MODERN STEAM PRACTICE.

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To determine this point correctly the shipbuilder and engineershould work hand in hand; and by studying the lines and configu-ration of a particular dass of vessel, with a knowledge of the poweractually required to propel her at a certain speed, they may beable to adapt the power to the requirements of future vessels.

Rule for tonnage .— Multiply the length of vessel between per-pendiculars, minus three-fifths of the breadth, by the square of thebreadth divided by 2, and divide the result by 94 as a constant:the quotient gives the tonnage in old builders’ measurement.

Performance of screw vessels .—To find the coeffident for screwships, multiply the cube of the speed in knots per hour by themidship section of the vessel in square feet, dividing the result bythe indicated horse-power: the quotient will be the coeffident ofperformance—the higher the number the better the result.

To find the speed with the coefificient, multiply the indicatedhorse-power the engine is intended to work to by the coefificientfor the dass of vessel, dividing the result by the area of midshipsection in square feet: the cube root of the quotient is an approxi-mate of the speed the vessel will attain.

Another method for finding the coefificient of performance is tomultiply the cube of the speed in knots by the cube root of thedisplacement in tons squared, and divide the result by the indicatedhorse-power. Hence the following formulas—

(First method) Speed 3 x midship section in square feetIndicated horse-power

= coeffident.

(Second method) .Sp eed 3 x displacement 8Indicated horse-power

= coeffident.

For 14 knots per hour, the coefificient for ironclads by theformer method—the length of the vessel being seven times itsbreadth—may be taken at 600 as a constant, and 500 when thevessel’s length is five times its breadth. For the merchant Servicethe coefificient varies according to the length of the vessel—thegreater the length the better the coefificient becomes. For instance,the steamship Cadiz , with a proportion of length of eight beams,has a coefificient of 800; while in others, with a length of sevenand three-quarter beams, it is about 662. It will thus be seen thatlong vessels are the most economical in carrying power, the speedattained being better than in a shorter vessel for the same indicatedhorse-power, while of course more stowage is afforded for cargo;and many screw steamships, after running for years, have been