I need to realign my engine/shaft and want to pick your brains to do the job as efficiently as possible.

Reason for the alignment. The mounts have settled over the past 8 years and I need to lift the engine a bit. One of the mounts is a bit corroded and the adjusting nut on the underside of the mount won't move. The mount will have to come out to clean it up and free the nut.

The situation. The engine is rubber mounted. The shaft (1" diameter) is quite long (about 8 ft) and is unsupported from the gearbox flange to the stern bearing. The distance from the gearbox to the stern tube is about 3 ft. The stuffing box is about a foot behind the gearbox and connected to the stern tube by a rubber tube about 8" long.

One benefit of the shaft arrangement is that a slight amount of misalignment isn't as critical as on a fixed shaft.

Feelers will identify major misalignment but I can't see that I can use feelers for the finer alignment because the shaft, being unsupported, flops around at the gearbox end.

My intention would be to use feelers to get it close and then make adjustments under way to get it as best as possible. I see all sorts of problems using this hit and miss method.

All constructive advice most welcome.

When I had the new gland installed the other day, the mechanic spent some time re-aligning the engine. At first he couldn't turn it over by hand but revolved fairly freely when he finished. A few days later the boss and I motored over to Jibbon, about 2.5 nm. When I was sitting in the cockpit I could feel my vision being effected by the vibration, not greatly but affected just the same. Sitting on the 'princess seat' the vibration was not evident. Afterwards I rang the guy to have another look when it was convenient. He did it all by feel, not feelers.

MorningBird said..

The stuffing box tube was increased in length because it was felt an improvement with the inherent vibration in such a long shaft. It does improve the ride.

Not sure about a ceramic seal but we looked at a dripless seal some years ago. The consensus was that the long unsupported shaft is not suitable, due to the vibration issue.

It has been quite good at various times, I just need to get it there again. Or throw an excellent little engine away and put in a sail drive. Can't afford it.

The long stuffing box would dampen the vibrations somewhat and act slightly as an intermediate bearing. The whole rubber mounted engine driving a shaft in a fixed bearing is a weird set up anyway. Engine bolted down solid and shaft and flange aligned using feeler gauges/wedges crowbar etc would probably give less vibrations. The problem is that long shaft supported only at the ends. Flexible flange and new engine mounts will help http://polyflex.com.au/Hardy-Spicer73.php But a flexible intermediate flange bearing support would be the best but expensive.

Keep your motor.

My S&S 34 (now sold) had a similar arrangement, ie long unsupported shaft but the engine was solid mounted and the gearbox and shaft flanges were hard bolted. This is a brilliant set up as long as there is absolutely no bend in the shaft.

Morning Bird will be a fairly much an "Olin Original" and I don't think you should mess with the configuration. I have never been a fan of sail drives and they seem to give more trouble than they are worth.

Presumably the work is going to be done out of the water so the first step is to withdraw the shaft and have it spun up on a lathe and checked with a dial indicator for straightness.

If it is bent I recommend replacement, preferably with pre-ground shafting. This will obviously be expensive as the ends will have to be machined to take prop and flange.

Second step is to ensure the prop is accurately pitched and balanced. This makes sure none of the horsepower the engine is delivering is wasted.

Thirdly I would be getting rid of the flexible mounts and solid mounting the engine. Cicely June's engine was bolted onto hardwood blocks that were glassed into the hull with shims under the mounting lugs for alignment.

Engine alignment can never be too accurate. Even with a Poly Flex coupling the maximum allowable misalignment is .005". If you can get it to zero, great but I would not be happy with anything more than .003".

With your long unsupported shaft, as long as the stern bearing has adequate clearance on the shaft you have considerable leeway with lateral and vertical misalignment but no leeway on axial alignment ie the flange faces must be parallel.

When doing the alignment I suggest you have two bolts opposite each other loosely holding the flanges together and use two sets of feeler gauges. Insert in one side with one then measure the gap on the other. Your flanges may be spigoted to each other. This can be helpful but can also be a hinderance.

When the alignment is getting close but you still have to screw the engine around to right or left, leave one mounting bolt tight and pivot on it for sideways aligning. For vertical aligning keep the front or rear pair of mounting bolts tight.

Do all gap measurements with all four mounting bolts tight. As far as doing adjustments under way goes, forget about it because that is plain dangerous.

When making adjustments use tyre levers and/or a hammer with a timber block to cushion the blows. Only use brass shims as steel will rust and expand. Sheets of brass shim material are quite cheap and easy to cut with tin snips. If you have one sheet of five or ten thou material and one of two or three thou material you should be right.

Engine and shaft alignment is one of the most important items on any vessel and final alignment should be done with the vessel floating. Adding a bearing half way along the shaft I feel is not a good idea and I would keep the stern gland as close as practical to the stern bearing. There is nothing wrong with conventional Walker's packing type glands and the teflon packing is quite low friction. Place the cuts of the packing opposite each other and angle the cuts at 45 degrees.

Adjust the packing compression with the shaft turning at low revs to the point when the shaft is at rest it will leak one drop of water every 30 to 60 seconds. When the boat is moored up you can nip it up to stop the drip.

