Maple Leaf IV

Length overall

40' 0" (12.192 m.)

Length, waterline

40' 0" (12.192 m.)


8' 5" (2.565 m.)


3' 0" (0.914 m.)


5.25 tons (5,334 kilos)


55 knots


total h.p. 800

Propeller speed

1,100 r.p.m.

Propeller diameter

25" (0.635 m.)

Propeller pitch

47" (I.206 m.)

Beam length ratio

4 to 1

Speed ratio .


Rise of floor midships


Rise of floor aft



Maple Leaf IV is historic as she was the first boat in the world to attain a speed of 50 knots. She defeated the Americans and all the world in the 1912-13 races for the B.I. Trophy, or, as it is also known, "The Harmsworth Trophy".

I believe she would have again successfully defended this trophy in 1914 in spite of the strong American and French challenge; but the August start of the 1914-18 war cancelled this series of races, arranged for September, and the various challengers sadly returned home to America and Europe.

In addition to being a world-beater and a most historic boat Maple Leaf IV was the first boat I worked on as a young apprentice to S. E. Saunders, so she has a very special place in my heart and mind, that no other powerboat can ever take; I admired her, loved here very line, her every detail and her construction, with an affection that is still as strong as ever even to this day.

Although designed and built over 50 years ago, it is quite interesting to compare her speed with the present-day boats of similar size and horse-power described in this book. These are amongst the best in the world and, remembering that all the present-day boats have engines of less than a quarter of the weight per horse-power of Maple Leaf IV, very few go as fast.

Until this chapter all the designs in this book have been similar in that they have all been displacement boats, due to the heavy weight-per-horse-power of the propelling units, whether man or engine, for a man weighs a great deal for the power he produces; so does a steam engine which, in addition, must have its fuel and water supply.

William Henry Fauber of Chicago and Nanterre (Seine), France, was one of the great names of the early history of hydroplanes and he took out no less than nine British patents between the years 1906 and 1909.

Three years previous to designing and building Maple Leaf IV S. E. Saunders had built his first single step and other single step hydroplanes. But in Maple Leaf IV he went straight to the patent number 7834 taken out by Fauber on 8 April, 1908. Saunders, by applying his own knowledge and ideas to this patent, improved it out of all knowledge for sea work. He reduced the number of steps from 8 to 5 and, instead of the absolutely flat bow advocated by Fauber, he built in his own convex ‘V’ sections forward. His bow, as well as the lift from displacement through the concave sections, also had great lift from its down-sweeping chine and buttock lines combined with the gradual opening from the plumb stem to the ‘V’ sections; so that the ‘V’, gradually changed from the plumb bow to almost a 2 rise of floor at the forward step, a bow that was quite good in a seaway. Then, instead of having the fore-keel or drop-keel extending over the first two steps, as advocated by Fauber, S.E.S. designed in a quick hollow ‘V’ along the centre-line which gave a certain amount of displacement and grip on the water; there was no need for a forward skeg, as this kept the boat straight on its course.

It will be seen that Maple Leaf incorporated Fauber's idea of having a flat ‘V’ shaped to the steps when viewed from underneath, raking aft, so taking the step farther aft on the centre-line than at the side of the ship, a feature that Fauber claimed to give the boat more stability. But, generally speaking, Maple Leaf IV is exactly to Fauber's patent, for all the steps had the same rise of floor and all the points are on a straight line. The boat is, in effect, designed and built on an absolutely straight line fore-and-aft in elevation, except for the bow line which rises 2 from the fore-step forward. This is a form having the greatest lift, as all the steps throughout the length, being on a straight line fore-and-aft, have equal power. Maple Leaf IV is the best example ever built to Fauber's patent; S. E. Saunders' wonderful genius married to Fauber's patent producing perfection of line and construction, a superb combination of two great men.

By 1912 the petrol engine had reached such a stage of perfection that the engines of Maple Leaf IV only weighed 9 lb. per horse-power. This was an advantage over the great weight per horse-power of steam engines as this lightness enabled designers and builders to enter into an entirely new phase of design. Previously boats, of necessity, had to plough their way through the water, whereas now, in 1912, with the lighter petrol engines, a new prospect was opened up-that of travelling fast enough to lift out and hydroplane over the surface of the sea. From now on many of the boats in this book conform to this new set of laws.

