My 33-2 had a martec when I first got it - it was badly worn and not terribly effective in reverse. I replaced it with a 2 blade gori which performed well. Same engine as yours. The boat would easily run at 2800 rpm all day at speeds exceeding 6kt. I wouldn’t hesitate to change the prop. Make sure you understand any mods to the shaft/nut which may be required.
Dave ex 33-2 Windstar. Sent from my iPhone > On Nov 10, 2024, at 8:40 PM, ejwills1993--- via CnC-List > <cnc-list@cnc-list.com> wrote: > > > 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.
