"Roger Long" wrote in message
...

A two blade prop is inherently more efficient than a three blade. A single
blade would be even more efficient if there was a way to avoid the
vibration due to imbalance.

Related to this a strange thing hapened to me a few years back. The boat is
a 31 foot, 3500kg sailing yacht with 18hp diesel, shaft drive and 2-blade
folding prop. One day I was not able to back out of the harbour, there was
simply no power in rewerse. I checked the shaft and it was turning! When I
got out and shifted to forward there was absolutely no problem, speed was
normal, no vibrations, nothing whatsoever to indicate trouble. But still no
reverse.
After carefully checking everything on the inside I decided to dive under
the boat to check the propeller and there it was, one blade was missing!
So I can agree with Roger that one single blade can be very efficient but
based on the above experience the vabration may not be that big a probem.
Does anyone have an explanation why a one bladed folding prop does not give
any trust in reverse but works "normally" in forvard?

CS