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6 MARINE REVIHW. CHICAGO LAKE INTERESTS. WESTERN OFFICF, MARINE REVIEW, { No. 13 Western Union Building, CHICAGO, IIl., Dee. 1. The movement of the underwriters to seeure a thorough inspection and classification of steel boats isone which doubtlsss will receive the hearty sup- port of ship builders and vessel owners. The invitations have been sent out for a general meeting next week. Of course, the underwriters are very con- servative in talking for publication, but in private conversation the sentiment is clearly expressed that the time is come when some such move must be made, and they think that it is better to force it themselves than to have it forced upon them by outside influence. In this they seem to be entirely in'the right. It is certain that insurance on steel boats will be considered in an entirely dif. ferent light next season than ever before. If the movement is undertaken with an amicable feeling all around, owners, ship builders and underwriters ought to be able to come to an understanding, which will alike be beneficial to all these interests. When one gets down to the bottom of things, the three diverse interests are the same. Ship builders certainly do not care to construct boats whose seaworthiness may be questioned. Owners do not wish to send out craft which may drown their crews, and underwriters have no burning desire to pay many such losses as they have this year. A single doubt as to seaworthiness increases insurance rates. When all three are really of the same mind, Chicago vesselmen hope that there will not be much difficulty in forming the proposed association for publication of the proposed Inland Lloyd's Vessel Register on broader lines. The Chicago branch of the Shipmasters' Excelsior Marine Benevolent _ Association has fitted up very pleasant quarters at No. 2 Market street, and will have its opening meeting for the winter there next Monday afternoon at 2 o'clock. New British-Built Steamer for the Lakes. Special Correspondence to the MARINE REVIEW. Kryeston, Ont. Dec. 1.--The new steel steamer to be built in England for the Montreal Transportation Company will be modeled after the style of boats known as spar deck steamers, with three masts and single screw, and will cost about $150,000. Her dimensions are: Length over all 254 feet, beam 40 feet, moulded depth 23 feet, depth of hold 20 feet. She will have eight water compartments, with a capacity of about 800 tons. The engines will be triple expansion of 1,000 horse power, and steam will be generated in a battery of steel boilers, capable of withstanding a pressure of 170 pounds to the square inch. The boat will make 12 miles an hour when loaded and 133 miles when light. The new boat will be constructed entirely of steel--hull, deck, cabins, masts and all--and her capacity will be 62,000 bushels of wheat when drawing 14 feet of water, and 85,000 bushels at 17 feet. Marine Engine Design. Written for the Marine Review by W. fF. Durand, Principal of graduate school of marine engineering and naval archt- tecture, Sibley College, Cornell University. In the problem of engine design, the I. H. P. required is usually the fixed quantity, and the design, as a whole, must pro- vide for the development of such power, at the same time ful- filling such other general conditions as apply to the case in hand. In the first place we shall assume that our engine is to be triple expansion. 'In such an engine the power obtained is no greater than would be obtained from the L. P. cylinder with the same initial and final pressure. In fact it would be less, due to a drop of pressure between the successive cylinders. is shown graphically by the difference in area between the sum of the three parts of a combined indicator card from a triple ex- | pansion engine, and the corresponding card from a single cylin- der. Reference may be made on this point to the combined cards given in connection with the test of the steamer Wilbur, published in the MARINE REvIEw during December, 1891. Experience has shown that this loss will be from ro to 20 per cent. "But," it may be asked by those not familiar with the matter, "why then use three cylinders, when more than the same power could be gotten from the IL. P. cylinder alone ?" The answer is that while this is true, yet the single cylinder would use much more steam for the same power, and therefore much more coal. The crank effort, moreover, would be ex- tremely variable, and for marine work this would require a heavier constructton of the engine, besides tending toward a waste of work in shaking instead of propelling the ship. It is beyond our present limits, however, to discuss the ad- vantage of multiple expansion over single engines, and we there- fore proceed with the problem of design. From what has preceded, it is seen that we may take asa starting point the proper size of the L. P. cylinder to develop under