I don’t have a lot of great input, but a couple tidbits. We had a 1980 34 with a Martec folding prop and the Yanmar 2GM20.
At some point in its life (we had the boat for 35 years), we replace the cutlass bearing, it had some sloppiness. However, I don’t ever recall that caused any particular vibration. We just noticed that during a haul out and decided to replace it. The Martec was terrible in reverse. We replaced it with a Maxi Prop feathering prop which gave us really good reverse. Richard Arper C&C 34+ Xanax rtar...@wavecable.com From: ejwills1993--- via CnC-List [mailto:cnc-list@cnc-list.com] Sent: Sunday, November 10, 2024 5:40 PM To: cnc-list@cnc-list.com Cc: ejwills1...@gmail.com Subject: Stus-List CnC 30 Mk II - Expected Crusing Speed under Motor? Hey all - I have a 30 Mk II with the original Yanmar 2GM20F and factory Martec 15D x 11P x 1 2-blade brass prop. About 850 hrs on the engine, seems in great shape. Issue: I can only motor at 2200 RPM before the engine/stern begins to vibrate. This puts me at a max cruising speed of 5 kts. >From the survey, one of the prop tips measures about 1/8 inch farther AFT >(axially) when at 12 o’clock position versus when the other tip is rotated to >the same 12 o’clock position. The prop blades are not chopped/scraped and the >prop appears to be otherwise symmetrical in all other dimensions. The engine does not vibrate when revved to 2800-3000 rpm in neutral. The shaft does not wobble, and there is no leakage from the shaft packing. Q: What cruising speed should I expect from this boat and the Little Yanmar? I think the spec in the Yanmar manual says cruising rpm should be 2700-2800 rpm without breaking a sweat. I’m not expecting to motor at 8-9 knots like a big sailboat but I do expect to be closer to the 30-footer hull speed of around 6.7 kts. I’m trying to figure out if this is a valid excuse to get a folding prop :) Thanks! -Eddie W.
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