The International HISWA Symposium on Yacht Design and Yacht Construction 2004 ______
“The Maltese Falcon: the realisation” Hiswa Symposium 2004
By Tom Perkins, owner and project manager (USA) Gerard Dijkstra, naval architect G Dijkstra & Partners (NL) Perini Navi project team (IT, TK) Damon Roberts, Director Insensys Ltd (UK)
CONTENTS
ABSTRACT
BACKGROUND 1. DynaShip history 2. Past Experience The scale of things Sail plans suitable for large ocean going yachts Development of free-standing rigs 3. Maltese Falcon Proposals Why the DynaRig Hull 3-Ultra Yachts 4. The team
RESEARCH 5. Research and testing Historic research tests Scale model (1:6), single sail, operational tests Tank tests Scale model (1:6), structural tests Friction tests “luff” tape Virtual sailing CFD sail camber CFD sail loads Scale model (1:40), sail trials Test rig (full size), single sail and sail handling systems tests. 6. Defining boundaries General Performance Load cases Operational limits Safety
THE “MALTESE FALCON” 7. Lines and appendages, the concept 8. Hull structure 9. The rig Sail plan Sail handling systems Spars 1 The International HISWA Symposium on Yacht Design and Yacht Construction 2004 ______
Mast rotation 10. The sail 11. Operational aspects Performance Manoeuvring Sail sets Safety
CONCLUSIONS
ILLUSTRATIONS
AKNOWLEDGEMENT
REFERENCES
ABSTRACT
The DynaRig owes its origin to work done in the Sixties and Seventies by W Prolls, at the time he believed the system could provide propulsion for ships. The rig was never build. The idea has been resurrected for a remarkable three-masted square-rigger that can point like a fore-and-aft rigged yacht. Due to the application of the now available Carbon composite materials the idea has become a reality.
The authors describe the thinking behind - and the development and research put into realisation of this revolutionary rig using the results from wind tunnel, towing tank, FEA analysis, test models etceteras. The rig will be placed on an 87meter long hull.
The DynaRig is a square rig. The masts are free-standing with yards connected rigidly to the mast. The sails set between the curved yards in such a way that when deployed there are no gaps inbetween the sails enabling each spar’s sail plan to work as a single sail. The sails roller furl into the mast. The sail is trimmed to the wind by rotating the mast. The low windage (no stays) spars, fitted with the curved yards, effective single piece sails and freedom of bracing angles combine to give the rig improved aerodynamic efficiency when compared to a traditional square rigged ship. Efficiency of the DynaRig is about two times the efficiency of a traditional square rig.
The 87m vessel is currently in build by Perini Navi. Naval architecture for hull and rig is by G Dijksktra & Partners and interior design and exterior styling is by Ken Freivokh. The styling is at least as innovative as the rig concept. The rig final engineering and build management is by Insensys. Sail handling systems are by Perini Navi. The owner is also, in effect, project manager.
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BACKGROUND
1. DYNASHIP HISTORY (Ref. 15)
The vision. In the beginning of the Sixties, a man dreamt up a vision of modern automated sailing vessels - tankers, bulk carriers and even cruise vessels and big yachts- sailing the oceans with speeds up to 16-18 kts. The ships could be big, up to 60.000 DWT, and with sail areas up to 12.000 square meters divided over as many as 6 masts. Because of the automatization, the numerous crews of the windjammers were no longer necessary, the new type sailing ship could be managed by the same limited number of crew as onboard a conventional, diesel powered vessel. The possible fuel saving, depending upon the trading route, were in the order of 40% to 60% with all related environmental advantages.
The name of the man was Wilhelm Prölss, a German engineer living in Hamburg. He named his sail-system the DynaRig and the ships: DynaShips or DynaSchiffe.
Institut für Schiffbau der Universität Hamburg Mr. Prölss himself was neither naval architect nor marine engineer; his line was hydraulic systems. Hence, in order to further his project, he contacted the Hamburg University to get practical assistance with his idea.
Already during the Fifties, some theoretical studies regarding sail propulsion had been carried out by H.Thieme and B.Wagner (later also by P.Schenzle) and the DynaShip idea was well received. The Hamburg Senate provided funds to carry out a number of wind tunnel tests in order evaluate the DynaRig. To this purpose small ship models were constructed as was a part of a mast. The tests showed, not surprisingly, that the DynaRig was superior in performance to traditional square sails.
Developments In 1967-68 Mr. Prölss took out patents on his rig in all shipbuilding countries worldwide. He also tried to interest German ship owners in his ideas, but to no avail. In 1974 Mr. Prölss died. Before that time Capt. Jens Bloch had already shown interest in the DynaShip and, together with an American partner, he took over the patents and started marketing & promoting the project. None of the contacts however ended up with a building contract. Partly because the first oil crisis, after a couple of years came to an end and partly because at that time no full set of working drawings and specification of the DynaRig existed. No shipyard was willing on the existing basis to build a prototype and guarantee her performance. No further research was done and no test rig was constructed.
In 1978 an agreement was made with the holders of the patents and the Belgian Cockerill Shipyard Hoboken to develop a 30.000 DWT bulkcarrier equipped with a DynaRig. Dertailed drawings and a specification was worked out and an EEC grant for building a test mast was secured. But the same year the yard ran into grave economic problems that forced them to close down. The design work completed was lost.
Another reason for the DynaRig not having been built in the past is technical. The open slot in the front of the mast made it very difficult to build a mast in metal and yet with sufficient stiffness to withstand the torque loads. This problem was not solved.
Modern windships (Ref 9) In the 1996-1999 period wind propulsion for cargo vessels, named WindShips, was again researched. The DynaRig managed aerodynamically well in these tests, but was beaten in the end mostly by a new competitor, the so-called “hard” sails. A “hard” sail is constructed as an inner core of steel, clad with fibreglass. The total cost of sails measured over the expected lifetime (18-20 years) of a commercial vessel is more economic for a “hard” sail than for a “soft” sail.
