acceleration is specified as 0.25 g as compared to 0.50 g for High Poitzt. Large Hydrofoil Research Ship, AG(EH) Propulsion Sysrcm The US Navy has under construction at the Puget Sound The propulsion system for AG(EH) consists of two General Bridge and Drydock Company in Seattle, Washington, a 320 Electric gas turbines of 14,000 bhp continuous rating, connec- ton Hydrofoil Research Ship, AG(EH). This ship is intended to ted by shafting and gearing to two supercavitating propellers permit investigations of the performance at sea of a large at the aft end of propulsion pods on the main foils. This trans- hydrofoil ship. It is also intended that operational testing will mission scheme is designed to accept double the horsepower be done to determine its suitability for various naval roles. in the subsequent high speed version. Air for the main turbines Design and preparation of contract plans and specifications is introduced at the top of the deckhouse, and flows over a Tor this ship were done by the Grumman Aircraft Engineering bank of sheet metal spray separators. There is a dam for solid Corporation under direction ol the Bureau of Ships. water separation and four right angle turns before the air The ship, when built, is to operate in the subcavitating speed reaches the engine bellmouths. This complicated system is regime, which is arbitrarily thought of as less than 60 knots. necessary to minimize the amount of salt reaching the turbine However, the design provides for subsequent doubling of power blades, since performance deteriorates rapidly as salt deposits and replacement of the foils with a high-speed type. The hull, build up. therefore, is designed for wave impacts at 90 knots. Two Curtiss-Wright 700 hp diesels drive two outboard drive Foil Systcm units, port and starboard, for hull-borne propulsion. These The foil system is fully submerged and automatically con- units are steerable through 360" and rotate about their hori- ..*trolled to permit operation in the highest possible sea state zontal drive shafts for retraction while in the foil-borne mode. compatible with the size. The foil arrangement is of the con- Srrucrrire and Matcricrls ventional type with 907, of the weight carried on two main The hull structure will be welded aluminium with extensive foils fonvard and the remainder on a single foil aft. This use of integrally stiffened extruded aluminium planks. Certain arrangement is easier to stabilize longitudinally in the non- points of concentrated loading, such as strut foundations, will contouring mode of operation which will be required of the be stiflened by high strength steel fittings. high-speed version. The stern foil and strut rotate about a The hull shape of AG(EH) is designed to minimize the vertical axis for steering. All foils and struts rotate about structural loadings due to wave impacts. The bow shape has horizontal axes to retract completely clear of the water. Com- been developed with this purpose paramount. Bottom dead- plete retraction makes shallow draught operation possible hull- rise is carried all the way to the transom with a similar objec- borne and greatly decreases hull-borne drag with consequent tive. increases in speed and range. However, the most important The foils, struts and pods will be welded assemblies of steel advantage is the ability to clean and inspect the foils and the with a yield strength of 100,000 psi. Foil actuation system and to make minor adjustments or pro- Fig. 10 is an artist's concept and Table III gives dimensions peller replacements without resorting to dry-docking. and data.

TABLE I11 PRINCIPALCHARACTERISTICS OF AG(EH) Length over all (hull) ...... 212 Tt Maximum breadth (hull) ...... 40 (t Draught (hull) ...... 6 ft Span over foils ...... 71 ft Draught hull-borne -foils down ...... 25 ft Designed displacement ...... 320 tons Designed speed foil-borne ...... Over 50 knots Foil-borne power - 2 General Electric 28,000 bhp continuous LM 1500 gas turbines 40,000 hp take-off Hull-borne power - 2 Curtis-Wright diesels ...... 1,400 bhp continuous Foil arrangement - Two foils forward - 90% of the weight One steerable foil aft - 10% of the weight

The schedule oE construction for AG(EH) calls for com- 1 Figiire 9. The Canadian anti-submarine hydrofoil skip pletion near the end of 1965. I"igiircs 10. The 11ydrofoil reseorch ship, AG(EH)

Landing Craft There are a limited number of towing tanks in the United Hydrofoils show promise of solving some of the problems of States which can test at iull-scale speeds up to 50 or 60 knots. speeding the landing of troops and material in amphibious The high-speed channel at David Taylor Model Basin is one. operations. One experimental craft built with this objective is Another is the high-speed basin at Langley Field, Virginia, the LCVP(H) Highlar~dcr.This craft has four retractable, sur- which is now the High Speed Phenomena Division of the David face piercing vee foils and can carry about 8.000 Ib to the beach Taylor Model Basin. The Convair Division of General Dyn- at 40 knots. A more recent programme will produce two types amics has a 60 knot tank. The Davidson Laboratory at Hobo- of hydrophibians for use of the marine Corps. The first of ken, New Jersey, has recently raised the speed of one oP its these, the LVHX-2 built by FMC Corporation, has