SEA KINDLINESS AND SHIP DESIGN BY 'CAPTAIN K. MACDONALD, .0.B.E, AND E. V. TELFER, D.Sc., Ph.D4, Vice President A Paper read before the North East Coast Institution of Engineers and Shipbuilders in Newcastle upon Tyne on 2the 18th March: 1938.(Excerpt from theInstitution . Transactions, Vol. LIV) NEWCASTLE UPONTYNE PUBLISHED BY THE NORTH EAST COASTINSTITUTION OF ENGINEERS AND SHIPBUILDERS BOLBEC.HALL. LONDON E. & F. N. SPON; LIMITED, 57, HAYMARKET,S.W.I. 1938. THE INSTITUTION IS NOT RESPONSIBLE FOR THE STATEMENTS MADE, NOR FOR THE OPINIONS EXPRESSED, IN THIS PAPER, DISCUSSION, AND AUTHOR'S REPLY MADE AND PRINTED IN GREAT BRITAIN Printed by J. G. Hammond & Co., Ltd., Moor Street Birmirohatn, and London. SEA-KINDLINESS AND SHIP DESIGN BY CAPTAIN K. MACDONALD, 0.B.E., and E. V. TELFER, D.Sc., Ph.D., Vice-President SYNOPSIS.-/t is suggested that modern progress in ship design has been principally directed to improved smooth-water performance and not suffi- ciently to improved behaviour under adverse weather conditions.Such behaviour as is good is known as "sea-kindliness," a quality not to be confused with seaworthiness. Rolling considerations are used to introduce the subject of sea-kindliness. Sailing ships and steamers are compared and light versus concentrated cargoes are discussed.Various design aspects are mentioned.Next, pitching is considered in relation to cargo distribution and to external form. Particular attention is given to the modern fashion display in stem design, and a preference registered for the old-fashioned clipper stern as having scientific justification.Fine versus full cruiser sterns are discussed. Course- keeping as effected by rudder and stern design, for loaded and ballast conditions, receives some attention, and the adoption of the topgallant forecastles in shelter-deckers and trysails aft is considered in this connection. Adequate engine power to face normally heavy, but not dangerous, weather is next introduced for discussion as it is felt that this aspect of the problem has been seriously overlooked in the modern economy ship.Propeller design is also touched upon. The behaviour and control of ships in really dangerous weather is next studied and reference is made to recent Board of Trade enquiries into the loss of various merchant vessels.The importance of heaving-to is empha- sized and its technique is outlined, various alternative methods being dis- cussed.The difference between sail and steam is again emphasized and a plea is made that the training of officers should compulsorily include training in small steam or sail vessels.Finally, the possible use of model experiments in assisting the better understanding of sea-kindliness and possibly the better interpolation of freeboard between various types of deck erections, concludes the paper. HE following notes are intended to serve as an introduction to -the general subject of the sea-kindliness of ships and its useful discussion before this Institution. Much has been written on the so-called economy ship, and of the immense amount of model experiment that has largely made such economy 228 SEA-KINDLINESS AND SHIP DESIGN possible.Little, however, has been heard of the nautical handling of these vessels, or for that matter of that of their less efficient predecessors. It is quite certain that efficient handling and loading in adverse weather conditions are of an importance at least equal to that of the economy of an economy ship.It is further certain that some ships lend themselves better to efficient handling than others.This fact suggests that ease of handling can be inherently a ship quality which, together with other features of good behaviour, constitute various acceptable aspects of sea-kindliness.In what follows, discussion will first be directed to those aspects of sea-kindliness that appear to depend upon ship design as distinct from those which essentially involve the skill of the navigator. It is, incidently, to be suspected that many of the intrinsic design qualities may be entirely negatived by poor seamanship.This fact must be anticipated in design work, and every endeavour made to reduce the possible relative importance of the human factor, while of course still allowing this factor full scope in the better handling of the ship.Design and navigational skill call for separate and also joint discussion, and the particular joint authorship of the present paper has been undertaken in the hope that extreme diversity of outlook may in itself assist in producing a discussion sufficiently stimulating to excuse any lack of novelty from which the paper, as such, may suffer. 