Unless we will see a marked drop in the square meter price of “soft” sails, it is not likely we will see commercial vessels equipped with a DynaRig. However, sailing cruise ships and mega yachts present a potential market for the DynaRig.
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2. PAST EXPERIENCE
The scale of things The past experience of Perini Navi and GD&P in large sailing yachts is combined in Maltese Falcon. Without this experience the undertaking of the project would have lacked a solid basis. Illustration 2a shows large sailing vessels GD&P has designed or has been involved with. There has been a gradual but rapid increase in size. The sail plans shown are to the same scale. Of particular interest to the project is the 47m Aerorig sloop. This yacht carries a free-standing rig which is just as tall as Maltese Falcon'c rig. Unfortunately the launching of the Aerorig yacht is delayed and we can not use the experience of this large Aerorig in the design stage. However, early 2005 we might get some sail trials experience with this large freestanding rig.
Perini Navi has build more large sailing yachts over 50 m l.o.a. than any other yard and has a lot of in-house experience with their proprietairy sail handling - and sail control systems.
Sail plans suitable for large ocean going yachts Already as far back as 2001 GD&P researched rigs for 80m + sailing vessels. The study was done for Greenpeace International. At the time they were looking into the feasibility of building a 80 m loa environmental friendly campaign vessel. Around the world range was requested. Sail was to be main propulsion, the diesel engine was the secondary propulsion. Hence the designs show "soft" sail rigs and no "hard" sail rigs. The "hard" sail rigs would have been too small in area. Even with their associated high lift coefficients they would not have been sufficient powerful as main propulsion. Illustration 2b shows the result. The sloop rig was never considered but is included in the illustration for comparison. Missing in the illustration is the staysail fisherman three-masted schooner, due to the fact that the hull was medium/light displacement there was no need to fill all possible area with sails to get sufficient sail area. Discussing the pro's and con's of each rig would be a book in itself and is outside the scope of this paper. At that time the Aerorig two-masted schooner was selected as the most suitable option. Both from economic, performance and handling points of view. The Dynarig was a close second, but the rig would have been too expensive to develop and build at that time.
Development of free standing rigs Illustration 2c shows the development from traditional square sail to solid (folding) wing sails and the place of the DynaRig in this development. Also the development from traditional fore-and-aft rig to solid (flapped) wing sails is shown. The Aerorig can be seen as a square rig or a fore-and-aft rig, it is probably more correct to consider the Aerorig as a fore-and-aft rig since the rig, though it can be used squared, is not symmetrical. The report on WindShips, Reference 9, gives a comprehensive overview of rig development for commercial application.
3. MALTESE FALCON
Proposals In 2000 Perini Navi contacted several naval architects and asked them to come up with a proposal for the completion of the Perini Navi 87m hull. Emphasize was to be on fast and safe ocean passage making. GD&P proposed the four rigs shown in Illustration 3a to the same scale: A schooner rig, with semi automated sail handling, basically the same rig GD&P designed for Athena. Sail area 2800 m.sq. Air draught 60 m. A traditional barque, with sail handling made easy by roller furling systems for all sails, Sail area including main and mizzen staysails 2700 m.sq. Area excluding main and mizzen staysails 2300 m.sq. Air draught 54 m. A modernised barque. Again all sails are roller furling. Performance is greatly improved by moving the shrouds more inboard and fitting a yard to the clews of the courses. Much smaller bracing angles to windward are now possible and the courses can be sheeted much better. This rig would sit inbetween the "traditional square rig" and the "modern square rig" shown in Illustration 2c. Sail area 2900 m.sq. including main and mizzen staysails. Area excluding main and mizzen staysails 2300 m.sq. Air draught 54m. The DynaRig. Shown is the configuration with wider mast spacing. The version with the mast spaced as close together as possible was selected later. Sail area 2300 m.sq. Air draught 54 m. Also a 4-masted DynaRig was shown, but for efficiency's sake this option was deleted. 4 The International HISWA Symposium on Yacht Design and Yacht Construction 2004 ______
The square rig versions and the schooner version arbitrarely demanded a change of the stem profile to a classic clipper stem with bowsprit.
The DynaRig version was quickly selected by the owner, the DynaRig is the logical choice when considering the specification put forward by the owner, but the selection of this rig caused mixed feelings on how to implement this.
Why the DynaRig ? Why to try to revive the clipper concept ? With modern technology the sail handling potential is excellent and the windward performance is good. The large sail area required for large sailing ships can be split over many masts and yards. The DynaRig is ideal for single instrument panel operation. One man can control all functions. The square rig allows precise manouevring under sail.
The rig looks easthetically pleasing and matches the styling of the Perini Navi hull.
But most important; the square rig allows safe – and high average speeds in ocean conditions.
Hull The origin of the project was the existence of the 87m Perini Navi hull of great beauty. The concept of the hull was that of a slender hull form which can be driven by a relative small sail plan. For fast ocean passagemaking this is fine, but since windward performance crept into the project, the decission was made to increase sail power by adding ballast and positioning the ballast lower, increasing the draft to 6 meters. This increase in sail power was also driven by the fact that current launched large sailing vessels went for high sail area / displacement ratio’s and to be able to match this ratio and to carry this increased sail area the stability had to be increased.
3-Ultra Yachts Illustration 3b. shows Mirabella V and Athena, the two ultra yachts recently launched, compared to Maltese Falcon. Each yacht has a legitimate claim to being the biggest in her category. What sets them apart from previous build large yachts is not only their size but more so their high sail area / displacement ratio. This ratio is the same as for much smaller performance cruisers and hence the 3 yachts can all be properly sailed as a yacht. In light winds and coastal waters it will be Mirabella V that is the quickest, but in heavier winds the long waterline of Maltese Falcon and her good length / displacement ratio will come into effect. Anything better than 16 is good from the performance point of view.
