Flexible coupling on prop shaft.

[Appleyard]

Having replaced the engine mounts on the VP 2003,I intend to fit a R&D coupling to the drive flange. Doing this will mean that the prop shaft has to be moved back approx 32 mm to accommodate the thickness of the coupling. Is this a good idea? that is, would the extra length of unsupported shaft outboard of the cutless bracket add to any unbalance of the prop/shaft? Would it be better to cut off a corresponding 32 mm from the shaft at the coupling end and keep everything in its original position. ( This would have the advantage that I would not have to move the rope cutter ,which might be difficult to shift) It is a standard split coupling.
I am aware that the alignment has to be done following the work.
Thoughts and advice appreciated.

 

[Cliveshep]

Apart from other considerations, would the prop then get too close to the rudder? I'd have thought hacking off 32mm was a safer bet from what you say about the rope cutter.

 

[Appleyard]

Sorry,I should have said..there is plenty room between the prop and the rudder.

 

[Cliveshep]

Still, I think you have answered your own question really, maintaining the relationship between bearing and shaft projection makes most sense. Presumably your shaft, from what you say, has no keyway on the inboard end but one of those infuriating clamp/compression type couplings, so a few minutes work with an Inox 1mm disc in a mini grinder would shorten it and leave everything as the original build and give you a spare lump as a paperweight?

 

[VicS]

32mm is not a lot but now is the time to cut it rather than discover you should have done later.

Make sure you have some spare blades for your hack saw /forums/images/graemlins/grin.gif

 

[Cliveshep]

Hi again Vic!

No answering you here.............

If your propshaft is stainless steel and not phosphor-bronze you'll probably be glad of the loan of a mini grinder and an Inox disc because if not you'll want an awful lot of elbow grease and loads of blades plus endless patience to hack through any sizeable shaft thickness.

Edit.............
Just noticed you have the boat in Greece - Inox discs come from our old favourite Screwfix in 1.5mm thickness and will go in your flight bag assuming you can borrow a 115mm grinder out there. If not, 115mm grinders are under £20 from Machine Mart (Google(.

 

[Appleyard]

Hi gents, and thanks for all the advice.
My original feeling was to shorten the shaft at the inboard end ,and your replies have confirmed this .
I do have an angle grinder ,so I guess that it will accompany us to Greece this spring. I assume the shaft is s/s,and will get some discs to suit.
Looking forward to it!!!!

 

[dunedin]

When I got my boat (36ft) we could not motor above about 4.8 knots without severe vibration.
A flex coupling had been added by the previous owner and there was therefore a gap between P shaft and prop.

Engineer advised removing the flexi joint - his guide was gap to P shaft should not exceed shaft size (25mm in our case).
Removal transformed things - and now motors up to 7 knots.

Why is the joint needed in the first place if shaft aligned and engine mounts sound ?

 

[GeorgeTina]

Hi
I fitted a R & D coupling to the shaft on my Beneteau. I fitted it without shortening the shaft to see the effect it would have on gearbox transmitted noise. Magic !!. Much better than before, smoother and quieter. At the next lift out I shortened the shaft by 32mm. Well worth the effort.

 

[Heckler]

Just a thought for you, stainless is relatively eay to cut with a hacksaw blade IF the blade is new and sharp AND you take long SLOW measured cuts. I fitted some 5/8ths SS bar on my boat last year and had to cut it on the pontoon, I used a pair of mole grips to hold it to a cleat and easily cut through it with a new blade in a matter of minutes. If you use an angle grinder it WILL harden the steel and make it difficult to cut plus the cuttings and sparks will go everywhere and will embed themselves in the figlass around it.
Stu

 

[vyv_cox]

Stu is right again. No problem at all cutting a 1" shaft with a hacksaw, I've done at least three shaft cuts when fitting my Aquadrive and again with my new shaft last year, and nobody could describe me as muscular.

 

[matelot]

shouldnt make any difference to the balance at all. Saw it off at the gearbox end to keep the cutter where it should be. Disc cutter or hacksaw.

 

[Phoenix of Hamble]

and has the huge advantage that it doesn't spray red hot steel filings all round the engine compartment......

 

[Gaz22]

Did the same thing with my VP 2001 12 months ago. if you have the clamp type coupling you can push your shaft in through the coupling towards the R+D coupling leave 3 mm clearance between the shaft and the plastic coupling, if memory serves me correct l only had to push my shaft outwards 3 mm.
This would save cutting the shaft and you could revert back to your old set-up,ie no R+D coupling if you had problems with vibration or anything.

Good luck with what you choose to do, after fitting mine l could place a full cup of tea on the cockpit floor at full throttle there was no ripples in the tea.

 

[Appleyard]

Hi Gaz I was thinking that there might be enough room in the coupling to slide the shaft in and avoid cutting it. Hopefully this will be possible. I will have a go and let you know how it works. I can't do anything till the end of April as boat is on the hard in Greece.
Thanks for the info.

 

[misterg]

[ QUOTE ]
Stu is right again. No problem at all cutting a 1" shaft with a hacksaw...

[/ QUOTE ]

A very knowlegeable, time served fitter recommended Starret 'Red Stripe' blades to me, and by heck he was right - cuts through stainless like it was brass. Would have no hesitation in tackling a 1" shaft, PROVIDED there's room to get a saw in. I concurr that a grinder will make a hell of a mess if used inside the boat.

Andy