the expected conditions, and after making allowance for the loss spoken of above, the desired I. H. P. The general relationship of the various factors entering into This loss I. H. P., may be most conveniently discussed by means of the formula: LHP. PL, A N-- 33,000. in which P=Mean effective prsssure in Ibs. per square inch. L--Length of stroke in feet, -- A--Area of piston in square inches. N--Number of revolutions per mt. It may be seen that P A is the total mean effective pressure or load, and 2 L, N the distance traveled by it per mt. The pro- duct is therefore the foot lbs. per mt., and this divided by 33,000 iste. F. ries se In general then, any combination of the quantities repre- sented by PLAN will fulfill the conditions. Practically, various restrictions limit their values so that the practicable com- binations do not cover a wide range. We will note briefly the various considerations affecting the relative values of these quan- tities. First with regard to pressure: 1. 'To obtain much power from a given weight of engine,the initial pressure should be high, the expansion slight, and there- fore the mean effective pressure (me p) large. >. 'To obtain much power from a given weight of steam, the initial pressure should be high and expansion large, thus making the final pressure and the m.e. p. low as compared with clause 1. Expansion in one cylinder, however, can not be carried very far without serious loss from initial condensation, and it is to avoid this that the expansion is split up among two or more cylinders, as in multiple expansion engines. : . Increasing the pressure of steam necessitates increased care in points relating to packing and lubrication, requires heavier pipes, and other things being equal, a heavier design through--- out. Other minor points enter into the consideration, but taking everything into account there seems little doubt but that the present tendency toward higher pressure steam is the correct one, and that this tendency is at present limited by the boilers for its production, rather than by the engines for its use. © Next as to the factor Ll: Thelonger the stroke, the lower the revolutions for a given piston speed, or, vice versa, the greater the piston speed for a given number of revolutions. A long stroke is favorable to small diameter of cylinder for given power, and with low speed tends to avoid troubles due to the inertia of reciprocating parts. A long stroke, however, lengthens all the connections, or else introduces great obliquity of the connecting rod with its attendant difficulties. A short stroke tends to avoid trouble from the obliquity of the connecting rod, or with given obliquity allows a lower and more stable en- gine. It requires, however, for equal power, an increase in revo- lutions, or diameter of cylinder, or both. -- As to A, the piston area, it readily appears, of course, that its increase will allow a decrease in the other factors, and wzce versa. Aside from general limitations as to size of cylinders, or from some limitation specially related to the case in hand, the area is not especially restricted, and for this reason it is fre- quently left as the quantity to be determined by the desired values of the other factors. Any such determination is, of course, subject to revision by a modification of the other factors, ' until a harmonious design is obtained. Finally as to N, the revolutions per mt.: A high value of N raises the power per lb. of engine, or allows shorter stroke or less diam. for the same power. It tends to introduce trouble due to the inertia of reciprocating parts, and on the whole requires a stronger design and better workmanship than low speeds. A low value of N tends opposite to the above. The question of the value of N can not be considered apart from that of L, the pro- duct z< N L, being the piston speed per mt. From the standpoint of efficiency, this should be as high as possible. Mechanical re- strictions limit us at present to speeds about 1,000 feet per mt. To illustrate and apply these principles we may consider the chief points in the design of a triple expansion engine to de- velop 1,500 I. H. P. We will take the boiler pressure at 160 tbs. gauge--L--=3'--6" and N--roo. The fixing of these quantities is a matter of judgment or experience, and we may here note relative to N, that for a given pitch, ratio and diameter of screw, and for a given amount of power to be absorbed by it, there is a certain value of N at which the screw will utilize such power most efficiently. If therefore the problem of propulsion were also before us, we should preferably fix the revolutions at least approximately in-- this way, and then design the other factors so as to make a prac- tical combination. As it is, however, we assume the revolutions at a point not far from what it would be, had we started with a well designed propeller and designed the revolutions to corre- spond, (CONTINUED.)