Remove gearbox with boat in water - risky?

[Durcott]

Hi Folks,

I have a grp yacht with inboard motor / gearbox driving a short prop shaft. Boat is circa 1970.

The gearbox needs to come out - see infinite previous mailings.

I'm at a brokerage, where the owner is telling me not to remove the gearbox until the boat is lifted for other work. The shaft will move - disturb gland - drip turns to trickle turns to flood... However, I've just found a gland grease pump, so I reckon I could prevent any leakage.

On the other hand, this guy is not without experience, whereas I have none.

Would I be taking a big risk in sliding the prop shaft out of the way with the boat still in the water?

Thanks

Jeff

 

[pvb]

Should be OK...

Should be OK, but you ought to clean the exposed propshaft very carefully before you start so that it will slide backwards into the stern gland without causing damage to the sealing material. Only other consideration is if you have a certain type of ropecutter installed - you normally need to be able to see it when returning the propshaft to its normal position, so that you can engage the rotating cutter with the fixed holder.

I've taken my gearbox out whilst the boat was afloat. Nothing dramatic happened.

 

[Durcott]

Re: Should be OK...

OK - hadn't thought about cleaning it - I'll have a look at the state of it.

What about supporting it during the operation to keep the thing more or less in line?

Jeff

 

[Gordonmc]

I did this job two seaons ago with the boat in the water. I undid the coupling and pushed the shaft back without any ingress of water.
Logically the section pushed into the stuffing box will be less worn and a tighter fit so the drips should decrease.
The man advantage doing it in the water is that the lump only has to go on a pontoon or dinghy, rather than dropped ten feet to the ground. Don't underestimate the weight in a gearbox.
My engine has four bearers so I didn't bother propping anything.

 

[Birdseye]

No - but just make good and sure that the shaft cant go the whole way out, and once you have the box removed return the shaft to the position it normally occupies and where it doesnt leak.

 

[spannerman]

We routinly removed gearboxes with the boat on the water especially when they were Princess 40-50 footers with no problems, and the shafts were a lot heavier than the one in your sail boat, if you are worried about it sagging and causing the gland to leak just put a block under it to hold it at its normal height. No problem about pushing it back to give you some clearance, the problem is if you pull it in as the crud is on the outer side of the shaft thats in the prop tube.

 

[simonfraser]

i'd support it and clamp it as well, you don't want to knock it out now do you . . .

 

[davierobb]

I've dropped the shaft out the stern gland several times with no problem. I use large mole grips to prevent the shaft disappearing. Ideally the job is best done on the hard but if it does not leak to start with why should it start.

 

[eidiohir]

Hi
Changed the gearbox on a colvic watson 34 last year while she was in the water.There were no problems at all.In fact when you are checking the alinement of the engine before tighting up the prop you can be sure that it won't change

 

[boguing]

Just put a worm drive clamp (Jubilee clip) round the shaft and it can't come out.

 

[Rick]

Some can, some can't. Mine can, but only because it's easiest to lock shaft, then remove engine gearbox as an assembly. Some shafts will slide back. others won't - depening on what is behind them. If I didn't know how things would go (ie never moved shaft on this boat aft before) then I'd probably err on the side of caution unless doing it afloat was the only option.

 

[Strathglass]

It really depends on what type of shaft seal / stern gland is fitted to your boat. As you have a conventional stuffing box or if you had any seal that uses the prop shaft as one of the sealing surfaces then it is safe to move the shaft to allow removal of the gearbox.

In your case as you have a gland and oiler I don't see any problems.

If your yacht had been fitted with one of the propritory non drip seals such as a 'deep sea seal' then you could not move the prop shaft as it will open up the seal and this could cause severe problems and allow a LOT of water to enter. It may be possible to move the whole assembly as you try to move the shaft back but it would be quite a wet job.

I think that your yard person is wrong in this occasion.


Iain