MARINE ENGINES.
485
on a suitable washer, the whole being inclosed within the hollowboss properly strengthened in the casting.
The mode of attaching the blades to the boss is by a cotterpassing through the shank and boss, and held in position by nutsand lock nuts at each end, bearing on washers, the hole being cutof a wedge form, tapering to the centre of the cotter. By thinmeans the blade can be turned in either direction for feathering, orfor adjusting the pitch; and when the pitch is once fairly adjusted,
Fig. 369.—Bolt Fastenings.
a, Boss, b, Blade, c, Bolt. d, Plate.e, Guard plate.
the blade can then be firmly held in the proper position by drivingin wedge pieces between the boss and the cotter, the washers andnuts preventing them shaking loose.
The bolts for the Hanges of theblade when so fitted are generallytapped into the boss, the head bear-ing on a plate fitted to two of them.
Various plans are adopted for pre-venting these bolts from turninground: by notching the head for asplit pin, or by notched washerplates fitting to the heads and se-cured with set screws, or with stud and split pin tapped into thebottom plate, or by small square pieces butting against the nut,held with a single set screw, the bottom washer or plate being