H34 Speed with Yanmar 3GM(F)

[Ed]

I don't think your problem is the engine since 3000rpm is high enough to get 6+ kts if the prop is OK.
I had a problem with max rpm @ 2800,which was caused by the throttle arm inside the pedestal hitting the housing before moving the engine arm far enough - had to grind to provide more travel. Remove compass to see if this could be your problem.

 

[Capt Terry Griggs]

Low speeds on 3gmf yanmar

I would suggest that before you get into tearing apart the mixing elbow and changing props, you should check on the alignment of the shaft w/ the engine. It may require adjusting the motor mounts to make sure there is no misalignment. Misalignment can cause the engine to work harder with results of slower speeds, and possibly heating it up a lot higher than usual, and naturally, the vibration you mention you are experiencing w/ the increased speed. The other thing, is, do you perhaps have a bent shaft? Very seldom do I cruise at any thing more than 2800 RPM. 3400 is somewhat screaming and unless you are heading for a fire somewhere, don't think I would go there.

 

[Steve Dion]

There is an issue with the engine. It may be linkage or something else, but these engines should be able to reach 3500-3600 rpms.

The max rpm's when the engine is in gear is directly related to the prop size. This would be like have an automobile with a .500 rear end vs a .300 rpm. There is only som much power.

The H'34 were equiped with two different props. I believe there was a 15 x 15 and the 15 x 12.

The real issue here is that the boat cannot get 3600 when in netural. Fix that problem and there may not be any other issue.

 

[Dan Johnson]

Speed test today...

Launched this afternoon, clean bottom, two persons aboard, achieved 3,300 RPM WOT with a 15x12 RH two blade prop. GPS not hooked up, against 9 knots of wind on the nose and an incoming tide, instruments not turned on for the 10 minute run from winter storage to marina.