"Garland Gray II" wrote in message
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This was not at all my experience when I lost one blade of a folding prop.
Thrust both directions, but shook like the devil.
I would have expected just that.
This is a saildrive, but I wouldn't think that would cause any difference.

"C. S." wrote in message
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"Roger Long" wrote in message
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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

As somebody else pointed out the answer to the "no vibation" may be counter
balance. There is about one meter of free shaft between the bottom of the
boat and the support in front of the prop. Maybe the shaft flexes enough to
counterbalance the missing blade? But why is there no power in reverse?

C.S.