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Vol (IV FIG represents a vessel)

IV FIG. 3 represents a vessel inclined whose centre of gravity is improperly placed in reference to the centre of buoyancy. In this case the arm, ZG, forms an upsetting couple, as the force of buoyancy, acting perpendicularly upwards through Z, tends to capsize the vessel. centres of effort the centre of effort for the whole of the sails can be deduced. The true effective centre of effort, and also the effective amount of lateral resistance, differ no doubt considerably from results theoretically derived; but by means of these preliminary calculations a designer gets a rough but fairly accurate idea as to the dimensions, displacement, stability, and sail area possible under the rating formula to which he is confined.

A designer in selecting an example need not confine himself to a vessel of the same size as that which he is shaping out in his brain. A basis of comparison has been established between the actual ship and her model, and equally therefore between big and little ships of the same shape. This measure, which is known as "Froude's Law of Comparisons," may be roughly stated to consist in this, that the equivalent speed of a ship and of its small scale duplicate or model, are proportional as the square roots of their lengths: for instance, if a vessel 100 feet long is represented by a model 4 feet long, the speed of the ship would be five times the speed of the model, and at these equivalent speeds all the phenomena which the ship would exhibit in the water would be fairly represented by the phenomena observed in the case of the model.

Though this law requires special qualifications, BB for various obvious reasons, in respect of sailing vessels, yet it is no doubt fairly accurate, and the late Mr. G. L. Watson put it on record that, relying on this law, and judging from his experience in small boats, he carried out the design of his first large racing vessel, the "Vanduara," with confidence and with success.

Acting within the constitutional limits of these general laws, the object of a designer is to obtain the greatest possible speed out of a vessel of a given size; in other words, his problem is to find the maximum motive power that is to say, the greatest sail-carrying capacity, relatively to resistance. This sounds fairly simple. But "size" is, in a ship, an indefinite and undeterminable quality, and "size," so far as the designer of a racing yacht is concerned, is "rating"-a certain ratio arrived at empirically in reference to certain dimensions, and frequently modified and changed; resistance is of various kinds, and is due principally to wave-making and to skin-friction; sailcarrying power is not a constant quality, but varies directly in reference to wind force; other qualities also besides speed pure and simple must be considered, such as lateral resistance, which mainly determines the weatherly qualities of a yacht; and, moreover, all the above-mentioned factors in determining design are affected by the condition of the element through which the body has to be driven, and vary in magnitude and effects according to whether the sea be rough or smooth. The solution of the apparently simple problem becomes, under these circumstances, a most complicated matter.

Speed may be considered first apart from size.

It is well known that, in sailing boats, size is an element of speed, and that, given two boats identical in lines but of different sizes, the larger will be the faster of the two; and this characteristic of "size," regarded an an element in speediness, is not easy to eliminate in any definite way. Thus, in considering two yachts of different design, it may be very difficult to say which is the larger boat of the two, or how much larger she is, or to determine to what extent the extra speed of the faster boat of the pair is due to superiority in design, or to superiority in size.

Nevertheless, if too close a definition of statement is not insisted upon, it is possible to study the features of design which make for speed, without introducing the question of size, and it is desirable to do so, because size cannot be considered apart from rules of measurement, and from what may be termed the artificial influences which these rules have upon design.

If, for the present, the quality of "closewindedness," which, though of great importance, may be best considered separately, be ignored, the secret of speed in a sailing boat may be said to lie in obtaining the maximum of sail-carrying power relatively to resistance. It may be objected that, in sailing in very light winds, at any rate, the question is one not of sail-carrying power, but of actual sail spread, which is a very different thing. But ceteris paribus, in virtue of certain practical reasons which are not far to seek, the actual potential sail spread which it pays to give a boat bears a fairly fixed proportion to sail-carrying power; and, therefore, the propulsive force, whether the wind be light or strong, may be regarded as approximately measured by sail-carrying power, in other words, by "stability." Hence, in judging of the wisdom of any contemplated modification of design such as, for instance, increase of beam, draught, or displacement, the question to be asked, on general principles, is whether the consequent increase in stability is worth the increase in resistance. On the other hand, if the contemplated change were of a nature to decrease resistance, the question would be whether the decrease in resistance outvalued the loss of stability. The features of design principally conducive to resistance are large wetted surface; unfairne ness of lines; big displacement. But before entering upon these topics, a few words on resistance are advisable.

