John Thornycroft

Talks With Our Boat Designers: Sir John Thornycroft [1910]

John Isaac Thornycroft
John Isaac Thornycroft

Born in 1843, Mr. Thornycroft founded the firm of that name at Chiswick on the Thames. He subsequently studied shipbuilding with Messrs. William Palmer, of Yarrow, and afterwards entered the University of Glasgow, where he studied under Lord Kelvin and Professor Rankin, and made his mark as a mathematician of great ability. His career at Chiswick may be said to have started about 1870, when the Miranda was planned and built by him and evoked praise from engineers of the caliber of Lord Armstrong and Sir Frederick Bramwell. Mr. John Donaldson was in partnership with him from 1873 until his death in 1899. The firm is now a limited liability one, the change being made in 1901. , and carries on extensive ship and boat building work at Chiswick and motor vehicle work at Basingstoke. Knighthood was conferred on Mr. Thornycroft in 1902. His son, Mr. John Thornycroft, is now an active partner and a leading spirit in the business. As an expert who has been working for 40 years on fast boats, Sir John Thornycroft was asked what he thought of the possibilities of speed in the future.

"With certain classes of boats, notably the hydroplanes and similar designs, the limits are not yet reached, though in my opinion the ocean-going vessels must follow he rule of power in its relation to speed, have nearly reached their practical maximum. The internal combustion motor, however, is far from reaching its full development, and with it higher speeds might well become commercial.

"In the hydroplanes we have a new field in which the laws governing speed and displacement boats are being disproved every day. Here the speed is rapidly approaching 40 knots and will undoubtedly pass far beyond that in a short time. The improvement has been rapid. I was proud enough of the Gitania in 1878, when she, using a forced draught for the first time, did 20.6 knots on the lake of Geneva. We have come along a bit since then. Look at the torpedo and destroyer speeds, beginning with Lightning in 1876, 18 knots, up to Tartar in 1908, over 35 ½ knots. Miranda IV has done 30 knots here on the Thames and Gyrenus 22 at Monaco last year; this last I consider a good speed taking the great sea-going qualities on the boat into account.

As to the Miranda type, a few notes may be interesting. The main idea is to combine the boat and hydroplane, formed in a practical way, and the Miranda III did this in a way which encourages me to believe in the evolution of this class of vessel. She has an over all length of 22 feet and a beam of 6 feet 10 inches, which gives plenty of engine space. She tapers away greatly at the stern. Built of single skin mahogany, she has an almost flat bottom, which begins to run up astern about 3 feet aft of the centre. At this point there is a small "step," little more than a notch; in fact, it seems, however, to break the adhesive water from the after hull sufficiently well. Under the bows is a vertical web carrying a spade-shaped plate which just touches the surface at skimming speed, the rudder being just abaft of this. From one-third to half the boat’s length forward is clear of the water at speed, as of course is the tail, aft of the main plane. This plane at speed gives a supporting surface of some 6 feet fore and aft by say 6 feet transversely, 36 square feet in all, while the fore "foot" has about 10 square feet. With an 18-inch propeller the boat, loaded with four passengers, the total weight being about 1 ¼ tons, has planed successfully, and I think would do even with a considerably larger weight. The foot has a useful action in steadying the boat in choppy water and preventing the tendency of the hydroplane towards an erratic "wriggling" motion. I hope to see the type "skim" down to as low as 16 knots before long; at present 20 knots is about the figure. All this field is so new that there is a lot to be learned, and the speeds shown by the hydroplanes recently defy all the usual calculations. I think some compromise between hydroplane and boat will be the surviving form and there is room for indefinite improvement in this direction."

(Transcribed from MotorBoating, September, 1910, p. 17.)

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