successCully tanks to 60 knots. For speeds over 60 knots, the only facility demonstrated its ability to carry 10,0001b of cargo, retract its is an outdoor tank under NASA control a1 Langley Field. This foils to negotiate the surf and extend its wheels to proceed on tank rapidly accelerates the tow carriage to 80 knots and then the beach. It is capable of 40mph on the highway. The foil permits the carriage to coast at decreasing speeds. Lift and system is surface piercing forward and submerged aft and is drag data can be obtained up to 80 knots, but the lack of a combined wit11 an automatic control system (Fig. 11). steady state speed makes observation 01 cavitation rather un- satisfactory. Model Testing of Very High Speed Foils Simili/rcde for Cavitcrtiot~Eflects New Foil Testing Eqriipmcr~t Experience with two large hydrofoil ship designs confirms Several different approaches to solving the probkm of mode1 that the lilt and drag characteristics of a hydrofoil system can testing cavitating Coils have been tried recently. The Grumman be predicted very closely using aircraft design techniques as Aircraft Engineering Corporation has constructed a whirling modified Cor the near surface effects. However, the prediction tank or 100 in diameter which spins to produce water velocities of cavitation inception by analysis oC pressure distributions is up to 100 knots. At this peripheral velocity the water is sub- not so successful in three dimensional cases. The prediction is ject to a radial acceleration of over 200 g. The water surface in particularly inexact for regions involving intersecting struts the test tank, thererore, is very nearly vertical. Models are in- and foils or propulsion pods. Neither is the pressure distribu- serted horizontally into the water flow. In this test method, both tion over flapped surfaces sufficiently well understood to make cavitation and Froude numbers can be simultaneously simu- cavitation prediction feasible. lated by proper selection of model scale. Disadvantages are the For this reason, one of the more important objectives of very small scale of the models, less than 2 in chord, and the testing a foil system in model size is to explore the cavitation fact that the model runs in its own wake. Observation of situation and to make necessary changes to clean up the flow cavitation is possible only from the "upper" side ol the model. as test results indicate. Nevertheless, this facility has proved to be very useful in com- paring foil characteristics and has also been useful in design To duplicate cavitation conditions in model scale, it is neces- work. sary to reproduce the cavitation number,^ , which is defined as : Another approach has been that of The Boeing Company, which has employed a specially designed jet-driven hydroplane as a towing carriage on Lake Washington. The model mount and dynamometer are located forward in undisturbed flow. There is a high percentage of time when the water is very calm where Pa = Atmospheric pressure in some portion of the lake. The system permits use of a Ph = Water pressure due to depth reasonably scaled model and by continuously recording data. PC = Pressure in the cavity (vapour pressure) a large number of data points can be obtained in a short period v = Freestreamvelocity of testing. The system has not yet been perfected, however. p = Mass density ol the fluid Good data has been obtained up to 50 knots, but testing Examination of this formula indicates that a reduced scale between 50 and 80 knots has been marred by a slight porpois- model in open water will require almost full-scale velocity to ing action of the hydroplane. duplicate full-scale cavitation numbers. Ph, which must vary The Bureau of Ships has had two modest test facilities built as the linear ratio to reproduce the surface efTects, has a small which will lower the atmosphere pressure during loll testing. L)L influence on the cavitation number. PC can be changed to One of these consists of a towing carriage system installed in some extent by control of the water temperature, thus chang- the Lockheed Underwater Missile Facility (LUMF) at Sunny- ing the vapour pressure. vale, California. LUMF was originally built to investigate k. Figrt re 13. Sripercnvitulir~g foil ritzdc,r lest irt rhe vciriable pres-

underwater ejection of Polaris missiles. Atmospheric pressure technique was employed by the Canadian Naval Rcsearch over the water surface can be lowered to a few pounds per Establishment prior to building Brirs &Or. Grurnman, prior to square inch. A wave maker is also incorporated. A recent completing De~risori, built and tested a scale model called alteration to the facility permitted installation of a towing Grcot E.rpec/n/ions. As previously mentioned, the US Navy system. Recently put into operation, it has not yet been fully High I'oirzi (PCH-1) was the outgrowth of tests on a similar calibrated and checked out. foil arrangement in Scci Lc>ys. Another tcst dcvicc which the Burcau of Ships now has is a Descripiio~iof "F'rc,sh"- 1 circulating water flume with variable pressure over the test This need for a manned model becomes more acute when section. 