Vibration at 3100-3500 rpm

[TuxedoPk]

My GT has developed a vibration when I am running from 3100-3500 rpm. The local mechanic/hack doesn't seem to know what is causing the problem.

Prior to this problem the rudder hit bottom at slow speed but bent and was sent out to be straightened. The prop looks fine like it has never hit anything but the marina is telling me that I should send it out to be reconditioned because if it was slightly knocked out of balance it could be causing the vibrations. This could be the problem but I just don't seem to be buying into it and had the stainless steel prop reconditioned a few months ago so I don't see any benefit to having it done again if this isn't the problem- I'd rather invest in a cheaper spare so at least I'd get some benefit if it doesn't solve the problem.

Q. What are the most likely causes of a vibration at these speeds?

[MOP]

Opinion it may very well be the prop! If you hit something like a log which may not leave much if any mark on the prop but still bent the rudder good chance you tipped one of the prop blades forward a bit. If the boat is out of the water you can set a block of wood so it just touches the aft end of one of the blades then turn the prop to bring each blade to the same position to see if any are out of whack. Don't take a hell of a lot to cause vibration. Many times a prop will not show much, it screws forward where as a rudder hits square on.

Phil

[mphatc]

Phil,

Let me understand this . .it's 7:38 AM , your on vacation with your signifigant other, your on a remote island, and your posting here???

I would expect:
A. you would be in bed with your lady :smileybo:
B. sitting on the deck enjoying a cup of AM Java :)
C. blasting up and down the channel in your Donzi waking up the world around you . . . . :boat:
D. you didn't drink enough last night to have a bighead this AM. :smash:


Mario . . boatless in 2004

[mattyboy]

bent prop
or bent prop shaft


Matty

[gcarter]

bent prop
or bent prop shaft


Matty
I agree! :)

[TuxedoPk]

I'll be taking the prop up to the shop tomorrow and hoping that it is out of balance and the problem isn't the shaft.

[David O]

Tux
If your prop shops says the prop is balanced don't just assume your problem is in the shaft, it still may be the prop.
I have a prop that shakes the boat like it has 4 wheels all out of balance and out of round. Two props shops have checked the prop and both say it is fine. I borrowed a prop from one shop and ran very smooth on the boat. I since have bought a new aluminum prop and a stainless prop and both are very smooth on the boat. The original prop still vibrates the boat.
It is now at the third shop and this guy says he thinks he can see a crack in the housing around the hub therefore allowing the shape of the prop to change under load and also the hub has rotated some with in the prop. I marked a line on the hub and one on the prop, ran the prop, checked the line and sure enough it moved.
Try another props before you assume it is the shaft.

[TuxedoPk]

Dave- Thanks for the tip.. I'm hoping that if I camp out at the prop shop they'll take care of it while I wait otherwise I'll know for sure on Thursday when I'm getting ready to leave for 1000 Islands.