1984 H31 2GMF13 Yanmar I'll make this as short as possible. Bought the boat and the 16 inch, 2 blade feathering max-prop pitch was WAY off at 16 degrees. Diesel would rev to only 2300 rpms, but boat would really move out at about 1800 rpms, but was also belching black smoke at full throttle. Hauled the boat and moved down 3 settings to 10 degrees (per marina suggestion). Now the diesel revs 3200 rpms full throttle in forward, and tops out at about 4.5 knots (Yanmar specs the engine at 3400 rpms). Black smoke decreased somewhat. I know that my girl is a little underpowered with the 13 horses, and I know that prop issues are a give and take between power and speed, and the need for little diesels to stay at high rpms.....Now I just need to tap the vast knowledge base out there and tell me if I should learn to live with such a slow motoring speed, or haul the boat again (can't adjust prop in water) to move up one notch to 12 degrees for some more speed and risk dropping the rpms too much. Max-prop literature says about 14% change in rpms per setting. This would drop my rpms from 3200 to 2752. Is that too low? Any advice appreciated.....Gary
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Yep, call PYI. They're the experts. They need
your vessel design, (H31) engine and reduction gear ratio. Also your prop diameter and number of blades. But you'll probably have to haulout again. Good luck.
your vessel design, (H31) engine and reduction gear ratio. Also your prop diameter and number of blades. But you'll probably have to haulout again. Good luck.
prop adjustment and RPM
I can only describe my H31. Same 2GMF engine except I believe mine is rated for 15 horse (I never knew they went as low as 13) Upper attainable rpm is 3200. I typically cruise it at 2800. Very little smoke. Boat does just under 7 knots.
I can only describe my H31. Same 2GMF engine except I believe mine is rated for 15 horse (I never knew they went as low as 13) Upper attainable rpm is 3200. I typically cruise it at 2800. Very little smoke. Boat does just under 7 knots.
Pitch
Gary, I understand your predicament but cannot figure your degrees (of pitch). A 16" dia prop with blades set at 10° has an effective pitch of only 6" so this is why you can reach these revs. At 16° the pitch is about 9.7" and should be roughly okay for your engine. My guess is that, either the engine is not developing full power, or there is something wrong with the prop which could be overloading the engine. There are many reasons for a diesel not achieving full power and these include insufficient fuel supply (blocked filters), air entering the fuel line, one injector not working, burned out or mal-adjusted valve, hole in piston. The list is endless! If you are not an engineer then may I suggest that you consult someone who knows about such matters.
Gary, I understand your predicament but cannot figure your degrees (of pitch). A 16" dia prop with blades set at 10° has an effective pitch of only 6" so this is why you can reach these revs. At 16° the pitch is about 9.7" and should be roughly okay for your engine. My guess is that, either the engine is not developing full power, or there is something wrong with the prop which could be overloading the engine. There are many reasons for a diesel not achieving full power and these include insufficient fuel supply (blocked filters), air entering the fuel line, one injector not working, burned out or mal-adjusted valve, hole in piston. The list is endless! If you are not an engineer then may I suggest that you consult someone who knows about such matters.
I'm listening to a great mechanic and the marina..
I certainly would not trust my limited judgement on this science. The best mechanic in these parts has checked out the engine and was very pleased with the way it cranked, ran, sounded, etc. (with the exception of some black smoke under full power). When he shifted into forward at idle, he was shocked at the way it leaped forward, and immediately began asking questions about the prop. When he was told it was a max-prop, and was only turning 2300 rpms at full throttle, he said this was most probably the problem, and accounted for the black smoke as well. He said the engine MUST turn up at least 2700 rpms at full throttle or it will be operating under too much load and blow black smoke, and damage the engine over time. The marina staff agreed.
I certainly would not trust my limited judgement on this science. The best mechanic in these parts has checked out the engine and was very pleased with the way it cranked, ran, sounded, etc. (with the exception of some black smoke under full power). When he shifted into forward at idle, he was shocked at the way it leaped forward, and immediately began asking questions about the prop. When he was told it was a max-prop, and was only turning 2300 rpms at full throttle, he said this was most probably the problem, and accounted for the black smoke as well. He said the engine MUST turn up at least 2700 rpms at full throttle or it will be operating under too much load and blow black smoke, and damage the engine over time. The marina staff agreed.
The folks at Max...
...have a formula you plug into. Clutch or final drive ratio and prop diameter will give you the ideal pitch. Set your closest reading +or- 1*. Using the wrong pitch can damage your engine and/or your prop. Cavitation will remove metal from the prop blades over time and cost power and /or speed.
...have a formula you plug into. Clutch or final drive ratio and prop diameter will give you the ideal pitch. Set your closest reading +or- 1*. Using the wrong pitch can damage your engine and/or your prop. Cavitation will remove metal from the prop blades over time and cost power and /or speed.
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