Aligning sailboat propshaft w flexible shaft coupling between motor and propshaft?

[Q Xopa]

Agreed with everything you say. All good information.

In fact I have recently installed a Thrust bearing on mine so I'm onboard.

But as you dont need a thrust bearing to Align a driveshaft it is drifting off the subject of thread title.

[skipperpete]

Originally Posted by GreenHeaven

I have a mysterious flexible coupling from the mid 90s, probably French since its in a Jeanneau, between engine and propshaft. It has two "CV" joints, one at each end of a short stubshaft. see pic

This will permit engine misalignment due to vibration etc, but how to set it up optimally? I presume minimizing the angles would be the guiding principal.

Here’s the installation guides for the Vetus and Python drive CV shafts.

[Elie]

I installed long time ago this Python shaft coupling mainly because the original setup was very dificult to align properly due to the almost unreacheable transmission coupling. To do so, the first thing was to install a bulkhead where the python coupling was solidly attached. Everything is perfect : no vibrations at all and as a bonus, the transmission push bearing is not in fact now submited to any pressure. The most important thing is this structural bulkhead that assume all the push from the propeller now.

[Nicholson58]

CV and Universal joints need a small offset in order to promote proper lubrication distribution and to prevent the ball bearings from brinelling due to only operating in a single position. Don’t sweat the offset if it is within allowed range.

Look up Aquadrive as a modern replacement and suggested alignment.

Remember that the CV joint in your auto trans axels is never close to in line

[blubaju]

CV ist a fine wonderful mechanical device. imho over sophisticated on a small sailboat. I used w/o any failure since 1990 flexible disc couplings. Any machine shop can adapt the drive shaft for you. Price compared to CV is next to nothing. I use
https://www.pyiinc.com/flexible-shaft-couplings.html
But there are many others too. These to my knowledge are made in UK where I bought them. They are NOT designed for severe misalignment!

[crossbow]

I had one of those on a Jim Brown tri. Coming out of Port Aransas in a strong westerly and running up the coast it burst into flames. By the time I’d put it out I was in surf. Long story short, the surf ground the little skeg into the sand and I watched it pop through the hull. Within 20 seconds the boat was full, sitting comfortably in 3’. And full of sand. I walked away and took a tourist ferry back. Months later someone managed to salvage her. I hope they’re still enjoying her. Kittywake.
I think the moral of the story is: beware those flexible joints.

[blubaju]

Well, then you had a severe misalignment, not following instructions, 3° occasionally and not more. twisting it all time, that will produce internal heat. No twist, no heat, no fire. It depends on the brand used too, some have kind of safety bridge built in, but I never had a problem, do not know about their performance. CV-joints sometimes fail too and saltwater is not their best friend. But if much much more expensive is much better, it may be. Anyway, I do not receive any commission, so never mind

[Q Xopa]

Originally Posted by Nicholson58

CV and Universal joints need a small offset in order to promote proper lubrication distribution and to prevent the ball bearings from brinelling due to only operating in a single position. Don’t sweat the offset if it is within allowed range.



Look up Aquadrive as a modern replacement and suggested alignment.



Remember that the CV joint in your auto trans axels is never close to in line

Agree with your comment about potential of bearing brineling.

However in practice this isn't likely to occur as the alignment of a propeller shaft coupling with an engine on flexible mounts is not static for long. So the balls and rollers get to pick up a little fresh grease every time the motor rocks in a wave, or twists as torque is coming on and off going up and down waves or throttle changes.

I would suggest instead of leaving an offset to cycle the rollers or balls back or forth every revolution may be more wear than beneficial lubrication?

Of course this is all getting pretty insignificant and theoretical at this point.