2 Sea-kindliness must not be confused with sea-worthiness. A ship is regarded as seaworthy when her hull and machinery are sufficiently sound, structurally and mechanically, to admit of any projected voyage being undertaken and completed with dispatch, and with complete safety to both ship machinery and cargo. A seaworthy vessel need not, of course, be sea-kindly, although it may easily happen that the deficiency in sea-kindliness is so marked in adverse weather as to result in the vessel's sustaining such structural or mechanical damage that she is rendered unseaworthy.Sea-kindliness is thus a very desirable adjunct to seaworthiness, and for some voyages may even be regarded as a very necessary adjunct.This aspect of the problem is best illustrated by a consideration of transverse stability in relation to seaworthiness and sea-kindliness.Sufficient stabilityin amount and angular extent is apparently essential for seaworthiness.The use of "apparently " here requires justification and qualification since it is well known that too much initial stabilityas is usually possessed by a vessel carrying ore can result in very excessive rolling and thereby exposethe vessel to a greater likelihood of heavy-weather damage than would be the case with a vessel rolling slower and less violently in response, notonly to less initial stability, but probably actually negative initial stability. It is generally considered by sea-going people of experience that a sailing ship is more sea-kindly and seaworthy in heavy seas than a power- driven vessel of the same size, since the sails very effectively prevent heavy rolling, and consequently also prevent the shipping of dangerous SEA-KINDLINESS AND SHIP DESIGN 229 athwartship seas.Accepting that this is so for the moment, it is interest- ing to contemplate how essentially different the sailing vessel is from the steamer in this respect.The former, because of the relatively high centre of gravity, must be designed for a high vertical position of meta- centre.The beam can therefore be expected to be large and the rise of floor pronounced, particularly where beam is restricted or excessive beam is to be avoided. A sailing ship carrying ore has a greater metacentric height than a steamer having the same homogeneous-cargo metacentric height.Despite this, due to the steadying influence of the sails and the more circular frame sections in the vicinity of the waterline, rolling is not severe.Where the beam wind does not accompany the beam sea the sailing ship will, of course, suffer excessive rolling, and it is probable that vessels were usually dismasted under such conditions.In some modern power-driven vessels there is a tendency to design for rounder sections and greater beams.Such forms, although low in wetted surface, must necessarily have large metacentric heights and thus suffer from excessive rolling.Sufficient experience must have now been obtained with these vessels to compare their smooth-water and heavy-weather performance, and it is hoped that such data will be available in the discussion of this paper.Large-beam vessels, which maintain their full amidship beam down to the ballast draughts, suffer extremely from excessive metacentric heights.Their rolling is excessive and it is not improbable that such vessels become unmanageable more frequently than do vessels of more moderate beam. At the other end of the scale, the low-beamed ship, while good for ore cargoes, becomes under suspicion for, say, timber cargoes.The majority of timber cargo vessels trade for at least the latter part of each loaded voyage with either a negative or a very small metacentric height.Such vessels generally develop a list to leeward and then behave in a remarkably sea-kindly manner, and lost deck cargoes represent a relatively small percentage of the total carried.Evidently here also, as in the sailing ship, the wind steadying effect and the long easy roll are factors that contribute to seakindliness.A well lashed and secured deck cargo represents a very material increase in reserve buoyancy and stability at large angles.Provided that the greater vulnerability of the hull at large angles is adequately protected against, the intrinsic safety arising from excellent sea-kindliness in association with ample angular stabilityis fully recognized in the latest international freeboard regulations where increased draught is allowed vessels carrying timber.The design principle here involved is evidently that sea-kindliness at small angles is relied upon to ensure seaworthiness at large angles.This principle appears to be of real importance. 3 In the previous section the subject of sea-kindliness has been introduced and illustrated chiefly by reference to rolling.The next feature of behaviour involving seakindliness is that of pitching.Under suitable sea and swell conditions all vessels pitch, but obviously the manner and 230 SEA-KINDLINESS AND SHIP DESIGN amount of pitching must differ between ship and ship.The worst kind of pitching is that when a vessel heaves and pitches into an on-coming sea. The easiest type of pitching is that of a vessel whose stem is rising in anticipation of the crest of the on-coming swell.The phasing of a vessel's pitching between these limits is essentially a matter of relative swell and wave frequency and pitching frequency.