"Then began a long and rather tedious, but interesting, series of experiments with floats of many shapes and sizes, weighted with sand-bags to represent the weight of my airplane, plus pilot, and towed at the top speed of our motor launch. From these experiments there evolved the first successful float." - Edward Wakefield.
On 25 November 1911, Waterbird made the world's first successful flight to use a stepped float, only achieved after two years of persistent experiments and when a second step was added at the stern.
The concept was described by Gertrude Bacon, who flew at Windermere in July 1912, in her book All About Flying, published in 1915:
The lower surface of the hydroplane float, instead of being all of one piece, changes or 'steps' abruptly to another level. The main object of the steps is to help the float become 'unstuck'. There is a great tendency for water to hold on to an object lying flat upon it. Lay the palm of your flat hand on the water and feel the resistance offered when you lift it straight upwards. The step allows the air to come in underneath the under surface of the float and so does away with the suction effect.
The following are examples which used steps: Miss England powerboat, Bluebird K3 and the glider flown from Windermere in 1943 by Cooper Pattinson and Wavell Wakefield.In earlier Sunderland flying boats, the hull step was an abrupt one, but in the Mark III it was a curve upwards from the forward hull line. The Mark III was the definitive Sunderland variant, with 461 built of which 35 were built at White Cross Bay, Windermere between 1942 and 1944.
"It was a clergyman, Rev. C. M. Ramus, who first suggested the hydroplane in 1872, and he drew the attention of the Lords of the Admiralty to his experiments and their results, for war ships, but the scheme as a whole was abandoned." – Flight magazine, 22 February 1913. "So far as one can gather, the patent taken out in 1906 by Albert Edward Knight is the first patent on record relating to 'stepped hydroplanes' [for boats]." – The Aeroplane magazine, 4 September 1913.
In 1911, Wakefield successfully applied for patents to cover the stepped float and its method of attachment. "This invention has for its object an aeroplane with means for enabling it to alight, float and travel along the surface of water and to rise again therefrom." Wakefield had successfully combined features of construction in a novel way.
On 15 March 1912, Wakefield entered into a contract with the Admiralty for his float and its method of attachment, but initially they had not been interested in his invention.
"The hydroplane float is 12 feet long by 2 feet wide by 1 foot deep, the sides are of ¼" mahogany, the bottom of 22 gauge aluminium and the top covering of Willesden waterproof canvas. Wooden lattice girder frames are fitted internally 8" apart to stiffen up the float and a centre longitudinal of wood runs centrally from bow to stern inside. Wood beading is used at the corners inside to ensure watertightness. No watertight compartments are at present fitted but Mr Wakefield says he can fit seven with about 15lbs extra weight. The weight of the float is about 96lbs, but with a new one under construction should weigh only 70, this latter has a duralumin bottom on which the sea has no bad effect. Two steps occur in the bottom of the hydroplane, one at about half way of 4" and the other 8" from the stern of 3 ½". The float is attached to the machine by a rubber spring 3 point suspension, the struts being of steel tubing." - Lieutenant Arthur Longmore, who test flew Waterbird on 20 January 1912.