High Speed Motor Boats [1905]

The Influence of Powering, Propellers and Hulls Upon the Speeds Attainable With Small Boats

A. Tellier. — Societe' des Ingenieurs Civils de France

Apart from the importance of the development of mechanically propelled vehicles on common roads, the efforts to produce light and powerful motors for automobiles have resulted in effecting an unexpected influence upon other methods of locomotion. There is no doubt that the recent progress which has been made in dirigible balloons is entirely due to the improvements which have made possible the reduction in weight of the internal-combustion motor, and, in like manner, the so-called motor-boat, an unfortunate appellation for an otherwise nameless craft, owes its existence to the development of this same high-speed, light-weight engine.

In a paper presented recently before the Societe' des Ingenieurs Civil de France by M. A. Tellier, fils, some valuable information is given about the construction and performance of some small racing boats propelled by gasoline motors, and the manner in which the data and results are presented renders the information of more service than is usual. The trials recorded in the paper extend over a period of three years, and include information about boats of different designs, using various motors and propellers. Apart from the direct value of the information thus gathered, it may be useful for consideration in connection with the extravagant statements sometimes made, such as the prediction that internal-combustion motors may soon be expected to replace steam engines for torpedo-boat propulsion, whereas the largest engines of the internal-combustion type operating regularly in such boats do not exceed 150 horse power in capacity.

The first boat considered by M. Tellier the the Lutece, built at the close of 1901. This is a vessel of 15 meters length, with a hull of cedar, having a displacement of two tons (metric), the hull itself weighing bu 600 kilogrammes, or only 30 per cent of the total displacement. The Lutece was originally equipped with two four-cylinder Panhard motors, each of 40 horse power, arranged with a magnetic coupling and differential speed gear. The propeller had three blades, the generatrix being perpendicular to the axis, the diameter being 0.7 metre. Under these conditions, with both motors in operation, at a speed of 850 revolutions, a speed of 18.4 knots was attained. Although the weight of the motors was only 7.5 kilogrammes per horse power, this soon was found heavy by comparison with later machines, and in 1903 the boat was fitted with an improved Panhard motor, giving 80 horse power with one four-cylinder engine at 900 revolutions, this machine, including the fly wheel, weighing only 300 kilogrammes, or 3.75 kg per horse power, or one half that of the old motors.. Although an improvement in working was apparent, the speed was not materially increased until the old propeller was replaced by an improved design, with increased pitch, the generatrix being inclined 10 degrees aft to facilitate the contraction of the liquid vein. Under these conditions the speed attained was 19.5 knots, the trial giving the same result as had been attained by calculation.

M. Tellier gives some data concerning the boat La Rape'e II, of 8 metres in length and a displacement of 0.8 metric ton, this making a speed of 16.25 knots with an indicated power of 33 h.p., and then proceeds to describe a still later model, La Rape'e III, built in February 1904. This hull is an example of the tendency to place the greatest cross section further and further aft, the hull resembling an elongated flatiron, with the greatest part at the stern. The midship section is almost circular, flattening rapidly toward the rear, the hull being absolutely flat at the stern. With this shape the water leaves the hull tangentially without showing either contraction or suction.

The Rape'e III, with a length of 7.88 metres and a total displacement of 1.158 metric tons, made a speed of 18.4 knots. The motive power under these conditions was a Panhard-Levassor four-cylinder motor, giving 40 horse power at 900 revolutions, the weight being 5 kilogrammes per horse power. This engine was then replaced by one similar to that of the Lutece, and a new propeller was also fitted. These changes were computed to make possible a speed of 21.8 knots, and this speed was attained on trial with 960 revolutions per minute of the engine.

M. Tellier gives data concerning trials of several other boats, including the Princesse Elisabeth, the Titan II, the Hotchkiss, and the Pertuisane, the results comparing well with those already cited. In general the progress made by reason of the experience of the past few years is clearly marked by these results. The reduction in weight is a notable element, and it is interesting to compare the Rape'e III with the Tubinia, this latter boat representing the most remarkable results which have been attained with steam propulsion. Thus the Rape'e III has a powering of 80 horse power per ton of displacement, with a total weight ratio of all machinery of only 6.25 kilogrammes per horse power. The Turbinia, on the contrary, has only 21.2 horse power per ton of displacement, and the machinery weighs 23.6 kilogrammes per horse power. If the Deutschland, for example, be compared with the Rape'e III by the law of similitude she would develop the enormous speed of 110 knots.

The principal criticism which has been made of the mechanical features of these little boats has been directed towards the motors. Their speeds of rotation have been considered enormous ranging from 800 to 1,500 revolutions per minute, but, as a matter of fact, the actual piston speeds are lower than those of the torpedo-boat engines or express locomotives, and the weight of the reciprocating parts is proportionally much lighter. M. Tellier maintains that such motors give little or no trouble in operation, and cites the fact that in the races at Monaco the engines of the Rape'e III were operated for six consecutive hours at 950 revolutions per minute, or a total of 342,000 consecutive revolutions, and, as there are four cylinders, there were 684,000 explosions. The speed of the boat over the sixteen laps of the course did not vary more than three seconds per lap, showing the uniformity of the motive power under these trying conditions.

Tellier considers that further improvements are to be looked for in connection with the design and construction of the propellers for the specific conditions required, and the results already obtained with these small screws at high rotative speeds gives encouragement for future improvement in this direction.

So far as the form of the hull is concerned, it is interesting to note the differences which have developed in comparison with the models of high-speed steamboats. The practical results are altogether contrary to the famous wave-line theory of Colin Archer and Scott Russel, with the sinusoidal bow and trochoidal stern. The facts are that the motor boat does not cut the water, and thus act to displace it; rather may it be said to plane the surface of the water, becoming thus a sort of hydroplane, analogous in design and action to that of the aeroplane. it is by a consideration of these differences in operating conditions that still higher speeds may yet be attained.

Down to the present time the improvements which have been made in these high-speed motor-boats have had the same end in view as in the case of automobile vehicles--the production of racing machines for sporting purposes. The recent endurance trials in England, however, have shown that such boats may be made useful auxiliaries for general marine and naval service.

(Transcribed from The Engineering Magazine, February, 1905, pp. 838-839. )

{It is interesting to note that the critic of M. Tellier's paper essentially agrees that the motor launches and autoboats are the trend of future motive power on water, especially brushing close to the subject of "hydroplanes", a term that would become a part of boat racing jargon as early as 1908. On the other hand, if these basic elements of power to weight ratios, propeller configurations and hull modifications were true, how is it that the writer could not see the inevitability of torpedo-boats becoming gasoline powered, given the fact that a steam powered, high-speed vessel had to carry many times more weight in fuel as well as much more area for motive equipment to generate the speeds of the Arrow and Turbinia. - GWC}

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