. A manual of marine engineering: comprising the design, construction, and working of marine machinery. epresent the initial friction ot the machinery. Curve of Revolutions.—A curve of revolutions is constructed in a similarway, by taking points r^ r., r^ on the ordinttes, so that Br^, Gr^, Drg areproportional to Rj Rg R3. When the slip is constant the curve of revolutionsbecomes a straight line. Curve of Slip.—The slip may be shown by a curve whose ordinates areproportional to the slip at the speeds S^ S., S3. Examination of Curves will show—(1) what indicated horse-powerrevolutions, and slip
. A manual of marine engineering: comprising the design, construction, and working of marine machinery. epresent the initial friction ot the machinery. Curve of Revolutions.—A curve of revolutions is constructed in a similarway, by taking points r^ r., r^ on the ordinttes, so that Br^, Gr^, Drg areproportional to Rj Rg R3. When the slip is constant the curve of revolutionsbecomes a straight line. Curve of Slip.—The slip may be shown by a curve whose ordinates areproportional to the slip at the speeds S^ S., S3. Examination of Curves will show—(1) what indicated horse-powerrevolutions, and slip corres|)ond to any speed intermediate to thoseobserved; (2) the efficiency of the engine at its lowest possible speed; andfrom it an idea may be formed of its general efficiency, and a compaiisonmade with other engines; (•5) the efficiency of the ship, as tested by the rateof increase of power for speed, which is seen by the form of the curvetowards the higher speeds—if it begins to mount upwards suddenly it iscertain that the resistance has there begun to increase abnormally ; (4) that,. Speed in 18, if the curve is one fairly following the law of resistance increasing as thesquare of the speed, an estimate may be made from it of the power requisiteto drive a similai- ship at speeds higher than the hii;;hest observed curves, orlower than the lowest; (5) any sudden rise in the slip alone indicates thepropeller to be defective in either diameter or surface, or i oth. Another method of expressing the results of progressive trials is bysetting out A B, A 0, A D proportional to Sj^ Sg^, and erecting ordinates,&c., as before. If the Indicated Horse-Power througliout varies as the cubeof the speed, the power curve or line drawn through the points 6, c, d,will be a straight line; and if the power increases at a higher rate ihan tliecube of the speed at any point, the line will again assume tiie curved advantages of this plan over the one before descr
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