'Illis was designed and built by Hydronautics, lnc., of venturing into the relatively unkno\vn region of superve~ltilat- Kockville, Maryland. The most important feature of this device ing or supercavitating foils and speeds between 60 and 100 is its ;lbility to remove air bubbles from the water during the knots. In anticipation of this need, the Bureau of Ships has ;L, yycle so that the water in the test section remains clear. This been developing a high-speed test craft for hydrofoil systems, IS done by passing the water through a very low velocity sec- called Fresh-1 (Foil Research Hydrofoil Craft). Fig. 14. Design, tion in which the average downward velocity oS the water is construction and initial testing have been done by The Boeing less than the terminal rise velocity of all but the very smallest ('ompany. This craft is designed to test foil systems with three bubbles. A number of tine mesh screens serve to catch and or four struts arranged in either canard or conventional dis- coalesce the small bubbles into larger ones. This test device is tribution of areas and with up to 807h of the lift on the main in operation and is producing good quality data. It is possible foils. The catamaran configuration of hull was chosen to facili- to test complete foil systcms simulating 500 ton ships at 80 knots tate this flexibility in foil location. l'hrust is provided by an with both Froutle and cavitation numbers matching full scale. aircraft fan-jet engine to avoid complications in propulsion Visual observation and photography of the cavity flow is pos- arrangement with various roil locations. The vehicle carries ex- sible I'rom all sides. Foils and foil systems can be oscill;ited in tensive instrumentation and recording equipment lor data col- heave or pitch during testing to obtain data for stability cal- lection relative to motions, velocities and accelerations, control culations. Fig. 12 is a view of the upper portion of the variable positions, propulsion, navigation, and autopilot functioning. pressure flume. Flow is from the lel't thn)ugh the glass-enclosed This data is obtained on magnetic tape and can be put through test scction to the bubble elimination tank at the right. The a computer for thorough analysis or through an oscilloscope pump, driven by a 1,000 hp electric motor is at the bottom of lor "quick look" analysis. Since the craft is expected to be the loop and, therefore, not visible in the photo. The planar used principally for submerged foil investigations, it is equip- motion mechanism for oscillalion of models under test can be ped with an automatic control system designed to be readily seen above the test section. Fig. 13 shows a supercavitating Coil adaptable to the requirements of widely varying foil systems. under test. The craft structure is designed to meet test conditions up to The accelerated hydn~foilprogramme has made it necessary 100 knots in state three seas. Crew safety has been stressed in I to add new testing equipment at the David Taylor Model the design. The structural integrity ol the hull and cabin takes Basin at Carderock, Maryland. This equipment is principally into consideration the loadings due to various attitudes of crash concerned with the need to make new types of tests in the high- which can be predicted as the result of system failures during speed channel at speeds up to 50 knots. Included are a wave- test. maker. a planar motion mechanism for measuring motion and It~iiitrlIlerno~rsircz/ion Foil Sy.sie17i stability derivatives, a pitch-heave oscillator For studying un- The initial foil system Tor Fresh-I is intended primarily to steady elrects on foils, a 1,000 hp propeller dynamometer lor demonstrate that the principal goals ol the hull, propulsion, I supercavitating propeller investigation and increased capacity control system, instrumentation and foil mounting system have in thc analogue computers to cnable study of 6" of motion in been met. The first foil system, therefore, is referred to as the hydrofoil craft. "demonstration foils." Thcsc foils are three equal area foils arranged on three separate struts. One strut includes a flapped High Speed Test Craft for Foil Development rudder for steering. The foils have base-vented cambered para- Emplovmo~i(1s 11 Design Dcvrlopmozt Tool bolic sections. The slnlts are also blunt based parabolic sec- fi In the course of design of a large, expensive hydrofoil ship, tions. These toils have been demonstrated on Fresh-l in a it often appears prudent to build and test a manned model. canard arrangement and in a conventional arrangement. Speeds This increases confidence in the adequacy of the design and slightly over 80 knots were obtained in both configurations and gives needed insight into craft responses in a seaway, and quite satisfactory foil-borne flat turns and.banked turns.were made often reveals defects which are easily corrected in design. This at these speeds. LOW SPEED INTERMEDIATE SEED

HIGH SPEED Figrirc, 14. High-speed test craft, "Freshv-l Figrirc 15. Dillgram of trtrt~silJoil opertrriotz

