R&D Flexible couplings

boatmike

boatmike

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I have 2 TAMD41a's that are bolted directly to the shaft flanges. To the best of my knowledge they are aligned pretty well and run fine up to about 1/2 throttle. Then I get vibration through the boat. Shafts and props are true and not bent. The classic answer would be to fit R&D flexible couplings but I don't want to move the props back so it would mean moving the heavy old lumps forward. Before I do, can anyone with similar size engines tell me if it's worth it. Obviously the first thing to do is check alignment and engine bearer condition, but how many of you run direct coupled, and how many with flexible couplings and what is your experience? I don't know of any other coupling other than R&D at a reasonable price, does anyone else?
 
boatmike said:
I have 2 TAMD41a's that are bolted directly to the shaft flanges. To the best of my knowledge they are aligned pretty well and run fine up to about 1/2 throttle. Then I get vibration through the boat. Shafts and props are true and not bent. The classic answer would be to fit R&D flexible couplings but I don't want to move the props back so it would mean moving the heavy old lumps forward. Before I do, can anyone with similar size engines tell me if it's worth it. Obviously the first thing to do is check alignment and engine bearer condition, but how many of you run direct coupled, and how many with flexible couplings and what is your experience? I don't know of any other coupling other than R&D at a reasonable price, does anyone else?
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I don't have them. Floating Preferably does. Same boat. Long time since we've been on each other boats, you are welcome to a ride on both.

I did my shaft alignment several times to get it spot on and all vibration is now gone.

Surely to make the R&D unit fit you'd shorten the shaft a little? Assuming there isn't enough room to slide it further into the coulping at the front (Or its not tapered at the front)
 
My shafts are bolted straight to the gearbox as well - again no vibration at all.
Are you sure you havent got a dinged prop? as no vibration at low speeds that builds with revs would indicate that. Also how old are the engine mounts they may be getting a bit spongy.
 
Hi Ben,
Thanks for the reply. I am a bit confused though as I don't think we have met or been on one anothers boats. Your profile suggests you have a Fairy Huntsman (nice) but mine is an Aquastar 33 and has just been launched after extensive refit. When I bought the boat it had been fitted with R&D couplings but the shaft had not been shortened so the props were further aft of the rear bearing than I wanted as I have fitted H4 Quick Cutters so I thought, well, they weren't original equipment so I dispensed with them. Now I have some vibration which comes in at about 2000RPM and shakes my teeth out at full RPM. As the boat is now in the water I am reluctant to haul out again to shorten the shaft which would require a new keyway to be cut. It may be that the alignment is not perfect but I could move the engines forward although I really don't want the work... The question is, can I cure this by better alignment do you think?
 
burgundyben said:
you are welcome to a ride on both.
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I'm sure he wouldn't mind!

I was referring to forumite Floating Preferably - he and I both have Huntsman 28's.

boatmike said:
The question is, can I cure this by better alignment do you think?
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I couldn't say. But I can say it took me 3 attempts to get it spot on. Was your alignment checked afloat? I think that is essential.
 
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kashurst said:
My shafts are bolted straight to the gearbox as well - again no vibration at all.
Are you sure you havent got a dinged prop? as no vibration at low speeds that builds with revs would indicate that. Also how old are the engine mounts they may be getting a bit spongy.
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Good thoughts but the props are perfect and I have the problem on both engines. You may be right though that the bearers might be a bit spongy as it's 1989 vintage. I might invest in new ones if I am going to re-align anyway......
 
burgundyben said:
I'm sure he wouldn't mind!

I was referring to forumite Floating Preferably - he and I both have Huntsman 28's.



I couldn't say. But I can say it took me 3 attempts to get it spot on. Was your alignment checked afloat? I think that is essential.
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No actually, aligned ashore. Not sure if a big heavy lump like the Aquastar would flex much when launched but yes, technically you are right. Should be fine tuned afloat. What engines do you have in the Huntsman?
 
