Shudder at displacement speeds

[Ianfs]

The other day when taking a little trip down the Beaulieu river I noticed a distinct shudder through the boat. I thought it might be a propeller imbalance /blade adjustment and described it on the South West Sportsboats group FB page as a vibration at displacement speeds.

Martin Lines thought it could be the UJ's, which I hadn't thought of previously but thinking about it more it is a shudder. Then he said it feels like going over rumble strips and that's what its like.


Has anyone here replaced UJ's in situ, i.e. with the U Joints still attached to the stern drive?

[mlines]

Ours were not replaced, the shaft was simply pulled out, everything greased and painted up (and the bellows replaced as a tiny split was letting a small amount of water in that caused the corrosion that caused the stiffness)

Martin

[Ianfs]

Ours were not replaced,

Thanks Martin, yes I remember this now, your UJ's looked a gonna then they were cleaned and they looked like new.

So after the greasing Martin are they still shuddering or has it stopped now?

[mlines]

Its stopped now

Before

Afer

[mlines]

However looking up those pictures did remind me we had another, similar, problem. Symptoms were similar but at higher revs, this time it was because the duo props were not indexed

http://www.sportsboat.org.uk/index.php/ ... -the-props

[Ianfs]

So after you had greased the U joints did that stop the judderdering?

[mlines]

Yes, two separate incidents

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[Ianfs]

Which one caused the shuddering?

[mlines]

Both. We felt the UJ at the end of the previous season as we came down off the plane to displacement. The props were different with a resonance at a mid rpm.

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[Ianfs]

Thanks Martin much appreciated. I think I'll get the prop done anyway, it needs doing as I'm selling her and I'd hate to put her up for sale with a scruffy possibly unbalanced prop. Then if the shudder persists I'll change the U joints out.