4. THE TEAM
Managing the project Perini Navi: 100% responsible for power boat aspects. Insensys: 100% responsible for mast and spars, reporting directly to the owner. Perini Navi: 100% responsible for the sail control systems, reporting directly to the owner. Doyle Sails: 100% responsible for the sails (not high tech) Freivokh: 100% reponsible for interior & exterior styling Dijkstra: 100% responsible for naval architecture TJP in effect: the project manager.
Obviously there is a good deal of overlap between the various disciplines, but it is essential that final reponsibilities are clear.
RESEARCH
5. RESEARCH AND TESTING
Historic research The first step was to study what was done in the past, instead of trying to invent the wheel again. Fortunately all research papers are still available. A comprehensive study was completed in the Sixties and early Seventies. 5 The International HISWA Symposium on Yacht Design and Yacht Construction 2004 ______
Highlights are shown in Illustration 1 and details can be found in References 1-8. The single sail - and single mast/5 sails windtunnel tests were not repeated for Maltese Falcon. The conclusions arrived at in the past are logical and lead to a practical rig. The camber of the sails researched was in the 6%-18% bracket. Two shapes were tested; the circular and the “elliptical” cross-section. The final choice for 12% camber and circular cross-section for the Falcon’s DynaRig was driven by optimising windward performance. Optimising for reaching would have indicated the use of a deeper camber. Also for practical engineering reasons a deeper camber is more problematic.
The DynaSchiff tested in the wind tunnel of the Hamburg University was a 6-masted bulk carrier. Loa 160 meter, sail area 9100 m.sq., auxiliary power 3 x 500 HP. 16000 DWT. This ship was compared in the wind tunnel with a traditional windjammer and also with a tripod mast square rig. The Dyna Tripod shown in Illustration 2c. The DynaSchiff’s rig proved to be about twice as efficient as the traditional square rig and much higher average speeds could be maintained over selected ocean routes. The windtunnel tests for the complete rigs could not be used for Maltese Falcon due to the difference in aspect ratio between a 3-masted and a 6-masted configuration.
One operational test was performed with a small model of a single sail. The feasibility of the furling system was demonstrated in the wind tunnel. Prolls designed the sail handling system and controls around a pure mechanical system, with a single central mandrel for the sail and the outhauls. Spring loaded sheaves kept a constant tension on the outhaul lines (Illustration 1c.). A single hydraulic motor was foreseen. The sail handling system was never tested in full size or with larger models. Most sail handling ideas proved good, but the central, large diameter furling mandrel / outhaul drum required a large cavity in the mast, making it near impossible to build sufficient torsional stiffness in the metal mast structure. The original masts were thought to be constructed in steel.
Wind tunnel tests The geometry of the rig tested is shown in Illustration 5. The testing was used for the following reasons: 1. Obtaining lift / drag coefficients for performance calculations, including predicted angles of heel. 2. Obtaining the aerodynamic centre of effort for balance under sail predictions. 3. To learn how to trim the masts (how to sail the boat) for a variety of courses. 4. To check air flow with smoke sticks. 5. A single mast with 5 sails was tested for obtaining torque loads over the full range of angles of incidence. 6. Aeroelastic behaviour was checked.
Lift / drag coefficients for the 3-masted Dynarig are shown in Illustration 5c. and compared to: 3-masted schooner, two-masted Aerorig schooner, traditional barque and a sloop. Obviously the sloop has the steepest lift/drag curve, but as soon as wind angles become wider the potential of the DynaRig is evident. As is the potential of the schooner rig for reaching.
The rig geometry illustration shows the effect of the wind gradient on the angle of attack. Fortunately, with the sails trimmed for optimum performance the CE of the sails sits just forward of - and near the centreline of the mast. Hence twist of the mast is low and has no great negative influence on the angle of attack. The aerodynamic forces on the rig cause the rig to twist the wrong way, closing the “leech” instead of opening it. However, the complication of making the yards hinged was not thought worthwhile for the performance gain expected.
The figures obtained from the torque measurements were used for specifying the mast rotation system.
The flutter test concluded that windspeeds needed for aeroelastic behaviour to become a problem were well outside the operational windspeeds.
Scale model (1:6), single sail, operational tests A working model of a single sail was built, at first to check the sail handling system. The sail handling system of the model copied – and validated the pure mechanical system of the DynaSchiff design. The only completely new component added to the model was a “docking” system for the clews. Also sail shape optimisation already started at this stage. A natural extension of the tests was to go sailing with the rig, which caused for some excitement in the port of Amsterdam. Nevertheless a good feel was developed on how to sail with a modern square sail.
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Tank tests Tests with a 1:30 scale model were performed in the tank of the Delft University of Technology. The length/beam ratio of Maltese Falcon did put her beyond the standard resistance polynome of the Delft Hydrodynamic VPP module. Hence testing was needed to be able to perform proper VPP calculations. However, the research of a variety of appendages was probably more interesting. The tests showed that it is perfectly possible to sail Maltese Falcon without a daggerboard, without paying a high performance loss. However, fitting the daggerboard reduces induced resistance and certainly improves windward performance.
The photos of the bow wave and the stern wave give a practical result from the tests. Especially the stern wave is of interest for designing and positioning the exhaust scoops in relation to the dynamic water level.
Finally the tests are used for finding accurate CLP positions, including the shift in CLP for a number of rudder angles.
The use of a bulb proved less successful. In the 16-17 Kt. speed range there was a slight reduction in resistance, but the increased resistance at all other speeds outweighed this.
Scale model (1:6), structural tests This test is reported in detail in Reference 14. One of the papers of the HISWA Symposium 2004. A section of the hull was fabricated to the scale of 1:6. Laminate build-up is scaled and scaled loads were applied. Or better put, the wind-induced loads were calculated for a 1:6 scale rig following the load cases as defined for Maltese Falcon. Strains were measured using fibre-optic technology. The FE calculations for the mast structure were checked in this way, as were the laminate properties.
The tests showed that the model performed slightly better than calculated.
