The value of C for depth amidships can be found from the following table for varied proportions of length and breadth : It must be clearly understood that this is not an attempt to set up an arbitrary value for depth in yachts of varied proportions and sizes. But the formula is the outcome of the examination of many yachts of different sizes and different proportions of breadth to length, and so far can be taken as a guide to determine depth, if depth be not already determined by some other conditions.
We have hitherto only considered the proportions of length, breadth, and depth from a cruising point of view, but the proportions would only require very slight modification for a yacht intended to compete under the Y.R.A. tonnage rule; but it is pretty certain that this tonnage rule—whether wisely or not need not be considered—has checked the full realisation of speed that a yacht of any given weight or displacement should be capable of.
It was shown in the last chapter that, with a given displacement, an excess of beam is an enormous advantage for effective sail-carrying power ; and, according to some experiments made by Mr. Froude, and recorded by Mr. W. H. White in his valuable work on "Naval Architecture," * an increase of beam may result in a decrease of resistance. In designing two river gun boats for the Royal Navy of 110ft. length, and 6ft. draught of water, the question arose as to whether it would be more advantageous for speed to give them a breadth of 34ft. instead of 26ft. Experiments were made, and the result was clearly pronounced in favour of the greater beam. The broader vessel had practically no straight of breadth, or great length of middle body; and she thus obtained a longer entrance and longer run, with a greater area of midship section. The displacement of the broader
vessel was 370 tons, and that of the narrower 350 tons. The resistance of the broader boat at a speed of nine knots was only two-thirds that of the other, and this great advantage was mainly due to lesser wave-making. Whether in the case of vessels propelled by sails the advantage would be maintained by good performance in a strong wind and disturbed sea is perhaps open to doubt (assuming of course that there was no limitation in the draught of water), as there is no question that a long and deep body with any given length and weight has some advantages over a short and shallow body in a sea. Still there equally can be no question that vessels like the Guinevere and Seabelle would have an accession of good qualities by a moderate increase to their beam, even though such increase were attended with additional displacement.
The lines of the famous cutters, Kriemhilda and Vol-au-vent, in a certain degree, form a notable illustration of the use of length of body for a sailing vessel under some circumstances. The Kriemliilda is remarkable for her long body, and comparatively full entrance and run. The Vol-au-vent, of equal displacement, length, breadth, and depth, has a greater area of midship section, and her ends are finer; in fact, she has a shorter and fuller middle body. So far as the evidence of the performances of these two vessels go, there is not much doubt that for high speed in smooth water the Vol-au-vent has some advantage ; but in a much more marked degree the advantage rests with the Kriemhilda when sailing in a disturbed sea. If the Vol-au-vent had been given a little more beam, she would, in all probability, judged through the Arrow, have exceeded the performances of Kriemhilda on all points of sailing, and under all con ditions; but an addition of lft. to Vol-au-vent's beam would, under the present tonnage rule, have put a penalty of 12 tons upon her for com petitive sailing, and no doubt the penalty would justly value the effect of the additional beam. Thus far the rule apparently operates with the strictest precision; but it is only fair to state that, if the rule took no cognisance of beam, both Vol-au-vent and Kriemhilda would probably have been given a foot more beam, and both would have been the better for it.