To go at length into the laws affecting solids in fluids would far transcend the limits of an article of this kind, and those who require information on that interesting subject must study the exhaustive experiments and conclusions of Mr. Froude, Professor Macquorn Rankine, Mr.

Scott Russell, and others. But, as the results of the resistance of water upon vessels is of paramount importance in yacht designing and sailing, a few words on the subject are necessary.

Resistance is caused by skin friction and wave making. The effects of friction are so well known to all in a thousand ways in the ordinary affairs of life that the resistance due to wetted surface, or, as it is called, skin friction, needs no explanation. But wave making is a factor with which seafaring people alone have any experience, and some explanation of the phenomenon is therefore desirable.

A body, a ship, for instance, travelling through a fluid such as the sea, imparts to the particles of fluid the motion requisite to enable them to get out of the way in front, and to fall into their places again behind. This change from a condition of quiescence to one of motion involves the creation of a system of local excesses and defects of pressure in the fluid, which system moves with the moving body. The surface of the sea being covered by atmosphere exercising uniform pressure, this moving system of excesses and defects of pressure must be satisfied by elevations and depressions resembling waves; and such waves, if really natural, or, as it is called, "free" waves, would travel at a speed determined by the length of the waves from crest to crest. But the quasi waves here referred to are not natural waves, but are artificial, being created by the body moving through the water. If the speed of that body is much less than the speed proper to a natural wave of the same length as the artificial wave, the latter will acquire no natural wave life; it will consist merely of an undulation which moves with the body, but which does not spread into the surrounding water, nor throw out any train of waves. Very little power is required to maintain such an undulation; in other words, the undulation produces very little effect in diminishing speed. But if the speed of the body coincides with the speed proper to a natural wave of the length of the artificial wave, the latter will acquire natural wave life and all the properties of a living wave to the fullest extent. It becomes accentuated; it propagates a train of waves extending sideways and backwards, according to the natural properties of waves, and covers more and more water with waves. The resistance which causes the formation of a wave system of this character requires a great expenditure of force to overcome it, or, in other words, the action of such a wave is to greatly diminish speed.

A natural free wave system, originated in the disturbance caused by a ship moving through the water, takes the shape of a series of crests and hollows ranged in a certain plan relatively to the line of progression. This series consists of low but massive transverse or athwart-ship waves, and of echelon, or diverging waves, forming steep ridges. The different component parts of this system are not always all equally well developed, because their development depends upon the degree in which the various parts of the system harmonise with the conformation of the undulations satisfying the pressure. Those parts only which harmonise with the undulations obtain life and become active.

In practice it will be found that at the bow of a vessel sailing at quite a moderate rate of speed, a portion of undulation exists, sufficiently small and steep to fit in with a similar portion of the diverging wave, with the result of giving birth to a lot of little live echelon waves, trailing away from the stem and bow. The resistance to which these waves are due does not consume much power. A similar state of things occurs at the stern, where even at moderate speeds a series of little live transverse waves are formed, which require greater power to overcome. But, on the whole, these bow and stern wave formations at low and moderate speeds have not much effect in reducing speed. The real trouble commences will delay the formation and mitigate the severity of the fatal counter wave.

Skin friction that is, the friction of the water upon the immersed surface of the boat, is the most important cause of resistance up to a certain rate of speed proportionate to the size, or rather, principally, to the length dimension of the vessel.

After that proportionate rate of speed has been attained, skin friction ceases to operate as the chief form of resistance, and "wave-making" takes its place. Hence, other things being equal, a large-bodied boat will be faster in light winds than a vessel designed on a hollow midship section.

Midship section A has obviously less wetted sur- A A A D D D E E E E D -B C C B B A B is the mean level of the water.

C is the wave thrown up by the bow.

Dis the first transverse wave.

