Monday, October 31, 2011

New Prop

Went for a sail on the weekend of the 23rd Oct - had a great run for 10 nautical miles out into San Pablo bay hitting 7.5 knots before the wind died, even though it was a light breeze. Unfortunately, I misjudged slack water under the Carquinez Bridge and had to slog all of the way back against a 3 knot tide. LUCKILY I had just changed out the standard prop on my 5hp Honda for the spare which had a pitch 20mm (~3/4") smaller. Even though this doesn't sound like much, the difference is remarkable. The standard prop would drive the boat at 5 knots at half throttle, but anything over half throttle caused terrible ventilation i.e. 5 knots was max speed and in rough weather it might be 2-3 knots. With the smaller pitched prop, I can run the motor at full throttle and it will now do 6.6 knots in calm water. More importantly it is much more resistant to cavitation/ventilation giving more thrust when the water is rough. So, on my slog back up the Carquinez channel, I was able to drive it at more than 3 knots (luckily it was not rough) and I would have been doing about 1.5 knots with the original prop. If you have cavitation/ventilation problems with your outboard, I would suggest considering a prop with a smaller pitch - it worked for me.

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