A PROPosition

WhiskyJack on the Travel-Lift

Yesterday I hauled the boat at Rocky Point Marina to swap props.

The background:  The 14x8 (14" diameter by 8" pitch) Campbell Sailor that Norm at West by North recommended would not let the engine reach maximum engine RPM, meaning that I could not harness all the horsepower from my little Yanmar.  It also caused the engine to produce copius amounts of black, sooty, smoke at WOT (wide open throttle); definitely not good for the engine or the environment.  As I have previously described in an earlier blog (see here) , I chased a number of leads (exhaust restriction, injectors, injector pump) to this problem (see here) before coming to suspect that the propeller had too much pitch, despite Norm's insistence that it was correct.

The test:  I had Sheffield Marine Propeller here in Portland, build a "Michigan Wheel" (MW) type 14x9 three bladed wheel.   This, was Yanmar's propeller recommendation for the 2QM15 engine that I have.  The boat, when new, had a 14x10 prop, but the 1978 test sail article in Pacific Yachting leads one to believe that the engine would only reach 2600 RPM with that prop.  I swapped the new MW 14x9 with the 14x8 Campbell Sailor.  It took all of 30 minutes and I was ready to be go back in the water.

The results:  The new MW 14x9 prop lets the engine rev to 2700 RPM which is a vast improvement over what I had.  Speed looks to be just over 6 knots via GPS (average up-river/down-river).  If the engine, when new, could only rev to 2600 RPM with a 14x10, then getting 2700 RPM with a 14x9 is great.  The rule-of-thumb here is 200 RPM change for each 1" change in pitch.  So the "new" engine should have been able to rev to 2800 RPM with a 14x9 and, if so, the 100 RPM difference I'm seeing now is acceptable with a dirty hull and over 2000 hours on the engine.  Now we know for sure that the 14x8 Campbell Sailor is over-pitched for my engine/hull combination.

Next:  What will West by North do to make this right?  I'll be sure to keep you posted.