Drive shaft for remote v installation, please advice

[Magnus W]

The boat I'm going to stretch (see other thread) is going to get a remote v installation.

The new engine will be put in the stern and we'll install a remote v transmission and I'm looking at the best solution for connecting the engine to the transmission.

The distance between the flange on the engine and the flange on the transmission is approximately 4000 mm.

The engine will be installed at a 0 degree angle. The transmission will be tilted forward by 3,7 degrees.

The best thing would be if it could be a single shaft the entire way as it would simplify the installation greatly.

The engine can be mounted a such height that the shaft joints "only" have to deal with the 3,7 degrees (the engine output flange can sit higher than the transmission input flange).

However, the engine flange sits at 292 mm and the transmission input flange sits at 391 mm (above lowest point).

In the interest of keeping the engine as low as possible it would be nice if the engine flange could be positioned lower than the transmission input flange even though the transmission flange is ”pointing the wrong way”.

In turn this would mean that the shaft angle will be 1.43 degrees resulting in the engine joint at 1,43 degrees and the transmission joint at 5,13 degrees. With what I know of drive shafts this is not a good solution (both running different angles and 5,13 degrees being too much) but it’s a question worth asking.

The engine is a FPT C90 380 with a maximum torque of 1500 Nm at 1400 rpm and maximum power of 380 hp at 2000 rpm. It's heavy duty rated at continuous duty at 100 percent and so should the shaft be. Transmission is a Twin Disc MGX-5136RV.

 

[jorgepease]

what about using Belt Drive

 

[Magnus W]

A belt drive would take care of the height difference issue but I'm still stuck with the angle difference. And have both a belt, with associated supports, as well as a drive shaft seems pretty complicated.

 

[jorgepease]

and you can't put the engine at same angle as transmission?

 

[Magnus W]

It's a possibility but since it's facing backwards I'm not sure if it's ok with the manufacturer (I have asked the sales rep but so far no reply).

 

[Rumars]

The solution you seek is a CV joint. You can engineer the whole thing yourself using some CV joint from a high power car (racing applications) and a truck driveshaft or you can buy it of the shelf directly engineered for marine applications from this guys, directly there in Sweden: Torsional  Damping https://www.aquadrive.com/torsional--damping.html

 

[gonzo]

Automotive CV joints are not designed for high thrust. You would have to add a thrust bearing to take the force.

 

[Angélique]

The Dutch Python-Drive offers constant velocity off angle propshaft joints / thrust bearing units from 10 to 1,000 Hp, many languages available, just click the prefered flag.

Python-Drive manufacturer is Dintra (also click the prefered flag for language choice), check the left column and/or the top bar for some more products and info.

 

[Rumars]

Automotive CV joints are not designed for high thrust. You would have to add a thrust bearing to take the force.

A thrust bearing is needed between engine and transmission? I would have tought that the V-drive has it's own and is rigidly bolted down to the boat.

 

[Angélique]

A thrust bearing is needed between engine and transmission? I would have thought that the V-drive has it's own and is rigidly bolted down to the boat.

(my below text is green where the picture shows these items in green)​

remote v-drive gearbox - - - - - - - - - - - - - - engine

The above picture from the link¹ in post #6 shows a torsional damping shaft plus couplings¹ between the engine and the gearbox, then you need a constant velocity off angle propshaft joint / thrust bearing unit² between the gearbox output shaft and the propshaft, when these are not in line.

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Aqua Drive ---> Models Technical details (the three below quoted lines come from this link)
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¹ TORSIONAL DAMPING

‘‘ Aquadrive torsional rubber dampers combined with CV shafts (CVT units) are available in a full range of power applications involving remote mounted propulsion equipment. ’’
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² MODULINE B20 & B30 SERIES

‘‘ The Aquadrive Moduline B20 and B30 series is our mid-size systems for powers between 100–420 hp (73–310 kW). ’’
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² HEAVY DUTY LINE (HDL)

‘‘ Aquadrive HDL series is built to meet the high standards expected for ocean crossing and commercial crafts, suitable for engine powers between 400 to 1630 hp (300 to 1200 kW). ’’
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[gonzo]

V-drives have a thrust bearing included. However, automotive cv-joints are not designed to take the force generated by the propeller thrust. There are cv-joints that can take thrust though.

 

[Magnus W]

I've been in lengthy discussions about the drive shaft issue today and while it's certainly something that can be solved it seems it would require an expensive, complicated and maintenance heavy installation.

My main reason for having such a long shaft is that I would like to have the prop shaft at the smallest possible angle, in this case about six degrees. However I'm now leaning towards accepting the 10 degrees that the gearbox has.

I'm not sure how much the extra 3,7 degrees will affect the prop performance but I'm thinking that it will be in some part offset by lower transmission losses (only two joints vs most likely four as well as two support bearings).

If I go for 10 degrees the length of the drive shaft only needs to be approximately 2200 mm assuming a engine coupling depth of 90 mm.
Another benefit is that the engine can be mounted at a more suitable height (100 mm from the bottom) which should benefit the stability as well as making the rear deck (above the engine) more useable.
The drive shaft angle between the engine and transmission will be 1,28 degrees which is very reasonable.

What are your thoughts? Is a prop shaft angle of 6,3 degrees so much more beneficial to the performance (translated into economy) than 10 degrees?

My initial estimate is that the complicated drive shaft solution will cost approximately 10 times more than the simple solution as well as having about half the time between overhaul. And not to mention introducing more stuff that can break...

 

[gonzo]

It won't be significant. The thrust difference (cosine of it) will vary about 0.8%.

 

[Angélique]

You could consider to tilt the engine till the max the manufacturer specifies for the output side down, this will also tilt the gearbox and reduce the propshaft angle.

Take note the engine will be tilted back towards horizontal when the bow comes up.

Good luck !

P.S.

Edit: Removed the original P.S. and edited the post a bit, since I was mistaken in some parts by the backwards position of the engine.

 

[Rumars]

Ok, maybe I missunderfood something so please correct me. There is a planned angle difference between motor and V drive. At the initial planned angle there would have been a need for a CV joint in the motor to drive shaft, plus a torsion dampener, but not a thrust bearing.
If the shaft driving the propeller does not match the V-drives output angle then yes I agree he needs a thrust bearing on that shaft besides a CV.
Now it seems the motor to V drive shaft issue is solved. Does that mean that in this case the propeller shaft angle is also solved?