Knock in Stern

[ahutchin]

Went for a test sail on a Hunter 28.5 I am thinking of purchasing and noticed a load knock when boat is under power (Yanmar). Noise is under portside at stern with engine at about 2500 rpms. Any ideas of what the noise is?

 

[Bob Madeiros]

Possible Source of Knock

You might want to check the shaft as it enters the stuffing box and shaft log. If the engine isn't aligned well, the shaft may be positioned too close to the metal shaft log. At RPM, it may be wrapping against the shaft log. This was the root cause of a similar sound I had on my 31 some time ago. Try pulling up and down on the shaft to see if you can duplicate the sound. (... I'm not sure if you can do this on the 28.5... The 31 might have more space to get to it...) Bob

 

[Steve O.]

knock knock who's there?

could also be the cutless bearing in the prop strut. use same method for testing

 

[Marc Honey]

Like they said...

Definitely check shaft alignment and cutless bearing. My 87 28.5 was very low hours when I bought it 2 yrs. ago and it needed the shaft aligned. One of the engine mount nuts was missing. Once aligned, the drive train smoothed-out considerably. I usually run at 1400-2200 rpm.but then I'm on a lake with no current no waves. Yanmar has been flawless...boat is great!!!

 

[s/v Brenda Gail]

Same Knock?

I too have a knock on a 89 h30 - I have aligned the shaft/engine but at certain RPM's it will still knock. I have looked under some boats on stands and there just isn't too much room for error. (though thats not the measurement one checks for alignment) I could pull/push on the shaft log and the noise would go away. I have the engine/shaft alignment set according to all read material - I wonder how much damage can be caused?