dur
Well-Known Member
I did both sit on it and lift it the other night and it didn't make a difference but it wasn't very scientific. I'll see if I can do at least a couple of the pads under the mounts this weekend and see if that helps.
For the engineers - torsional vibration? - long winded! - Help!!
- Thread starter dur
- Start date
I did both sit on it and lift it the other night and it didn't make a difference but it wasn't very scientific. I'll see if I can do at least a couple of the pads under the mounts this weekend and see if that helps.
trthebees
Member
Just some thoughts, as you've had a lot of good suggestions above. Particularly with regard to the prop, which has some quite detailed assembly instructions, and well worth investigating.
Even the best of engines have some out-of-balance forces, as do the best balanced props as they rotate through different water flow patterns top and bottom etc. Others have already said this.
It's also worth keeping in mind that shafts put more demands on radial support in the forward direction than reverse. Also reverse flow may be smoother as the suction water is cleaner. Speeding up in forwards may increase smoothness as water flow becomes faster and have more inertia to feed the prop. Also, of course, engines tend to smooth out at higher revs.
Looking at your pics, it appears you have a cutlass bearing at the shaft end, and a stuffing box at the front. Is there another bearing at the stuffing box end? If not, it's worth checking if, when aligning the engine and coupling, the shaft was centered in the tube. It's not certain that the packing will do this automatically. It's also worth checking the clearance between the stuffing gland thrust collar and the shaft. If there's a lantern ring, I'd expect that to be clear of the shaft. I notice that the collar bolts are wired. Possibly that should have been done after the shaft had run a bit and the packing settled and retightened a bit. On long shafts, with flexible engine mounts, the packing provides a degree of radial support.
After all this waffle....and assuming the A bracket is solidly mounted to hardwood framing and not moving....I'd agree with others that the high engine mounts are allowing too much movement...and possibly the shaft is knocking inside the collar if it's a close fit. Possibly this could be checked by adjusting the gland nuts.
As ever, comments and criticisms appreciated as all is good for better understanding!
Even the best of engines have some out-of-balance forces, as do the best balanced props as they rotate through different water flow patterns top and bottom etc. Others have already said this.
It's also worth keeping in mind that shafts put more demands on radial support in the forward direction than reverse. Also reverse flow may be smoother as the suction water is cleaner. Speeding up in forwards may increase smoothness as water flow becomes faster and have more inertia to feed the prop. Also, of course, engines tend to smooth out at higher revs.
Looking at your pics, it appears you have a cutlass bearing at the shaft end, and a stuffing box at the front. Is there another bearing at the stuffing box end? If not, it's worth checking if, when aligning the engine and coupling, the shaft was centered in the tube. It's not certain that the packing will do this automatically. It's also worth checking the clearance between the stuffing gland thrust collar and the shaft. If there's a lantern ring, I'd expect that to be clear of the shaft. I notice that the collar bolts are wired. Possibly that should have been done after the shaft had run a bit and the packing settled and retightened a bit. On long shafts, with flexible engine mounts, the packing provides a degree of radial support.
After all this waffle....and assuming the A bracket is solidly mounted to hardwood framing and not moving....I'd agree with others that the high engine mounts are allowing too much movement...and possibly the shaft is knocking inside the collar if it's a close fit. Possibly this could be checked by adjusting the gland nuts.
As ever, comments and criticisms appreciated as all is good for better understanding!
dur
Well-Known Member
Thanks for your notes. I confess I don't know if there is a bearing at the inboard end of the shaft - I presume not but I would have to check.
But as prompted I purchased a stethoscope £ 2.99 delivered next day. It confirms the ensign staff test no noise from gearbox (to the extent that neutral astern and ahead all sound pretty much the same) Listening in the stuffing gland you can hear the knock but not big time and the same listening on the shaft log. Listening on the plank which the A frame is bolted into you can hear (very very) loud knocking.
So further as prompted in went the packing under the mounts:
Result... I would say it is slightly quieter. Same noise, same pattern /frequency, possibly a little less extreme. Not much in it. Engine definitely not moving as far - as you would expect.
So also as suggested by several, it was to the hard for a prop change...
from:
to...
I have never used this prop before but it is what was on before the previous owner bought the feathering job and you can see why - it is like the proverbial bucket.
And, entirely as predicted, it is quiet going ahead or astern, thus confirming where the noise is coming from. It was dark when the water came back so I didn't notice if the engine is moving about so much. My guess is not but it will be interesting to see.
Now what? Beta are supposed to be talking to Centa but we'll see. So far I pretty much have to sit on the phone for them to do anything so I am not holding my breath.
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trthebees
Member
Now what? Beta are supposed to be talking to Centa but we'll see. So far I pretty much have to sit on the phone for them to do anything so I am not holding my breath.