It can be a time consuming and frustrating job but once you have got it right it is very satisfying. Poly Flex couplings are designed only to reduce rotational vibration. They are not designed to absorb poor alignment.

Cheers Cisco.

Do not adjust while underway. Its not just a matter of raising the front or rear, they both have to be adjusted at the same time. Hence the shims, wedge, crow bar etc. or though you may be able to adjust the lower part of the rubber mounts. You will never get a perfect alignment with rubber mounts and that much unsupported shaft. Soon as you undo the flange bolts and slide that shaft back a few mm it must drop an enormous amount. Some how you are going to have to support that shaft as straight as possible and adjust the mounts to get an even gap around the flanges with a feeler gauge. Can't see how its possible with that long rubber hose.

The trouble with flexible mounts is also to instal the correct ones. Often the rear are different ratings to the front, depends on which end the flywheel is. Real marine engines have it at the front.

Like the idea of the balance weight. Could also get the same effect by shortening the rubber hose for the stuffing box so that it does the same job, have it about 1/3 the way instead. The trouble with long shafts, especially 1 inch size is the ease at how they can bend. Even transporting the shaft from Porters in Sydney for my fishing vessel I had to make a hard wood frame to support it. One strike of a hammer while people pull a prop will bend a shaft. Also interesting the same bent shaft can be straightened by someone also with one strike of a hammer.

Thanks guys. I won't touch the mounts underway, I take your advice.

As the engine has only been moved up and down on the mount adjusting nuts she will still be aligned athwartships. I am going to put the mounts back to where they were before I touched them so it should be very close.

The long shaft is the bug bear. If I lift the shaft at the stern gland, just enough to take the weight, the harmonic beat disappears. If I run above 2400rpm it also disappears, probably as the shaft self centres.

I adjusted the mounts incrementally, about half a turn each, to see if I could reduce the beat. I had little success, it reduced a very little. It must be putting strain on the gearbox bearing but it is 30 years old and still ok.

Cisco, I can see how a weight would stop the shaft getting a harmonic going. However, my shaft runs through the hull to the prop which exits just above the keel/hull join. No space for a weight except just behind the gearbox in front of the gland. That wouldn't help.

I could make a flexible mount of sorts to support the shaft at the gland by hanging something from the cabin sole, looping it around the gland just to take the weight. I might try it. Just a piece of rope looped under the gland and secured to the underside of the sole.

Karsten, I will be interested in how you go with the new flange. All the advice I have had so far is that a flex flange with the rubber mounted engine would increase the movement, but I have an open mind on it.

MorningBird said..

The long shaft is the bug bear. If I lift the shaft at the stern gland, just enough to take the weight, the harmonic beat disappears.

That sounds to me like you have excessive clearance between shaft and stern bearing. General rule for a clearance/running fit of shaft to bearing is .001" per inch in diameter. For a water lubricated stern bearing an extra thou is probably good and the bearing needs to have deep grooves to allow the water in.

I adjusted the mounts incrementally, about half a turn each, to see if I could reduce the beat. I had little success, it reduced a very little. It must be putting strain on the gearbox bearing but it is 30 years old and still ok.

Incremental adjustments are great. If it improves, you go another increment. If it is worse, you go the other way.


Cisco, I can see how a weight would stop the shaft getting a harmonic going. However, my shaft runs through the hull to the prop which exits just above the keel/hull join. No space for a weight except just behind the gearbox in front of the gland. That wouldn't help.

Cicely June has at least 700 mm of unsupported shaft between the stern bearing and the gearbox coupling and I ran the engine up to revs with water lube to the bearing in the cradle in the yard and there was no vibration as you describe. Her engine was mounted about 300 mm behind the mast step. Is your engine mounted further aft?

I could make a flexible mount of sorts to support the shaft at the gland by hanging something from the cabin sole, looping it around the gland just to take the weight. I might try it. Just a piece of rope looped under the gland and secured to the underside of the sole.

That could only ever be a temporary arrangement. The rope would wear out or it might wrap itself on the shaft and start tearing your cabin apart. Don't do that!!

What I was suggesting was a dampening weight between the stern bearing and the gearbox. If the shaft is bent it will most likely exacerbate the situation.

Karsten, I will be interested in how you go with the new flange. All the advice I have had so far is that a flex flange with the rubber mounted engine would increase the movement, but I have an open mind on it.

A coupling that is designed to compensate for poor alignment is just a band aid for bad engineering practice and will itself fail so that the manufacturer can sell you another one. I put Crane Seals and Cutlass Rubber Bearings in the same disposable bag as those things.

Your prop shaft appears to be more steeply angled than Cicely June's. You will also probably notice a fair bit of Cicely June's trailing edge of the keel is missing too. That happened before I owned her.

Some gearbox flanges will have a spigot for centering / alignment and if this is the case you can move the flanges apart and have it semi supported still, this allows you to gauge the weight on it and see and measure misalignment.
I put 4 new mounts on recently and it only took an hour or so to align things by eye and feeler gauges.