Description of Accident Near the conclusion of thcse demonstration runs, in the TABLE IV canard configuration and at a speed of 70 knots, Fresh-l went out of control and rolled completely upside down. The three HIC;II-SIJEF.DHYDROFOIL TEST CRAIT ("FHESII"--I) - crew escaped with relatively minor cuts from the glass of the DIMENSIONSAND DATA blown-in windshields. The major damage to the craft was to Length of catamaran hulls ...... 46.0 St the Can-jet engine which suffered considerable delormation of Length overall ...... 53.0 Ct the first stage blading and corrosion damage elsewhere. The 4.0 fl electrical and electronic equipment in the control system and Beam at deck, individual hull ...... the instrumentation were put through an immediate drying-out Breadth overall ...... 22.0 It process and will be salvaged with only a minor percentage of Full load displacement ...... 35,800 Ib replacement. The hull, cabin and foils were undamaged. Light displacement ...... 17,330 Ib Cnltsc of Accidcr~t,from Slibsequctzt Atznlysis Maximum speed (structural limit) ...... 100 knots The instrumentation recording tape was undamaged and Maximum engine thrust ...... 18,000 Ih has made it possible to analyse the sequence ol events during Continuous r~tingthrust at 100 knots ...... 13,000 Ib thc accident and to determine the cause. This analysis revealed Turbine fuel carried ...... 7,470 Ib that the incidence settings and flap trim settings tor this par- Number ol' I'oils (demonstration foils) ...... 3 ticular run were such as to seriously reduce the control effec- Area oC each foil ...... 7.45 sq ft tiveness of the flaps. This situation pennitted a gradual in- Aspect ratio-foil ...... 7 crease in height during the run which the autopilot was un- able to correct and which was not detected by the pilot until Span-foil ...... 4.72. I't all three foils were very nearly broached. With the foils in a Thickness ratio-(oil ...... 0.10 near broached condition, the craft lacked both lateral stability Thickness distribution ...... parabolic and rudder effectiveness. It, therefore, went into a divergent Camber-foil ...... a=l.O yaw to starboard which the pilot was unable to check with 1 Sweep () chord) foil ...... , 18" rudder action. The large yaw angle coupled with the inertia Flap h~nge forces due to deceleration resulted in complete overloading ...... At 70% chord and stall of the port foil and a rapid roll over to port. Needless to say, this type oC acc~dentwas not [oreseen during The transit foils for Fresh-1 are being cast in a solid, high. the design of Frcsh-I. The critical lesson learned is that a foil strength propeller metal known by the trade name of Super- system in a broached condition should retain both stability in ston 40. This metal was chosen for-this particular application yaw and steering effectiveness. Th~sshould not be a particularly because ol its corrosion resistance and high Catigue strength. dlficult design requirement to meet Cor any foil system. A complete discussion of the design of Fresh-l is contained "Ant1c.r" Type of Foil Sysretn A third type of high speed foil is being studied for possible in Refs (I1) and (9.For completeness, a tabulat~onof charac- teristics is given in Table IV. testing on Frc,slr-l at a future date. This Coil employs a true supercavitating section. To enhance its strength characteristics, "Trc~nsit" Type of Toil .Tystenz however, an extension has been added to the foil base. This Another high-speed foil system is being designed and built extension, or "annex". remains entirely unwetted within the for Fresh-1 by the Grumman Aircraft Engineering Corporation. cavity at high speed. This Coil type is relerred to as the "annex" This system will also be designed for 80 knot operation. The foil (Fig. 16). The foil system includes a large take-off flap for configuration will consist of two main foils and a tail foil with increased lilt coefficients up to about 30 knots. At higher speeds 907L of the weight on the main foils. The tail strut and foil this flap retracts into the cavity. There is a smaller split flap will rotate for steering control. Control of lift force will be by on the lower side of the lifting surface for lift control at cruise change of incidence of all three foils. The designed speed puts speeds. A third ilap on the upper surface acts as a spoiler to these Co~lsinto the cavitating regime. However, the foil sec- reduce liCt at high speed. The foil system is designed to operate tions are not of supercavitating type. Very thin subsonic air- fully ventilated. The strut, therefore, is blunt based and its foil sections are used and by control of load distribution, the design includes side flaps to induce ventilation and to provide cavitation growth is encouriiged to begin at the tips and with an air path to the proper points on the foil. 4 increase in lift coefficient, to envelop the foil toward the roots The design study of the annex is intended to check the (Fig. 15). Because it is hoped that the loils will provide a hydrodynamic characteristics by model testing and to determine smooLh transition between all-wetted and cavitating conditions, the structural and mechanical Seasibility of the foil and its com- they have been called "transit" or "transiting" foils. plicated control system. SPOILER FLAP- / ANNEX /

TARE-OFF rn

TYPICAL SECTION

CAVITY @-- 7@57<<3 &// $/>\- CRUISE SPEED CONTROLLED LIFT REDUCTION AT HIGH SPEED Figrtre 16. Diagram of ar2rzc.r foil opera ti or^ I 0oWoozio 40 3ko 4Ao 4Ao DESIGNED FULL LOAD DISPLACEMENT-TONS Figrcrc 17. Maximum wave height for continuous foil-borr~e operation versus hydrofoil ship size

