Gori folding prop vibration in overdrive

[CharlesBarnes]

We own a Jenneau 43 DS with a 75 HP yanmar and 3-blade Gori folding prop - about 200 hours since fitting. Recently I noticed a vibration in the boat when overdrive is used. Has anyone previous experience of this nature and what steps to take to rectify.

[tkeithlu]

Welcome to the forum, Charles.

I take it that the only problem is vibration, and it only occurs in overdrive, not at particular engine RPM or prop rotation.

In theory that narrows the field of possibilities a problem in the particular gear train used in the transmission for overdrive. But, that's not a very likely source of a vibration. I recommend that you do some testing to make sure. With the engine in and out of overdrive, examine the prop shaft (should not vibrate), the transmission (should feel to the touch as the source of vibration) and the engine (should not shift on it's mounts).

The shaft and prop are a likely source - there are components there that can start vibrating, such as a worn Cutless bearing or a bent prop blade. At the engine end, there are the mounts.

In other words, I'm recommending that you challenge your own conclusion, testing for other possibilities, before you pull the transmission for a rebuild. Good luck chasing it down.

[skipperpete]

Originally Posted by CharlesBarnes

We own a Jenneau 43 DS with a 75 HP yanmar and 3-blade Gori folding prop - about 200 hours since fitting. Recently I noticed a vibration in the boat when overdrive is used. Has anyone previous experience of this nature and what steps to take to rectify.

The Gori overdrive function gives the prop about 20% more pitch which can really load up the engine and driveline if you exceed the parameters defined by Gori...... calm to flat seas and low rpm up to just below hull speed ....or motor sailing. Using full power while in overdrive will overload the engine and with enough power, cause prop cavitation and accentuate any slight driveline imperfections.
Pete.

[kenbo]

What Pete said plus include motor mounts in the analysis.

That's a lot of horsepower for that boat's displacement, it would not be difficult to overload the drive train. Do you know what engine RPM you can achieve at wide-open throttle when you do not have overdrive engaged?

[Dsanduril]

Motoring or motorsailing?

Motoring - do you notice the same vibration in reverse? In overdrive the blades are in the reverse setting, if you notice the same vibration in reverse it could be an indication that one or more blade(s) are not reaching quite the right position.

Motorsailing - while Gori says to keep the RPM down, if you are sailing enough that you exceed the speed of the prop turning you can overrun the prop and cause vibration. In that case increase RPM slightly to see if vibration goes away.

Otherwise, what has already been said about drivetrain, mounts, etc.

[CharlesBarnes]

to tkeithlu, skipperpet, Dsanduril and Kenbo,
thankyou for your support and feedback. I will follow up your advices and see what results. CB