TEN-TONNER YACHTS The design for the yacht of 5 tons can be used for one of 10 tons by multiplying all the linear measurements by 1.25 ; or by dividing the linear measurements by 0.8. Thus, take the length on the water-line of the 5-tonner as an example. The length is 32ft., then The cubic quantities will, of course be doubled, and it might appear to be a rather anomalous condition for a yacht of " 10 tons" racing tonnage to have 18 tons actual weight or displacement ; but such an apparent anomaly is very likely to occur whilst only two dimensions are used in the Y.R.A. tonnage rule to express nominally a quantity in cubic measure. We apprehend no objection to a " 10-ton " yacht having 18 tons displacement, providing so much weight secures some good quality not otherwise obtainable at so small a cost. For instance, say a yacht 40ft. long has to carry 1200 square feet of canvas in her lower sails to obtain a given speed ; this sail, we know by experience, a yacht can carry if she has about 9ft. beam, 6ft. 6in. draught of water, and 18 tons dis placement. But then such a yacht would be termed by Y.R.A. measure ment 1314 tons; and, as Y.R.A. " tons" are a kind of assessment, the object of every yacht designer is to design a craft that can carry the sail and obtain the given speed, and yet be assessed at less than some given value, say 1314 tons. The design we give (Plate XXVI.) has been prepared with a view of obtaining the utmost advantage out of the Y.R.A. rule. It is for a 10-tonner, 40ft. long, and only 7ft. 7in. in breadth ; but, by virtue of increased depth, she has the displacement and sail area of a 13-ton craft, 40ft. by 9ft., and in all probability would be the equal of such craft in point of speed. In designing a yacht of such extreme proportions the main things to consider will be a sufficiency of depth, a proper amount of displacement, and as small a frictional surface as possible. The principal dangers of increasing the depth are these : too great displacement may be the result, and too large an area of wetted surface. The inconvenience of too great displacement is that, with any given length, the entrance or the run may be too full, or the middle body may be too full, so that when high speeds are contemplated exaggerated wave-making would be the result. This inconvenience may, however, exist with a comparatively small displacement, but of course will be less pronounced.
The objection to an excessive area of wetted surface is that at low velocities, or in light winds, the frictional resistance will be exaggerated, and the results anticipated from the large sail area may entirely fail.
To avoid a too great displacement, a suitable quantity was determined upon at the outset in making the design for a 5-tonner ; and to avoid any unfair fulness, it was disposed of on the wave principle by Mr. Colin Archer's formulae (see ante, page 49). In order that the fore body might be of the wave form, without being unduly lean, it was necessary to cut away the fore foot, or what is usually termed gripe, as much as possible, and this condition necessarily involved that the depth of body amidships should be great. Here two objects were at once secured : a reduction of wetted surface, where it most needs reduction on account of the intensity of the friction on the surface of the fore body ; and the practicability of stowing the weights at a great depth to compensate for the reduction in beam. To what extent the objects sought have been attained can only be surmised by a comparison with other yachts of similar pretensions. In point of length and breadth the Florence affords an example, judged through the Y.R.A. rule, that enormous advantage, so far as speed goes, is dependent upon length irrespective of beam. The Florence, however, has, compared with the design, a moderate draught of water and displacement, and she is not conspicuously stiff, although so very fast at reaching. The Lily, on the other hand, whilst not con spicuous for speed, is an example of the influence great stiffness has on weatherliness.
The design has greater length than the Florence, and larger sail area, and yet would be much stiffer. Her wetted surface is probably about the same, and the conclusion is that she should have greater speed in strong winds. The only circumstance to excite doubt about this is the displacement; but, as it has been so carefully disposed, it is unlikely that it will interfere with the anticipated speed qualities.
With regard to the sail area, it will be observed that it is greater than is the sail area of either Florence, Lily, or Quiraing. The lower mast, however, is comparatively short, but the boom is long. The spar plan was purposely planned like this for two good reasons : in the first place, a long heavy mast very seriously interferes with stability ; and farther, for any given area, a high narrow sail has a much greater heeling moment than a low broad one. However, there is nothing unusual in the length of boom to length of mast, as it is exactly in proportion to the length of boom and mast of Formosa. The bowsprit is comparatively short, but the foresail is large ; and it is expected that the sail plan would, on a wind, be found well balanced.