I agree with Velera's comment, and will modify my previous response to provide more detail.
My boat has a 16"D x 14P" double bladed prop. I believe that was the prop that was provided standard on the W50. I'm not exactly sure what the reduction ratio is on my transmission. I've found two ratios quoted in the boat's documenation: 1:1.8 and 1:2.0. I've never bothered to actually determine mine, but these different ratios, if they do exist between boats will make a big difference on the pitch needed. Perhaps, when I get a chance I'll determine mine so I can be helpful to others. UPDATE: I measured the reduction ratio of my transmission. It is 2:1.
When I first got my boat, I had some overheating issues. I fixed all of the typical sources: new raw water pump, broken impellor vanes in the raw water pump elbow, possibly fouled HXs, radiator cap, thermostat, fouled intake screen, etc., etc. All these fixes caused some improvement, but I couldn't run the engine above ~2300 to 2400 rpm, without having the temperature to start slowly rising above 180F. At this RPM, the boat was clearly at hull speed, and I would create a wake like a power boat. My guess was that the engine was actually running close to rated HP, at this RPM, but the cooling flow was running at about 3/4 flow at max RPM (~2400/3200 = 0.75), hence the overheating. Remarkably, the engine exhaust was normal, and not black, which would have been a clear indication of overpropping.
About 3 years ago, I had my prop re-pitched to 12" (i.e., a 2" reduction). After I did this, I gained about 300-400 rpm, which means I now get the same symptoms at 2700 -2800 rpm. But, importantly, I can now cruise indefinitely at 2400 to 2500 rpm, which is 75% to 80% of max RPM - my minimum goal. By extrapolationg my data, I would guess that 9" to 10" pitch would be ideal for a two bladed 16"D prop. Perhaps I'll change sometime in the future.
BTW, I checked the calibration of my tach. It's right on (+/- 50 rpm).
Jim #191
_________________ Jim Voelxen Odyssey #191 Home Port: Osterville, MA
Last edited by jvoelxen on 26 Nov 2012 19:16, edited 1 time in total
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