u-joints on prop shaft?

[Hoghead]

I am re-powering my Flying Dutchman FD12, and the old system uses a hydraulic drive with a separate thrust bearing. Motor is connected to the thrust bearing and pump is mounted on the engine.

My Diesel Duck trawler had a u-joint auto style drive shaft between the engine and thrust bearing, and I am wondering why such a set up would not work on my sailboat?
When I remove the hydraulic motor, I will be left with a thrust bearing output flange. It would be a simple matter to fabricate a constant velocity drive shaft to connect the thrust bearing to the conventional gearbox output.

There would be several advantages:
No alignment issues. This is important to me as I have little faith that the "mechanic" in Subic can align the engine properly.
The engine could sit horizontal, or in any attitude required to fit
Beta engines have the gearbox output from 3.5 - 5" lower than the crank centreline so a drive shaft simplifies clearance issues.
Engine mounts are easy to fabricate
Any change in alignment when the boat goes into the water, or the mounts sag is a non issue


The downside is that unlike my DD there is no room to install a dripless shaft seal so I have a conventional drippy stuffing box.
Rust on the u-joints is a concern, unless there is such a thing as SS u-joints?

Or is there a commercial version of this concept, a CV style joint, or a flex type shaft?

There must be a reason why this is not more common..................

[boden36]

Scatra Aquadrive if they are still made. One of those is on our DD also. I fittted one on our yacht 30 years ago and it is still going well.

Regards,
Richard.

[Hoghead]

I see a couple of marine CV joint solutions but with the thrust bearing which I already have.

Or a simple CV joint in its rubber boot on a SS jackshaft??

[Hoghead]

Originally Posted by boden36

Scatra Aquadrive if they are still made. One of those is on our DD also. I fittted one on our yacht 30 years ago and it is still going well.

Regards,
Richard.

Aquadrive have an integral thrust bearing and I already have that built into the boat
What I need is a jackshaft to join the 2 flanges together with a CV or U-joint at the end(s)

[jimbunyard]

Many marine engine manufacturers supply them, but you usually pay through the nose for them.

CV shafts are more the norm now for jackshafts, but many people have used u joints.

Since you're already set up with a thrust flange, you can have a shaft made locally, with or without a slip yoke as necessary.

A quick search for 'marine CV shaft' brought up many suppliers like this one who can easily make one specific to your needs. The flanges are standardized, and can be ordered off the shelf.

Marine

[Bill whitmore]

Much better than a U-joint is a Thompson Coupling (thompsoncouplings.com). It is a true CV coupling, like an Aquadrive but can handle larger misalignments without problems. Very smooth with no issues of overheating. I have had one for 8 years of heavy use with great performance.

[oleman]

There is a very simple reason why there are few U-joints in fixed alignment prop drives basically they are just another wear item and are not required in the majority of the installations.

[Cheechako]

I wouldnt worry too much about rust on the U joints, car joints are exposed to road salt for years and they are lubricated. No reason it wont work. BTW, dont align them perfectly straight. Drive shaft makers will tell you to have something like 3 degrees of bend in the joint. Contact a drive line maker with your specs and they will tell you what you need.
Years ago a company I worked for put U-joint driveshafts in about 50 military boats they built.

[Hoghead]

Originally Posted by Bill whitmore

Much better than a U-joint is a Thompson Coupling (thompsoncouplings.com). It is a true CV coupling, like an Aquadrive but can handle larger misalignments without problems. Very smooth with no issues of overheating. I have had one for 8 years of heavy use with great performance.

I sent them an email earlier today. They look very nice and I bet expensive.

I do not need the ability to carry axial loads as I have a thrust bearing.
My misalignment should be well within the range of a CV joint so this big benefit of the Thompson is of little value to me.

All the same they are very nice and I look forward to hearing the cost

[boat driver]

the thrust bearing is the important issue-and from description you only need a drive shaft- if you are having to make this up in a remote location (subic bay,Philippines?) - use standard truck u-joints that have grease fittings and be sure to maintain- a good shaft can be primed and epoxy coated to offset surface rust assuming the shaft is not sitting in salt water. remount the engine on soft mounts and amazing how quiet and less vibration. cheap enough to take an extra set if you feel corrosion concerns- the quality grease will protect the bearings- use anti-seize liberally on the bolts.

The stuffing box- look into dripless packing- easy to install yourself in or out of water- (out is easier though first time or difficult acess area)

https://catalog.hydrasearchrecreatio...ype=2&filter=1

This product I have used/installed literally hundreds of times and will stand behind that it works (maybe get +2000 hours?) and will suggest there are other products on the market for less money- but I have no experience with them. The only inside experience is if your stuffing box is significantly large diameter contact them and mention the packing dimensions- sometimes it takes an extra kit to fill. (particularly on larger shafts) This product also works well with rougher faced shafts with pitting and some wear.

[sailndoug]

Take a look at Sigmadrive. This is a thrust bearing and cv joint in one unit from England. Available in the States. I installed one for 1 1/2" shaft because of similar issues you have. I highly recommend.Sigmadrive – Bruntons Propellers
Doug

[Dymaxion]

Remember that u-joints should be installed in pairs or you risk inducing vibrations in the propshaft from the speed variation as the joint rotates. A hint is that CV stands for CONSTANT velocity.... and thus one CV joint works fine. Having said that, at a very low change of angle across a u-joint this vibration effect is quite small. U-joints will handle push-pull forces fine, CV joints won't. Does your thrust bearing work when prop is in forward AND reverse direction?

[captmikem]

I used to sail a 65' Phil Rhodes yawl that had a centerboard. The main engine was offset to the port side of the centerboard well. It was connected to the prop shaft via a truck drive line with U joints. Worked fine and I never had any problems with it..

MY

[MartinR]

I had this on one of my boats. Thrust bearing. Automotive drive shaft between engine and prop shaft. Worked perfectly. Another advantage is you can use much softer engine mounts, practically eliminating vibrations.

You need to use a shaft, though. 2 U-joints are needed, because of the radial movement of the engine.

[Captndave1]

Good solution, I think.
Unrelated, what hull # FD12 is yours.? I am familiar withe FD 12s, I had the opportunity to sail on hull #24 for several thousand miles with the Owner/Builder of FD12s, Mr, Will Ekholt including 8 trips from Tampa to Cuba and the Grand Caymans.
The FD12 is an excellent boat, I very much enjoyed sailing the boat
I hope all goes well with your project.