Where under the old conditions of displacement, wave-making was reduced by long length and surface friction by narrow beam and circular sections. the skin friction could now be reduced by lifting the boat out of the water, so that approximately only half of her touched it; this eliminated wave-making, for a boat hydroplaning over the water makes no waves, only light spray thrown out on either side. So the years leading up to the 1914-18 war were packed with interest and excitement for naval architects in the high-speed powerboat field.

That master-builder S. E. Saunders was one of the pioneers and one of the greatest experts in the world of hydroplanes and flying boats and their light construction, and I was fortunate in being a young apprentice to him, for he was a most wonderful man. Not only had he great knowledge of designing and building, but he knew men, probably the most important virtue for anyone to possess in this world.

There are good workmen all over the world in every town and village; but never in my life, before or since, have I seen such a collection of good workmen of all trades as were collected by S. E. Saunders, for once you get over twelve duds creep in, unless the man at the top has great ability and knowledge of men.

When, years later, I founded my own firm, which soon started to grow and flourish, I engaged any new workman for two weeks only; directly he arrived I had a good look at his tools-their condition and sharpness immediately revealed his ability as a tradesman.

I would give him a week to settle into the saddle; then, during his second week, at the start of the day I would look at the job he was doing; and again at mid-day see how far he had progressed with Nat and how good a job he was making of it; then again at knock-off time in the evening. So I would see exactly what he had done and what sort of job he had made of it and I would do this every day possible during his second week.

Towards the end of this second week I had decided whether to keep him for ever or let him go; if he was going to leave I would generally say ‘There is another week's work for you-you leave at the end of three weeks,’ and he was pleased as he had an extra week's work above the two he was taken on for.

Workmen believe that if they are not caught sky-larking and lazing their time away, their employers do not know what they do; but I always judged men by the amount of work they did in a day or a week and how well it was done. You do not have to watch a man, only the work he does. This, and many other items of knowledge, I learned from that master builder S. E. Saunders throughout my wonderful apprenticeship with him.

The first hydroplane S. E. Saunders built in 1908 was 26' long and was, like most of his boats, built of that first-class wood, Honduras mahogany, but she was only a partial success-she proved the way without being perfect. She would get up and plane along perfectly at 26 knots; then her bow would rise higher and higher till it overbalanced and crash down swiftly and plunge in until the water was level with the top of her stem. This would slow her down to 8 knots. Then she would start to climb out again and do the same thing all over again, re-lifting her bow and going at 26 knots until it was top heavy, once again plunging her bow in and dropping to 8 knots; this has since been called porpoising, but she did prove that hydroplaning was both sensible and possible.

I bought this old hull and made a 16' sailing and paddling canoe from the top-sides, which were single skin. The bottom, being double diagonal and fore and aft planking, was so well fastened together that nothing could be done with it. I sailed and paddled many hundreds of miles in this little paddling and sailing canoe built from the top-sides of S. E. Saunders' first hydroplane, so it was only natural my thoughts often roamed to high-speed powerboats as I enjoyed my cruises in her.

Even to-day, some sixty years afterwards, very little is known about hydroplanes at sea, yet Saunders' idea of a single step hydroplane was right and has been improved by many in the years that came after.

Although we call this a single-step hydroplane, she actually runs along on two planing surfaces or steps, one amidships, the second at the transom right aft; the hydroplane has a great advantage over the normal stepless chine boat as her angle of attack is built into her, so she does not have to alter trim in order to plane, like the stepless boat. The hydroplane just lifts bodily out of the water, fore and aft the same amount, and skims along the top. She is more stable fore and aft than the stepless boat which is only skimming along on her transom, for a single-step hydroplane, skimming along, is supported at two places, amidships and aft, and this keeps the bow in contact with the sea, so that waves cannot strike with their own force; such a hull resists pitching and also scending, whereas the stepless boat, planing on its tail only, must of necessity ride with its bow out 3 or 4, chopping continuously up and down, up and down on its way along.

Another point in favour of the hydroplane is that when she is in disturbed water the 3 or so angle of attack built into her fore-body as well as her after-body gives her bow a definite lift over the waves forward of amidships and helps her in a seaway.