Last edited by dur; Today at 00:19. Reason: Jura
If the feathering prop is off, and you've got a nice pile of bits, it does seem an opportunity to get them looked at by Darglow in case it's setting unequally, or out of balance or whatever. They seem to be local to Chichester, but I don't know what servicing arrangements they offer. I'd really guess that Beta and Centa will say similar, and that whatever they could do would only be attempting to cover up a problem elsewhere. Like it or not, at the moment the noise is your friend, warning that if ignored something at the back is going to fatigue, or fail, or wear rapidly, or loosen the A-frame.
The engine end of the installation does look rather nice, and to my eyes improved by raising the monts.
Last edited by dur; Today at 00:19. Reason: Jura
If the feathering prop is off, and you've got a nice pile of bits, it does seem an opportunity to get them looked at by Darglow in case it's setting unequally, or out of balance or whatever. They seem to be local to Chichester, but I don't know what servicing arrangements they offer. I'd really guess that Beta and Centa will say similar, and that whatever they could do would only be attempting to cover up a problem elsewhere. Like it or not, at the moment the noise is your friend, warning that if ignored something at the back is going to fatigue, or fail, or wear rapidly, or loosen the A-frame.
The engine end of the installation does look rather nice, and to my eyes improved by raising the monts.
mtb
Well-Known Member
so now you'll be after a refund and compensation
from who ever fitted the engine incorrectly which caused these problems
It wasn't rocket science to see the mounts were set far to high had you accepted their bullshooo with time it could have caused even more damage
Any marine fitter would know mounts are never set that high, it is such a basic thing. When I did marine craft fitting city and guilds, we were taught things like that right in the beginning
As yet there needs to be a careful inspection to ascertain what damage they caused through negligence
from who ever fitted the engine incorrectly which caused these problems
It wasn't rocket science to see the mounts were set far to high had you accepted their bullshooo with time it could have caused even more damage
Any marine fitter would know mounts are never set that high, it is such a basic thing. When I did marine craft fitting city and guilds, we were taught things like that right in the beginning
As yet there needs to be a careful inspection to ascertain what damage they caused through negligence
JumbleDuck
Well-Known Member
Did you read the posting? Did you see that changing the mount configuration made little difference but that changing the propeller solved the problem?
30boat
N/A
Still the mounts were incorrectly set up...
penfold
Well-Known Member
It made little practical difference; the OP has learnt that his installation is incompatible with this feathering prop, and possibly by corollary all feathering props; if he has bottomless pockets it might be interesting to see if an Autoprop would give vibration free service. A lower cost compromise option would be to try a folding prop, somewhat less reversing thrust but still reducing drag when sailing.
mtb
Well-Known Member
As yet I would wait until its been tested, and the engine has settled.
We don't know yet if the alignment was set with the boat in the water which may have implications
The fault was not there before the new engine was fitted.
Any problem should have been ascertained straight away by the people paid to do the job not left to the customer, so blaming them is justified
I think a fault any where in the drive train could show up any where along the drive train, not just at the weakest point
dur
Well-Known Member
Thanks all for latest comments. I am hoping (very much) that the installation is not completely incompatible with feathering props especially since the whole install was based around the existing prop. It is clear from the prop that the ten or so hours running has accelerated the wear on it which obviously won't help. But based on the diagnosis from Darglow it is the lack of flywheel which is the fundamental difference and so may be the correct damper plate will be enough to cure the problem. My other thought is whether it would be possible to add some more rotating weight (maybe to the front crankshaft alternator pulley if there is no room at the back) but that needs an engineer with an understanding of the specs of this engine and what additional loads it can take and what impact that might have. My guess is that it would not take much to tip the balance in the right direction.
It is not my style to go chasing the fitter - he is way way more experienced than I will ever be and I reckon 99 times out of 100 his install would be absolutely fine. I am more upset at Beta for not mentioning in the long preamble to buying that this problem was a possibility, even if remote. I had thought I was doing the boat a favour by giving her a new engine but as the feathering prop is almost a necessity it seems I have done anything but. I certainly could have rebuilt the Volvo several times over for what this has all cost and it looks like it is not over yet.
Anyway, fingers crossed that they might come up with something yet.
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JumbleDuck
Well-Known Member
I think you have just been incredibly unlucky to have a system with a resonance right spang in the middle of the tickover / slow ahead rev range, and I am sure that there will be a way to sort it. I agree that it's not the fitter's fault ... in fact, it's not anybody's fault.
penfold
Well-Known Member
Space allowing it should be possible to add a disc weight to the prop shaft, ideally on the aft side of the coupling; a disc of the largest possible diameter cut out of perhaps 10 mm steel, with holes drilled equispaced on an outer PCD so extra weight can be bolted on without having to continually separate the coupling. The disc itself could be split in two and a bolt flange added but it would then need to be statically balanced to avoid introducing a new problem. The extra weight I had in mind was smaller discs of steel but large washers would do if carefully weighed to get matching sets.
