Double universal joint style drive systems

[GILow]

A few weeks back a fellow yachtie wandered past clutching a short drive shaft with a universal joint at both ends. Just the sort of thing you seen on live axle 4WDs. It is part of his drive system, connecting the engine to the prop shaft. (His boat is a fascinating thing, with all sorts of technical ideas including a pushpit that doubles as a jockey pole to lower his tabernacle mast.). In his case the setup is needed because his engine is actually lower than the propellor shaft. Unusual to say the least.

Anyway, I didn’t think much more about it until this week when I was considering what to do with the new boat. I am removing the heavy old Perkins 154 with VelvetDrive transmission and replacing it with a smaller, lighter and, above all SHORTER Beta 50 with a TMC manual transmission. The shorter bit is a problem as it would sit way aft in the engine bay and cause problems with fore and aft trim. I am fitting a new prop shaft so one option was to make the prop shaft longer (with all the associated issues of whipping).

But now I’m thinking that the double uni joint idea might be the way to go. I’m assuming I’ll need a thrust bearing on the prop shaft (should be easy enough to arrange) but has anyone had experience of such a setup and if so can you comment on it in terms of reliability, noise etc?

Engine is a 50 HP Beta with a 2:1 reduction gear. Shaft will be 1.25” with a maximum rpm of 1350. Shaft itself is currently pretty short, I think a bit over a meter. The extension with the uni joints would likely need to be a bit over half a meter.

Matt

Edit: for the record, I know there are some commercial versions of this out there (python?) but they are waaay out of my budget.

[Bowdrie]

It's been a couple of years or so back, That the "Salt and Tar" vids on YouTube went that route, and they show and explain some stuff.
I saw such an installation on a power boat that really was quite simple.
A steel fabrication made-up the thrust bearing mounting and the rest of it was just regular automotive driveshaft stuff, go to the local parts store for U-joints.
A thrust bearing is no big deal, all sorts of industrial and agricultural parts that are cheaper and more easily available than some "marine store" part.
I see no reason a well thought out set-up wouldn't give long/smooth service.

[wholybee]

It is very important to get the angles right. In order for a u-joint to work, the U joint on each end must be at exactly the same angles. In a car, that is done by rotating the rear axle, easy enough to do. But you don't have that easy adjustment on the boat. You can adjust the engine mounts somewhat.

The "exactness" is probably less important on a boat than a car, but I think still needs to be as good as you can get it. If off, the speed of the prop will change every half revolution. (or is it every 1/4?) This will turn into a vibration in the driveline and the engine.

As long as the angles are correct, it should be pretty simple to set-up. U joints are not maintenance free. They need to periodically be greased and eventually changed.

[GILow]

Originally Posted by Bowdrie

It's been a couple of years or so back, That the "Salt and Tar" vids on YouTube went that route, and they show and explain some stuff.

I saw such an installation on a power boat that really was quite simple.

A steel fabrication made-up the thrust bearing mounting and the rest of it was just regular automotive driveshaft stuff, go to the local parts store for U-joints.

A thrust bearing is no big deal, all sorts of industrial and agricultural parts that are cheaper and more easily available than some "marine store" part.

I see no reason a well thought out set-up wouldn't give long/smooth service.

Thank you, I’ll look up those videos.

And yes, I feel like the parts should be blessedly free of the marine price tag. Already found some promising stuff used for power takeoffs on tractors.

[GILow]

Originally Posted by wholybee

It is very important to get the angles right. In order for a u-joint to work, the U joint on each end must be at exactly the same angles. In a car, that is done by rotating the rear axle, easy enough to do. But you don't have that easy adjustment on the boat. You can adjust the engine mounts somewhat.

The "exactness" is probably less important on a boat than a car, but I think still needs to be as good as you can get it. If off, the speed of the prop will change every half revolution. (or is it every 1/4?) This will turn into a vibration in the driveline and the engine.

As long as the angles are correct, it should be pretty simple to set-up. U joints are not maintenance free. They need to periodically be greased and eventually changed.

The angle thing is interesting. From what I’ve read so far it seems I can by telescoping shafts with the uni joints correctly offset already. That will help for sure.

[Uncle Bob]

Originally Posted by GILow

A few weeks back a fellow yachtie wandered past clutching a short drive shaft with a universal joint at both ends. Just the sort of thing you seen on live axle 4WDs. It is part of his drive system, connecting the engine to the prop shaft. (His boat is a fascinating thing, with all sorts of technical ideas including a pushpit that doubles as a jockey pole to lower his tabernacle mast.). In his case the setup is needed because his engine is actually lower than the propellor shaft. Unusual to say the least.