All vessels, whether sail or power, planing or displacement, dread broaching and a fore-body with definite lift is the best antidote to broaching; so a well-designed hydroplane is no worse off, except for her higher speed, than a normal powerboat, and her speed can be reduced to suit the seas.

Laws for high-speed powerboat design from now on were completely changed, for instead of a vessel cutting and ploughing her way through the water, as in the past, she could be driven up out of it and skim over the top far beyond the speed dreamed of by designers confined to displacement hulls and heavy-weight machinery and fuel.

S. E. Saunders' first single-stepped hydroplane was designed for smooth water and to plane at all costs; so her bottom was flat throughout its length in its athwartship direction. There is no argument that the level bottom has the greatest lift and that as we increase the rise of the floor athwartships so we decrease the lift. To illustrate this point we could say that the flat-floored boat has 100% lift; if the bottom has a rise of floor of 45 it has only a 50% lift and if the floor went up plumb it would have no lift at all.

A flat-floored boat, however, while having 100% lift, also receives 100% pounding from the sea whereas the 45 rise-of-floor boat, with only 50% lift, only receives 50% pounding from the same sea and the design of any high-speed powerboat, hydroplane or stepless boat must be designed with this broad picture in mind.

Where 100% speed and planing ability is required, providing this is to be in smooth water, the boat can be designed with practically a flat bottom and the fore-and-aft angle of attack designed into her various steps to suit her speed. The naval architect must keep in the forefront of his mind the purpose for which the vessel is to be built; if she is for smooth water and high speed only she can be broad and short and flat bottomed; but if she is to go to sea he must sacrifice ultimate speed for sea-keeping qualities.

To-day a great many people find water-skiing delightful, for here they are standing on a pair of skis (sometimes only one) and planing over the surface of the water at whatever speed the boat ahead tows them at. These skis are absolutely flat throughout their length with the fore-end curved up like a sledge to go out over the waves. As these skis are approximately 6" wide and 6' long they have a beam length ratio of is to i and, though this proportion is inefficient for planing, they do plane. They have the great advantage of not being thrown out of water by every sea they hit for the narrow (and badly proportioned for planing) water-skis cut partly through waves and partly lift over them, thus eliminating most of the shock of the waves.

At low speeds these skis run with an angle of attack of 45, but as the boat and the skier gather speed the angle of attack flattens until finally it is from 3 to 10 depending entirely upon the speed of the boat towing the skier. Some skiers of great skill carry another person on their shoulders and here the angle of attack of the ski is approximately doubled because the weight on the skis is also doubled. From watching a water-skier a naval architect can study problems of a planing boat, for we can learn from almost everything we see in this world providing we have eyes with which to see.

Under the new set of conditions and laws that govern planing boats, the wider the boat and the shorter she is, the more efficiently she will plane. We have only to look at a bird or an aeroplane to see this. A bird's or an aeroplane's wing, on which each planes, is short in its fore-and-aft direction and very wide; the wider and the narrower the wing, the greater the lift. And so it is with high-speed powerboats. This truth is undoubtedly the reason that hydroplanes are not as popular at sea as they should be.

Designers out to get the utmost lift developed broad, short hydroplanes. They lost sight of the fact that singlestep hydroplanes halve their length in the bottom, for this is divided into two by the step amidships; the aspect ratio is therefore double what it appears to be. If hydroplanes for sea work are designed with narrower beams, they can combine the softer-riding qualities, found in the long, easy lines developed by displacement boats in a seaway, with that of great lift, and so can have the best of both worlds-soft sea-going ability, with the high speed and great economy in fuel of hydroplanes. If the transom is kept fairly wide the two sides of the boat submerged in the water aft act as skegs and keep her steady and free from broaching in wind and sea.

Maple Leaf IV, it will be noted, has five steps which were very effective for she lifted up bodily fore-and-aft and skimmed over the water on these five wide narrow wings. As each step was the full width of the vessel, and very short in its fore-and-aft length, each step in contact with the water had much the same proportions as an aeroplane's or bird's wing.

