Drive shaft vibration problem.

[vyv_cox]

This problem starts some time ago. In February 2001 I had a Yanmar 27 fitted to my Sadler, replacing the previous Bukh 20. During trials before accepting the job, everything was fine except that at one specific engine speed, from memory 2200 rpm, there was a knocking from the stern gear. The engine installer thought this to be play in the cutless bearing. I thought it more likely to be a consequence of the softer engine mountings, allowing the shaft to contact the stern tube. During the long drive (50 miles) back to our berth, the noise became much worse at a wider rev range.

There then ensued a long period of repeated engine/shaft alignment, replacing engine mountings for harder ones, etc. Eventually, we reached the stage that there was no knocking on flat water but some in a seaway. During the summer we replaced the two-blade propeller with a Brunton Autoprop, with no major change in the levels of knocking. However, we knew that something had to be done in the interests of long-term reliability. So this winter I have fitted an Aquadrive, as being the expensive but best way to control shaft alignment.

All of the fitting has been carried out exactly as instructed. The mounting plate is rock solid. Shaft alignment within the stern tube is spot on. I have fitted a new cutless bearing (although the old one was not bad) and there is no play between it and the shaft. I cannot detect any movement of the P-bracket when heaving it laterally. The shaft seal is a greaser type that has not been changed and it works perfectly.

After launching last Tuesday we carried out our first trials on Friday. The noise from the stern gear is abominable! At any revs over about 2200 there is a very loud knocking that sounds as if it is coming from the P-bracket. If revs are increased further the noise gets progressively worse. The noise sounds like once-per-rev, typical imbalance. Only below 2000 revs is it acceptable but this is unlikely to give sufficient power in adverse conditions. On top of that there is an enormous amount of general noise being transmitted to the hull.

My only thought at this moment is that maybe the shaft is bent, unfortunately I didn’t think to check this at the time of installation. At the inboard end it looks to be straight and there has never been a problem before the Yanmar was fitted. So this seems unlikely. I have now run out of ideas. Any suggestions? I would welcome any ideas that others may have.

 

[Charieis]

I wonder how stiff your hull is. Was the propshaft aligned with the boat ashore, standing on its keel?
My old Jouet 760 hull used to distort by getting on for half an inch with the hull pushing down on the keel, rather than the keel pulling down on the hull. This led to the Deep Sea Seal wearing off centre as well as the odd knocking noise from the shaft hitting the stern tube. I had to re align the engine to the prop shaft (usual trick with feeler gauges etc.), as well as centreing the shaft in the stern tube once afloat.
This can be a bit tricky as water tends to come in! I had to make up some alignment jigs to help so I didn't disturb the seal too much!
Alternatively you might be able to do it with the boat held in strops - not necessarily so good , but drier!

 

[pvb]

Are you sure it\'s the stern gear?

Just a thought, but as the noise started after the installation of the new engine, is it possible that the noise is engine/gearbox based? It's often difficult to determine where a noise is coming from.

 

[Guest]

I know they are daft questions but with all the changes you have made:

1. Have the changes moved the position of the prop so that it is now catching on something?

or

2. Can the rudder (or anything else for that matter) shift slightly when you are underway so that it can touch the prop?

If "no" to both then either "when in the water - alignment is different" or "bent shaft" are both possible.

Best regards })

IanD

 

[Seapepper]

I have a similar problem with a 1gm10. My latest thoughts are that the new shaft that I put in last year is not exactly the right size for the coupling. It was quite a loose fit in the clamp type Yanmar coupling, and it is possible, that if the allen key screws are not tightened evenly, then the shaft runs off centre in the coupling. I detected it when slowly turning the shaft by hand and noticing that the engine moved slightly on the bearers. Hope this helps.
Seapepper.

 

[vyv_cox]

The hull is built like a brick spithouse! I don't detect any distortion at all, alignment of the gland to the sterntube is unchanged in the water and even if I pull/push the gland there is no change in the noise. When I first found the problem I was regularly taking the gland off and checking that the shaft was central in the tube. I'm now almost completely convinced that there is no contact between the shaft and tube.

Thanks for your thoughts. Vyv.

 

[vyv_cox]

Re: Are you sure it\'s the stern gear?

No, I don't think so. The new engine is very quiet. The noise is clearly coming from well aft of the gearbox, although I agree it could be generated in the gearbox or its drive flange. Thanks.