Sea State Capability of other important qualities. It should have a degree of tear resistance or notch toughness at normally experienced tempera- Nrcd for Mennirigflrl Pcrformarzce Data tures. As desirable qualities, the material should be light in The particular feature of hydrofoils which gives them an weight and yet have a high modulus of elasticity. The material advantage over other watercraft is their ability to maintain a should also be able to resist the erosion of high velocity water high speed in rough water with minimum motion. Yet this very and the erosion due to cavitation. feature is one about which there is the least factual informa- Materials investigations have eliminated all but a few mater- tion. Scientific data on the motions of hydrofoil craft in a ials. Several structural steels can be used but must be protected specific sea condition are not easily obtained. The US Navy against corrosion and erosion by a coating. High yield ship- hopes to gather this type of data on each large hydrofoil ship building steels up to 100,000 psi yield are available now and as it is put through special trial periods. The difficulties, how- 120,000 to 130,000 psi material may be only a Cew years away. ever, are the expensive instrumentation of the craft, the lack This steel can be welded without great dificulty and requires of a wholly satisfactory wave measuring apparatus and the no heat treatment auter welding. Aircraft structural steels can usual refusal of the weather to co-operate during a scheduled be used with higher yield strengths and are weldable, but with test period. somewhat greater difficulty, especially in thicknesses of 0.75 in S~cmmarvof Available Information or greater. These steels require stress relieving in a furnace Using what data is available. the empirical chart of Fig. 17 after welding, which is an expensive complication and limits the has been prepared. This shows the relationship between ship size of single weldrnents. size and wave height at which foil-borne operation is con- One corrosion resisting steel, 17-4PH, with a strength of sidered to be possible. The several curves represent three 165,000 psi is a possible choice. Although nomally corrosion general types of foil systems. The submerged foil curve is sup- resistant, this steel is known to be subject to corrosion when ported principally by computer studies of various designs. This standing in motionless sea water for a period or time. There- type of data supports the opinion that maximum wave going fore, if it were to be used uncoated, the foils would have to be performance is obtained with the fully controlled submerged kept retracted whenever the ship was at anchor or at a pier. foil system. It is interesting to note the increasing wave heights For use at very high speeds, the material may not be satis- that can be negotiated by a surface piercing system which em- factory in resisting erosion without a coating. ploys an automatic stabilizing system. Titanium appears to be'very attractive in almost all respects Fig. 17 does not make allowance for several factors which except cost and difficulty of fabrication. If the increasing use should enter into a rigorous comparison of the sea state ability of this material reduces its cost and improves the methods of of various hydrofoil craft. Speed maintained is one factor welding, it could very well be the best choice of hydrofoil which should be considered. The data used to form the chart materials. includes craft with design speeds between 30 and 60 knots. The list of other materials which have been considered is However, the fully submerged foil craft are expected to be able long, and the reasons for rejection at this time may quite to maintain full power up to the wave heights indicated, since possibly disappear in a future material development. the curve is essentially an expression of practical wave clear- ances that can be engineered into the designs. The surface Propulsion Systems piercing curves are considered to represent full power opera- Gas Turbine Prime Movers tion For craft with design speeds up to 45 knots. The power plant and method of obtaining thrust for large hydrofoil ships presents many problems for which the best Foil Structural Materials solutions are not yet apparent. The prime movers for the foil- The perlormance of large hydrofoil craft can be greatly im- borne drive almost certainly must be gas turbines in order to proved if a very high strength material can be used for foil obtain the required power in a light weight. Gas turbines being and strut construction. The ideal qualities for a foil material developed for hydrofoil ships, utilize existing aircraft jet do not exist in any one material known today. High strength engines as gas producers, with specially designed gas turbines permits the use of thin foil sections to permit high cavitation- to convert the gas energy to rotative power. The choice of free speed and also permits high aspect ratios which reduce engines of this type is not large, but permits a selection of + drag. The qualities of the material must permit use of the high powers in combinations of one to four engines from 1,000 hp strength, without failure due to fatigue in salt water or due to to 80,000 hp with few serious gaps. The jet engines were not stress corrosion cracking. The material should be corrosion designed with marine service primarily as a criterion. This