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.

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