 

[vyv_cox]

Both props (old two-blade and new Autoprop) are in the same position as before, a long way from the rudder. Thanks

 

[vyv_cox]

This is the thought that is occurring to me. The Aquadrive manual gives a procedure for tightening the coupling clamp joint, although the one I am using is the one that came with the Yanmar. I did follow the procedure, which ought to result in a square joint. If I tightened the grub screw beforehand, or if the coupling itself is not quite square, the shaft would run slightly eccentric. It does look a little out of true but I would not have thought enough to cause this problem. It won't move the engine because of the Aquadrive. However, it's the only chance at the moment. Thanks for the contribution.
Vyv.

 

[ean_p]

Is it not strange that you have no vibration in a flat sea, but significant vibration in a large sea.....as the Aquadrive effectivly splits the drive train into two halfs instinctivly the only part that would suffer from significant motion would be the mass of the engine/gearbox assembly.....but don't see how this would cause vibration / noise at the other side of the Aquadrive.....

 

[Guest]

I love a good problem - so another daft question.

Did the change of engine include a change of gearbox - if so has this changed the shaft rpm?

Also what is the unsupported shaft length v. shaft diameter? Long and thin enough to get bent if a dockyard matey stood on it?? At 2,000+ rpm a thin shaft with a long unsupported length will start making it's own hole with even the slightest bend in it!!

I wouldn't be too quick to blame the Aquadrive - you bought it to solve the problem - so the problem was there before you fitted it. On the other hand - see comment above.

Best regards )

Ian

 

[PeterGibbs]

Alignment issues will show themeselves at quite low revs usually. And the Aquadrive should take care of much of that in any event. I think the hull shape moves about a little more than you credit, Vyv; it's not just the yoghurt pots that flex!

That your problem is so closely related to higher revs leads me to suspect a thrust contact problem. Especially with a new prop that presumably deliveres quite a lot of it! The whole engine train on a shafted drive moves a suprising amount when thrust is piled on. Without putting yourself in danger of getting tied up with rotating machinery do check thrust movement when the throttle is hard down, and look for signs of contact wear especially in the prop/P bracket interface. If there are hardly any symptoms when reverse is engaged, you have probably found the answer.

Good luck,

PWG

 

[vyv_cox]

Thanks to all for the thoughts. Any further ones most welcome.

Some answers to questions. The shaft is a one-inch and is now shorter than it was before, as I cut about 6 inches off it to accommodate the Aquadrive. So its natural frequency and stiffness have gone up. There is no possibility of anyone standing on the shaft, the new engine was fitted with the boat on the water, so it was never removed. The only amount of it protruding into the boat was about what I cut off this winter, so I really don't think bending is very likely.

Thrust is carried entirely by the bearing/thrust plate of the Aquadrive. This prevents flexure of the engine mountings, and hence any possibility of shaft/stern tube contact. I studied the whole arrangement at the wekend, as revs were increased. There is no detectable movement of anything. One possibility that occurs is that the clearance between the thrust plate and the thrust bearing may be insufficient. The two are connected by two 10 mm bolts surrounded by stiff rubber bushes and possibly these are compressing enough for contact. However, I paid particular attention to this when making the plate, so I don't think so.

The engine and gearbox were new. The ratio of the box is very similar to that of the Bukh, so shaft speed is virtually unchanged, except that the Yanmar rev limit is 3600 whereas that of the Bukh was 3000. This is currently academic, as I don't have the nerve to create that much vibration!

I haven't yet tried the Aquadrive at sea. The previous higher vibration occurred with the normal arrangement, hence my belief that its cause was contact between the shaft and stern tube. It would be difficult to imagine worse vibration than I am currently getting on flat water.

It's a good idea to try high power in reverse - could give me some more information. Although I still don't know what the answer would be. Thanks for that one.

 

[Plum]

Vyv, you must be very frustared by this one, especially as you appear to be a very knowledgable person when it comes to mechanical things. Some thoughts: it all obviously started with the new engine and obviously it has nothing to do with the prop, shaft, coupling system as you have made changes to these since the new engine with no change to the problem. Are there any components that are common to both engines? Did you get a new gearbox with the new engine? While waiting for those answers, here is another thought: I know you think the noise is coming from the shaft, but I had a noise problem from that area on my previous boat shortly after installing a new engine and gearbox. The noise was actually traced to the drive-plate coupling between the engine and the gearbox. This coupling was of the tortional damper type and as a result of the gearbox shaft not being concentric to the engine crankshaft the damping elements wore out in the first season. The misalignment was only 30 thou of an inch! I fixed the alignment and fitted a new drive plate and I then had no problems for the next 13 years! It could be that 2200 rpm, the speed at which you first noticed the problem, coincided with one of the natural frequecies of the drive-plate damper elements.

