Most, if not all metal boat props have a shear pin or a rubber hub or both. The rubber hub flexes to absorb small impacts and slips to absorb larger ones.

Another company, Comprop I think, makes cheaper plastic props designed to shear off with impact. Obviously losing a blade is not so much a problem in the water but I can imagine that the vibration would be pretty awesome spinning at 5000 RPM!

Most of the lakes around here are shallow and I hit bottom all the time. Aluminum props get pretty beat up but the stainless prop I have on one of the outboards is solid. It never bends or chips and I'd probably have to hit something metal or cement/rock to do any damage to it.

A friend of mine is building an airplane from scratch and I believe his engine/gearbox to prop incorporates a harmonic balancer and some kind of flex drive on the composite prop IIRC.

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-Evan


Benz Fleet:
1968 UNIMOG 404.114
1998 E300
2008 E63


Non-Benz Fleet:
1992 Aerostar
1993 MR2
2000 F250