Another thing which occurs to me is that there may have been wear in the feathering mechanism of the prop which this new installation is exciting, and creating more and more rapid wear; how long had you been using the feathering prop with the volvo? Was there a flexible coupling or was the shaft bolted straight onto the volvo's gearbox?
Another thing which occurs to me is that there may have been wear in the feathering mechanism of the prop which this new installation is exciting, and creating more and more rapid wear; how long had you been using the feathering prop with the volvo? Was there a flexible coupling or was the shaft bolted straight onto the volvo's gearbox?
Hypocacculus
Well-Known Member
I'm curious - how much difference to your sailing performance has the fixed prop made?
dur
Well-Known Member
I was thinking more along the lines of whether it is OK to add a disc to the crankshaft alternator pulley. This would be easy as it is accessible and has the advantage that it would be spinning at engine speed not 2.45 times slower. I think the maximum diameter of the disc would only be 11 cm with a central hole of 5 cm so if it were 2 cm thick the approx weight would be maybe 1.1 kg. I have no idea whether 1.1 kg at 700 rpm at this small diameter makes any difference to anything hence the need for the engineer. Plus I need to be sure it is safe to add that to that bit of shaft, those bolts etc.
The prop is fairly old and at the beginning of the season there was a little play but nothing excessive. As I said those few hours using it with the knocking have not helped but it is still OK.
The Volvo had an R & D coupling.
dur
Well-Known Member
I'll let you know after next weekend if the weather behaves!
penfold
Well-Known Member
I'm not sure that putting more weight on the crank nose is the best idea; the faster rpm means it needs more secure fastening and greater attention to balancing, and it's at the wrong end of the system. I'd be concerned about swapping one problem for another(i.e. exchanging wobbly props for a busted crankshaft). That said the crank may ultimately be the source of the excitation so who knows what may be the best way forwards.
Having had fun with bonded rubber torsional dampers on Landrover crankshafts in the past I wonder how DIYable one would be; ensuring the outer weight was secure in the event of debonding would need a bit of design and a jig needed for holding everything concentric while the goo was poured into the gap and allowed to set. Pouring polyurethane resin can be bought readily enough.
Having had fun with bonded rubber torsional dampers on Landrover crankshafts in the past I wonder how DIYable one would be; ensuring the outer weight was secure in the event of debonding would need a bit of design and a jig needed for holding everything concentric while the goo was poured into the gap and allowed to set. Pouring polyurethane resin can be bought readily enough.
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gordmac
Well-Known Member
Don't know how the prop works but would it be possible to make the blade rotation stiffer?
I would be reluctant to add inertia to the front of the engine, have you asked the engine manufacturer if there was a different front pulley?
Unlikely it would be enough to make a difference but what about adding something like a disc rope cutter to the shaft?
Different torsional stiffness in the coupling would be worth trying, indeed even a coupling with a different mass may make a difference.
I would be reluctant to add inertia to the front of the engine, have you asked the engine manufacturer if there was a different front pulley?
Unlikely it would be enough to make a difference but what about adding something like a disc rope cutter to the shaft?
Different torsional stiffness in the coupling would be worth trying, indeed even a coupling with a different mass may make a difference.
fisherman
Well-Known Member
I fixed the propshaft doughnut on my Volvo, car that is, circular rubber concertina in a steel ring housing. The rubber tore off, put back with Sikaflex six years ago, still OK.
dur
Well-Known Member
Thank you to all who have taken the time and trouble to think about this. I need to research the Land Rover (and Volvo) dampers which you have mentioned. I wonder if they don't have to take the thrust forces which the boat one does. One landrover one I saw looked like the same idea as the Centaflex coupling but possibly without the thrust force.
The fixed prop had a good trial this weekend - motoring and motor sailing to Bembridge from Chichester in bumpy and blustery conditions (for me at least). The fixed is quiet and smooth at 700-800 rpm - i.e tickover speed in gear. Also at 1800 rpm plus. At c. 1500 rpm it makes a pretty loud fairly high pitched whine. Too rough to use the stethoscope but sounds like it is prop or shaft. No knocking but I wonder if it could also be a similar root cause. Who knows!?
I will chase Beta this week and see if they have further thoughts about the coupling.
dur
Well-Known Member
Well - rolling, yawing and surfing downhill in F5-6 and three reefs in this afternoon was not the best test conditions but my impression was that we were touch early 6 knots when I reckon we would have been over 7. But very unscientific. I think in very lights winds it will take the fun out of ditch crawling and short tacking etc. I'll let you know.
