The brittleness is an indication of surface hardening and roughening, either
by mechanical or electrochemical means. Since the neutral axis of the chord
of the blade lies in the concave region of the cusp, the entire blade acts
intension and the surface hardening has caused the cusp to increase (shorter
surface length on the inside of the cusp) and the water displaced with each
turn of the propeller is more.

Now to your anticipated answer, which is wrong. The new prop does not slip
because it has less surface friction. The surface friction only drags the
water in the direction of the propeller rotation, it cannot create a water
trajectory normal to the propeller surface. In fact, propellers with less
surface friction are faster.

Amen!

Bob Crantz


"Bart Senior" wrote in message
. net...
5 points (Impress me with your genius)

You just bought a new boat and notice the prop is old and brittle.

You replace it with an identical prop. After motoring around for a
while you find the top speed of the boat is much lower, estimated to
be 2.5-3 knots and the prop seems to be slipping.

What is the most likely cause, explaination, and cure?