Flexible Coupling

MASH

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My engineer has suggested I think of fitting a "flexible coupling" in the drive-train (Yanmar 3GM-F in Sadler 32) to reduce vibration and excessive cutless bearing wear.

The shaft and prop are being checked for straightness and balance.

Will a flexible coupling improve vibes and shaft alignment to a useful degree?

Can anyone say if this is lilely to help - and if so what products are recommended?
 

JerryHawkins

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Flexi Coupling

Our last boat had a 3GM30 (raw water cooling) and it initially had a solid coupling from the gearbox to the shaft. It vibrated very badly. I replaced this solid coupling with a flexible one from R&D and it made a huge difference. I would recommend it.
 

Tranona

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Worth fitting - but an R&D will move the shaft back 25-30mm depending on type. Alternatives which replace the half coupling are Bullflex and Centaflex couplings. Superior, but inevitably more expensive.
 

Neil_Y

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The shaft bearing wear may be bearing carrier alignment, this should be checked as well. I'm not sure if the 32 has a stern tube bearing as well as the P bracket bearing? if it does then the alignment of these will effect the bearing wear far more than an engine that moves a lot. You also want to look at the length of shaft aft of the P bracket bearing, too mush here will also accelerate bearing wear.
 

30boat

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I have a Halyard coupling and the benefits are huge.Alignment is never an issue and the engine's vibration is not transferred to the shaft.There's still some structure noise but a lot less than on a similar boat( Fulmar) with a similar engine that belongs to a friend.He has a R&D coupling.
 

yoda

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I have a Halyard coupling and the benefits are huge.Alignment is never an issue and the engine's vibration is not transferred to the shaft.There's still some structure noise but a lot less than on a similar boat( Fulmar) with a similar engine that belongs to a friend.He has a R&D coupling.

I couldn't agree more. If you have the room it just takes away a world of trouble. Very nice people to deal with and while expensive the couplings seem to be very well made and last acordingly. You will also find that because you no longer have to worry about alignment you can adjust the engine mounts to even the loading and minimise vibration.

Yoda
 

Poignard

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I have a Halyard coupling and the benefits are huge.Alignment is never an issue and the engine's vibration is not transferred to the shaft.There's still some structure noise but a lot less than on a similar boat( Fulmar) with a similar engine that belongs to a friend.He has a R&D coupling.


If I had had the room I would have fitted a Halyard coupling.
 

doug748

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As you are no doubt aware the Halyard is much more than a flexible coupling and does away with alignment problems, some would say a good enought reason to fit one. Like parsifal I do not have enough room, and I think you may have the same problem.

I fitted a Centaflex flexible coupling (CF-M-127) which can cope with a small amount of misalignment but the makers are careful to stress that the engine should still be set up as accurately as possible. I particularly value the elegant method of clamping the prop shaft, within a collet, which makes it easy to take apart. It is very expensive. It will provide a good cushion against transmitted noise but not a quantum leap better than more affordable alternatives. I think the Sadler set up is quieter than my, earlier, design anyway.
 

MASH

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Doug, are you saying that the original Sadler setup is not so bad after all, or have I misunderstood?
What are the "more affordanble alternatives"?
 

doug748

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Hello MASH, no I don't think you have misunderstood, I think the Sader has a fairly modern set up, and is, as you say, not bad. You will probably have a simple flexible spacer already, a bit like one of these:

http://www.tnorrismarine.co.uk/randd.php

Your engineer is right to suggest the upgrade, but I think the noise improvement might be marginal and as the spend will be about £200, it is a matter of nice judgement. If there is no spacer fitted at all, then the cheaper option is there.
 

vyv_cox

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Following up Doug748's post, your Sadler may well have been fitted originally with a Bukh, as was mine. Although the Bukh has nominally flexible mountings they are quite hard and their movement is minimal. When I replaced mine with a Yanmar 3GM30 I began to encounter various alignment and vibration problems, due to the softer and more flexible mountings. There is a harder grade that can be substituted but this was also not effective in my case. In the end I fitted a Halyard (full story on my website) which has improved it considerably.
 

scottie

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Not all Sadlers were yard built so I would suspect a variety of installations

The rule of thumb is that any 2 of engine mount/ coupling / stern gland may be flexible but not all 3

If the coupling is RnD you may get away with it
 
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