Help!!!!!! Unusual knocking!!!!! New shaft!

[Libby Thompson]

I have been frustrated for three months..... I replaced the bronze factory shaft with a stainless shaft direct from France for my Beneteau First 35.New cutluss bearing, new PSS dripless, and the original fixed two blade prop. I own a Maxi Prop, but the stainless shaft nut threads do not match the new prop, so I had to install the fixed blade. I plan on reinstalling the new prop when I can have a rethreading job done on the nut.In the meantime, my boat is out of commission. I cannot even leave the dock in forward gear. At 900 RPM a shock wave develops from the aft shaft area outside the boat and resonates through out the shaft and engine and shakes the boat violently. I at first thought it was the gear box, so I had it checked out. Then I had the engine checked and the motor mounts and the engine realigned. All checked ok. I called the parts dept. at Beneteau and all I got was that they are willing to sell me another shaft! The shaft was sent direct from France and there is no warranty.Has anyone had this problem with a replaced shaft?

 

[Mark Smith]

Your shaft may be bent....

Don't want to insult your boat knowledge but that is usually the cause of violent shaking. With my boat it usually turns out the simple answer is the right answer.

 

[Kevin]

Vibration problems.

Hello Libby,A few things pop to mind. If the shaft came from Benn. France, was it ever check for trueness? Such as a fit and face to the existing coupling and whether the shaft is in fact true? The shaft is still a machined item, which requires some checking prior to the actual use. Second. I assume the fixed blade was removed in order to try the Max-Prop onto the shaft? (You mention the nut did not fit) Was the two blade then put back on? If so the prop could be riding on the key. (very common problem) The Key should not cause the propeller to sit proud onto the taper, making contact to only one side of the taper by the propeller. (The top of the key should not hit the top of the keyway cut into the prop.) When the cutlass was replaced how was it removed. Did someone pound the heck out of the strut to remove it? Doing so can VERY easily cause the strut to loose its bedding. Is the shaft slamming into the stern tube opening in the boat? You may see that the shaft is not sitting centered in stern tube and because you removed a stuffing box, which may have provided some support, the support may now be gone and the shaft is striking the tube. If the frequency increases as the Rpms increase I would think it could be located anywhere along the running gear. If the vibration is a constant no change with increased Rpm’s, I would think it is transmission coupling forward. Hope one of these works. Let me know about the Max-Prop and we will get to taken care of. Kevin

 

[Stanley J. Rogacevicz]

Why France ???

Libby, I'm having a SS shaft made for my c320 by H