Great stress has always been laid on the importance of air in the space behind each step, as a vacuum here would cause the boat to slow down or, if formed on one side only, might make her sheer and become unsteerable. Maple Leaf IV had five pairs of great brass tubes behind each of her steps to prevent this; but never once, in any of her trials, could any suction of air flow be felt down or up any of these tubes by putting a hand over them and stopping them off. It would seem from this that when a boat is travelling over the water at 50 knots and more, aerated water is passing swiftly under her bottom, water with a fair amount of air imparted to it by the bow wave, and that whatever amount of air is needed is there in the aerated water rushing along under the bottom. In these days we do not fit tubes behind steps, saving work, material and weight, and avoiding the possibility of leakage.

The highly efficient steps in the hydroplane cost extra money to build, and, in addition to this, take away the continuous flow of strength through the bottom of the boat. For where the topsides, port and starboard, form a continuous girder the full length of the boat, the keel and the bottom planking have by necessity to be cut off at each step; to compensate for this it will be seen that the engine bearers of Maple Leaf IV are built as a continuous lattice-work wooden girder almost the entire length of the boat. In these days of the cruising hydroplane, I design the girder to form the support for the cockpit floor, the fronts of the galley, W.C., and the fronts of various bunks and berths; it is not an added expense or weight, as it also forms the engine beds running the full length of the vessel and so strengthens and stands the boat in good stead in a seaway.

The lines of Maple Leaf IV show that her bottom sweeps down in a deep hollow little ‘V’ on the centre-line. This undoubtedly helped her steadiness in direction for she was very easy on the helm; this hollow ‘V’ was in effect a long keel that chopped up and down and eased the first impact with the sea. The section sweeps out of the hollow ‘V’ into a 2 continuous rise of floor throughout her length, there being no change in her rise of floor from midships to her stern.

It will be noted that each of the five steps has an angle of attack of 2, so she did not have to lift her bow out to give an angle of attack-it was already put into her hull on the designer's bench; these steps cut Maple Leaf's skin friction down some 50% and her wave-making to nothing, which explains why she could skim over the water at 55 knots.

Topsides are flared off forward to throw the spray and water out and away from the boat, but aft, it will be noted, she tumbles home, so there was no great broad stern to suck air in behind her and stop her; it also eased the resistance of side winds on the hull, quite an important factor in high-speed work.

Her construction was of Honduras mahogany, the bottom and topsides being of three skins, the two inner double-diagonal, and the outer fore-and-aft planking all sewn together with copper wire. This form of construction made S. E. Saunders famous, for Maple Leaf IV belongs to the days before plywood could be used in sea water, glues of that day being unable to stand up to salt water as they do to-day.

A great many improvements in metal and glues have taken place during the 50 years since Maple Leaf IV's day, all of which enable us to build lighter and stronger boats. But even with all these modern advantages, boats of Maple Leaf IV's size to-day, with the same horse-power, are no faster than she was, for she compares in size with the largest boats allowed in the Miami to Nassau Race and the Cowes to Torquay Race.

Of course there have been faster hydroplanes, such as the record-breaking Bluebird, as in her we have a much smaller boat with an engine of much greater horse-power and less weight per horsepower. But the total of 800 horse-power in Maple Leaf IV compares exactly with the 800 horse-power Daytona and the 800 horse-power Ford engines used regularly in the Miami and Cowes-Torquay long distance races of to-day, the only difference being that the engines are now a quarter of the weight per horse-power to those fitted in Maple Leaf IV. Maple Leaf IV herself, at 40' waterline, compares exactly in size with the largest allowed in these two great International Races.

All this proves how pleased and proud (and possibly biased) I am to have started my apprenticeship to the shipwright's trade on her, and how wrong naval authorities and naval architects are to have neglected hydroplanes for sea work for almost So years. Compare Maple Leaf IV's 55 knots with Ursula's 35 knots and remember that both boats were designed and built by the same builder at much the same period, and were exactly the same size with exactly the same horse-power. This will give us an idea of the increased speed, and with it increased economy, of the hydroplane over the stepless hull, for Maple Leaf IV would go eleven miles to Ursula's seven miles with the same horse-power and fuel, an increase in speed and economy of well over 33?%.

(Reprinted from Seamanlike Sense in Powercraft by Uffa Fox, [published by Peter Davies (London : 1968)] pp.39-45.)

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Leslie Field, 2001