Torque

Posted By: Ted
Date: 11/15/07 1:42p.m.

Report: outside forum guidelines

In Response To: prop pitch (pic) (Bob s-v Watermark - Mac26S - Ottawa River - ON)

Other factors being equal (same boat, same engine) the 5" prop pitch should give you more authority into waves and wind than the one you're replacing. That's not to say that you had any problem with the 6.5" pitch, I wouldn't know. In my experience, it's not hard to cavitate with an outboard on a sailboat at motoring speeds. That's because the boat behaves like a displacement hull at these speeds and in many cases, outboard props on small engines tend to be speed props that try to move boats by just shoving as strong of a stream of water behind it as it can push, regardless of whether there's adequate payoff. A 9.9HP on a Johnboat would be a much different story. So, if there was any issue before with regard to the engine reaching a running speed beyond which the boat would not move faster, thereby wasting power, then the finer pitch should be like dropping down a gear and not waste the revolutions. You could discover you'll move as well but at a lower engine RPM, or you'll gain a little speed due to less waste, or what's the most likely is you'll lose a pinch of speed but fail to loose way as badly as before when going into a headwind, thus creating a gain in the instances where you need the auxillary motor the most. In any case, either those results can only be good. And if your old prop had no issue with wasted energy before, then there probably would be one if you moved to a higher pitch. So you're doing the right thing on a sailboat, making the error toward the lesser rather than the steeper pitch. Or so I would think.