resistant in sea water under service conditions. It should be necessitates replacement of magnesium external parts with a reasonably easy to weld to full strength without deterioration more salt water resistant material. Protective coating of the blading against salt water ingestion is also required. Testing of the larger engines is being done to determine the effective- ness of these coatings and to determine the effect of using light diesel fuels in the marine environment. A future development which would be desirable is the regenerative type of gas turbine to obtain a lower fuel rate 1.0 and to extend the useful power range of the engines into the hull-borne powering requirement. J v Geared Transmissions The only truly feasible method of transmitting power be- 5 0.8 tween a gas turbine in the ship and the propeller at the foil W V location appears to be by reduction gears, shafting and right IL(L W angle bevel gears, as has been done in the designs of Deriison, o TULlN 2 TERM HYDROFOIL High Point and AG(EH). A further useful refinement may be u CLd=.39 R=l d=18O E 0.6 - to take the final speed reduction in the propeller pod by use - dlc z.85 NASA TR R-93 of a planetary gear system. In order to keep the weights and -I sizes of such a gear system within useful limits, it is necessary to use pitch line velocities and tooth bending stresses as high as any ever used. To discover whether the geared transmission 0.4 1 I I I I I can be applied to higher powers, a 50,000 hp unit is being built 0 10 20 30 40 50 for testing under full torque and rpm and with deflections VELOCITY-KNOTS applied to the strut. A high power planetary gear is also being Figure 18. Lift versccs speed for a typical sicpercavitatir~gfoil designed and built for test. The transmission design for to illustrute the "Lift Break" AG(EH) has also been tested in this manner. These tests will determine the practicability and life of such high powered systems. The time between overhaul of geared given the general classification of supercavitating. If the cavity transmissions is expected to be about 2,000 full power hours is fed air in some manner, it is referred to as superventilated. which is comparable to that of gas turbines. These are short True supercavitating foils are designed to spring a cavity from lives in terms of usual marine practice. their leading edges. The cavity is intended to extend over the High Speed Propellers top of the foil and beyond the trailing edge to collapse well The marine propeller becomes a marginally satisfactory astern. The leading edge and the bottom shape of these foils thrust producer under the high speed and power requirements determine their lift and drag. The upper surface can be any of hydrofoil craft. At about 40 to 45 knots the all-wetted pro- shape which remains clear of the cavity. The difficulty with peller begins to have serious cavitation problems. At these these foils is in controlling their lift as they go from the all- speeds, the supercavitating propeller is also difficult to design wetted regime at lower speeds or at low lift coefficients to the for fully cavitated operation. At higher speeds, the supercavitat- fully cavitated regime at higher speeds or higher lift coeffi- ing propeller can be designed for satisfactory efficiency. How- cients. The character of the lift curve changes abruptly when ever, there is no proven method for analysing the stress or unwetting occurs. The lift coefficient is reduced to one-half and vibration characteristics of its highly loaded, wedge shaped the slope of the lift curve is also reduced to one-half. Fig. 18 blades. The failures of the Detlison propellers were of a fatigue is a portion of test data illustrating the lift break. The desired nature. Arbitrary thickening of the sections or use of a better solution would be to have the foil become unwetted before material may solve the current problems without increasing take-off and to be able to vary the lift for speed and sea con- the basic knowledge of how to design these propellers. A great ditions after take-off without falling back into the wetted con- deal of hard work needs to be done to enable the use of super- dition. Induced ventilation of the foils is being studied with cavitating propellers with complete confidence. the objective of promoting earlier unwetting and maintaining it over a wider range of speeds and lift coefficients. The annex Water let Propulsion foil described earlier is intended to do this. Water jet propulsion offers the best immediately available approach to solving many of the hydrofoil machinery prob- The base-vented foil is designed to operate with the venti- lems. This is a system in which the turbines drive pumps loca- lated cavity only at its base. This foil also suffers a lift break if ted in the hull. Water enters the struts and is pumped as high either its upper or lower surface unwets. The desire in operat- velocity jets above the water line and directed astern. The ing this foil is to keep the surfaces wetted. The tendency of system does not promise to equal the overall efficiency of this foil to cavitate from the leading edge is no less than that gears and propellers until speeds in the 80 to 100 knot range of the conventional airfoil section. However, the pressure distri- are reached. However, some loss in range