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11N Motor Cavitation

Steve W

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Yesterday I tried a 4HP Mercury standard shaft (15") outboard on my 11N. I built the boat exactly to the plans. As it sits, the OB "plate" just above the prop, sits just slightly lower than the hull. Of course the short keel aft is slightly below the plate. This motor seems to be a good match, but as soon as I turn even a little bit, the prop cavitates and sucks air, sending it revving and only biting when I run it back close to idle.  I want to use this as a fishing platform when not sailing.


I put my long shaft Honda 2HP from my Sea Pearl on it and it works great, although she draws 5 more inches and I hate the noise of that Honda with a passion.


Has anyone encountered this?


Take Care,




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Please, please-


It's ventilating, NOT cavitating. The plate on the motor is correctly an Anti VENTILATION plate. Stops the  prop from sucking air down the outboard leg


"Cavitation" occurs when props move fast enough to vaporize air from the water, and usually explosively, leaving little pits in the prop.




VERY high performance race boats have the problem


Answer? Lower the engine more into the water.

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