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This is just an idea so I'm going to throw this out there for comments. I've ordered plans for a tiny might which should be here tomorrow! Yay! Now looking at the design, the shaft for the prop is set at 14 deg and the motor would set mounted the same angle as direct drive. Now if I were to put the prop shaft at 9 deg which is a better angle for speed and made a chain sprocket to fit the 1" shaft, then esentially I could turn the 2 stroke PWC eng backwards monte on top of the prop shaft at the same angle with a reduction sproken on the end of the engine output and drive the prop shaft with a chain correct?? That would give me a better prop angle, lighter eng, gear reduction for the high rev motor, and the eng is already marinized(vs converting a automotive motor). Opinions???

Hi Mr Sik.
Sounds feasible, but you might be better off with a toothed rubber belt or serpentine rubber belt than the chain. Chain would be noisy and prone to rust. You also would need to add a bearing onto the shaft to take the side load imparted from a drive belt or chain. Does that engine run the right way?

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By the time I have built a boat, I'll be ready to build a boat....

Yea I was thinking about a gimler belt as well. Problem being is finding the right size as it would be pretty short. I do beleive that the are right hand rotation in which I would need a lh prop but they do make left and right rotation props. Supporting the prop shaft is a concern as well. My neighbor is an engineer and I've been plugging him for advice as well.

great idea for going backwards.

The engine running 180 degrees from it's factory install and using the stock output shaft side of the engine would mean the rotation would be reversed in respect to the impeller.

A gilmer is easy to find in about any size you are willing to pay for. a 2" wide would handle anything you are going to find in a PWC. Alignment is ultra critical to power handling capacity. The load needs to be evenly applied to the belt. Gilmers must run true, they don't react well to being pushed back into place by an idler.

The shaft of the pump was designed with a thrust bearing intended to support the forward driving load of the pump shaft. It was not designed to support the lateral loading of the belt spinning it. Typically they use a pair of captive small needles, and a thrust bearing running in an oil bath. Sufficient for driving an impeller that just basically pushes forward, but add 100hp trying to rip it out of the top of the pump housing, and there is a whole new dynamic the factory never built it to survive.

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Some plan to stroll through Saint Peter's Gates, I plan to go through them at 150mph... backwards... in a screaming ball of flame, with a glimmer belt wrapped around my head, and a NOx button in my hand.

Your idea of the chain or belt drive is a good thought and it will probably work well, but I would recommend keeping the shaft angle near 15 degrees and here's why. My tiny might had a 10 degree strut and shaft angle and the boat would ride flat and smooth in a straight line, but when turning it would plow the front portion of the hull bad enough that the person riding on the inside of the radius would get soaked every time! I tried adjusting the cavitation plate to eliminate this and even with the plate up beyond the plane of the bottom the boat would still bury the bow in any turn. I then changed the strut angle to 15 degrees and the bow rides a little higher and when turning it does not bury the front portion of the chine, now we don't get wet in a turn. I didn't notice any speed loss with the increased angle, just a better handling boat.

Gates Rubber had a project making toothed belts (cog Belts) for Ocean going boats with Diesels. You might look that up.
I like the idea of Chains. Making the tension equal on multiple Sprockets is really tough. That along makes a Cog Belt look good.
But lube, Rust, stretch, mungelulena in the Chain case and maybe noise might make you project a mess.
If the tension is not equal, you have only ONE chain at a time pulling the load.

Snow machines use a chain final drive running in an oil bath. There is a given amount of reduction ratio in their final drive, it's not a 1:1 ratio, however, all of the power handling requirements inherent in the snow machine application would be parallel with those of a marine drive. It would work fine, and many of the components are off-the-shelf. An oil-immersion type case would simplify alignment, or more, maintaining alignment.

Without using an oil immersion system an unsealed roller chain, and associated components are going to short lived, and a link-belt is out of the question. Water penetrates the chain, the pins oxidize, the chain breaks. I guess you could soak it with MC chain lube, but what a mess that would be. O-ring chain would do better, but you still have a rust/wear problem with the sprockets.

Gilmers are noisy, really noisy. The wider, and flatter the teeth, the noisier they are. Drive cogs from blower drives may be adaptable with a reasonable amount of machining talent.