Friction tests “luff” tape Unknown was the friction coefficient for sliding the head/foot tape of the sail in the track. This figure was needed to specify the pulling loads of the outhaul winches and the mandrel winch. As design load we took an AWS of 20 Kt. with 5% vertical camber in the sail. This load was simulated by plenty of lead supported by a length of tape running in a track. Then loads needed to slide the tape were measured. At the same time the effect of track gap width, tape material, boltrope construction and diameter was assessed. Friction coefficient achieved was in the order of 0.2. It is assumed that, at higher wind speeds, rotating the masts and allowing the sails to flutter can reduce pressure in the sails and thus loads on the tapes.
Virtual sailing Though of no scientific importance a virtual model of the hull and rig was made. The model was sailed and tacked on the screen and this gave a feel for the real thing. The virtual model is purely optical, no sailing characteristics are incorporated. The view from the helm was checked and overall aesthetic appearance appraised.
CFD sail camber The selected 12% camber for the DynaRig was based on tests done by the Hamburg University in the Sixties. A CFD approach for optimising camber was presented during the 2002 Hiswa Symposium (Reference 10.). The CFD approach showed that the camber selected at 12% might have been on the low side, even if the original tests showed that to windward a deeper camber was not favourable. The CFD approach also showed, obviously, that how wider the wind angle how deeper the camber could be for optimum performance. Also a different camber for each mast improves results. However, it is not on all courses the same mast that needs the deepest camber.
For practical reasons the results from the CFD approach have not been implemented. Yards with adjustable camber are something for the future. It would have stressed our collective imagination too far at this stage. Also, with 12% camber the yards already look quite extreme in shape and for now at their practical geometrical limit. The CFD calculations have not yet been validated and it is not confirmed that for the aspect ratio of Maltese Falcon’s rig a deeper angle is an advantage. For future development the CFD approach should not be ignored.
CFD sail loads Reference 17 details the calculated sail loads. This has been very helpful for Doyle in designing the sails and confirming the project’s assessments of the loads on the yards and outhauls. 7 The International HISWA Symposium on Yacht Design and Yacht Construction 2004 ______
Figure 5f. shows the fill stress on the sail in 50 Kt. of wind. Fill stresses run from 23 – 34 kg/5 cm except for band near luff and leech where the stress rises to 45 kg/5 cm. Warp stresses are less than 11 kg/5cm. Stress distribution shows no peaks as is common in conventional sails. Typical leech / luff tension in 50 Kt. wind speed is around 900 kg. But this depends on the amount of hollow allowed. Outhaul tensions are in the 650 – 400 kg bracket.
The angle of incidence for a single, 5 sail, rig was calculated at 10 dgrs. A figure compatible with the wind tunnel results.
Scale model (1:40), sail trials The radio controlled model started as a hobby, but quickly became a valuable tool in assessing the feasibility of manouevring and sailing with the DynaRig. Model speed, pitching period, rudder rate of turn, model rate of turn all scale as the square root of the scale. Also true wind speed scales as the square root. Hence sailing can only be done in very, very light airs to be realistic. The following table shows how to assess the model sailing: Model 1:40 Maltese Falcon Factor 1 6.3 Boat speed 4.4 Kt 30 Kt 3.0 Kt 20 Kt 2.4 Kt 15 Kt 1.6 Kt 10 Kt Wind speed 9.5 Kt 60 Kt 4.8 Kt 30 Kt 3.2 Kt 20 Kt 2.4 Kt 15 Kt Tacking time 9.5 sec. 60 sec 150 dgrs rotation of mast 9.5 sec. 60 sec.(max rate of turn onboard) 20 dgrs rudder angle 1.4 sec. 9 sec. (max rate of turn onboard)
The inertia of the model was not scaled to realistic values.
The model is controlled with two proportional signals. One signal for the rudder, one signal for the mizzen mast rotation. Main – and foremast are driven by a mix function related to the mizzen mast signal. A rudder offset can be given. Signals are given with auto centering joysticks.
The mix function automatically sets the rotation rates between the mast. Downwind all masts are square, but when rotated closer to the wind the ratio is set in such a way that the optimum trim (rotation angle) to windward for each mast is gradually reached. The foremast has a switch on/of to allow freezing the foremast when tacking in the traditional mode as is explained in Chapter 10. Under normal conditions the model tacks like a fore-and-aft rigged yacht, all three masts swing to the opposite tack at the same time.
Test rig (full size), single sail and sail handling systems tests Illustration 5 e. shows the full size, single sail, test rig at the Perini Navi yard in Tuzla. The rig has been operational since early summer 2004. Results have been good thus far, though lack of wind has been a problem. The rig is used for: 1. Testing sails, shape and construction 2. Training in working aloft, fitting sails aloft and improving equipment for working aloft 3. Testing and improving the mechanical components of the sail handling systems 4. Testing and improving the electric winch controls: primary PLC controls, the manual back-up controls and the mobile control panel. 5. Measuring the torque loads on the rig 6. Measuring the torque loads on the outhaul motors and the mandrel drive 7. Testing the manual emergency furling systems
During the fall and winter the testing will gather speed and the project expects to put the rig through her paces in stronger winds this winter.
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6. DEFINING BOUNDARIES
General At the start of the project the specification is known, or at least the basics are known. But than the sailing of Maltese Falcon becomes a brain storming event. All possible – and impossible scenario’s are discussed and solutions have to be found. With a novel rig this becomes not only a long process, but also a very interesting – and rewarding process. The testing provides the data, the operational (and other) boundaries are brain stormed and values put to them. This translates in operational limits, a large number of load cases and an expected performance profile.
Performance The performance is really driven by what is physical possible; starting with a slender hull, accommodation requirements, Class regulations, structural materials selected, draft limitations and many other aspects. Within the boundaries dictated by all this we try to get the best performance. The VPP (Illustration 10a.) figures were not the set goal but rather show what has been achieved in theory.
