R+D Semi Flexible Coupling with Volvo Dripless Seal

[stranded]

When I bought Nooka at 5 years old she had an R+D coupling with a Volvo dripless shaft seal - I assume this was fitted as standard from new - certainly there is no reference to a change among the copious pre-delivery additions undertaken by the importing dealer or in subsequent invoices.

I had the coupling replaced with rigid coupling before a planned long term blue water cruise that never came to pass and have been putting up with the consequent increased noise and vibration ever since.

I would like to change back to R+D, but Volvo advise against using their seal with a flexible coupling. Are there other dripless seals which would be compatible with an R+D?

The French yard I asked about this say I would need “a braided stuffing box or similar”.

ChatGPT says that the main concern would be shaft whip but given my relatively low power engine (Yanmar 75hp) and chunky 35mm propshaft, that should not be an issue. As ever, ChatGPT is very plausible, but is conspicuously light on sourcing for this element of its advice.

Assuming that failure of a Volvo seal would be catastrophic and a non-approved installation is unlikely to impress my insurers, I’m a bit stuck. Any advice or observations would be gratefully received. In particular, how big a deal is replacing with a “braided stuffing box” - such things are mythical beasts in my limited sailing breadth of experience.

 

[Paul1962]

My Beneteau Antares 7 had an R&D shaft coupling and a Volvo dripless stern seal - never a problem all the time I owned her

 

[Tranona]

Shaft whip is a function of length of unsupported shaft in relation to diameter. You don't say what the shaft length is nor whether there is an intermediate bearing in the stern tube. Generally speaking the R&D is not very "flexible" and in many boats there is no problem with using a Volvo seal if the shaft is short. In my new installation, because the shaft is "long" (54" from memory 30mm) I chose a better flexible coupling (Bullflex) and put an intermediate bearing in the inboard end of the stern tube, then used a Radice Volvo type seal. So more information needed on the shaft length and position of any bearings. The Volvo recommendation assumes long shafts with only one bearing, usually in a P bracket.

If a Volvo seal does seem impractical then the best alternative is a Tides Marine Sureseal which has lip seals like a Volvo but mounted on a flexible bellows like a stuffing box you French source referred to. Proper well engineered job with replaceable seals should they ever wear out (unlikely!) shaft-seals.co.uk/product/propeller-shaft-seals-sure-seal/

 

[stranded]

Thanks Tranona. Yes, bit light on detail atm - boats in France - had assumed would be straightforward as just returning to builders OE setup. Suspect shaft is longer than R+Ds benchmark 1:30 dia/length ratio so (subject to measuring in March) not going to pursue the R+D w. Volvo option - I’m confident Sunbeam wouldn’t have done it if it wasn’t sound, but...

I’ll look into the Bullflex and Sureseal. Do I take it that the alignment bearing referred to in Tides Marine Sure-Seal bumph would serve as a rigid bearing for bringing down the shaft length/diameter ratio or would you expect I would need to fit an additional bearing as you have done?

 

[stranded]

My Beneteau Antares 7 had an R&D shaft coupling and a Volvo dripless stern seal - never a problem all the time I owned her

Yes, it doesn’t seem an uncommon combination and seemed to have worked fine in the 4 1/2 years before we acquired her including a trip to the Caribbean and back. But I recalled in thinking about this more after getting Tranona’s reply that I was advised a few years ago that moving the shaft anode closer to the p-bracket might reduce vibration - I did that to no noticeable effect but it’s got me thinking about adding an additional bearing at the stern tube anyway. Need to look into it more.

 

[Tranona]

Thanks Tranona. Yes, bit light on detail atm - boats in France - had assumed would be straightforward as just returning to builders OE setup. Suspect shaft is longer than R+Ds benchmark 1:30 dia/length ratio so (subject to measuring in March) not going to pursue the R+D w. Volvo option - I’m confident Sunbeam wouldn’t have done it if it wasn’t sound, but...

I’ll look into the Bullflex and Sureseal. Do I take it that the alignment bearing referred to in Tides Marine Sure-Seal bumph would serve as a rigid bearing for bringing down the shaft length/diameter ratio or would you expect I would need to fit an additional bearing as you have done?

I think the alignment bearing is part of the housing for the seals and is there to keep the shaft concentric with the housing and the lip seals. This performs a similar function to the back part of the Volvo seal which is a fluted water lubricated rubber bearing. The whole assembly is flexibly mounted to the stern tube. It may not be possible to insert an additional bearing in the stern tube. A common arrangement with a P bracket is to use a short plain tube glassed into the hull, maybe 40-45mm ID with an OD of 48 or 54mm to take the Volvo seal. If it is 54mm there would be just enough room to bore it out to take a cutless bearing (these are available with either 1 7/8" or 50mm OD shells) but whether it is feasible to do this in situ not so sure. On my boat we used the old stuffing box housing. As you can see from the photo it just fits with a 3mm wall thickness (30mm shaft but principles the same. Of course all this comes apart and the housing was bored on a lathe. This is the second one I have done like this. You can see the Bullflex and the complete seal arrangement in the second photo

Hope this helps