IMHO. If your shafts and props are sound, I would very carefully check alignment before slipping. As the load is increasing the push on the back of the gearboxes is increasing to the extent that you will have close to a ton of 'end pressure' going up the shaft to the gearbox. It would not be that unlikely that if the mountings are original they may be distorting under the loading thereby missaligning the drive line, maybe inducing shaft whip. The fact that both engines are giving the same effect makes me want to eliminate the possibility of mounting distortion. I would do that before putting flexible couplings in. I would not move the engines forward but definitely shorten shafts if I was going to fit R & D's.. getting shafts shortened and keyways cut is no big deal to any machine shop. R & D's may cure the effect, but mountings distorting could be the cause, better to eliminate that first. I fitted R&D's a while back because I was really struggling with alignment (due to access largely, but partly due to time and patience. Now I have spent more time and the alignment is probably as good as it has ever been, with or without R & D's and there is very little vibration. I replaced my mountings when changing engines a couple of years back.
Trying to simulate the problem by somehow pushing on the back of a gearbox is probably not possible, but if you could, and movement detected it could cause missalignment. Let us know how it goes.:encouragement:
 
Just an update. Just went down to the boat and examined the problem and it is clear that the old mounts which are compression type are in poor condition. One of the front mounts, with the boat tethered to the pontoon can be seen to deflect when in gear with about 2000 RPM on board. I can't shift the thread on the boogers anyway so its new mounts all around. Talking to R&D they do very nice shear mounts that will do a better job but they are imperial sizes rather than metric on the volvo so its new drilled and tapped holes in the bearers anyway. So the engines are going forward 45mm and I will fit couplings as well. Belt and braces maybe but having done it before, tuning the alignment with R&Ds in place is much easier than without as you can rotate them and check the gap on the red bolt head. Can't cut the shafts anyway as they are already pretty close to the stuffing box and its difficult enough to contort my 72 year old bones into the small space down there as it is. I will update with progress in due course..........
 
Surely the imperial sizing only refers to the central stud. So imperial or metric doesn't matter.
The bolts securing the mounts to the bearer can be your existing ones or like for like new bolts.
 
No. The central stud on the volvo is 18mm but the spacing of the bolts on the feet are 110mm. The Imperial ones are 4 inches and 3/4" bolt so I drill the main hole out a millimetre (no sweat) but the bolts would have mismatched centres by approx 1/8". Does not matter to me as I intend to move the engines anyway so I will use 5" centre bolts which will put my new holes well clear of the existing. If I was to leave them where they are I would have had to file out the bolt holes. Not a problem either way.
 
That's great Mike, problem confirmed. Engines going forward 45mm is not going to cause problems unless you have a bulkhead 25mm in front of the engine now! It certainly wont upset trim which was what concerned me originally. It sounds good, yes, please update us in due course.
 
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Too right it won't. Boat weighs over 8 tonnes and engines are 1 tonne. 45mm is nothing. Anyway it's in the right direction as flat out her nose rises out of the water but her stern remains buried. Trim tabs are almost useless!!
 
Assuming the boat used to run vibration free and now does not then something has changed.

Engine mounts could have compressed.

have you checked for loosened mounting bolts or sheared studs.

A shaft could be bent, unlikely to be two shafts unless you picked up a rope.

How long since you checked the cutless bearings and how old are they?
 
Bandit said:
Assuming the boat used to run vibration free and now does not then something has changed.

Engine mounts could have compressed.

have you checked for loosened mounting bolts or sheared studs.

A shaft could be bent, unlikely to be two shafts unless you picked up a rope.

How long since you checked the cutless bearings and how old are they?
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Most of your questions have been answered already but

1. Boat has just been relaunched after extensive refit.
2. Engine mounts are in poor condition,
3. Cutless bearings have been renewed,
4. Shaft has been clocked and isn't bent,

Previously the shafts were coupled through R&D couplings but instead of shortening the shaft 45mm the previous owner moved the shaft back in its bearings which meant the flange was backed up to the stuffing box so I removed them. My guess is they were fitted to solve a problem thet was really due to knackered mounts and I now have the vibration back. The solution is to replace the mounts and re-align and as I have to do that anyway I will move the engines forward 45mm and re-fit the couplings which should well solve the problem.
 
Ok folks. It has taken a while as I have been on holiday away from the boat but for those who asked for feedback here it is.

Both engines moved forward 45mm, R&D couplings fitted and new engine mounts (also from R&D) fitted. The old mounts were standard Volvo with the rubber in compression and moved quite considerably under load. Main reason for replacing them was the bolts were rusty making adjustment impossible but the guys at R&D suggested shear type mounts rather than compression which I have fitted. This entailed drilling and tapping new hold down bolts in the bearers which are encapsulated stainless which has not been easy but the result is that both engines run up to 3500RPM with no discernable movement and the result is well worth all the trouble. I get 22 knots under full power and the good old TAMD41a's purr like kittens. I am a happy chappie and the result has exceeded my expectations. For anyone contemplating similar I can recommend the R&D mounts in particular. They were very helpful and calculated precisely the resilience required for both forward and aft mounts which are not the same (unlike the Volvo originals) I now have a very smooth and vibration free boat!
 
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