If you want to try a weight on the shaft, start small, use a hose clamp or 2. They have worked on tailshafts for 100 years.

Well it is very good that you pursued the original problem and got it fixed but by doing so uncovered a worse problem which likely had somewhat to do with the original problem.

Like you say, better to find out now than half way to LHI.

I am pretty conservative and only accept defects after a risk assessment. I suspect you do much the same.

A mate and I removed the various bits and pieces this morning, except for the manual and auto bilge hoses and the shaft which need to remain until we get the boat out of the water permanently. It is being moved around while waiting for a permanent space on the hard. The marina are full with Christmas jobs and have gone right out of their way to accommodate my emergency slipping.

I took a photo this morning while waiting to be put back into the water, so I know where everything goes back in, in which you can just see the stern tube underneath on the left, leading up into the rubber tube to the gland and so to the gearbox, about 12" further to the right.



Now that all but two bilge hoses and the shaft are out it has opened up considerably. The stern tube leak is on the underside near where it goes through the bulkhead (to the left on the photo). The bulkhead leak is about 1/2" under the stern tube. The bulkhead appears solid elsewhere but there is a 1/2' soft patch of rotten material.

It is possible that the bulkhead was drilled, when they were putting the shaft in they may have mistakenly drilled a pilot hole and filled it in. I'll know more when we get the stern tube off.

Spot on Cisco. I have been annoyed by lack of access to the gland, especially when it should have been easy in that space. This is the first time I have had this part of the boat apart, it just hasn't got high enough on the priority list so far.

You can see the corrosion around the stern tube at the bulkhead, it has gone through the tube underneath. You could say it was a design defect but the tube has been there for 30 years. We don't know how far in the stainless tube goes into the structure, maybe 6", maybe all the way to the stern and maybe set in concrete. The repair is to cut it off, put a fiberglass tube into the bulkhead and fully glassed in. The tube will have a shaft bearing supporting the shaft at this end. This should make it easier to get an accurate alignment at the flange but maybe a flex coupling would be an advantage. It can be added later if needed.

I'm going to remove one of the two manual bilge pumps and reroute the two inflexible hoses from directly above the shaft/gland, they come from the exhaust elbow, to where the current two bilge pump hoses go through the same hole near the top of the photo. The one bilge pump hose will then go over the shaft or through a new hole. It is very flexible so can be easily moved to do the gland. The small hoses are fuel and fuel return lines and some electrical conduit. They can stay.

I will also clean it out and paint. What paint would you recommend in the bilge? You don't want it peeling off and blocking pumps.

Karsten said..

And its a bad feeling to punch a large holesaw through a perfectly good bulkhead.

I agree with you on that one 100%. That bulkhead on Morning Bird has that many holes in it that it almost says "tear along dotted line", it sort of negates the purpose of the bullhead being there.

Whoa!! I would be very wary of chopping out that floor.

The problem seems to be under that concrete through which I see two keel bolts emerge. For the life of me I cannot understand why they put concrete in a fibreglass hull. Not exactly compatible materials and I am sure that after 30 years there will be some separation of the concrete from the hull which of course means water seepage.

Maybe it would be worth power chiselling the concrete out and starting from scratch with the stern tube installation.

Your wallet did not want to hear that but in comparison to the overall value of the yacht, what is the %age.

Re paint, the bilge is always the dirtiest and most contaminated part of a boat so no matter what paint you use cleaning and preparation will determine whether it holds on or not. I think White Knight single pack epoxy in white would do the job as well as any other.

An excellent page on stern glands.

http://coxengineering.sharepoint.com/Pages/Sternglands.aspx

A pdf on the Volvo Seal here.

forum.katera.ru/index.php?app=core&module=attach§ion=attach&attach_id=66301

We have done the repair and the shaft aligns properly and spins freely. It is a vast improvement.

However there is a very small leak into the area of the bilge filled with concrete. The water now seeps through two spots, pin pricks, in the coating over the concrete at about a litre or two a day.

The leak is probably from a small leak through the repair to the stern tube. It is possible the leak into the concrete filled area might have been there previously and from another part of the stern tube. This isn't likely but possible. Any previous leakage was even smaller than now.

There appear to be 3 options to fix the leak.

1. As Cisco says, look at digging out all the concrete and installing a new stern tube. This would involve removing the new arrangement that works well, significant hull work at the keel/hull join where the stern tube exits the hull with unknown risks, removing concrete in the vicinity of the keel bolts (they run through tubes in the concrete) which adds further risk. The job will be very expensive (even without a risk becoming a problem).

2. Remove the repaired part of the stern tube and reseal it. As there may be another leak in the stern tube this option may not fix the leak, or the resealing job my not be any better than has been done already.

3. The concrete is only covered by a flow coat, it isn't glassed in, so there is no water tight structure. The leak is very small with no pressure behind it so we figure we can glass it in properly and make it a watertight area. This is pretty simple, negates any current or future leaks and maintains the new well supported prop shaft.

Option 3 is my preference.

Any advice/comments welcome but am posting more to give an insight to boat maintenance/repair issues that we can face.