Problems with Sureseal stern gland and shaft alignment

[MILLPOND]

I would like some advice please.

This winter I had a Sureseal dripless sterngland fitted to replace the ageing stuffing box on my 1992 Nauticat 33. I asked the engineer at the boatyard to fit the unit. He took the water feed to the unit from the oil cooler of the engine. First outing of the season all was well. When I went down this weekend though, pre-departure oil check revealed that the engine was full of water. The engineer had not installed a siphon break or vented loop in the water feed, so when the engine cooled, it sucked in sea water through the stern gland which siphoned up to water level.

I took 20 litres of emulsified water and oil out of the engine and changed the oil and filter four times. I also installed a siphon break in the water feed hose. The engine has been run for three trips of four hours, and the oil now looks cleaner than ever with no trace of mayonnaise! Hopefully the problem is solved.

Are four oil changes enough?

However, there is now another problem. When the prop shaft is running, there is a knocking noise coming from the stern-tube or cutlass bearing area of the hull. It is getting louder. On close examination the shaft appears to be slightly out of alignment and there is a tiny amount of lateral 'wiggle' in the shaft as it rotates.

I think there are two potential causes - either the cutlass bearing has been damaged during the stern gland installation, or the prop shaft is not correctly aligned with the transmission coupling. Either one is beyond my capability to fix. Before incurring the cost of having the boat hauled out, has anyone got any other suggestions? Is there anyway of checking shaft alignment with the boat still in the water?

Would you ask the engineer to fix this at his own expense? Should I go somewhere else - the track record of not installing the siphon break does not instil confidence.

Thanks for the advice.

 

[Talulah]

I have a mistrust of employing people to work on our boat and so would first do some checks myself. Having said that there are many very capable engineers who get tarnished by the few.
I would disconnect the prop shaft from the gearbox and rotate it. See how big the gap is. If the gap is significant you'll see it but for final alignment feeler gauges would be used.
Depending upon what I found would dictate my next course of action.
I wouldn't be using the boat until I had checked the alignment.

Another course of the knocking noise though could be the rope cutter. If the shaft has been pushed back and then pulled forward again the rope cutter may not be correctly sitting in the fixed part. Depends what rope cutter you have if any.

 

[Tranona]

Relatively easy to check shaft alignment. Undo the bolts holding the coupling between the gearbox and shaft, slide the shaft back and check the clearance between the two faces. It is quite possible the shaft is misaligned as the new seal is flexibly mounted and suspect the old stuffing box was rigid. Therefore more care needed to align the shaft and engine to prevent the shaft from hitting the side of the stern tube. realignment can be done - indeed should be done - with the boat in the water.

 

[MILLPOND]

Thanks for the speedy reply! Can I disconnect the shaft from the gearbox with the boat afloat? I take it is just a case of undoing the five retaining bolts. When you say there may be a gap, do you mean that the shaft and gearbox don't sit squarely opposite one another?

The rope cutter is another good thought. Although this will obviously need to be visualised out of the water.

I am now slightly mistrusting of the engineer - with adequate reading and preparation I am sure that I would have been more than capable of fitting the seal myself, and could have avoided the fairly catastrophic result of 20 litres of sea water in my engine!

 

[MILLPOND]

Thanks Tranona,
Am I right in thinking then that you have to align the engine with the shaft rather than vice versa. How do you adjust the engine alignment? Are the mounts adjustable?

 

[Tranona]

Thanks Tranona,
Am I right in thinking then that you have to align the engine with the shaft rather than vice versa. How do you adjust the engine alignment? Are the mounts adjustable?

Yes. The mounts have up and down as well as lateral adjustment. Can be a bit tricky visualising the effect of changes as they are 3 dimensional.

As Talulah suggests the noise may well be the rope cutter if (as is likely) you have a Stripper. The fitter will have pushed the shaft back when fitting the seal and it could be that the fixed cutter has not gone back into the striker block. No way of telling without having the boat out or sending a diver down. Easy to correct though! Still worth having the alignment checked - the fitter should have done this as a matter of course.

 

[skip50]

I think I am right in saying that prop shaft alignment can ONLY be checked/corrected fully with the boat in the water? The boat changes shape slightly when ashore/in slings etc.

 

[Tranona]

I think I am right in saying that prop shaft alignment can ONLY be checked/corrected fully with the boat in the water? The boat changes shape slightly when ashore/in slings etc.

That "rule" dates from the days when boats were built of flexible wood and were much more likely to change shape when in the water, as well as having rigidly mounted engines and shafts.

Less relevant with GRP boats (particularly heavily built ones like the OPs) and flexible mountings.

 

[superheat6k]

My last boat had a Volvo Blackjack seal and this was tricky to check the concentricity in the water. This is the method I developed.

1 Angular alignment. Loosened the coupling bolts and slightly separate the halves, then measure the gap between the two faces as the coupling is drawn together, but before any spigot registers engage, and check it is even right in at least 3 or 4 places close to and around the periphery ideally this needs to be +- 0..005" (five thou)

2 Parallel / axial alignment. Also with the coupling not quite engaged hold a straight edge against both halves edges and check the two halves have equal alignment again around the periphery.

3 Concentricity in the stern tube. The gap around the shaft was about 2-3 mm, so the engine/gearbox didn't have to be far out for the shaft to rub the tube. I used a laser level strapped to the output coupling, pointing to a spot on the stern tube end, along towards the wider part of the seals taper. I then rotated the shaft and observed the shape described by the laser pointer.

If a circle then shaft and tube are concentric, if an ellipse then the shaft and tube are out of alignment.

If any position of alignment requires adjustment then further checks of the other positions of alignments are needed. Getting it right can be time consuming, especially if access to the mount bolts is awkward.

Also if the output coupling half droops downward then it might necessary to support the shaft in its natural position, and some judgement as to whether or not this is right might be needed.

 

[Robert Wilson]

Thanks for the speedy reply! Can I disconnect the shaft from the gearbox with the boat afloat? I take it is just a case of undoing the five retaining bolts. When you say there may be a gap, do you mean that the shaft and gearbox don't sit squarely opposite one another?

The rope cutter is another good thought. Although this will obviously need to be visualised out of the water.

I am now slightly mistrusting of the engineer - with adequate reading and preparation I am sure that I would have been more than capable of fitting the seal myself, and could have avoided the fairly catastrophic result of 20 litres of sea water in my engine!

I have just fitted my new seal - having read the instructions thoroughly and was watched by the engineer (who was too big to fit into the space behind the engine!!) The boat won't be in the water for another four weeks.
I HOPE I won't be re-visiting this thread shortly after re-launch and motoring out to my swinging mooring. Gulp!!!

Good luck with your problem, and here's hoping you obtain a speedy and complete solution.

 

[MILLPOND]

The prize goes to Talulah, who correctly diagnosed the fault as coming from the rope cutter. Had the boat craned out and the inner sleeve of the rope cutter was loose and out of alignment with the blades, resulting in the banging noise. Probably not correctly re-installed after the shaft had been moved to install the stern gland seal. All sorted, and as it was the engineer's omission, no charge for the lift either! Thanks for the advice all.