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MARINE REVIEW. © 9 Cards from Engines of the Merida. Cards printed herewith are from the engines of the steamship Merida, a two-page illustration of which was published in Vol. VII No. 8 of the REvinw. The Merida, which was built by F. W. Wheeler & Co. of West Bay City,Mich., for D. C. Whitney and others of Detroit, was engined by the Frontier Lron Works of Detroit. The cards were taken on the steamer's maiden trip, and for new engines they show a remarkable performance. The Merida gives promise of being a '"'flyer" and we hope to be able soon to chronicle some fast time for her. James Norton is chief engineer of this boat. NMP ME hE 663. ---- Lake Hurun, vy une 4, 10vv; sup ivadcd, Engines, 23, 37 and 62 x 44 inches. Steam, 167 pounds. j Vacuum, 24 inches. Revolutions, 86. Total I. H. P., 2,084. Referred M. E. P., 36.1. Marine Engine Design--Cylinders.* (Continued from Vol. VII, No. 19.) It is by no means an unusual idea among those unacquainted with the actual process, that problems of design are settled by simple substitution in some mysterious formula, the result so found being forthwith adopted without further question. Nothing, of course, can be farther from the truth. If di- mensions depended solely on the strength necessary, and if it were always possible to know what stress would come ona given piece, and howstrong the ma- terial of such piece were, then such simplified methods might be followed. Un- fortunately, none of these conditions are fulfilled, and in addition, a number of considerations other than strength must be taken into account. Such are stiffness, corrosion and wear, frictional work, refitting, cost and ease of manu- facture, and included withal, must be a large factor of safety to guard against the unknown and the unknowable. This factor is commonly called one of safety, although with equal propriety it might be called a factor of ignorance; or perhaps, rather it might be considered as a product of two factors, one of *Written for the MARINE REVIEW by W. F. Durand, principal of Graduate School of Marine Engineering and Naval Architecture, Sibley College, Cornell University. safety proper, and the other of ignorance. It must not be supposed, however, that this ignorance can easily be avoided, or that it is an ignorance of which we need feel ashamed. It exists largely in the inherent nature of things, and only in small measure and by patient search, can we gradually decrease its amount. Nowhere, perhaps, are these remarks better illustrated than in the case of cylinders for marine engines. They must not only be strong, but stiff as well, and perhaps have a margin in addition, to provide for future reboring. The actual condition of stress is due to internal pressure and irregular stresses' arising from vibration and unequal expansion and contraction, must always contain a large element of the unknown. The ultimate strength of the mater- ial itself must also be uncertain, at least in a very considerable degree. Under these circumstances, nothing but the integration of extended experience with these various factors can be of any practical value in the treatment of such problems. At the same time, it is highly desirable to put this experience into such shape that its results may be applied to proposed cases. This is done by means of various empirical forraulae which have been proposed for the thick- ness of cylinder wall. This question depends, moreover, somewhat on the question as to whether or not liners are to be fitted. If steam jackets are used liners, of course, are fitted, but in some cases, especially in the high pressure cylinder, liners are fitted even when the space is not used as a steam jacket. The difference in thickness does not so much depend on the element of strength, as on the desirability of sufficient metal to admit of reboring. With vertical engines, this operation is not nearly as common as with horizontal, and there is no doubt but that the addition of metal to admit of such refitting is a matter, the utility of which may be well called in question. Many engineers, however, | still prefer tohave such surplus, and if the cylinders are unprovided with liners, the extra thickness must necessarily go into the barrels, while if liners are fitted, it will naturally be put into the latter. Without discussing in detail the various formulae which have been proposed for this purpose we will state at once that the one which seem on the whole most satisfactory is of the form t=CD-----a f In this formnla, t and D are thickness and diameter in inches, while C: and a are constants. The valueof these constants will depend somewhat on whether the formula is to be applied to the cylinders of large marine engines or small light yacht engines. Taking first the fo mer and considerng that liners are not to be fitted, the value of C may be taken as .01 and aasg 1 inch.' We have for such case therefore: t = .01D + 1". If liners are fitted, C may be taken the same as before, anda may be' taken as .8 inch. These values will give reliable results for cylinders of 20 inches diameter and upward, the material being the best cast iron. ; For small cylinders, C may be taken as .02 and a as .6 inch without liners and .4inch with, For such cases we should have, therefore t = .02 D + .6"" and t= 02D + 4%. In the case of the engine used for illustration in these papers, the diam- eters are 204 inches, 333 inches and 54 inches. The thickness of cylinder barrel without liners would then result as follows:-- H, P. t = 1/7.205 I. P. t = 1/7.835 L. P. t = 177.54 As the nearest shop dimension we may take 1} inches 1 inches ard 14 inches. It may be observed that it isnot uncommon to find the intermediate and low pressure barrels of the same thickness, or occasionally all three. In such case, the value taken would equal that required for the largest cylinder of those whose thickness was taken the same. If liners are to be fitted we should find: : es ta 124.005 I. P. t = 1/7.135 L. P. t = 1/7.34 Or as shop dimensions we may take 1 inch 1} inches and 1§ inches. Liners may be made from .7 to .8 the thickness of the barrel. It is not ° uncommon, however, to make them all of the same thickness, in which case about .8 of the I. P. cylinder wall will give, for usual sizes a fair value. In the present case, this would indicate a thickness of .9 inch, or say § tol inch. The flanges of a cylinder may have a thickness of about 1.25 t, and the | metal of the valve chest and passages about .75 t. For the cylinder head and covers, either a single or double shell is used with radial strengthening ribs. ° Nothing but experience can indicate their proper dimensions. In thickness, © these vary but little with the diameter, extra strenght for large diameters being ' better obtained by deepening the ribs than by thickening the shells. The thickness of the shells and ribs varies but little from 1 inch or slightly less for small cylinders. For large cylinders, or where the ends are to be jacketed, the double shell is fitted. On small unjacketed cylinders, the single shell will answer, though between the terms large and small no sharp line of demarcation ° exists, The ribs are usually six or eight in number, radiating from a central © ring or boss outward. Their depth increases from the center, outward and as a maximum may be taken as about one-tenth the cylinder diameter. British charts of Lake Superior cover the entire north shore. We have them for sale at $1.