If the distance CD is the natural distance due to two waves travelling at the same pace as the boat, then these waves become natural waves and give birth to an enormous succession of transverse waves which consume an enormous amount of energy to overcome or rather create. When this state of things occurs, a vessel may be said to have attained her limit of speed, as any addition to her driving power will be expended in increasing the size of her transverse waves. when the speed of the vessel through the water is sufficient to lengthen out the distance between the crests of the transverse waves to about the same length as that of the vessel. Then the pressure undulation and the artificial wave system fit exactly, from end to end of the boat, and a strong live natural wave system is produced..

A great and fully formed transverse wave is thrown off from or hangs on to the counter, followed by a series of equally well-developed waves. Wave making is then at its maximum.

The resistance causing this form and degree of wave making is enormous; in other words, speed is most seriously interfered with. So great is the resistance that as a matter of fact it may be said to put an end to any further development of speed, for in practice it is found that as soon as a vessel throws out this well-defined complete wave, at about right angles from her counter, she has attained her maximum speed, and no amount of pressure will make her go any faster. The only way to increase her speed would be to reduce the wave-making characteristics of her hull. That problem involves very deep and complicated questions, and the most that can be laid down shortly and broadly is, first, that a boat relying on depth for displacement will, length for length, suffer more from wave making than a boat relying on breadth for displacement. For one thing, in a broad shallow vessel the trough of the undulation amidships materially lessens the immersed section of the vessel amidships, and consequently mitigates the pressure disturbance in which the wave originates. Secondly, such a form of entry as will throw the displaced particles of water upwards and outwards, and more especially such a form of run as will permit the displaced particles of water to close in upwards and easily, face than midship section B, and a vessel built on A will be faster in light winds and slower in strong winds than a vessel built on B. To lessen skin friction, a smooth immersed surface is most desirable. Black varnish applied to perfectly smooth wood makes a good surface; but it has this great disadvantage, that it fouls quickly, and a vessel so coated must be docked or laid ashore and scrubbed every few days. "Valkyrie III." was coated with black varnish. Her opponent Defender" was built, up to the aluminium topsides, of a manganese bronze polished to the smoothness of a mirror. Cold drawn copper sheathing was the material formerly used among us on wooden skinned yachts of any size, but of late the metalling of racing vessels has rather gone out of favour. 66 Unfair lines, abrupt curves, and thick endsespecially of the after body-are also important features as producing resistance, principally at low rates of speed.

Conformably to the principles already considered, largeness of displacement, especially when associated with small length, is important mainly at high speeds, as, for instance, when sailing off the wind in a good breeze. It is conducive to resistance in proportion to the degree to which displacement is taken in the form of depth of underwater body, because displacement at a low level specially conduces to the formation of the end to end wave which boats create when hard driven. In fact, boats with very large and deep underwater bodies may be almost said to have a hard and fast limit of speed dependent on their length, beyond which no conceivable power can possibly drive them. This resistance-creating function of displacement is much less marked in its effects if the same displacement is associated BB 2 with greater beam, and is therefore spread more widely over the surface of the water. So much for design in relation to resistance.

The features of design principally conducive to stability are:- Breadth of beam; which-with a certain laxity of expression-may be said to measure the width of the base on which the vessel stands. Its efficacy is, of course, largely increased if a heavy crew can be utilised as live, shifting ballast.

Lowness of weight; which measures the leverage with which the weight acts to keep the vessel upright.

Quantity of weight at low level; which measures the amount of weight acting at that leverage.

If these several expedients for obtaining stability be considered in connection with the elements of resistance which they involve, the following points may be noted :- Increase of beam must generally increase wetted surface, and consequently resistance from skin friction, especially at low speed; but the loss through increased resistance is not proportionate to the gain due to increased stability. The limit to the advantage which can be thus gained by increase of beam arises apparently out of the following circumstances. Beyond a certain point, unless the increased beam is accompanied by a considerable increased displacement, and thereby of resistance at high speeds, the stability it gives extends to a very limited angle of heel, and, apart from the risk of an actual capsize, the boat will sail very badly in squally and unsettled weather unless under-canvassed for the average strength of the wind. In rough water increased beam means greater resistance owing to the greater effect of the waves upon a broader boat, and from this cause a boat of large beam and small displacement will probably sail very badly in rough water, especially if the wind be light. These conditions are aggravated by the larger spars necessary to utilise the extra stability given by increased beam. Stability derived entirely from beam, in other words unballasted boats, reached the height of perfection or absurdity-as the case may be considered-in the productions of Mr. Linton Hope, who, with his -raters, swept the Thames and Solent. They were wonderfully speedy little craft in any weather, but they were capsizable, and did capsize; and their existence was perhaps wisely terminated by a decree of the Yacht Racing Association, that no certificate should be granted to boats weighing less than 17 cwt.

