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.esistance Importance of Model Tank Trials is Baloeced fa Lines Forward With Considerable Flare, Also Cruiser Stern Advocated HE subject of the determination ; of ship resistance naturally di- vides itself into two parts = of primary importance, one concerning fine types of ships, and one concerning full types; where the line between the two should be drawn is by no means clearly defined, but, in practice, warships and passenger liners constitute the fine types and cargo steamers the full types, with, of course, some exceptions to be found both ways. Motor boats, sub- marines and hydroplanes are now the subjects of increasing investigation; the usefulness of the two latter types in the great war insures a measure of atten-, tion hitherto given only to the larger naval vessels. Published data are already assuming considerable dimen- sions; but there remains, however, plenty to occupy the staffs of the vari- ous experimental tanks the world over. Need Uniform System This article will deal more particu- larly with general naval and mercantile types. One of the first things that strikes the reader of the various authorities on this subject is the desir- ability of a uniform system of notation throughout the technical world. Any- one who can do something to bring this about will have earned the grati- tude of all naval architects and naval engineers. When we read recent and valuable papers written abroad, we naturally find different systems of no- tation in use. There is, in practice, danger of serious error in using first one reference and then another, be- sides the labor of reduction of results from one system to the other, so that anything tending towards an_ inter- national standard is well worth encour- agement and advancement. In recent years marked reductions in the power necessary to drive a given weight of ship and cargo at a given speed have been made; the experimental tanks are justly proud of the cuts they have been able to make in the power for models submitted to them for test. They are the people best placed to keep in touch with developments so far as smooth water results are concerned and are now producing tangible results for merchant ships of all types as well as From a_ paper read at the twenty-third an- nual meeting of the Society of Naval Archi- tects and Marine Engineers, New York. for warships, both here and abroad. In 1912 the author read a paper before this society which pointed out several in- stances of saving due to experimenta- tion; before and since then much has been written and something has been done to keep down coal bills. At the Franklin Institute, Philadelphia, in the same year, I ventured to suggest that the saving in coal made by the naval architect might well be handed back to him in part to provide extra subdi- vision and stability for passenger ships —by no means a bad reply to the ques- tion of extra first cost of additional beam and bulkheads—so that the pas- senger need never really know any material difference in the price of his ticket due to increased first cost of ship. The studies of twin-screw drives for full cargo ships, both steam and motor driven, have recently shown some un- usually good results. Recent colliers built for the navy are cases in point, and their trials and service results are of. particular value in all similar twin- screw vessel design, steam or motor. In recent years a strong tendency to con- duct systematic experiments on ship re- sistance is noticeable, and for this we cannot be too grateful. Isolated pull- ings of models as submitted are neces- sary, but it is only when the lessons drawn from these experiments are fol- lowed by systematic research that the profession as a whole begins to derive benefit from the work done. We have passed from the stage of individual and disconnected experiments to that of sys- tematic research directed along lines that are already having a marked effect in reducing power or increasing speed in shipping generally. Progressive Trial Required It should be remembered that model experiments are only half the battle; they must be followed by a progressive trial on the measured mile in order that the design of the propellers may be veri- fied and the performance of the ma- chinery properly noted. This trial should be conducted at the same trim and draught as the model was towed, and this should be as near the working load draught as possible and deep enough to give proper immersion to the screws. It will not always be easy for the builders to arrange for the loading of the ship, except in the case of oil 165 By Ernest H. Rigg tankers; but this can generally be managed at the expense of a few hours’ delay to one voyage after the vessel is in service, once the owners realize the’ savings that are at stake. At the time of the publication of Ad- miral D. W..Taylor’s manual on ma- rine propulsion, in 1910, the literature of this subject was beginning to assume good proportions. It was, however, scattered, and the naval architect who did not keep in touch with a good many sources of information was at a seri- ous disadvantage. This book brought together the best collection and ar- rangement of experimental data that we have. The work of obtaining the residuary resistances for the wide range of speeds and coefficients is in itself a gigantic task and for which the pro- fession all over the world is indebted in no small measure to the author and to the United States government, in whose tank it was so largely obtained. It can safely be said that this book marks an epoch in the methods in prac- tical use for designing and powering ships. Ship builders and owners are now fully alive to the value of the tank and are keen to take advantage of all it can teach them, to their no small bene- fit in coal bills and better service. Effect of Increased Beam Mr. G. S. Baker’s new work on ship propulsion, which has recently become available in this country, summarizes the present status of tank work and our knowledge of this whole subject inan able and clear manner. He uses, in the main, the “constant” system of nota- tion, which is perhaps not as much used on this side of the Atlantic as on the other, and his book is a most valuable contribution to the literature on the subject, the main results of recent ex- perimentation being carefully gathered together and presented in one volume. As in much other recently published matter, the full-cargo ship receives considerable attention in Mr. Baker’s book. The chapter on canal fowage contains in- formation not generally available in such useful form. It has long been known, and acted upon, that large beam, generally speak- ing, involved high resistance; we realize nowadays that too high a price can be paid for small beam and resistance. In- crease of beam, accompanied by increase BN a, Re