3GM30F and kanzaki gearbox- shaft drive

[Guest 129]

My setup has no bearing at tail of stern gland, so stern gland is supporting shaft from flexy plate to P bracket. Shaft length is approx 1m from GB to prop.

I have on going knocking/ vibration at certain revs which doesn't fill me with confidence. Cutlass bearing replaced 3yrs ago and really needs replacing again.

Makes weird noises with following quartering sea. Motor as little as possible so just forget about it.

Done multiple alignments with no change. new motor mounts.

Thinking of drilling out stern tube and replacing with new with bearing inside.

[waikiore 462]

Prop balance and shaft straighten? Is it a geared folder?

[Guest 129]

Kiwi prop. It was worse with the fixed blader.

Had shaft out last haul & Gordon said it was within spec on lathe.

[w44vi 18]

What clearance do you have from the tip of the prop blades to the hull ?

 

[Bradz 20]

what flexi joint do you have, alignment there would be where I would start, experienced something similar on our old Y88. Flexi joint was the issue.

[harrytom 689]

From engine mounts to barnys on prop.number of things. How does engine sound idling fast?get full revs?

[Guest 129]

3 hours ago, w44vi said:

What clearance do you have from the tip of the prop blades to the hull ?

 

25mm from memory.

[Guest 129]

3 hours ago, Bradz said:

what flexi joint do you have, alignment there would be where I would start, experienced something similar on our old Y88. Flexi joint was the issue.

R&D standard. I have aligned several times an doesnt seem to make any difference.

 

14 minutes ago, harrytom said:

From engine mounts to barnys on prop.number of things. How does engine sound idling fast?get full revs?

I keep it clean diving regularly. It has sweet spots and doesn't like 3000 revs, Smoothest at 2500, Has a rattle at 1100 to 1400 that has widened in range in last couple of years, so just push through that to 2500.

1100 to 1400 is fast idle. You are talking in gear aye? Out of gear it shakes the boat and drive train at about 1200 so push to about 2000 for battery charging.

Dunno about the extra bearing, as its a bit of work.

Hauling in Jan and will do whole rigmarole again.

[Frank 161]

16 hours ago, Guest said:

My setup has no bearing at tail of stern gland, so stern gland is supporting shaft from flexy plate to P bracket. Shaft length is approx 1m from GB to prop.

I have on going knocking/ vibration at certain revs which doesn't fill me with confidence. Cutlass bearing replaced 3yrs ago and really needs replacing again.

Makes weird noises with following quartering sea. Motor as little as possible so just forget about it.

Done multiple alignments with no change. new motor mounts.

Thinking of drilling out stern tube and replacing with new with bearing inside.

With such a short shaft and vibration issues I would be wary about putting a rigid bearing anywhere in the stern tube I think it will only transmit more vibration. I faced this issue with a previous boat, my take on it was 

1. Engine mounts were too hard but a softer mount would have allowed even  more engine movement making it worse.

2. Two bladed Folding prop was always out of balance, horrible thing.

3. Shaft flex coupling was too rigid.

4. Shallow draft hull meant I had to angle the shaft at 13 deg to the horizontal to get (barely) adequate blade/hull tip clearance (it was still less than recommended) 5, A two bladed propellor angled like this suffers assymetric loading as it rotates.

6. The cutlass bearing inner lining was not the fluted rubber type but some hard plastic that had no ability to absorb vibration.

7. Firbreglass seems to transmit vibration more effectivley  than wood.

I fitted a saildrive, OMG the best thing I ever did .

 

 

 

[Guest 129]

Hmmmmmm, I'm not going fitting a saildrive,  I'd rather just put up with it.

Your train of thought pretty much mirrored mine. I was going for Vesconite this time but it is even harder!

And as you say, a rigid bearing right next to the coupler may make it worse. Using the SG packing as a bearing doesn't thrill me either.

 

[K4309 395]

Do you have space for a thrust bearing? Supposed to be the ducks nuts for removing vibration, but it sounds like it might be hopeful with the dimensions you've already mentioned.

[waikiore 462]

A rubber cutless bearing will transfer less noise and vibration than a hard bearing , having said that it does sound like a prop issue and maybe too soft engine mounts. As the boat moves the shaft maybe leaning on the stern gland, this is where shaft seals on a glass tube have and advantage -moving with the shaft.

[LBD 176]

Funny noises that come and go with boat movements and swells are almost always a consequence of resilient mounts flexing.

This became more prevalent with the introduction of resilient engine mounts around the 80s onwards.

You may have the alignment correct stationary, but under load or as the  boat pitches and rolls with "G" forces in different directions, the mounts flex and the drivelive goes out of alignment.

A further complication is a down angle gearbox... under prop thrust, the forces are trying to lift the rear of the engine, even when motoring in flat calm water.

And the softer the mounts the more "quiet and vibration free the boat will be but the more the mounts flex under the various loads.

First place I would check is the age and condition of the mounts, make sure there are no cracks and the rubber is not perishing.

 

 

 

[Guest 129]

Haulout time fast approaching. 
If OD of copper tube around rubber fluted cutlass bearing is slightly smaller than P strut would it be acceptable to set in the thickened epoxy to make up difference?

Could be a cur to get back out next Time though.

[waikiore 462]

Yes the brass sleeve can be coated with epoxy if the strut has been bored oversize, you just gently warm it with a heat gun when you wish to change it again. The standard OD of a 1" cutlass bearing is 1 1/4" but they are also available in 1 1/2" and 1 3/4" !

[Psyche 775]

and when you need to remove the bearing next time, use a hacksaw blade and saw it into 1/4's