Lowering of weight, so far as feasible without altering the external shape of the bull, is, of course, pure gain. Hence, anything that can be done, by good design and workmanship, or by structural contrivances, to reduce top weight, whether of spars or hull, consistently with adequate strength, must tell in favour of speed.

With this obiect in view, vessels like "Audrey" were built with a double skin of thin planking, the inner planks being laid diagonally, and the outer planks longitudinally, which is, strength for strength, lighter than a single skin of thicker planking; the top sides of the "Defender" were made of aluminium; the booms of big cutters are of built steel tubes instead of solid wood, and the centre cores of topmast, topsail yards, and gaffs are bored out. So also structural contrivances may work wonders in the way of increase of speed if, by altering the disposition of the weights, they enable the shape of hull to be so altered as to give increased stability for the same resistance, or lessened resistance for the same stability. All the principal changes which the last half century has witnessed in the designs of racing yachts are, in the main, traceable to developments of this kind. The first step lay in substituting iron for stone. and then lead for iron ballast; the second, in putting the lead on the keel; the third, in forming the outside lead into an isolated fin, projecting deeply below the hull proper; the fourth, and last, in carrying the lead in a cigar-shaped bulb, at the lower end of a deep metal blade or plate. In some of these steps, and notably the last, owing partly to the difficulty of giving sufficient strength to the plate, the change was rather in the direction of obtaining the same stability by using less lead at a longer leverage, and so lessening displacement and resistance, than in that of obtaining greater stability; but the effect was equally to obtain greater speed by increasing stability relatively to resistance.

An absolute increase in the quantity of weight carried at a low level, in other words, of ballast, may, to some extent, be effected without increasing displacement by greater compactness of hull, or by any other characteristic tending to diminish structural weight. But otherwise it can be procured only by increasing the total weight of the vessel, and, for smooth water work, larger displacement generally results in a loss of speed, except in light airs and turning to windward. Nevertheless, up to a certain point, in rough water, especially combined with light winds, weight appears actually advantageous even apart from the extra stability it gives. The heavier vessel carries her way better through the seas.

The several foregoing considerations point to the conclusion that the type of cross-section most favourable to success in racing will depend very largely on the nature of the courses sailed over, and of the average conditions of wind and sea prevailing. The prevalence of reaching courses and sailing down wind, of smooth water, and steady moderate breezes, will tend to encourage light weights and dependence largely on natural stability-that is, stability derived from beam; while rough water and much turning to windward will encourage heavier weights and more artificial stability-that is, stability derived from ballast.

For normal average conditions, and barring the effect of measurement rules, the plate and bulb type, in some form, would appear to be the most efficient.

So far attention has been concentrated on considerations influencing the choice of type of crosssection, rather than of general proportions or of "lines," properly so-called, meaning by "lines" the longitudinal sections of the hull, whether in horizontal, vertical, or diagonal planes..

The lines, in this sense, are governed mainly by desire to fulfil two principal requirements. In the first place, a certain degree of sharpness and gentleness of taper of the afterbody is essential in order to allow the displaced water to close in behind, and to avoid the serious resistance that arises from eddy or "drag" behind the vessel.

So necessary is a fine afterbody that in boats of very large displacement in relation to length, or, to speak more strictly, of very large ratio of displacement to cube of length, such as the normal cutter yacht of half a century ago, an afterbody fulfilling this requirement absorbed more than half the length of the boat, thus making a bluff entrance a necessity. This seems to be the rationale of the "cod's head and mackerel's tail" precept of those days.

