A FORERUNNER OF THE SPEEDBOAT A CRAFT WHICH CLOSELY RESEMBLED THE SEMIDISPLACEMENT BOAT OF TO-DAY WAS DESIGNED AND BUILT FORTY YEARS AGO
TEL4 advent of the semi-displacement type of speedboat in this country came in the form of an invasion from America and like former invasions was soon accepted as part of the community, so that in quite a short while we were building speedcraft ourselves. But the home of the speedboat is definitely America, owing to her miles of inland waterways, and it is only an overflow of her trade that reaches this country. We have to rely upon our own constructors to produce boats especially suited to this country’s local conditions.
Literally hundreds of speedboats are sold annually in the States, and it is, therefore, with a certain amount of regret that I learnt recently that this country might have been in a position to have introduced the semi-displacement type of boat into America instead of vice-versa. Had this happened, the consequent benefit to our motor boat industry would have been immense, for at the best, American builders could have manufactured only under licence of the patent holder. I do think, however, that at even this late date we may justifiably pride ourselves on having had the first hard-chine boat in the world, as far as our knowledge goes, invented, built and sailed by an Englishman.
Commander Hodgetts was the man, and the first of Hodgetts’ Patent Non-Rolling Ships built in 1891-92 was known as the “Albatross.” This name was not idly chosen, for the gyrations of this bird were responsible for the first rudimentary idea. Commander Hodgetts was a naval man and thus viewed all progress of marine design from the point of view of naval significance. He was, therefore, much concerned with the overwhelming weakness of our cruisers when in attion irtba:d weather. This weakness was due to the rolling of the vessels, so much so in fact, that in even a moderate sea they could not use their heavy guns abeam, and were it slightly rougher, the oscillations of the boats caused their armour belt to roll high out of the water, exposing the vulnerable wooden hull to any stray missiles. Commander Hodgetts was on watch in the Indian Ocean one day about 1888 and. was watching an Albatross skimming round the boat, when the thought suddenly occurred that the bird’s flight was remarkably steady considering the gusty nature of the day. He had thought of designing a vessel with a steady gun-platform for some time, and he immediately seized upon the notion of incorporating any ideas that might be gleaned from the Albatross. The con
elusion arrived at was that the air caught under the steep curves of the wings, imparted a cushioning effect, and hence the steadiness.
Hodgetts* design was, therefore, a rather mixed example in which hardchine and ordinary displacement constructions fought for mastery, but as events proved he was willing to suffer a prolonged experimental period. About this time he associated with another inventor who was working on an uncapsizeable lifeboat. A disagreement arose over the particular kind, of curve to be used to form the arms of the V, and so, following this waste of time and money, Hodgetts had to continue alone. Experiments on an extensive scale with models were conducted in the Royal Aquarium by Mr. Walter Philips, M.I.N.A. during the summer of 1890, before a distinguished gathering including Admiral Sir Reginald Macdonald and Vice-Admiral Sullivan. These experiments were so satisfactory that the world patents were completed. The ” Albatross ” was completed in 1892, and a Mr. W. A. Scott was so pleased with the performance of this boat on trial that he immediately ordered a boat on similar lines from Marvin of Cowes. Below is an extract of the trial of this second boat named “Jack Heron,” taken from the Isle of Wight Herald of 24th February, 1894.
” . . . The phenomenon of non-rolling is due to two forces ; on the weather side there is in the channel between the keel and the new side keel a volume of water which must be raised to the surface for the ship to roll, but this is not possible on account of the molecular attraction, which renders this water for the moment as it were, a part of the ship, and is too heavy to lift, while to leeward the same form acts as an outrigger or lee board, -preventing that side from going down ; thus, between the two, the vessel is rendered stable, while the channels being open at each end the water continually passes aft and prevents her being too stiff. The experiments at Cowes with Mr. Scott’s “Jack Heron” showed :—
1. Remarkable steadiness with great ease of motion.
2. Extreme delicacy in steering.
3. Quickness in going about.
4. Great diminution of pitching.
5. Good speed.
6. Great power of going to windward.
7. Avoidance of leeway.
8. Reduction of bow wave and sidewash.
The last quality, on account of the side keels not having been brought so far forward as in the former experiments with the ” Albatross” was not so remarkable as in that vessel, where the side-wash almost entirely vanished and the bow wave was reduced to an almost imperceptible ripple.” Being before the days of the internal combustion engine, and thus of engines with a good power-weight and size ratio, the increased speed was not at once apparent, as 10-12 knots was considered high at that date. Nevertheless, even with the ” Albatross ” the difference was appreciable. Witness to this is the account published in The Isle of Wight Herald for 24th September, 1892 :—
” Arthur Scott, Esq. . . . invited the party to meet the inventor on board his s.s. ‘Elsie,’ and took the Albatross in tow. The speed of the ‘ Elsie ‘ never exceeds 9 knots, but with the’ Albatross’ in tow she ran the measured mile at 8/ knots and when she stopped, the acquired momentum carried the ‘Albatross’ on beyond the point reached by the Elsie,’ so that the new form of ship’s bottom is proved to be conducive to increase of speed.”
Commander Hodgetts had naturally looked to the Admiralty to take up his invention, but this body proved reactionary, for which attitude they were severely criticised in the public press by Admiral Sir George Elliot. Curiously enough, in the light of our later knowledge, the bone of contention with the Admiralty was the speed of vessels constructed on these lines.