Load cases Illustration 6 illustrates a selection of the load cases defined. Part of the load cases are defined by Class, but the project team added many more. Explaining all selected load cases in detail would be a paper on its own, only a couple of highlights are given. For the hull we have ofcourse the Class Rule wave bending moments to deal with and the Class required operational forces generated by the rig. We did not combine wave and rig extremes. Rig forces and wave bending moments were combined, but for operational, practical values only. For the hull structure the failure loads of the masts were also considered. A horizontal grounding load of 2G and a vertical point pounding load of 1.5G have been included.
For the rig we used a windspeed of 60 Kt with all sails set as design load. A safety factor of 1.8 was applied to the design load. For the mizzen a lower windspeed was allowed. You can not sail the boat with the mizzen sails set in high wind speeds. The 60 Kt seem high, but if the boat is running in 43 Kt apparent wind a gust can increase windspeed to 60 Kt. Reaching with the wind on the beam the stability can not sustain 60 Kt and full sails, hence one could limit the structure here to withstand maximum righting moment only. However, this was not done. From port side to forward to starboard the mast supports are equal strength. Only with the wind from forward, with sails aback, a lighter structure is considered. The Lloyd’s survival load case for sailing passenger vessels is also included; 122 kts apparent windspeed on the bare poles with the vessel pitching, heaving and rolling adding substantial inertia loads to the rig. The 60 Kt apparent windspeed, on the full dressed rig, is the most onerous load case.
Load cases dealing with fatique life expectancy are considered.
Operational limits Also discussed in Chapter 10. Summarised as: Acceleration at bow one G. Steady angle of heel 20 dgrs (for cruising 15 dgrs of heel), Apparent wind speed (AWS) on the full rig 60 Kt. for survival and 30 Kt. AWS operational on the full rig. No green water over the bow at regular intervals (4 per hour).
THE “MALTESE FALCON”
7. LINES AND APPENDAGES
Illustration 7 shows the concept. The dagger board is bolted on and removable. The board will only be fitted for ocean passages with a substantial windward component.
8. HULL STRUCTURES
General Hull structure is ABS Class. Superstructure is aluminium 5083-H321 and the hull and mid section of the superstructure is high tensile steel AH 36.
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Longitudinal strength, and the torque induced by the masts are obviously the determining factors for the structure. The hull structure was calculated according to first principles and scantlings were determined according stress levels resulting from the first principle calculation or resulting from ABS requirements.
Then the hull was put into a FE model; using MAESTRO software and a variety of load cases (see Chapter 6.) were applied. Detailed analyses for mast support related structures were performed using ANSYS software.
The FE calculations showed that the Class requirements are conservative and even, though the structure is on the limits allowed by Class, the stress levels are well below the von Misses allowable stress levels set at 284 N/mm2 for the HTS steel and 100 N/mm2 for the aluminium..
The mast support at deck level or at the heel looks awesome, but in reality this load is not much different from the loads of a conventional mast. The vertical mast heel load and the load in the vertical load from the rigging are quite similar to the horizontal loads from the deck bearing and the heel bearing. Hence global torque on the hull structure is similar. However, the stays remain in place and the free-standing mast rotates. Hence the reinforcings in the hull have to work through 360 dgrs. Requiring a more complex structure. Allowable stresses in the structures for the mast support are treated in the same way as used for chain plates; failure of the rig does not affect the hull structure.
9. THE RIG
Sail plan The sail plan shows a true square rigged ship. Sail area is about as big as could be fitted and still look allright. TJP always opposing any ideas to reduce sail on paper (one can always reduce sail when sailing). Easthetics had a lot to do with drawing the sail plan. No light weather sails can be pulled out of the forepeak, hence the sail plan shows the standard sails and the light weather sails. Much the same as what was custom onboard the traditional square-riggers. This means, as is discussed in Chapter 10, that the Royals are furled early and also the mizzen mast really carries only light / medium sails. For optimum (racing) use of the mizzen mast the dagger board is needed. The positioning of the rig on windjammers was customary neutral compared to the centre of lateral pressure of the underwater body. This allowed the windjammers to manouevre under sail in light winds, in stronger winds the mizzen had to reduce sails early. Maltese Falcon, without the dagger board, has similar characteristics.
Sail handling systems The original DynaSchiff design had a 100% mechanical sail handling system, fitted with one drive un it and four outhaul line tensioners (Illustration 9a.). On the 1:6 scale test rig this system was copied and although it worked well the system was sensitive to proper adjustment of outhaul lines. No individual trim of the four clews is possible.
After many brain stroming sessions and in view of perini Navi’s long standing experience with electric controls the system with one heavy mandrel drive motor and four light outhaul line motors was selected. In principle all five electric motors can be encoder controlled, but at present only the mandrel drive motor is encoder controlled and the other motors have electro-mechanic controls.
Though primary control is a single button operation, fine adjustments can be made from the deck.
Spars The spar engineering is detailed in Reference 14, which is one of the papers presented at the HISWA Symposium 2004. It is sufficient to say here that the rig could not have been build without carbon composite material. The structural solving of the torsion loads which can occur on a free-standing mast with a slot running nearly full length has been one of the most difficult aspects of the project.
Mast rotation Illustration 9b. shows the basic layout for the deck bearing and the heel bearing and mast rotation mechanism. To give an idea of size; the deck bearing weighs about 900 kg and the heel bearing and mast rotation mechanism is in the order of 9 tons. Four hydraulic motors drive the mast rotation. The motors are mounted in a housing which is fitted to the mast base, not to the ship. In this way the tolerance between mast gear and motor gears is independent of mast bending induced displacements. To avoid the hydraulic motors to rotate 10 The International HISWA Symposium on Yacht Design and Yacht Construction 2004 ______with the mast two anti-torque bars are fitted (not shown on the drawing), they anchor the rotation mechanism to the ship’s structure. The system is specified at 1000 Knm torque. This equals a brace load of 8 tons or 4 tons with two braces fitted. This is a very conservative approach.