Anyway, I didn’t think much more about it until this week when I was considering what to do with the new boat. I am removing the heavy old Perkins 154 with VelvetDrive transmission and replacing it with a smaller, lighter and, above all SHORTER Beta 50 with a TMC manual transmission. The shorter bit is a problem as it would sit way aft in the engine bay and cause problems with fore and aft trim. I am fitting a new prop shaft so one option was to make the prop shaft longer (with all the associated issues of whipping).

But now I’m thinking that the double uni joint idea might be the way to go. I’m assuming I’ll need a thrust bearing on the prop shaft (should be easy enough to arrange) but has anyone had experience of such a setup and if so can you comment on it in terms of reliability, noise etc?

Engine is a 50 HP Beta with a 2:1 reduction gear. Shaft will be 1.25” with a maximum rpm of 1350. Shaft itself is currently pretty short, I think a bit over a meter. The extension with the uni joints would likely need to be a bit over half a meter.

Matt

Edit: for the record, I know there are some commercial versions of this out there (python?) but they are waaay out of my budget.

Hi, you could try a driveline specialist that could produce a short shaft with cv joints similar to that on a mini, I'm sure that somewhere in the wilds of Adelaide there is someone, the whip problem can be resolved with a simple pillow block bearing and the thrust bearing for forward could be done with a tapered roller and reverse with a bronze bearing. It's all doable.

[wrwakefield]

You may already know that Aquadrive and Brunton Sigmadrive (and others?) are two commercial offerings for vessels in our size ranges using thrust bearings and CV joints.

A sistership installed the Aquadrive system and it sure is smooth and quiet... (I may have drive shaft envy...)

In case either are of interest.

Cheers! Bill

PS: Noticed your PS edit after I posted...

[skipperpete]

Originally Posted by GILow

The angle thing is interesting. From what I’ve read so far it seems I can by telescoping shafts with the uni joints correctly offset already. That will help for sure.

There’s no doubt that a shaft with conventional uni joints will work, Walter vee drives have been using them on island mounted drives since the 1920’s ...and you’re already aware of the need for that thrust bearing ( which will probably be the most labour intensive part of the whole job)....I’m sure it will work. The other big plus is that whatever stern gland you have, it will be happier, drier and longer lived with that bearing holding the shaft rock steady
Pete.

[Wotname]

All sounds a bit agricultural (pun intended).
If you opt for the longer shaft, then why not a single CV joint rather than double uni joints; plus the thrust and intermediate bearing.

[Searles]

The answer you seek ,is the Sigmar drive ,a single unit thrust and alignment drive ,originally from Scandinavia ,have fitted a few ,30 to 100 h/p ,never a problem ,the first one over 12 yrs old now, the normal rules for shaft instillations still apply ⛵️⚓️

[skipperpete]

Yes, Sigma drive is an option at $1,000 for the basic smallest drive alone but it still leaves the OP with the expense of a haulout and a new longer propeller shaft. On the walter drives often only one uni joint is used but its combined with a splined slip joint to allow for engine movement. The automotive/ tractor pto shaft is the easiest and cheapest option and you always have a place to shove in a screwdriver to stop the shaft spinning.... [emoji33][emoji33]just joking[emoji844]

[jharding]

my 1984 Irwin 52 came with that setup, I replaced the u joints a few years ago they were the same as a chevy 3/4 ton truck, the double u joint shaft has a slip splined section, I replaced the thrust bearing a couple years ago, went to a bearing house and fellow got one in a few days. I like the system, lets the motor work freely.

[Grattaway]

Gilow I have such a setup on a Hartley 32 with a Bukh dv20 driving the shaft via a transfer case - its unusual but reliable as boat built circa 1975. Parts readily available - I would say what has been fitted was from a farm implement of some kind
Replaced thrust bearing a few years ago and also the spider bush at one end otherwise no issues

[GILow]

It’s rare that I hear such consistently positive experiences of a system involved with the engine and propellor.

Thank you to all that have contributed.

[skipperpete]

Originally Posted by Searles

The answer you seek ,is the Sigmar drive ,a single unit thrust and alignment drive ,originally from Scandinavia ,have fitted a few ,30 to 100 h/p ,never a problem ,the first one over 12 yrs old now, the normal rules for shaft instillations still apply ⛵️⚓️

Searles you’re absolutely right, an excellent solution. The Sigma drive is a nifty idea but it still needs a bit of thoughtful alignment, the angle that the shaft makes with the engine can be quite large (3°max) but the flange on the gearbox/engine still needs to be adjusted to meet the Sigma flange at the same height as well as laterally. The prop shaft and Sigma position are not negotiable so the engine needs to be adjusted up/down... port/stbd, not a difficult task but nonetheless needs to be done as you suggested with “normal shaft installation rules”