The official body had found that the fitting of bilge keels had affected the speed of a vessel, by as much as a knot in some cases, and it was beyond Commander Hodgetts’.. power to :persuade them that. it would be otherwise with his craft. The matter became quite a public controversy and below is reproduced one of the many letters to the public press siding with the inventor. Although the supposed proof is a little weak as are the mathematics, I am including it chiefly for historical interest. This letter, together with the accompanying illustration, appeared in the issue of The Engineer for 23rd August, 1895.
tt The Rolling of Ships.”
SIR, I read with great interest the letter from ” M.T.” on this subject, and hoped to have seen it fully discussed in your columns, on account of its great practical importance. Admiral Elliot in a remarkably able letter to The Morning Post,
August 10th, has brought attention to the evil effects of rolling in causing the unarmoured sides of a ship below the water line to be exposed to enemy’s fire. If ships of war can be built so as not to roll without corresponding disadvantages, it seems to me it would be the blindest folly on our part not to do it. It appears beyond dispute that Mr. Hodgetts’ new form of ship, so far as it has been tested, has reduced rolling to an amazing extent. If the same results can be obtained with big ships as with the small yachts tried last year at Cowes, when tried in all weathers and waves, the practical benefit of adopting this form of ship, if the expense is not too great, seems to me beyond estimate, especially as the speed of the vessel does not seem to be reduced by the shape. In fact, I understand that it is claimed by the inventor that the contrary is the case, and that the experiment at Cowes showed a decrease rather than an increase in the resistance of this form of Ship to towing. This; I admit, puzzled me when I first heard it ; but I think it can be explained as follows :—It is well known that a great part of the resistance to the motion of a ship is due to what is called skin-friction, which depends on the external area of the ship below the waterline. Under certain conditions it can be shown that the new form of ship will have less surface in contact with the water than a ship of triangular section of the same displacement. For the purposes of this letter the following is a sufficient geometrical illustration of this problem : ABECD is an imaginary section below the water line of an old style of ship, and a bFed a section of the new style. In the latter the line b c is not really straight but curved as shown by the dotted line, the curve being a catenary ; but this does not appreciably affect the problem. To compensate for the slightly longer line, it is only necessary to make the sides a b and d c a little longer. Now the displacement being the same in the two ships, the area ABECD must be equal to the area abFe d. And since the area ABFCD is common to both, we get the area a b B AB E F and d e C D—C E F. Then it is obvious that b B is shorter than B 14, and e C than C E. Consequently since A B—a b and DC—dc: a h+ b c+ c d is shorter than A B E+ C D. As this must be true of every
other section, the external surface below the water-line of a ship of triangular section must be greater than that of the new form of ship, and consequently the surface resistance must be greater. It is manifest, however, that ink does not hold good when the comparison is made with the Hodgetts’ ship and a ship of the present box shaped section.
Mr. Hodgetts has, I am told, found in experiments with models, that the resistance ot a force tending to make the models of his form of ship keel over is greatly in excess of the resistance given by models of the usual shape. This indicates that in the models of his ship the centre of gravity was low and the stability great. In an ordinary shaped ship, under these conditions, we should expect it to roll violently ; but the trial with the yachts at Cowes showed that this was not the case. If the centre of gravity was as low proportionally in the yachts as in the models, it seems obvious that we must attribute their great steadiness to their external form. Mr. Fronde has shown experimentally that by the addition of bilge keels the period of roll may be very considerably increased.
For example, with a model of the Devastation by the addition of a sufficiently large bilge-keel, the time of a double roll was increased from 1.77 to 1.99 secs., while the number of rolls before coming to rest was reduced from 31/ to 4. In this case the model was made to heel over in smooth water through an angle of 81deg.—(” Encyclopaedia Brittanica ” Vol. XXI, page 813). The external form of Mr. Hodgetts’ yachts must, I think, act in increasing the time of roll in exactly the same way as bilge-keels, and is evidently in many ways a far superior method of obtaining the desired result.
There are two points among others which it would be interesting to know with regard to these ships : (1) Were there any great constructive difficulties to be overcome in building them of large size ? (2) Whether any experiments have been made with the yachts to find out their period of roll by making them heel over in smooth water ? Perhaps your correspondent, ” M.T.” could kindly answer this last question.
C. U. Baseri.
8, Norfolk Square, W. August 17th.
We ‘know to-day that Mr. Baseri was right when he assumed that a reduction of wetted surface accounted for the extra speed, but I am afraid his explanation of the decrease of skin-friction was somewhat far from the mark. However, a letter had, been written to the Pall Mall Gazette in the April of 1895 giving the precise reason why an increase of speed was stated. As the letter was signed ” A Field Officer,” and the explanation was in the form of a supposition, the letter unfortunately did not receive the attention it merited—people probably thought it a case of fools rushing in where angels feared to tread. Here is the material part of this letter. SIR,
. . Having noticed that torpedo catchers at full speed rise considerably out of the water, it at once struck me that this ship (Hodgetts’) which has all the advantages of a flat bottom on the point, must rise considerably and to some extent skim, for it cannot dive ; if this be the case I can readily believe the architect’s opinion, as to the greatly increased speed of this type, since in her case “the greater the speed the less the resistance,” whereas in the ordinary ship the exact reverse to this is the case, as by doubling the speed the resistance of the water is increased fourfold. . . .
“A Field Officer.”
In 1895 a company was formed to exploit the invention, but as the Admiralty had in their ignorance definitely turned it down, this company was not a success. Thus, we have another case in which a worthy invention coming only a few years too soon, is lost to the world owing to the reactionary principles of the accepted school of thought prevalent at the time.