| GENESTA, 1885. | VALKYRIE III., 1895. | |
| THISTLE, 1887. | SHAMROCK, 1899. | |
| VALKYRIE II., 1893. | SHAMROCK II., 1901. | |
| Fig. 42.—British yachts entered for the America Cup race, 1885–1901. | ||
In a very interesting article in Harmsworth’s Magazine, in 1901, Mr. E. Goodwin has traced the gradual evolution of the modern yacht, such as Shamrock II. or the Columbia, from the America.
No doubt the methods of “measurement” in force at the time, or the dimensions which determine whether the boat can enter for the Cup race or not, have had some influence in settling the shape. The reader, however, will see, on comparing the outlines of some of the competing yachts as shown in [Fig. 42], [20] that there has been a gradual tendency to reduce the underwater surface as much as possible, and also to remove the wave-making tendency by overhanging the bows. The only rule now in force restricting the yacht size for the Cup race is that it must not be more than 90 feet in length when measured on the water-line. In order that the yacht may have stability, and be able to carry a large sail-surface, it must have a certain depth of immersed hull. This is essential also to prevent the boat from making leeway when sailing with the wind abeam. But consistently with this object, the two great aims of the yacht-builder are, first, to reduce as much as possible the skin friction by making the yacht-surface smooth and highly polished. Thus modern racing-yachts are not always built of wood, but very often of some metal, such as bronze, steel, or aluminium alloys, which admit of a very high polish. This hull-surface is burnished as much as possible before the race, to reduce to a minimum the skin friction. Then in the second place, the designer aims at fashioning the form of the bow of the yacht so as to reduce as much as possible its wave-making qualities. A fine type of modern yacht glides through the water with hardly any perceptible bow wave at moderate speeds.
Thus the following extract from the Chicago Recorder of September 4, 1901, respecting Sir Thomas Lipton’s yacht, Shamrock II., during her trials for the Cup race, shows how marked a feature this is in the case of a yacht of the best modern type:—
“With her owner, designer, builder, manager, and sailmaker on board, the yacht Shamrock II. sailed her seventh trial race to-day off Sandy Hook. Although at times there was not more than a three-knot air, at no time did the yacht act sluggishly.
“She slipped through the water at an amazingly good rate under the influence of her great mainsail and light sails. The water was smooth, but even when pressed to a speed of 9 knots the yacht made a very small wave at the bow, and left an absolutely clean wake.”
We may say, therefore, that the ideal form of yacht is one which would travel through the water without making any wave at all at bow or stern. This condition can, however, only be reached approximately, but the clear recognition of the principle has enabled yachts to be designed with vastly greater speed powers than in the old days of bluff bows and tapering bodies.
Before passing away from the subject of waves made by ships, it is desirable to refer a little more in detail to the complicated wave-system made by a ship in motion. This has been most carefully elucidated by Lord Kelvin, who, in this as in so many other matters, is our great teacher. Lord Kelvin has shown that if a small floating body is towed through the water at a uniform speed, it originates a system of waves, each one of which is of the form shown in [Fig. 43]. The whole system of waves formed is represented in [Fig. 37], where the position of the ship or moving object is at the point marked A.
