Tadpole — A British Skimming Boat [1909]

Remarkable in the extreme is the latest product of that expert of all things marine—Sir John Thornycroft—who is the designer of Tadpole, the 22-foot skimming boat, which has shown herself capable of phenomenal speed by traveling at 27 knots. She is remarkable, too, in that even with her ability to go so fast she provides comfortable accommodations for a crew of four.

Tadpole combines the principles of boat and hydroplane. The "boats it" at slow and skims at high speed. In appearance under all conditions, says the Automotor Journal of England in describing her, the new craft looks like a boat pure and simple, but one having an abnormally developed forepart, which makes the name "Tadpole" unusually appropriate.

With a beam of 6 feet 10 inches there is plenty of room all around the engine, but right aft the cockpit narrows so much with the fine lines of the stern that the transverse seat placed there is only just wide enough for one. The hull, which is built of single-skin mahogany, has very peculiar lines which are not easily described. The bottom of the boat is to all intents and purposes flat, although actually it has a very slight radius in transvers section. Some 3 feet aft of the center, the bottom of the boat begins to run up towards the stern, and at the exact point where this change of slope takes place there is also a slight change of level, constituting a very small step, which, however, is of nothing like the proportions of the notch which commonly forms a feature of the hydroplane hull.

Its object, however, is the same, which is to break away the water from its adhesion to the hull aft, and thus to prevent the suction on the stern which would otherwise destroy the effect sought. Under the bow is a web placed edge on to the direction of travel, and carried by this web is a spade-shaped plate which juts down just like an external foot and just touches the surface of the water when the boat is skimming. Under these conditions the contrast between the hull proper and the water is limited to an area which it is difficult exactly to define. This surface must not in any way be regarded as a separate member like the foot. It is merely a portion of the hull itself, and can vary if necessary from the proportions shown in sketches.

The propulsive power is developed by a 4-cylinder engine having a bore and stroke of 4 inches by 7 inches, and it is estimated to give 58 h.p. when running at 1,500 r.p.m.

Various propellers have been tried. The one with which a speed of 27 knots in an average of six runs, and a total load of 1 ton, has been obtained, has a diameter of 18 inches.

(Transcribed from MotorBoating, October 1909)

[Thanks to Greg Calkins for help in preparing this page --LF]

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