 

[PaulJ]

'Bit of a long shot this one but do you have a rope cutter fitted? Is it possible that at some stage it could have bitten off more than it could chew and is now slightly distorted. As the revs (and therefore the thrust) increase the shaft could be moving just enough to cause parts of the rope cutter to interfere.....?

 

[Aja]

Vyv

The main thing that has changed is the engine. I know from experience when I installed a new 2GM20F in my boat from the old YSM12 that almost everything around the engine changed. The only part that remained was the raw water intake hose. The fuel hoses; electrical leads - they all had to be re-routed. I also had problems with the height of the engine rubbing against the cockpit sole. I also installed a water syphon - the old engine didn't have one. The first time I started the new engine I had to stop it smartish due a loud knocking sound. This turned out to be the pipe to/from the syphon being 'banged' against the enginge bulkhead. Once properly restrained problem solved. I know that this would be evident with the engine in neutral - you dont say whether this happens at >2000 revs in neutral but it is worth a check all round the engine compartment.

Good luck

Donald

 

[vyv_cox]

Thanks again for the contributions. Engine and gearbox were replaced in 2001. Most ancillaries remained the same, fuel, electrical, exhaust, virtually unchanged. The Yanmar is physically smaller than the Bukh, so it fits the space quite easily without contact with the compartment. I did not have a rope cutter previously but fitted one this winter. The engine runs very sweetly and the whole assembly is super quiet below about 2000 rpm. Before fitting the Aquadrive, and after much realignment, changing mounting rubber hardness, checking shaft/tube concentricity, the installation was super quiet at all revs, except under choppy conditions. I always assumed the knocking then to be due to shaft/tube contact, hence the Aquadrive. It is somewhat galling to have far worse performance after fitting equipment designed to improve it! I don't think the Aquadrive is at fault but I can think of nothing that could cause noise to appear to come from the P-bracket.

 

[ParaHandy]

Shame you're in Holland - we could stand on each others boat and compare notes!

My engine is Yanmar 3GM30F which is, I think, the correct number for yours? In 1996 it replaced a Perkins which was "eating" Vurth gearboxes. Gradually, it has got noisier. It isn't a harsh knock as you are experiencing - more of a harsh thrum - and I run out of bottle above 2,500 rpm, much as you.

There is a glorious "quiet" period after I do the annual service - the lot, oil everything - which lasts for a couple of outings but that's not always the case.

I am beginning to think it is the drive "clutch" which is not unlike a normal clutch with shock-absorbing springs in the plate. Can not prove that unless I replace it.

Otherwise, have you got the gear change on the gearbox set with the correct travel ie is it engaging fully? If you need 3GM workshop manual - you're welcome to mine.

Your post has given me the idea of asking the Yanmar USA engine forum. Suspect opinions will be drive train many, engine nil.

The reason I think it is my engine that's causing the vibration is that in neutral and doing 6 knots with the prop rotating, there is no noise - nothing. OK, that doesn't compare with it under load but I would expect to hear or feel something.

Douglas

 

[Andrew_Bray]

Vyv,
I'm trespassing a bit here, but as I'm suffering very similar problems I thought I'd add my ha'pennyworth. I have a Yanmar 4JH3 which drives a 3-blade feathering prop via an Aquadrive. Previously I had an Autoprop but suffered lack of power, vibration and knocking and the expert opinion seemed to be that a) the prop was not suited to a relatively light and easily driven hull and b) that one of the blades was damaged/was not opening properly. To begin with the feathering prop transformed performance but there was still prop noise at tickover (sounded like the zinc was rattling round on the shaft) and then a knocking started at around 2,000 rpm. This has got progressively worse although when she was lifted a couple of weeks ago the yard said that excessive shell growth on the shaft could have caused it.

Like your engine it runs very sweetly and is quiet in flat water (and interestingly in astern) but only gets noisy under load. The main suspects are: 1. P bracket bent/bearing wear (nothing visible) 2. stern gland not lubricating properly (I use one of the now defunct Halyard seals) and 3. the rope cutter. I'm tempted to remove this (and probably catch a line immediately) to see if there's any difference. A fourth possibility has been suggested by one of my crew. He says it is the nature of the Aquadrive to work best of all when the shaft/gearbox are not perfectly in line. Mine are and how I check/eliminate this I do not know. Mind you I had a very rude shock when I was checking this recently to discover that one of the fastenings from gearbox to Aquadrive (Allen key job) was hanging loose and all the others were only finger tight.

She's being re-launched in early May and if removing the cutter or any other ploys work I'll stray across from YW again and post something up here again.

Andrew

 

[byron]

I hope my information isn't of help to you but I have today just had a similar sounding problem solved. It turned out to be a faulty gearbox.

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