or payload may be bution for a given thickness is equivalent to that of a much acceptable in order to gain the water jet advantages. It should thinner airfoil. This, therefore, might be called a cavitation be less expensive, with longer life and be easier to maintain. delaying foil. Study is continuing of this foil type as a pussi- The pumps for the system should be specially designed to bility for moderate increases in speed beyond 60 knots. match the craft characteristics and must be of light weight. The transit foil appears to exhibit little or no lift break. Induction of the water at the strut and internal flow design There is concern, however, as to whether the partially cavitated must also be very carefully done. Design of the system must conditions can lead to foil damage from erosion. strike a nice balance between a high volume jet and a high velocity jet. The high volume design is heavier but more Hydroelasticity efficient. Hydroelasticity is a word recently added to the lexicon of A thorough design of a large hydrofoil water jet system is naval architects and particularly to that of hydrofoil designers. now being undertaken for the Bureau of Ships by Lockheed It may briefly be defined as the equivalent to aeroelasticity, Aircraft Corporation. The design study will include tests in the except that the fluid is water rather than air. The dreaded LUMF variable pressure towing tank to study internal flow. failures due to flutter and divergence are the extreme mani- festations of aeroelasticity. Recent experiments have shown High Speed Foil Research that hydroelastic flutter is possible. Ref. (9 is the first demon- The search for a foil system which will be satisfactory for stration of which the writer is aware. Other experiments such speeds over 60 knots has been the impetus for much of the as those of Ref. (10) leave no doubt that hydroelastic effects hydrodynamic research in the past four years. The premise has must be considered in the design of high performance hydro- been that the high speed foil cannot avoid cavitation and, there- foil ships. The method of analysis which predicts aeroelastic fore, must be of a type which is efficient while heavily cavitated. effects has not been successful in predicting hydroelastic pheno- Foils which are designed to operate with a massive cavity are mena. In Ref. (lo) a method of analysis was developed which conservatively predicted the flutter speed of simple, non-cavitat- small commuter craft are in commercial operation in the New ing strut forms. More complicated arrangements and cavitating York City area on runs of about 20 miles. There is indication forms have so far resisted successlul flutter analysis. At present that fleets of such craft may be used to transport passengers to designers preCer to model test their designs at high speed to the New York World's Fair, starting in April, 1964. A seventy- gain confidence that serious hydroelastic effects will not occur. five passenger hydrofoil ferry is under construction for service C, A considerable amount of theoretical study and testing is being in Puget Sound. This 35 ton craft will employ a submerged carried out with the goal of reaching a satisfactory method of foil system and be gas-turbine powered. solving hydroelastic design problems. Concluding Remarks Useful Load This paper has reviewed the programme of hydrofoil ship The useCul load of a hydrofoil ship may be defined as the development in the last few years in the United States. The sum oC the payload and the fuel weights. In the case of military limits of size have been extended and there is reason to believe ships, the practice in the Bureau of Ships has been to include that further growth is entirely possible. Some of the immediate in payload the armament, ammunition and all equipment such problems in developing these larger craft have been touched as radar, sonar, fire control and radio which are necessary to on. The success of sizes beyond those described in this paper elrectively employ the armament. The useful loads of the High may require that the importance of the programme justify Poir~tand of the AG(EH) are slightly less than one-third of the greater expenditures in development of engines specifically for full load displacement. In the case of commercial types of hydrofoil ships and the development of high strength material hydrocoil ships, the useful load will be considerably greater. and lightweight equipment comparable with the special marine This is because the military ship must include items of weight service environment. in the full load which are not necessary on the commercial The author would like to emphasise that most of the material ship. Examples of such items are standby electrical generators, used to prepare this paper was available to him because of his machinery Cor hull-borne cruise propulsion, a larger crew and position in the US Navy Department, Bureau of Ships. Never- accommodations lor the crew for extensive periods at sea. It theless, the opinions expressed are the author's own and do not should also be pointed out that the designs oC the two large necessarily reflect those of the US Navy. hydrofoil ships reflect a degree of healthy conservatism. This is a natural result of the desire to ensure the successful demon- stration of an important new type.