Sails The sail is not one of the most difficult design components of the project. The sail is supported along the head and the foot by the curved yards. The luff and leech are supported by a small (2%) hollow cut and a strong leech / luff line.
Due to the fact that the sail is supported over its full length there is no high clew load. The stresses in the sail are fairly evenly distributed with a doubling of the stress level towards the leech / luff. This is clearly illustrated by the CFD plot (Illustration 5f.). Hence all sails received a doubling along leech and luff as can be seen on the sail plan.
Due to the even stress distribution and low bias strain the cut of the sail is simple and the cloth conventional Dacron. Panels are laid perpendicular to the leech / luff. The panels have very little shaping in them. All ideas of radial cut, high tech sails have been shelved for the moment. The Dacron sails will be strong, pliable and fairly UV resistant. They will provide a long lasting service.
Ideas for radial cut, high tech material sails have been shelved.
The 12% sail camber is provided by the curved yards. The vertical camber is still being researched. Current thinking is 5% without load, increasing to some 7% under full load. The higher the vertical camber the lower the forces on the track and the lower the friction when furling. However, a flatter sail roller furls better and probably has a higher efficiency.
The leading edge of the sail is not made flat, but is slightly curved, like a miniature spinnaker luff. Trimming to the wind is easier this way and more forgiving. Nevertheless tell tales are fitted.
The heavy-duty topsails are 9.6 oz Dacron with doublings of 9.6 oz. The medium sails (courses and top gallants) are 9.6 oz with doublings of 6 oz and finally the light weather Royals and mizzen top gallant are 6 oz with doublings of 6 oz.
Much attention has been giving to the finish of the sails and a variety of head - and foot tapes have been tested. If the cloth is plain Dacron the material for the tapes is Kevlar warp and fill, with Teflon yarns woven in to reduce friction. Clew patches are small and light. This makes for easy furling. It is foreseen that the crew onboard can replace the tapes. A Code Zero type of roller furling mechanism is used to fit or remove the sails. The sail is rolled onto this furler from the mandrel, than the furler is lowered to the deck and vice versa.
10. OPERATIONAL ASPECTS
Performance Illustration 10a. shows the VPP generated polar diagram. The VPP used direct input from the wind tunnel measured sail coefficients. The resistance polynome was adjusted according resistance measurements in the towing tank. The optimum configuration, the “racing mode” is illustrated. Wind speed at 10m mast height. Waves included. Dagger board fitted and 50T water ballast in the wing tank. The performance looks promising and shows that Maltese Falcon is a real sailboat with the good sailing characteristics of a much smaller yacht. Tacking angles to windward of 100 dgrs TWA seem realistic. This is good for this size of yacht. What is more impressive is the speed at these angles, 13 Kt. boot speed for VMG sailing and 14 to 15 Kt. at just wider angles. This in 16 Kt. TWS.
Real life can differ from the polars by the fact that the atmosphere is seldom equal to the atmosphere’s characteristics used by the software. This is especially conspicuous in light airs, due to wind gradient and wind shear effects. Also the software seldom correctly applies wave resistance.
An interesting fact is that comfort level can be selected without paying an enormous price in performance. The VPP obviously shows that also vessels of the size of Maltese Falcon need to heel to sail to optimum 11 The International HISWA Symposium on Yacht Design and Yacht Construction 2004 ______
performance. Typically 22 dgrs for optimum windward and reaching performance. However, if for instance the boat is allowed to slow down from 16 Kt. to 15 Kt. the corresponding angle of heel might be reduced from 20 dgrs to 15 dgrs etceteras. The DynaRig allows playing around with this feature with ease. Just be rotating the mast to reduce lift force changes the heeling force dramatically, also reducing sail area is painless. Hence, for cruising a comfortable angle of heel does not mean you are slow.
An heel of 20 dgrs might seem high on a big boat, but the heel is steady and the pitching is less violent than on smaller yachts. An angle of heel of 15 dgrs is not a problem and does not cause the passengers to feel insecure. The criteria used for heel are based on experiences with the schooner Athena and the clipper Stad Amsterdam, a sailing passenger vessel. A good compromise is sailing at a steady 15 dgrs, with the boat heeling 18 to 20 dgrs in gusts.
Ofcourse during an ocean race higher angle of heels in the low twenties can be allowed.
The VPP does not show when you will start shipping green water over the bow. Hence in the higher wind ranges there might be a need to slow Maltese Falcon down to avoid this condition. Performance potential is higher that the vessel or crew can take. As a rule of thumb we use an acceleration of one G on the foredeck as an operational limit, shipping green water over the bow at regular intervals is another.
Motor assisted performance is presented in Reference 11, “Propulsion Aspects of Large Sailing Yachts”. One of the 2002 Hiswa Symposium papers.
Speed under motor is 17 kts. Cruising speed is 14 kts.
Manoeuvring The DynaRig is a square rig and has all the well-known advantages of a square rig for handling the vessel under sail. The radio-controlled model demonstrated this clearly. Precise control over course and speed is possible.
Gibing speaks for itself, just turn the rudder and follow with the mast rotation. The fact that gibing is not a risky affair allows the vessel to be pushed running under conditions that would not be possible with a schooner.
Tacking is a different matter. The radio controlled model tacks as a modern fore-and-aft rigged yacht. Go for speed then bring the head up into the wind. As soon as the sails tend to go aback the three masts are rotated at the same time to their opposite angle for the new tack. The weight of the vessel carries her through the tack.
A traditional clipper can not do this. She does not point close to the wind and by the time she is head on to the wind there is no speed or momentum left to carry her through. If the waves are not too high she can still tack by swinging the main and mizzen yards to the opposite tack, but holding on to her foremast. The foremast will be aback and she might push the head around, the vessel will be drifting astern by this time and the rudder will help to swing the stern in the desired direction. This sequence is shown in Illustration 10b. “Tacking modes”.
On Maltese Falcon the “3-masts rotated together” tacking mode, or the “foremast rotation delayed” tacking mode, might both be possible. However, the second option will certainly be needed with the seas running high.
