MARINE ENGINES.

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for every 2 feet in length, the mode of fastening being a nut on theend, with feather let into the shaft and boss. To find the area anddiameter of the lying shafting, divide the area of the cranked shaftat the journals by riß, the quotient gives the area in square inches;and by a table of areas the diameter is easily found, always allowingover rather than under, and even dimensions being preferred. Thethickness of the solid discs forged on the shaft is about one-thirdthe diameter of the shaft. A projection of ^ inch, and aboutfive-eighths of the diameter of the rest of the shaft, is left on, andaccurately fits into a recess bored out in the adjoining shaft, keepingthe shafts central the one with the other; the combined area of thebolts for the coupling is found by multiplying the area of the shaftby '35. A key is sometimes sunk into one of the discs and securedwith screws, one-half of the key taking each disc; thus the shearingstrain is taken off the bolts, which can therefore be greatly reducedin area. The thrust of the screw is received on a series of collarsaccurately turned on the shaft. The combined area of the thrustsurface is found by multiplying the nominal horse-power of theengine by 1-25, which gives the number of square inches of surfacein the whole series of collars, the length and depth of the collarsbeing one-eighth of the diameter of the shaft. The length of thepillow blocks for the lying shaft is one and a half times the diameterof the shaft. The length of the plate for the thrust block is aboutsix times the diameter of the shaft; it is well joggled at the endsto prevent lateral movement.

Hand gear .—The rods must either be unnecessarily large indiameter, or supported at the middle; the required strength veryrarely exceeds 1 inch in diameter. The joint pin is of the samediameter as the ends of the rod, the diameter of the eye equals thediameter of the pin multiplied by 2, and the depth of the eye equalsthe diameter of the pin. This rule is for single joints, which shouldalways be used when convenient, because they are more easilymade; when double joints are used, the distance between the jawof the joint equals the pin’s diameter, while one-half of the diameterequals the thickness at the smallest part. Sometimes hollow rodsare adopted with advantage.

Bolts in cylinder cover .—The bolts vary in size from 5 ^ to 1 %inch in diameter; the pitch from centre to centre of the holes isgenerally about eight diameters. To find the combined area ofthe bolts, multiply the area of the cylinder by the steam pressure,