Presuming this first requirement to be fulfilled, and presuming also that all sharp corners or abrupt unfairness of surface are avoided, the remaining requirement concerns the shaping, not primarily of the outline of any of the actual lines, whether "water-lines" or other, but of what is known as the "curve of cross-section areas," or curve of displacement."

In order to make the best use of available length in minimising resistance due to wavemaking, it is essential that this curve should 66 pretty closely resemble a curve of versed sines or "wave-line"; but the very finely tapered terminations of the curve must be somewhat blunted in order to make the most of the length. This being the real nature of the requirement to be fulfilled, it follows that the precise character to be given to the "water-lines,' or horizontal sections, must largely depend on the character of the vertical longitudinal sections, or "sheer profiles," and "buttock lines." Thus, in a vessel with a deep forefoot and straight keel, the surface water-line almost inevitably approximates to the wave curve," showing considerable hollow, and the fuller and more U-shaped are the bow crosssections, the more pronounced will the hollow be. On the other hand, in boats with no forefoot at all, like modern yachts, a concave water-line, or, indeed, anything except a convex one, would necessarily give too little area of cross-section in the forward part of the forebody. The clue, therefore, to the apparently inconsistent changes which have at various periods taken place in the character of the water-line, must be looked for mainly in the developments which have taken place in the profile. These, again, evidently hinge, to a great extent, upon developments in the shape of cross-section. Thus the cutting away of the forefoot and all "deadwood" was consistent with and fostered the fin, or plate and bulb, types of construction, though the feature was doubtless accentuated by the influence of measurement rules.

The question of proportionate length is the only one in the first rank of importance which has not been touched upon, and this cannot be fully considered apart from the effect of "size" and the influence of measurement rules. But it is worth while noticing, that besides the tax on length, which has hitherto entered into every measurement rule, there are certain natural considerations of importance, which tend to impose an early limit on development in the direction of increased length. Length, besides increasing the area of wetted surface, is a most potent factor in weight of hull. If an imaginary design of given type be taken, and length be increased without increasing displacement, the result must be diminished ballast, which, with diminished crosssection dimensions, will give very greatly diminished sail-carrying power; and, with the consequent rapid decrease in the proportion of sail area to wetted surface, the limit of advantage of length, for racing purposes, will be very quickly reached, so long as there is a reasonable proportion of light weather sailing and windward work to be reckoned with. Increase of length may, in fact, be properly regarded rather as an instrument to enable a fuller form of cross-section and relatively heavier displacement to be used without too serious a sacrifice of speed off the wind. In other words, speaking broadly, a certain displacement requires a certain length to enable the available driving force to be utilised with the greatest advantage in propelling a boat off the wind in fresh breezes; if greater length than this is given, the slight further gain obtainable under those conditions of wind and sailing will be too dearly purchased at the cost of greater loss in light winds, and in turning to windward. The allowance of length which a given displacement thus requires will be increased, indeed, by developments in structure and design which tend to increase driving power relatively to resistance, in the manner already considered, and thereby raise the standard of attainable speed. But, apart from developments of this kind, there is not likely to be any marked increase in length, except as the necessary concomitant of an increase in displacement. of close-windedness as affected by shape must be considered. It does not, indeed, follow that the closest-winded boat will be always the fastest, even to windward; but a certain high degree of close-windedness is certainly essential to first-rate performance to windward.

Close-windedness is of course favoured by high lateral resistance, but, strictly speaking, it depends not so much on lateral resistance simply, as on the ratio of lateral to fore and aft resistance; and it may, therefore, be favoured by decrease of the latter as much as by increase of the former. This is an important point to bear in mind, especially since decrease of fore and aft resistance, if secured without forfeiting sail-carrying power, means increased speed through the water also.

The lateral resistance of a vessel's hull acts as a lee-board and prevents her from being driven sideways or to leeward by the force of the wind.

In boats of the extreme "plank on edge" type, the entire area of the immersed profile must count at something approaching its full value by way of lee-board. In those of the extreme fin, or plate-and-bulb type, on the contrary, almost the entire leeboard duty may be presumed to devolve on the plate or fin and rudder. In craft of an intermediate type, theory can do little to assess the leeboard effectiveness of different positions of the immersed profile.

