Hello,
Please forgive me if this has been discussed before - I searched topic and didn't find it. We have a Cape Dory 25D with the original Yanmar 1GM. The previous owner swapped out her two-blade propeller for a nice bronze three-blade. I've had two friends who are licensed captains aboard who, independently, both queried whether the prop was the correct pitch, as the boat is very slow under power and the rpms at full throttle don't exceed 2,000.
>Does anyone know the correct prop pitch for the 1GM-25D combination?
>Is there a method for measuring pitch?
>Have others had issues with switching from two to three blades?
THANKS for any guidance you can provide.
Harlan Doliner
True North CD-25D #69
Correct Prop Pitch?
Moderator: Jim Walsh
Re: Correct Prop Pitch?
Disclaimer: I'm not an expert ...
"Does anyone know the correct prop pitch for the 1GM-25D combination?"
... most small marine diesels rev to about 3,000 rpm or even a little higher, 3,500 is not uncommon. Do you have a tach ? If yes, put engine in neutral and rev full throttle briefly just to check tach. If you can reach 3,000+ rpm then you can have some faith that the engine and tach are ok and you are probably over pitched ... if still stuck at around 2,000 while in neutral, either your tach is malfunctioning (not uncommon) or your motor/rev limiter/fuel delivery has problems or both. Excessive smoke is a sign of too much pitch. The tach on my Beta 14 is not very accurate ... it will wander +- 250 rpm then sort of settle down.
https://www.yanmar.com/marine/product/engines/1gm10/
"Is there a method for measuring pitch?"
.... many rigid props have pitch stamped on the face of the hub, ie not necessarily visible if mounted on the shaft.
"Have others had issues with switching from two to three blades?"
... I fitted a three bladed feathering prop on a new Beta 14 in my CD 27. The engine redline is 3,600 rpm. I can only manage 3,200- so the prop is theoretically over pitched. After some conversations with the mfg, Featherstream, I decided to leave well enough alone. I typically cruise at 2,000 -2,200 and motor sail at 1,600 - 1,800 where a little extra "traction" is probably a good thing. There is no smoke or even smoke residue on the transom.
good luck
"Does anyone know the correct prop pitch for the 1GM-25D combination?"
... most small marine diesels rev to about 3,000 rpm or even a little higher, 3,500 is not uncommon. Do you have a tach ? If yes, put engine in neutral and rev full throttle briefly just to check tach. If you can reach 3,000+ rpm then you can have some faith that the engine and tach are ok and you are probably over pitched ... if still stuck at around 2,000 while in neutral, either your tach is malfunctioning (not uncommon) or your motor/rev limiter/fuel delivery has problems or both. Excessive smoke is a sign of too much pitch. The tach on my Beta 14 is not very accurate ... it will wander +- 250 rpm then sort of settle down.
https://www.yanmar.com/marine/product/engines/1gm10/
"Is there a method for measuring pitch?"
.... many rigid props have pitch stamped on the face of the hub, ie not necessarily visible if mounted on the shaft.
"Have others had issues with switching from two to three blades?"
... I fitted a three bladed feathering prop on a new Beta 14 in my CD 27. The engine redline is 3,600 rpm. I can only manage 3,200- so the prop is theoretically over pitched. After some conversations with the mfg, Featherstream, I decided to leave well enough alone. I typically cruise at 2,000 -2,200 and motor sail at 1,600 - 1,800 where a little extra "traction" is probably a good thing. There is no smoke or even smoke residue on the transom.
good luck
Fred Mueller
Jerezana
CD 27 Narragansett Bay
Jerezana
CD 27 Narragansett Bay