Ultimate Size of Hydrofoil Ships Several quite comprehensive studies have been made by air- craCt companies, of which Ref. (2) is one example, which indi- cate that hydrofoil ships with displacements between 500 tons References and 3,000 tons are entirely Ceasible irom an engineering stand- (1) CREWE, P. R. : "The Hydrofoil Boat: Its History and point and can be expected to have useful load ratios similar to Future Prospects", TRANS.INA, 1958. those expected of today's 100-ton designs. Such studies assume that a degree of engineering and development effort is put into (2) "Study of Hydrofoil Seacraft", Report Number PB161759 w these large designs which is comparable to that given to a new Office of Technical Services, US Department of Com- large transport aircralt. As evidence that the development of merce, Washington 25, DC. larger hydrofoil ships approaches this degree of effort, it should (3) WENNAGEL,G. J.: "Characteristics of the US Maritime be noted that the two large military hydrofoils produced in the Administration Hydrofoil Test Vehicle", SAE National United States are expected to have cost between $50,000 and Aeronautic Meeting, 1961. 1670,000 per ton of full load displacement when they go into service. These costs, in part, reflect the fact that the ships are (4) SCMROEDER,J. CRAIG: "The Design, Construction and one-of-a-kind prototypes which are pushing at the frontiers of Flight Test of the HS Denison", Proceedings, National design knowledge and technology. This cost factor may quite Meeting on Hydrofoil and Air-Cushion Vehicles, IAS, possibly deter any programme involving very large sizes until September 17th- 18th, 1962. the demonstration of more modest sizes at sea has established that hydrofoil ships can indeed perform vital naval tasks better, (5) CYPHERS,R. J.: "The Design and Development of the cheaper, or uniquely. AG(EHjn, Proceedings, National Meeting on Hydro- foils and Air-Cushion Vehicles, IAS, September 17th- Without consideration of the cost effectiveness or economic 18th, 1962. factors involved, it is the opinion of the writer that the next progression in size of military hydrofoil ships should not exceed (6) LACEY,RALPH: "The Navy High Speed Hydrofoil Test 1,000 tons. This conclusion takes into consideration the prac- Vehicle", SAE, National Aeronautic Meeting, April 3rd- tical propulsion machinery which can be available in the next 6th, 1962, paper No 522A. five years and the materials which will be satisfactory for foil structure in that period. (7) KENNEDY,ALAN: "The High Speed Hydrofoil Test System (Fresh-1)". Proceedirigs, National Meeting on Hydro- Commercial Progress foils and Air-Cushion Vehicles, IAS, September 17th- 18th, 1962. The use of hydrofoil craft as passenger ferries continues to expand in many countries of Europe and more recently in (8) OAKLEY,OWEN H. : "Hydrofoils -A 'State of the Art' Japan. The Russian hydrofoils include sizes up to 100 tons and Summary", Proceedirlgs, National Meeting on Hydro- some reports claim that their numbers approach 100. Japan foils and Air-Cushion Vehicles, IAS, September 17th- has at least a dozen craft of 25 to 60 tons in service. These lath, 1962. ships fill a need for high speed transportation which is not adequately met by other types of ships, aircraft, automobiles (9) HILLBORNE,D. V.: "The Hydroelastic Stability of Struts", or railways. ARL Report ARL/RI/ G /HY /5/ 3 of November, 1958. In the United States the commercial use of hydrofoil craft (10) BAIRD,E. F., SQUIRES,C. E., Jun., and CAPORALI,R. L.: is just making a small beginning. This slowness to employ "Investigation of Hydrofoil Flutter", Grumman Report, hydrofoils in transportation is not difficult to understand in a Number DA10-480.3, February 7th, 1962. . country where nearly any point is easily reached by air, rail or highway. Nevertheless, there are some areas requiring transport (11) "The Economic Feasibility of Passenger Hydrofoil Craft across water where the distance is short enough that the hydro- in US Domestic and Foreign Commerce (1%2)", Report foil should be able to compete successfully both in time and Number PB 1811 19, Office of Technical Services, US fare with the airplane or the displacement boat, Ref. ('1). Two Department of Commerce, Washington 25, DC.