A small pitched propeller is less wasteful of power than one having a high pitch and so it is of no advantage to make a small screw do the work of a larger one. It is not only wasteful of energy but also permits the rubber skein to untwist too rapidly. The advantage therefore lies with a propeller of low pitch driven slowly.
FIG. 40. The first step in carving a propeller. The blank. Hollowing the first blade.
FIG. 41. One blade hollowed. Hollowing the second blade.
The average propeller should have a pitch of from 2-3 times its diameter, that is, the blade should have an angle at the tips of slightly less than 45 degrees.
The propeller diameter (of course this rule is not infallible, but only a general statement) should be about one-third the spread of the planes.
The edges of the blades should come to a clean edge but not be too sharp.
FIG. 42 Rounding the back of the first blade. Rounding the back of the second blade.