In survival conditions the vessel can always tack safely by wearing around.
Typical tacking time is 60 seconds.
Sailing backwards is possible and is something the crew should really watch out for. In theory the Maltese Falcon can sail backwards at nearly the same speed as going forward. Clearly a situation the rudder is not designed for. However the ability to slow down or even stop the vessel quickly with the sails is a big plus.
It will be satisfying to be able to sail away from the anchor in the manner of the windjammers and clippers. It takes 70 seconds to unfurl a sail. On each mast a single sail can be deployed at the same time. Hence in 6 minutes all sails can be set.
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Sail sets A selection of possible sail sets is given in Illustration 10b. Three sail types are uses. Lightweight, medium and heavy. The Royals (uppermost sails) are from very light cloth (6 oz) and are furled early on. In general the sails on the mizzen are also lighter constructed than on the other masts.
Basic furling sequence is from high up and aft, than down and forward.
The lower topsails (2nd sail from deck) on the main – and foremast are the storm sails. From the sail sets it is also apparent that, in order to maintain balance, the mizzen sails are furled first and the main - and foremast carry sail till the end. It depends on the course if the foremast or the main mast is the last mast to carry sail. The reason for the storm sails being the lower topsails and not the courses (lowest sail) is two-fold: 1. The lowest yard can not be fitted with diagonals, making them less strong than the yards fitted with diagonals both ways. 2. The lower topsails operate in a steady wind speed. Sails closer to the deck can be blanketed by the huge waves associated with a severe storm. In addition the view from the bridge is clear with the forecourse furled.
The sail sets diagram illustrates the flexibility of the square rig and illustrates the possibility to divide sail area in many small, manageable areas.
Safety Much attention has been paid to safety onboard. Not only from the crew point of view but also from the performance point of view. You want to be able to push the boat without unduly worrying about safety.
This in addition to Class and MCA regulations.
The test rig is very valuable in training the crew in working aloft and trying out rock climbing equipment in order to assure safe working in the rig. Also equipment is placed with easy - and safe access in mind. The crew working aloft is secured by individual man hoist lines and in addition fall arresters are used. Tracks are placed, running along the masts and along the yards. The yards are also fitted with handrails. Eyepads are placed in strategic positions. Jack stays (horses) are not fitted permanent to the yards, like on the square- riggers. On the rare occasion that the crew will have to go out on the yards they will be in a climbing harness or a sophisticated bosuns chair attached permanently to the man hoist line. This harness is also linked to the track/handrail combination by a short strop on a slider, which locks in position. This will arrest transverse movement. Temporary webbed loops as footrest can be fitted to the track/handrail to allow working on top of the yard.
When going aloft in the climbing harness the crew is secured to a fall arrester type of slider running in one of the vertical tracks running along the mast.
For working on deck in adverse conditions a jackline/safety line systems has been drawn onto the deck plan. However, if all is working there is no need for the crew to be on the main deck in order to sail Maltese Falcon.
From the manoeuvring point of view one of the biggest safety advantages is that an accidental jibe does not matter to the symmetric square rig, as has been mentioned before.
Final safety of the vessel lies in the ability to get rid of the loads on the sails, whatever the condition. With traditional rigs this can be achieved, in an emergency, by releasing sheets or even cutting them. The DynaRig does not have this luxury; there are no sheets to be cut.
Sail reduction is as follows: 1. Roller furl sails in the sequence as shown in the sail set diagram. 2. In case there is too much load on the sail and the friction in the head – and foot track becomes too high the rig can be rotated to reduce the load and some flutter might be introduced to break the friction. 3. In case of total power failure the sails can be manually furled. A battery driven, hand held, power “drill” will be carried for this purpose, but the crew will have to go aloft to furl the sails. 4. In case of a computer breakdown there are mobile remote control panels which allow each electric motor to be controlled directly by the operator. 5. If there is too much pressure in the sails and too much torque to be able to rotate the mast: alter course (rudder / thrusters) to reduce pressure on the sails and reduce sail area as described under 2. 13 The International HISWA Symposium on Yacht Design and Yacht Construction 2004 ______
6. The Royals are built lightly and are designed to blow out (as they would on the traditional rigged clippers) before design load wind speeds are reached. The flexibility of the free-standing masts is also a safety valve, shock loads and gusts can be absorbed. Down flooding angles are high hence a knockdown is not a problem from the flooding point of view. MCA requirements in this department are ofcourse fully met.
In case of failure of the mast rotation mechanism it is possible to rig emergency braces to the two lower yards. Winches on the deck are available for this purpose. Also emergency check stays are foreseen for use in survival conditions, but it is not certain they will be actually needed.
A sailing manual defines operational limits for the rig, the fibre-optic load sensing system will also give advance warning to the crew that limits are near. But ofcourse good seamanship is the ultimate safety factor.
CONCLUSIONS
It took one afternoon to sketch the DynaRig on paper. But it takes an owner with vision and - willing to take responsibility and many years of many people to get the vessel and rig build and working.
The geometry of the Maltese Falcon's DynaRig is still exactly the same as the one sketched in the fall of 2000. The geometry of a single mast differs hardly from the DynaSchiff mast.
The project was conceptual not difficult, but the real difficulty was (and is) in the proper design, engineering and building of the myriad of completely novel details needed to get all components to work and to work together.
The project approached the design issues in a step by step manner. First the feasibility of the operational aspects was demonstrated, then the performance figures published by Hamburg University were validated by wind tunnel research etceteras. Finally a full sized test rig was build. Thus far all R&D has given satisfactory results.
The DynaRig, done in carbon, shows great promise as a rig for large sailing yachts and as a rig for sail assisted cruise vessels.
The Maltese Falcon is the first clipper yacht built since the Thirties. The Maltese falcon is the first modern clipper yacht.
The project is on line for Maltese Falcon's launch in the fall of 2005.
