Degrees of pitch?

[Brad18489]

I have just bought a used Oceanis 400 with a 19" Classic three blade prop on it. The boat has a Perkins 50 hp with a 2:1 ration on the gearbox. I am experiencingsignificant problems with the engine that I am beginning to suspect are related to the pitch being set too high. I have a feeling that the desiel is labouring too hard and is smoking as a result of strain over an extended period of time. When moving forward I get about 6 knots boat speed at 1900rpm Pushing it any harder seems to really bring on much smoke and vibration. The tack goes to 6000 so I assume the engine should at least reach 3500 with ease. The best I can get is 2500 from her with about 7kts at that rpm. I have not touched the prop but assume that the yard that installed it did set it at 20 degrees. Can you comment on the correct setting and size of prop? Can you also advise on your experience on engine damage if the pitch is set too high?Lastly I am confused about fresh water sailing with zinc annodes vs magnesium which I have been advised are much more effective for a saltless sailing environment.

 

[Ed A]

what you need to know is.

You need to know the max reccomended operating rpm for the engine. the prop should be sized so the engine can reach that rph and no more. If you refence that nuber rpm and the ratio any reputable prop shop will tell you what pitch you need to achieve your goal. but you need the numbers.

 

[MIke D]

Comparing to H310

Brad, Michigan Wheel propellers has a website where you can input your boats specifications and they will email you with a recommendation within a week or so.Also, I looked up a Hunter 410. It is also 50 hp. The spec calls for 18 x 14 3 blade. Although it is not comparable without looking at the rest of the data, it may give you a reference.good luck,Mike D

 

[KOS]

Prop Pitch

The symptoms you describe (low RPM at or near hull speed and black exhaust when pushed harder) are classic ones for being over-pitched. This is akin to trying to go up a steep hill in a car with a manual transmission without downshifting. The proper pitch will push the boat at or near hull speed at the maximum rated RPM for the engine. Its generally ok to be a couple hundred RPM low of the rated (governed) RPM if you don't get black exhaust. Being overpitched will increase wear and tear on the engine.