The following text may have been generated by Optical Character Recognition, with varying degrees of accuracy. Reader beware!

166 THE MARINE REVIEW of stability and decrease of fullness, by no means necessarily spells increase of power; for the same or less power a healthier type of vessel can generally be obtained, at, however, a somewhat in- creased first cost of hull material in most cases, due to increased wetted sur- face and wider decks. We have ar- rived at a point where increased safety is demanded in passenger carrying ves- sels; it is no use putting in bulkheads to enable a ship to keep afloat after damage if the danger of loss due to lack of stability in the damaged condi- tion is not also provided for. Loss of buoyancy and loss of stability must both be kept in mind when settling on di- mensions in a given case. The effect of this on speed and power will by no means be proportioned to the increased beam, as might appear at first sight. Forward Waterlines A far worse enemy to good driving is full waterlines in the forebody. In two recent cases of relatively fine and fast ships that have come directly un- der my notice, the forward waterlines were forced out by considerations of stability to the point of a marked de- crease in speed when compared with similar ships of the same principal di- mensions and power. This _ feature, also, has its limitations, for in full and slow cargo boats the exact opposite is true below a certain speed. While this is true for smooth water there remains the question of loss of speed in head sea. This question has readily received considerable attention. It is-safe to say that passenger ships generally will show a tendency to increase beam in the future; extra life-saving equipment, the natural desire of passengers for deck cabins and extra stability for damaged condition all tending the same way. This will not necessarily entail more power, because we know more about good forms and because ships are tend- ing to be somewhat finer to give better sea performances. The cruiser stern is another way out of this difficulty. The British board of trade’s recent: instructions to steamers in the danger ‘zone throw an interesting light on this point, applicable almost as much to peace as to war damage: “In. order to prevent the vessel taking a sudden list if holed by a torpedo, the stability should be increased to the utmost extent prac- ‘ticable by filling ballast tanks or otherwise.” Another paragraph relates to longi- tudinally bulkheaded ships of small ini- tial stability; both these paragraphs point towards increased beam. The same reasoning points to in- creased beam in our line of battleships. For a 31,500-ton ship, a beam of 110 feet is already responsibly suggested abroad. Who knows but that battle- ships laid down abroad since the war began are not of this largely increased beam? It is probable that less weight will be available for machinery, owing to increased protective weights ; and that this, together with the new propor- ‘tions, will mean a decrease in speed. The beam to draught ratio is about 3.25 in recent battleship designs, whereas in the 110-foot ship mentioned above it goes up to 4.40. The Yorktown experiments quoted by Admiral Taylor in his man- ual indicate an approximate increase in power of about 11 per cent for the same speed for battleships of this displace- ment and with proportions varying as above. : A good smooth-water performance is not necessarily a good sea perform- ance; considerable attention has re- cently been given to this question and some interesting facts brought to light. Early this year Sir A. Denny cited in- stances of improvement in sea per- formances due to decrease in fullness compared with previously accepted prac- tice. His point was that low first cost and low operating costs did not always go hand in hand... Mr. A. Hamilton in 1911 gave data based on the compara- tive performances of ships of varying fullness, all tending to show that the vessel of somewhat finer lines, particu- larly forward, more than balanced the loss in dead weight per trip by an in- creased number of trips per year. It is difficult to deduce any rule, but the general lines to follow are obvious. The speed curves of the design should be run well up beyond the designed speed and attention given to the char- acteristics of the curves at the speeds beyond the smooth-water maximum as well as that maximum. It may often be that an apparent sacrifice at normal speed is no sacrifice at all, but really a decided gain in coal burned per an- num in a seagoing ship, particularly a transoceanic or great coastwise trader. Effect of Shoal Water This subject has come to the front recently in practice as well as in theory. Torpedo-boat destroyers have furnished the most interesting cases, and the sub- ject is worth very serious consideration by those responsible for the perform- ance of vessels running in shoal bays, rivers and lakes. The literature on the subject gradually accumulates and we are now in possession of a very con- siderable amount. It is not too much to say that knowledge of the effects, both bad and good, of shoal water is abso- lutely necessary to the. proper running of destroyer trials, and no less so for the designing of shoal-water vessels. It will pay those charged with running big vessel trials to be very careful where they run them. On a recent trial of a 400-foot vessel drawing 19 feet and of 15 knots’ the performance at sea in smoo was materially better than on the q ured course, due to deeper well as to the absence of the for frequently turning to run o course; the reduction in horsepoy ing about 4 per cent. In a d trial at 24 knots it was found th 15 fathoms the power required to tain standard revolutions was mate higher than on _ standardization that om going off into deep water at once changed. Cruiser Sterns Of late years an increasing numb merchant vessels have been built the form of stern considered to battleships and cruisers. There is much to be said in favor and the effect on speed may be noted here; for a given .o length this stern gives the maxim mean immersed length and a result decrease in power and consequent *“chinery weight, necessary for a g speed, varying with the size of ship, being greater in the smaller s The adoption of this stern is atter with increase in stability, in deck r and in protection to screws. in har The chief objection is increased — cost, appearance is another in §& eyes, but small increased first cost have a hard struggle against a poss 8 per cent saving in coal bills. The guments are very much in favor of crusier stern for all twin or more scre designs, with a good chance in the st gle-screw design providing the drat is large. Modified cruiser sterns 4 common in our waters, for ships that ¢ a large amount of warping into and 0 of docks, notably in the Chesapeake b and similar waters; also on the coast a few cases, some Old Dominion line being built that way. Doubtless mai other instances could be found. : It has been known for some time plays a part in ship resistance. Mess Denny Brothers, Dumbarton, Scotland, are reported to have been unable to ac- count for differences in summer and winter trials of sister ships in any othe! way, and the matter is also under if vestigation at the Teddington tank England. . Se Differences in resistance as high as 4 per cent per 10 degrees difference in temperature are reported, the lesser sistance corresponding to the higher temperature. Lately appendage resistance has f ceived renewed attention; since Taylors experiments in the Washington tank showing the run of the stream lines | ship models, designers have studi more carefully the placing of bilge