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ILLUSTRATIONS
1a. The DynaSchiff, 6 mast, auxiliary powered, sailing cargo ship (Ref. 1-6).
1b. The original DynaSchiff geometry (Ref 1-6). 15 The International HISWA Symposium on Yacht Design and Yacht Construction 2004 ______
1c. The mechanical DynaSchiff sail furling system (Ref 1-6).
1d. The optimum Cl-Cd at AWA 30 dgrs for the tested 6 mast DynaSchiff (Ref 1-6). 16 The International HISWA Symposium on Yacht Design and Yacht Construction 2004 ______
2a. The scale of things.
2b. Sail plans suitable for large ocean going yachts.
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2c. Development of free standing rigs (Ref 7-8).
3a. First proposals for Maltese Falcon.
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3b. Three ultra yachts.
5a. Rig wind tunnel geometry and CE’s.
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5b. The rig geometry.
5c. Sail coefficients and model in wind tunnel.
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5d. Single sail test rig, 1:6 scale model.
5e. Single sail test rig, full size and 1:40 scale sailing model. 21 The International HISWA Symposium on Yacht Design and Yacht Construction 2004 ______
5f. CFD plot stresses in sail (Ref 17).
6a. Selected load cases for hull structures. 22 The International HISWA Symposium on Yacht Design and Yacht Construction 2004 ______
6b. Selected load cases for rig structures.
7. Profile and appendages, the “Maltese Falcon” concept. 23 The International HISWA Symposium on Yacht Design and Yacht Construction 2004 ______
8a. FEA (Maestro) hull and superstructure model (Ref 20).
8b. FEA (Maestro) plot hull deformation, ABS rule wave, sagging (Ref 20).
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8c. FEA (Maestro) plot normal stresses, ABS rule wave, sagging (Ref 20).
8d. FEA (Ansys) plot, local stresses support mizzenmast, rig design load (Ref. 20).
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9a. Principle of sail controls.
9b. Principle of mast rotation.
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10a. VPP polar diagram.
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10b. Tacking modes.
10c. Sail sets. 28 The International HISWA Symposium on Yacht Design and Yacht Construction 2004 ______
AKNOWLEDGEMENT
University of Hamburg, P. Schenzle, original DynaSchiff data. Capt. J. Bloch, original DynaSchiff data and his contribution to the “DynaShip history” chapter. J de Vos and E Luijf, GD&P, design work and calculations. E Wassen, GD&P, design and fabrication radio controlled model The authors of the Maltese Falcon reports listed under References. R Doyle for his input in sail development. Last but not least, the project team.
REFERENCES
1. W. Prölls (1970), “The economic possibilities of wind propelled cargo ships”, AYRS, UK.
2. J Morwood (1970), “A Cutty Sark Yacht”, AYRS, UK.
3. B. Wagner (1966), “Windkanalversuche met gewölbten Plattensegeln mit Einzelmasten sowie mit Plattensegel bei Mehrmast anordnung”, Institute für Schiffbau der Universität Hamburg, Germany.
4. H. Thieme (1966), “Bildmaterial von der Funktionserprobung eines Dyna-Typ-Rahsegels im Windkanal”, Institute für Schiffbau der Universität Hamburg, Germany.
5. W. Prölls (1970), “Improvements in or relating to sailing vessels”, Patent Specification 1217587, UK (a.o.).
6. B. Wagner (1976), “Sailing ship research at the Hamburg University, a survey of the activities in the years 1961 - 1967”, University of Hamburg, Symposium Liverpool Polytechnic, UK.
7. P. Schenzle (1976), “Comparative sailing speed in wind propulsion, a standard performance model for early speed predictions for sailing ship designs”, University of Hamburg, Symposium Liverpool Polytechnic, UK.
8. P. Schenzle (1983), “Ship design for fuel economy, wind as an aid for ship propulsion”, Hamburg Ship Model Tank, Germany.
9. Knud E. Hansen A/S (1996-1998), ”Modern Windships”phase 1 and phase 2”, Pelmatic / Knud E. Hansen A/S, Denmark.
10. T. Doyle, M. Gerritsen, G. Iaccarino (2002), “Optimisation of Yard Sectional Shape and Configuration for a Modern Clipper Ship”, Stanford University, HISWA Symposium, Netherlands.
11. J. de Vos, G Nijsten (2002), “Propulsion Aspects of Large Sailing Yachts”, Gerard Dijkstra & Partners, HISWA Symposium, Netherlands.
12. K.J. Vermeulen (2002), “Model tests with the 87m S/Y “Maltese Falcon”, data report no.2”, nr. 1334 -O-D, Delft University, Netherlands.
13. I. Campbell (2001), “Wind tunnel tests on a 3 masted DynaRig”, nr. 1618, Wolfson Unit, UK.
14. D. Roberts, G. Dijkstra (2003)(2004), “The use of fibre optic strain monitoring systems in the design, testing and performance monitoring of the novel free-standing DynaRigs on an87m superyacht by Perini Navi”, Insensys Ltd, UK.
15. Capt. Jens V.Bloch (2002), “The DynaShip Story”, article, Denmark.
16. G. Dijkstra (2000), “Perini Navi 87m, proposals for sail plans, exterior styling and sailing characteristics”, Gerard Dijkstra & Partners, Netherlands.
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17. P. Heppel (2004). “Preliminary report S/Y Maltese Falcon”, Peter Heppel Associates, France.
18. I. Pierce (2004), “Maltese Falcon, main mast, natural frequency analysis and static analysis”, Insensys Ltd., UK.
19. J. van der Horst (2002), “FE calculation DynaRig mast, 87 m S/Y Maltese Falcon”, Nevesbu BV, Netherlands.
20. P. Martin (2004), “Finite element analysis Maltese Falcon”, Vuijk Engineering Groningen BV, Netherlands.
21. A.Vlasman (2004), “87 m S/Y Maltese Falcon, DynaRig Checkstays, FE calculation”, Nevesbu BV, NL.
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