knocking noise from shafts/props any ideas

PRM boxes can make a 'chatter' noise at very low revs, and have been known to wear out the splines on the drive plate due to it. May be you are in a similar state?
 
Sami, from personal experience could be one of two things:

If you have rope cutters fitted, it could be one has come lose.

Or your cutlass bearings shot!

Have had both. The cutlass bearing as well as knocking caused quite a bit of vibration and was only detectable at higher rpms.

The cutters caused knocking more so at lower rpms.
 
sounds to me like a cutless bearing. If it is the boat will need to be lifted im afraid. But what the hell its only money.
 
Is Gludy near you, I heard he has some underwater camera's /forums/images/graemlins/grin.gif

Ah! wait a minute, where is he anyway, I haven't seen him here recently /forums/images/graemlins/wink.gif
 
'fraid only way to be certain is to lift.

If you are getting vibration...and you will know if you are, then it's probably cutlass bearing.


should be no vibration with cutters, just a disconcerting knock knock knock...as the shaft spins..
 
I had a horrid noise on port shaft, worried me till i twigged
that the prop shaft anode had loosened on the shaft and
was banging on the P bracket!! I hope its summat simple
for you two
 
If it is the cutters, the most likely cause is one of the allen bolts had loosened and the cutter is slipping on the shaft knocking the P bracket or the hull (depending on type of cutter).

I'd get it sorted asap if it were me. Will it cause damage? Thats not really the point. You fitted cutters for a reason, if they aren't operational they need to be removed. I know I didn't want something banging about below, not knowing what it was, and not really knowing how much damage was beong caused to shaft, bearings, P bracket, hull .... etc etc.

May be something simple like a loose cutter... a stitch in time and all that.
 
Turn the prop shaft very slowly by hand with spanner on the coupling, see if you can hair the knock. Then try turn it back and forth fast as you can by hand and if you can feel a knock prop could be lose. Rope cutters would be very light noise.
Had a look at a Sealine T47 once for the owner, could hear a heavy knock when turning the shaft back and forth.

If there is a knock like this don't use!!

Got it lifted and prop was lose. (Thank God, otherwise I would have looked a prat).
 
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