The requirement of effective lateral resistance, for promoting close-windedness, though one of great importance, does not seem greatly to modify the problem of best design for speed, as already considered, because the depth of keel requi Lite for good sail-carrying power will generally in itself provide a fairly adequate leeboard. But it is clear that the general tendency of importing leeboard considerations into the problem must be to attach somewhat greater value to depth of keel than considerations of sail-carrying power relatively to resistance would alone warrant.

In theory the lateral resistance of immersed profile ought not to be affected by the shape of sections, and is not, I believe, considered to be affected by the majority of designers; but in practice, according to our experience, the leeboard action due to a given number of square feet of plate and bulb is superior to the leeboard effect of the same number of square feet of immersed surface of an old-fashioned keel boat. But when all is said and done the quality of close-windedness is still mysterious and difficult to trace. The productions of some designers are always more weatherly than those of other designers, and the reason why is impossible to detect. The shape of forward cross-section has much to do with it, as has also the securing of perfect balance of sail plan, and the proper relations of the centres of gravity, lateral resistance, and effort. The effect of wind on sails in beating to windward will be dealt with later on, and we may now turn to the consideration of speed as affected by size, and the influence of measurement rules upon design.

Imagine two yachts, the one a precise model of the other in every respect, but on a smaller scale; and suppose that they are both sailing in smooth water, with all sail set, on the same point of sailing, with sails similarly trimmed, and heeling at the same angle. A very simple calculation will then prove that in order for this condition of things to obtain, the wind speed in the case of the smaller yacht must be less than the wind speed in the case of the larger yacht, in the ratio of the square root of their respective linear dimensions. As an example, if the smaller one is onehalf the size by linear measurement of the other, the ratio of the wind speeds must be Beating to windward is the crucial test of excellence in a fore and aft vessel, and the quality or 0707; and under these circumstances, the speed of the smaller yacht through the water will be less than that of the larger, in the same ratio.

Subject to certain minor qualifications, this theoretical proposition furnishes a sound and nearly exhaustive exposition of the principle of the influence of size upon the speed of sailing yachts. It is important to notice this, because it is sometimes urged that the true factor of speed is not size generally, but length simply, because the length measures what is sometimes called the "finality speed"-that is, the speed at which resistance commences to mount up so fast as to impose a nearly hard and fast limit to attainable speed. But, as has been already pointed out, increase of length does not always afford a royal road to increase of speed, because beyond a certain point it involves, ceteris paribus, such a sacrifice of sail-carrying power that the critical point of "finality speed" will not be reached at all. In fact, it comes to this: that when the best has been done that can be done by selecting the best type and proportions, the most efficient way of getting more speed is by a simple increase of scale, in other words by increase in all dimensions proportionally. a That mere bigness, apart from difference in shape or proportions, is a factor of speed has of course long been practically understood, and as soon as yacht-racing came to be systematically pursued it was found necessary to adopt some system of classification or allowance for size.

There would have been no difficulty about this if the circumstances were such as to constrain all yachts to be built on substantially identical models, since in that case any single easily measured leading dimension would have sufficiently served as a measure of size for penalising purposes.

But as plenty of opportunity for variation of shape and proportions existed such a mode of measurement must necessarily tend to dwarf the particular dimension which is measured, relatively to the others. And in the same way, however elaborate a measurement rule may be made, however many dimensions may be taxed, and however carefully the several taxations may be adjusted, the rule must inevitably influence design, by furnishing the designer with an additional aim, namely, that of getting the biggest boat for a given measurement. And thus, side by side with what may be called genuine speed qualities, and in some degree to their detriment, others which can be best described as measurementcheating qualities will always be found. On this principle it would be easy to trace the conspicuous developments of design in racing yachts, during modern times, to the changes which have been made from time to time in the measurement rules. Nevertheless, it would be a great mistake to attribute them wholly to the direct and immediate effect of these rules. As has been already noticed, the most conspicuous developments in hull design seem directly attributable to the introduction of novel structural contrivances in the matter of ballasting and to the realisation by designers of the importance of the resistance due to surface friction; but, on the other hand, it is only reasonable to attribute the structural contrivances to the pressure put upon the designer by the various rating rules. These rules may therefore be regarded as at any rate the indirect and ultimate causes of the several developments of type and form.

