Opinions please

[byron]

Right! Who remembers my vibration thread? Well! It now seems that my starboard engine is 28 thou out of alignment. Is there any informed knowledge out there? Could this be the cause of the bad vibration I get when the boat is wound up to 1500 revs and above or should I still be looking? Bear in mind that even when this is done I will be unable to test the boat because until later this year I am still on the river Thames.

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[jfm]

Aah...Monica again

Hmmmm...

If you rev the starboard 'gine to 1500 in gear, and leave prt 'gine idling, does it still do it? And mot if vice versa?

What sort of flex couplings do you have?

28 thou isn't much (= a spark plug gap) but it could be the cause. The whole point about a vibration like this (well, I'm guessing, I haven't heard it) is that it is harmonic. A 28 thou misalignment on a bit of roatating machinery wouldn't cause much noise on its own, but when it occurs at a harmonic frequency of something else (like the hull, or some bulkheads, or whatever is making the noise) then that something else vibrates massively ("in sympathy" with the tiny source vibration) hence the noise. Putting it another way, when you hit the harmonic frequency you only need a tiny source vibrating force to make something big vibrate like hell.

As I say, 28 thou isn't much, and many boats will have this much error, and it may cause them no probs. But the point here is that ON YOU PARTICULAR BOAT it happens to interact with something else and hit a harmonic resonance at 1500rpm

If it's based on engine rpm, that's obviously the source. But it's hard to guess whether it is the shaft misalignment, or something else like crankshaft out of balance etc.

 

[jfm]

Come to think of it Byron....

...isn't it a piece of cake to fix the alignment? Just set up a dial test indicator and wind the nuts on the engine mounts? No shimming needed? I've never done it before, praps pauljs_eng knows. But worth a go to eliminate this from your enquiries?

 

[hlb]

Sounds more like a bent prop or prop shaft, broken engine mount, Mine breaks engine mountings for fun. Start with the simple and obviose and work up.

Haydn

 

[hlb]

Sounds more like a bent prop or prop shaft, broken engine mount, Mine breaks engine mountings for fun. Start with the simple and obvious and work up.

Haydn

 

[Freebee]

28 thou in old money isn't much I can't find your previous thread but to give an opinion we need to know how and where the misalignment was measured? for example you could be measuring by dial test indicator on the rotating coupling outer diameter whilst spinning the shaft or on the flat face of the coupling after disconnecting the shaft in which case 28 thou is much more significant. But based on the facts presented I think you have to look for something sympathetically vibrating or something like a shaft bearing that has developed wear. It would help to know more.

 

[Guest]

Re: MBM article

Byron just reading a test on the 435 from MBM (got the back copies) and one owner of a 1989 435 called
Fleetwind had 3 out of 4 port engine mounting fail and two of the four starboard bolts failed. Thats
the vertical bolts snapping. They go on to say that Volva made a couple of design changes on later models
though yours is a 1989, so could be a problem.
In the "subject to survey" bit it says :

"Problems are also found with the external transmission assemblies such as damage to propellors
and P brackets. Shaft misalignment and corrosion to shafts and sterngland assemblies are not uncommon"


cneighbour

 

[byron]

Re: MBM article

Yes! I met Fleetwind just before his happened, he's had his boat from new and knows every inch of it. My boat is coming out as soon as the locks are opened (one is busted) and in the meantime the engine is being realigned hopefully tomorrow. Yes! some engine mounts were replaced last year No! there's sod all wrong with my props Maybe! the shaft could have a minute warp, this has to be checked Possibly! the Cutlass Bearing is worn too, this has to be checked.

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[mtb]

0.003 or o.75
Any more then vibrations and other problems occur .
Yes I know what other posts have said but this is one of the specifications drilled into me when I did my marine engineering training .
Obviousely if you have a flexable coupling then depending on what type you can have up to 45 degrees of misalinement
you do need to asertain if its parrelel misalignement or angular / conical.
One thought though, what about the thrust bearing if the load is not being passed to the hull via mountings or gearbox properly .This can cause vibration
Cheers
Mick

http://homepage.ntlworld.com/boats
I want a big steel ex trawler / tug v/cheep or swap for tug

 

[Medskipper]

Hi Byron

Friend of mine had his boat lifted out a couple of years ago and when it was returned to the water he told me he had same sort of vibration on his port engine.
It just so happened that I was there when the boat was lifted and I noticed that the straps from the crane were pressing on his port shaft. I said nothing to him until he told me of the vibration. The shaft had taken the weight of the boat and bent slightly! Do you ever watch your boat when its lifted? and is it a possibility that this has happened to your boat?

Barry

 

[Deleted User YDKXO]

Re: MBM article

Had the same thing happen to my 435 when I owned one. The starboard engine 'fell off' its mountings in the middle of the Channel fracturing the coupling and bending the shaft. It took me a while to work out that all four engine mounting studs had sheared. Worse when I looked at the port engine, it was hanging on by 1 stud. The passage back to the Hamble was very sedate
I was told that the particular engine mounts used in this installation are too light and any corrosion weakens them. Any 435 owners out there would do well to keep a regular check on them
I agree that 28 thou doesnt sound enough to cause major vibration and it sounds more like a bent propshaft (when the mountings failed?) or worn cutless bearing

 

[Deleted User YDKXO]

Barry, this is a very valid point. Many boats dont have slinging positions marked on them and many hoist crews are non too careful about how they sling boats. I always try to be present when my boat is being lifted to check this particular point

 

[Medskipper]

Yes me too and I know exactly where I want the slings to be and instruct the crane driver and their crews. They always seem quite happy with this and tell me that they wouldnt be able to remember each model they lift and have no wish to create accidental damage!

