ON THE FORM OF SHIPS.

A pamphlet, under the title of "Experiments on the Form of Ships and Boats," has made its appearance in one of the unpretending series published by Weale; and, among various doctrines promulgated, it offers some already recognised, and some that will be new to the reader. The work affords another instance, it is believed, of the apparent anomaly, that discoveries and inventions in sciences and arts are often made by persons quite unconnected with the vocation which would be expected first to elicit them. The author certainly deserves credit for his ingenious consecutive, and methodical course of 70 experiments which he has clearly, though concisely, described, and which must have been gone through with much labour and some expense. An objection may be raised to the rather Lilliputian scale on which those experiments were made, but stronger denial would probably attach to the circumstance of their being all performed in still water.

Mr. Bland, the author, comes to one decision, which will be supported by many of the best constructors, though it is often lost sight of, namely, that it is impossible to combine in any single model all the qualities which are desirable in a vessel. To expect this is as reasonable as to expect the same horse to excel equally on the race-course, in the dray, and on the road; in fact it becomes a question if, to a certain extent, the possession of one quality (as capacity) in a high degree does not absolutely involve the sacrifice of another (as speed), and vice versa: The experiments, at all events, show that an approximation to the much talked of form of "least resistance" had also the least stability, and therefore least power of carrying sail, so that it would lose in the last respect more than it would gain in the first. It is nevertheless contended by the pamphlet that certain forms do largely possess several excellencies conjointly.

Among the novelities (if anything can be novel) which Mr. Bland brings forward is the dictum, supported by experiment, that the hollow "wave line" is not very favourable to speed; on the contrary, that it is rather inferior to the straight-lined bow of equal length and breadth, and slightly still more inferior to a bow with gently convex lines. Also that so prejudicial is the straight line in the "half breadth" plan of a vessel that a model with convex lines, although nearly one-fourth larger than a model with straight sides, proved, notwithstanding, equally fast under the same motive power. Thirdly, that while a moderate depth of keel is beneficial, a very great depth is injurious, and tends to overset!

An elongated bow always showed its superiority in speed over a bluff one, and it was found that the point of extreme breadth ought to be before the mid length of ship, as in the analogous cases of birds and water fowl. For sailing vessels great breadth of beam is advocated, because of the high ratio of stability, or power of carrying sail, which it confers, and for the same reason the depth is limited to a smaller proportion of the beam than is at present usual. The draught in amidships is fixed at such a measurement, as under a bracketed form of bottom, thus fig. 1. (AB being the low-water line),

would amount to only two-fifths of the beam; or, if the immersed part were perfectly rectangular, only one-fifth of the beam. The render perceives that in the latter case the draught of present three deckers would be reduced from 25 feet to about 12! Upright sides, and in amidships a "kettle bottom" are considered to be the best; and the latter is altered, as above, merely for the sake of making up a certain draught without increasing the displacement.

It is curious to notice that Mr. Bland adopts principles from each of those late bitter opponents, Sir. Wm. Symonds and the School of Naval Architecture: with the former he takes very great breadth of beam and overhanging stem, and with the latter wall sides and bracketed bottom. His rule that the centre of gravity should not be above the load water line, it would probably be impossible to carry out in large men-of-war and many merchantmen; and as before hinted, great exception must be taken to his trials being solely in smooth water. The most scientific naval architects are quite agreed that the mere form must not only be considered, but also the various changes of relation which the outline of hull and the waves must bear to each other under their many and complex motions. For instance, Mr. Bland, while he retained the straight keel, found velocity much improved by cutting up the bottoms of his models longitudinally from the deepest section in an inverted arch to the stem and stern, in this form (AB being again the load water line).

But, whatever advantage may be gained thereby would be more than counter-balanced by the pitching and 'scending when the vessel laboured in a heavy sea — in that state, the bow would at one time shoot above the water, and at another be suddenly buried in the midst of a rising wave; and the shocks would not only greatly retard the speed, but would make the vessel a most uneasy sea-boat, severely strain the hull, and endanger the safety of the masts. Mr. Bland observed that an overhanging bow in still water "threw the water off admirably, or rather it may be said to ride over it;" and the fact needs no proof whatever, but it is well known that Sir W. Symonds' vessels which have over raking bows, and sides somewhat bulging out above the water line, though they have (on account of those characteristics) great speed and stability in fair weather, are, for the same reasons, much inferior in both respects, and very uneasy, in foul weather. Besides which, it must be recollected that the fastest sailing frigate in the world, the Phaeton, 50, and the fastest brig, the Daring, 12, both built by Mr. White, of Cowes, have bows which, whether viewed from the broadside or from before the cut-water, present a very upright and even outline.

Mr. Bland deserves the thanks of his country for what he has already done, and he would be deserving of more were he to carry his researches further. It might be suggested to try his models across a strongly rippling stream, to repeat that experiment with the models heeled over by weights to an angle of five or ten degrees, and to try their speed and easiness by the traction of lines not fastened to the stem, but to the summit of a miniature mast or masts as high as one half or one third of the vessel's length, &c. It is more than likely that many of the experiments repeated under such change of circumstances would yield quite different results from those already arrived at, and would tend still further to elucidate the high art and mystery of shipbuilding.

H.Y.P.

H.Y.P.": On the Form of Ships.
The Mechanic's Magazine, 1857. p 5-7.

Transcribed by Lars Bruzelius.

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