The three tonnage rules which were successively in force from the earliest days of systematic racing till 1886 did not, except in the case of a change in method of length measurement, differ very seriously in adjustment of taxation between the two measurements, length and beam, which alone they took into account. Under all of them alike, beam was heavily taxed, and the endeavour of the designer was to secure the requisite sailcarrying power with the minimum beam. The developments in mode of ballasting were all in favour of this object, and when the whole of the ballast came to be placed on the keel, yachts attained the phenomenal proportions of six beams to length.

The introduction, in 1887, of the tax on sail area was nearly equivalent, so far as hull design was concerned, to a tax on sail-carrying power, irrespective of the cross-section dimensions whereby that sail-carrying power was obtained; and the substitution of this for the tax upon beam alone quickly led to transverse expansion and vertical shrinkage of the body of the boat; and this produced the fin type in order to secure economy in wetted surface. At the same time, the desire to lessen length, which was the only hull dimension subject to direct taxation, made economy of displacement a prime necessity, and directly led to the development of the bulb keel as an instrument for obtaining the requisite sailcarrying power from a smaller weight of ballast. Reference has already been made to the alterations in water-lines which have resulted from developments in ballasting, and to modifications in the character of cross-sections and the concomitant changes in profile. It only remains to notice that the convexity of bow water-line which is a necessary concomitant of cutting away the forefoot and of extreme rake of stem-if indeed an up-to-date racing yacht can be said to have any stem-has probably been accentuated by the desire to make the greatest use of overhang in order to increase the effective length when sailing, as much as possible beyond the length as measured for taxation with the vessel upright and at rest.

The shallow character of section favoured by the bulb keel type lends itself especially to this object, and so well has it been accomplished, especially in the smaller classes, that a boat measuring, say, 25 feet on the load water-line when upright will, when heeling over to a moderate breeze, lengthen out to, say, 30 feet. The additional immersion at the ends, due to the creation of waves, adds also to this result.

In considering the effect of the rule introduced in 1895, it may be noticed that as draught, as indirectly measured by girth, was taxed as well as beam, in principle the change consisted mainly of a partial restoration of taxation of extreme cross-section dimensions which contribute to sailcarrying power, in place of the mere taxation of the sail-carrying power obtained. The particular mode of measuring the girth, viz., all round the hollow of the section, was, of course, an additional hit at the bulb keel type, and at hollowness and leanness of section generally. At the same time the relaxation of the tax on actual total area of sail spread had already arrested, and to some extent reversed, the undesirable tendency towards the concentration of the whole sail spread into the mainsail. ar The results were in a measure salutary, and the rule answered fairly well in vessels of some size. In the small classes it certainly did not deter building; but it had the effect of transforming the five-raters from nice, wholesome boats, moderately canvassed with two or three working sails, into horrid little toy ships with topsails and jibtopsails and all the paraphernalia of a "yacht."

The inclusion of the "d" factor in the formula of 1901 effectually put a period to the construction of yachts with excessively hollow midship sections. The tax on girth difference, indeed, was so heavy that designers went to the opposite extreme, and the midship section of some of the boats built under this rule were too much of the "pegtop" type to be altogether desirable. Another feature in yachts of this period was an objectionable profile which was the result of the girth station being arbitrarily fixed at o'6 of the waterline from its fore-end. As any draught aft of that station escaped taxation, yachts were designed with exaggerated rake of keel, the greatest draught being at or near the heel of the sternpost and some distance abaft the girth station. Such vessels proved wild on the helm, and, when ashore, "stood on their heads." We have already referred to the long flat overhangs of yachts built under this rule, which proved an additional source of weakness to vessels that, in the absence of scantling restrictions, were already constitutionally weak, but from the point of view of "type" the yachts were a distinct improvement on their predecessors. Of the effect of the International Rule it is as yet premature to speak. It may, however, be noticed that steps have been taken to eradicate the defects noticeable in vessels built under the 1901 formula. To check undue rake of keel, the rule provides that the girth shall be taken at a station where the measurement is greatest, although a certain amount of latitude is allowed in the fixing of the girth station when the keel underside line is straight. To restrict the length of flatness of overhangs, the difference between the girth at the bow water-line ending and twice the freeboard at that point, and one-fifth of a similar measurement taken at the stern, are added to the length measurement. It is very doubtful, however, if this new tax will have the desired effect, as designers already show a tendency to ignore the impost, which, after all, does not amount to very much, and the overhangs of the Fife-designed 15-metre cutter "Vanity," which made her appearance in 1909, were quite as long as those of the yachts built under the last rule.