Barry

 

[byron]

Typical, the engineer who was to re-align the engine never showed nor did he even ring. Anyone know anyone on the Thames who will come and do it?

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[ChrisP]

Hi Byron I'm still here lurking in the undergrowth.

Friend of ours with Humber 40 had a gearbox job done. When we inspected the final assembly the whole engine rotated on it's engine mounts at tickover and smoothed out when reved up. Bent shaft was the mechanics explanation. Checked shaft. bo---cks was our reply. After even more money changing hands vibration still there and mechanic banished to the never recomend list. Finaly spoke to Mike Belamy at the L/B show. He explained that the plastic couplings between the shaft and the box get hot if the missalignment is too great. They become soft when under load and when they stop they harden out of alignment. Replaced coupling and vibration is gone £125. If your set up is the same could be worth looking at. By the way I've heard of quite a few 435's having engine mount problems someone even sugesteed that the engines are too heavy for the mounts and they bounce about like ping pong balls in a rough sea damaging the mounts and securing bolts. I've no experience myself but it's worth thinking about.
By the way, now you're in the Princess club you could ask Blakie for one of his Princess "repair kits" that Ron Pollard and I give him when ever we see him.

Say hello to the crowd from me and hope to see you soon.

Chris

 

[Guest]

I am sorry but 0.028 inches is a lot!

It is important to establish the nature of the mis-alignment. There is axial mis-alignment - basically the two shafts do not share the same parallel axis. There is angular mis-alignment where the shafts do not have parallel axis'. The type of coupling is very important. In general couplings are best at dealing with angular mis-alignment. The best way to look at this is to imagine a universal joint, it is brilliant at the angular stuff but hates any parallel mis-alignment.

To measure the axial alignment a magnetic clock should be attached to one of the shafts and the shaft rotated with the plunger againsts the other shaft - be careful here because the weight of the clock can have an effect when going from the top position to the bottom (believe me! I have have had all kinds of probs with this in the past) Any mis-alignment in this area shopuld be dealt with to better than 0.003 inches.

Angular mis-alignment can be measured two ways - Either using the magnetic clock as a slider on one of the shafts with the plunger on the other shaft - or, if one of the shafts has a flange on which the clock plunger can be place to establish run-out on the face. This method usually needs more space and the bigger the flange the more accurate the method but does need flange face to be square with axis of shaft to start with.

I apologise if I am teaching granny to suck eggs etc but I would not be happy unless the run out of any machine I was setting up was better than 0.003 inches on axis and 0.25 degrees of angle assuming that the coupling was a non-rigid and designed for angular mis-alignment.

My advice would be to initially establish what the coupling maker advises and work within this. There are hundreds of coupling types so it will have to be specific to the type you have. Secondly I would try to establish what loading the flexible engine mounts can take. Vibration attenuation is a technology that is quite complicated but the main factors are the 'forcing' frequency (Speed of engine) and the load on each mounting. If the mountings are not correct the effects can be dramatic.

I hope this helps rather than hinders.

PZ

 

[tcm]

Re: is 28 thou a big lot?

with tolerance on a run-in running fit from the gearbox of say 3-5 thou, and on gearbox of same amount, then it simply can't be better than 10 thou, ever?

So what's the effect of 20 thou out of balance. Half a millimetre. Hmm. Not sure how unforgiving these are but if you see

http://www.arweb.co.uk/boatsontheweb/leopard/dscf0041_thm.jpg

then you'll see how at least one boat co aligns engine and gearbox - no dials, it seems.....

But then, it sounds as tho you speak from significant experience in these matters, PZ?

 

[chippie]

Re: is 28 thou a big lot?

TCM, I visited the site you posted an unfortunately only got a 2"'x2"picture in the top left hand corner of my screen. Does it show a pointer bolted on to one flange and a reciever on the other? If so this would give accurate central alignment , but how do they gauge linear alignment? Or have i got it completely wrong.
I would appreciate it if you could explain it for me as engine alignment can be a pretty arcane science and the guys that built your boat are obviously first class at what they do.

Thanks.

 

[boatone]

Re: is 28 thou a big lot?

re website picture you can see a full size version at:
http://www.arweb.co.uk/boatsontheweb/leopard/dscf0041.htm

(tcm inadvertently gave you the url for a thumbnail image)


TonyR
boatone@boatsontheweb.com
www.boatsonthethames.co.uk

 

[tcm]

Re: is 28 thou a big lot?

http://www.arweb.co.uk/boatsontheweb/leopard

gives all the pics, and enlarge facility.

Didn't watch them do linear alignment. I suppose once the central alignment is done, needs a flange fitting and ensure same gaps around? I will have to have a word about it...