Boat Vibration

[Alan Liebnick]

This past summmer I've noticed that when my Yanmar is running at 1100-1500RPM the boatand aft stays would vibrate tremendously. There was a constant knocking below the boa. The sound was eliminated by either raising or lowering the RPM. The yard hauled the boat and said a the rudder shaft bearing needed to be replaced. The sound was coming from the rudder post I guess. The problem was solved initially however it has returned. This time at 2000 rpm. Also it does not happen all the time. If the seas are rough and we are motoring it does not occur. I am confused as to what it causing this and what to do. When the vibration occurs it really can be LOUD! My wife jokingly says our boat runs at 3 speeds 1. slow 2. medium and 3. who needs a man.

 

[Stephen Ostrander]

knock knock

Assuming that you mean 1100-1500 rpm under way, not idling. I would check some things first before I suspected the rudder post: 1) prop is clean, fair, balanced, nut is tight 2) shaft and strut are true 3) cutless bearing is not worn 4) shaft is aligned with engine and motor mounts are tight and not worn or broken.

 

[Scott Laird]

vibration

In addition to the items mentioned by others, check the prop shaft "key" behind the transmission. Be certain it, and the keyway slot, are tight and not worn. Any tolerance will result in intermittant vibration.

 

[Paul Akers]

Check Below

Alan, sometimes the inherent vibration will cause a door, panel or other object to vibrate and make the noise. I know that I have had a door that vibrates at certain rpm's. Next time it happens, send someone to investigate the sound and see if there is a vibrating panel. Good Luck.