In any case, you still have to deal with figuring out how to deal with the bearings on the shaft. You would be applying a lateral force to a bearing never constructed to handle lateral loads. A secondary shaft with a pair of pillow blocks maybe? The concept is fun to play around with, but not very practical.

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Some plan to stroll through Saint Peter's Gates, I plan to go through them at 150mph... backwards... in a screaming ball of flame, with a glimmer belt wrapped around my head, and a NOx button in my hand.

Most 4x4's have Chain drives to the Front output shaft as well. They live in an Oil bath and normally last the lifetime of the Pickup.

A more costly (potentially) option is hydraulics. You could use a pump on the engine mounted where you like and a hydraulic motor attached to the shaft directly. Have to add a reservoir and hoses and a control valve, but it should be do-able. Might have to add an oil cooler as well.
New stuff would cost a big sum, but if you hunted around bits might be available cheap. Critical would be choice of hydraulic motor to match the shaft speed at its best output.
Lots of options for you.

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By the time I have built a boat, I'll be ready to build a boat....

Here's an old post in the Electric Power thread :

http://glen-l.com/phpBB2/viewtopic.php?p=62067#p62067

For used snowmobile parts, try Al's Snowmobile Parts Warehouse in Newport, VT.

Heck, Caber might even have some parts up in Tundrasota

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Paul Kane
Kane Custom Boats Ltd.
Chelsea, Quebec

Building the Glen-L Hot Rod : http://www.kanecustomboats.com

Glen-L Boat Video Directory : http://www.kanecustomboats.com/pages/vi ... ctory.html

Hot Rod brought a question to my mind

Watts in equal Watts out!
Comparing 1, an Engine driving a Hydraulic pump, with a Hydraulic motor on the shaft.
To 2, an engine driving a Generator with a variable speed Electric motor on the shaft.
One will be less costly in overall operation. Not including maint costs!

And the other:
3, A set of Chain sprockets for chain drive to the shaft.
And 4, a big wide Cog Belt driving the shaft.

I know there's a guy with a slide rule that can tell us which is the best choice!

Thud, you'd have to do some research to come up with the best drive system. Sometimes it boils down to what you have in the parts bin !

Here's a photo of a chaincase for a 1968 Ski-Doo Olympique. The drive axle (bottom shaft in photo) has been cut. I hate butchering good snowmobile parts, but we're building a boat here, so I guess it's OK ... A coupler would mate the shaft to the prop shaft. The upper fixed pulley half will be removed. A coupler will be required to adapt the shaft to the engine.

Another option would be to cut the chain case, rotate it 180° and reweld it to make a Z Drive ...

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Paul Kane
Kane Custom Boats Ltd.
Chelsea, Quebec

Building the Glen-L Hot Rod : http://www.kanecustomboats.com

Glen-L Boat Video Directory : http://www.kanecustomboats.com/pages/vi ... ctory.html

Good looking stuff. Made as Frugally as possible and works well too.
I'm glad for your photo because of the "Scatter Shield" to protect the operator from a chain parting.
That chain looks like a Motorcycle chain for 125/350Cc bikes.

I planned to make my Riding lawn mower work off a Chain that size.

In a Boat you'd have to align for side-side and up-down variables or you'd have way too much chain wear and noise.

you would need a thrust bearing on the prop shaft to accept the prop thrust.
Why worry about reverse rotation? Just get a prop to suit.?
In any of the chain or belt drives mentioned, is there a neutral or reverse in it?

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God Bless our Troops; especially our Snipers

On the Cog belt drive, which would be the same as a Chain drive....
The engine and Reversing gear were mated.
Sitting above and to the rear of the shaft.
The Cog gear shiv on the end of the reversing gear, and the shaft had a shiv right below the end of the reversing gear.
Yes there's a Thrust bearing on the shaft to keep the shaft in one place fore n' aft.

Replacing a Cog belt was easy. Thumb screw on the Chain case cover lid. Cog belts don't need a tensioner if the 'distance' is set up right the first time.

I'd bet a gang of chains would be similar.
With Chains, the 'stretch' or 'wear' would eventually make all the chains pull in concert. I think...