Belt driven propellor shaft

[LeFevreBreeze]

My 36’ Roberts is powered by a Yanmar 3JH2E couple to a Kanzaki transmission.

Perhaps unusually the motor was mounted with the V belt facing aft and the drive shaft pointing to the bow. Output from the drive shaft is transferred to the prop shaft by cogged belt and gears 1:1. This allows the motor to be under the cockpit but above the propellor shaft / stern tube.

I have searched the Internet high and low for mention of other similar systems but it seems unique. Can any CF forum readers help with a name for the setup? Were they common placed in 1980’s custom boats?

[Pete7]

Normally its a V drive gearbox, but of late electric yachts are doing a similar thing, only using the gears to take the rpm down from the high revs of the electric motor to lower revs for the prop which improves efficiency.

Yours may be a one off custom build.

Pete

[LeFevreBreeze]

Originally Posted by Pete7

Normally its a V drive gearbox, but of late electric yachts are doing a similar thing, only using the gears to take the rpm down from the high revs of the electric motor to lower revs for the prop which improves efficiency.

Yours may be a one off custom build.

Pete

Thanks Pete for your response. Do you know the name (brand name?) of the systems that the electric drive propulsion use?

[formosa aus]

Brunei’s SS Great Britain was driven by a chain (like a scaled up bike chain). Evidently worked well.

[abroadreachtrvl]

Clogged belt drives are used in industry all the time. Gates makes a wide range.

They typically outperform an equivalent chain drive. In life,noise and vibration. If it’s appropriately sized and aligned, it should last a while.

Only maintenance was checking the tension and alignment.

[Mithril Bham]

Have similar system using 5 belts. 1978 BR 44. Fafir bearings.

[Pete7]

Originally Posted by LeFevreBreeze

Thanks Pete for your response. Do you know the name (brand name?) of the systems that the electric drive propulsion use?

Sure, something like this. Most will be the traditional way round, but an electrical motor doesn't care which way its mounted.

https://electricyacht.com/

https://www.thunderstruck-ev.com/ele...oard-motor-ev/

[PineyWoodsPete]

Oh the memories! Back in '57 or so I was given a beat-up Aristocraft 12' runabout, that I put the family old 15HP Evinrude on after refinishing the lovely, long mahogany deck, that left maybe 3' or a little more behind the single bench seat. The performance was disappointing - could barely pull up one skier, and hit maybe 27 MPH on a good day.

A friend's dad had a brand new Harley V-2 WW-II surplus engine, still in the cosmolene wrapper in his basement, that we appropriated, and I invented, or reinvented, the FWD facing over/under chain drive prop shaft, dead-ending it into a thrust bearing on an oak 2x6 across the 2x12 engine mounts, and a chain sprocket to match the Harley's. Had a garage fabricate dual exhaust pipes exiting the mahogany transom.

At any rate it actually worked, and sounded like the Hounds of Hell coming on Lake Allatoona N. of Atlanta! It would pull up two skiers easily, but I was disappointed that it's top speed was only 25 MPH, which no doubt could be have been increased by tinkering with the sprocket sizes a bit But life (and gals!) intervened...

[adjo]

The prop shaft on my boat was chain driven for more than 20 years and it worked OK. A bit clunky when going from forward to reverse and a bit of a whine when running - but not extreme.
Chain adjustment was simple and infrequent (shims under the motor mounts).
The duplex chain only needed replacing once in 2000+ hours of use.
It did need lubrication (a quick spray every 10 hours or so) and had a spatter guard to prevent lubricant going everywhere.
I would have preferred a toothed belt drive or a V-drive but when I did the installation (early '80s) these were beyond my very limited budget.
This setup allowed the motor to be further aft than would have been possible otherwise which made the saloon much more liveable.