Having thus sketched out the principal theories under which a designer works, it will be well briefly to consider the means whereby he proceeds to give tangible effect to the owner's ideas of what he wants, and concrete form to his own conceptions of the best means whereby those ideas can be embodied.

Two broadly distinctive methods of procedure may be followed: first, a small scale model may be shaped out according to rough general outlines, approximately answering to the form of the midship section, principal dimensions, displacement, and rating required; which lines may be modified by the designer as the work of shaping proceeds.

From this model, when thoroughly perfected and approved of, the "offsets"- which are necessary to lay off the lines of the vessel full size-may be taken, and drawn in chalk, properly faired, on the floor of the mould loft. This method, though it is still adopted to some extent, may be regarded rather in the light of a relic of former times, when hewing and fashioning to the eye was ill-important, and was, on the whole, the most effective agency in the work of designing. But in these modern days, when our insight into the laws governing the movement of solids through water, the effect of wind on sails and the results of the various forces acting upon a vessel under sail, is much keener than it was heretofore, geometrical rule and scientific accuracy of calculation count for more than eye, and the preparation of a design has become the product of the drawing office rather than of the model-maker's bench.

Nevertheless, the practice of first pleasing the eye by means of a model, which can be licked into shape with the gouge and the spoke-shave in hand rather than the pencil and the measuring scale, has still some votaries, and it must be admitted that in old times designers, relying upon THE TATE, LIBRARY, BRIXTON, S.W. the eye and practical experience, turned out remarkably fast and successful vessels. The superiority of scientific drafting to eye lies principally in this, that whereas the old-time designers made frequent mistakes, such accidents are very rare now, and a first-class designer can be relied upon to turn out a first-class article.

The second and more approved method is to scheme out and draft the form of the vessel on paper, to the scale of, say, quarter or half inch per foot, and to construct a half model from this draft, carefully faired.

But the best system of all consists, as is usually the case, in a compromise. Lines of the proposed vessel should be carefully drafted and faired on paper, then a half model should be made in wood, or, as I personally think better, in modelling clay, or wax, from those lines. This half model should be worked over and perfected by eye, and "VALKYRIE." finally the lines should be taken from the model, transferred to paper, and again accurately faired.

The lines can be taken off the model by shaping moulds of cardboard or thin wood to fit accurately to the model at stated and equidistant intervals; and by other methods known to designers. From the sections thus taken, the water and other lines can be arrived at, and the whole plan fairedthin wooden battens. that is, drawn to natural curves by means of Lastly, a wooden model should be made, not so much on account of its conveying to the owner, of the actual vessel than the plan of lines, but designer, or builder, a more realistic impression because it is almost indispensable as an aid to the draughtsman in arranging the framework and the plating and planking of the hull structure, and ordered. in measuring off the quantities of material to be The draft plan exhibits, by a series of curves, and straight lines, the contour of the vessel's hull longitudinal elevation, showing the lines of length on three distinct planes: the "sheer plan," or from stem to stern-that is to say, the sheer-line, water-lines, line of keel, and the lines of height from keel to gunwale-namely, frame stations and stem and stern; the "half breadth" plan, which gunwale or deck margin line and the water-lines shows the lines of length and breadth, namely, the from stem to stern; the "body plan," which shows all lines of breadth, such as water-lines, and line of deck, and all lines of height, such as frame stations.