CVT scooter motor as inboard?

About inboard or outboard motors.

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sproggy
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CVT scooter motor as inboard?

Post by sproggy »

Maybe it's the result of prolonged confinement at home driving me slightly crazy but I'm back thinking about a way to make my barrelback Zip something other than outboard powered....and to come up with a solution before my build progresses beyond the point of no return as far as hull construction is concerned.

Ignoring weight distribution, has anyone considered using a scooter drivetrain as a miniature inboard? A Piaggio Beverly 350 has 30bhp (plenty for my needs), is designed to operate in wet conditions, is compact (most importantly, not tall) and light, is economical and has a closed cooling system. This is a scooter that can be ridden flat out on the motorway at top speed for hours on end (fuel stops permitting) without issue so occasional flat out use in a boat shouldn't challenge it too much.

Twin electric raw water pumps (for redundancy), a heat exchanger for cooling and a water jacket on the exhaust. Plus an electric reverse, probably running chain-driven to the prop shaft via a centrifugal clutch to decouple the electric motor when running forwards. I see the CVT as an advantage - I should be able to use a relatively high pitch prop and let the gearing adjust itself for acceleration as required.

Anyone want to tell me I'm crazy and that I should go shopping for an outboard?

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Locutus
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Re: CVT scooter motor as inboard?

Post by Locutus »

I'm no expert on marinizing engines, but it seems to me that the critical difference between full throttle on the highway and full throttle in a boat is that on the highway you're basically coasting and only fighting wind and rolling resistance. In a boat you're always pushing tons of water out of the way as you push through it or plane over it. So the load on the engine is higher in a boat than on a scooter. My two cents. (Worth exactly what you paid me for it. :lol: )

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sproggy
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Re: CVT scooter motor as inboard?

Post by sproggy »

I ride a Vespa GTS300 to work. It's not as powerful as the Beverley (far cooler though 8) ) but otherwise comparable. At full throttle on the open road you're doing around 80mph with the little motor fighting against wind resistance (which is significant at that speed - motorcycles and scooters aren't at all aerodynamically efficient) and revving as high as the gearing will allow it to. It's got nothing left to give and it's definitely not coasting! If you're asking for everything the motor has to give is it any different on a boat or on the road?

In the UK there's little opportunity to run at planing speeds inland anyway which is why I'm less concerned about the effects of running flat out for extended periods. It's enough to know I could do on a rare calm day on the sea - most of the time it'll be running at sub-10mph. Actually, most of the time I could make do with a Torqeedo.....

TAB
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Re: CVT scooter motor as inboard?

Post by TAB »

What rpms do they run at? I would be worried you could not spin a prop at the correct rpm

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sproggy
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Re: CVT scooter motor as inboard?

Post by sproggy »

The Vespa motor has peak torque @ 5,000rpm and peak power @ 7,750rpm.

By my rough calculations the rear wheel is spinning at around 1,436rpm @ 80mph.

The missing information is what the engine speed is @ 80mph - there's no rev counter and the gearing is variable. But most sources reckon it is at or slightly above peak power - around 8,000rpm. So an effective gear ratio of around 5.57:1. Which probably means you're right about it not spinning a prop at the right speed - it would need to be running at double that speed. So the only viable way to use a scooter motor in a boat would be to take the drive off the engine output shaft, not off the final drive, and run it through a marine gearbox.

Sounding like a less appealing idea.....

JhlFin
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Re: CVT scooter motor as inboard?

Post by JhlFin »

It might not be that bad idea, probably needs lot of testing and tuning. I'm no expert at cvt:s but in know those can be modded to work on diffrent applications with weights and springs. You could also use chain drive from cvt to propshaft and do gearing there as needed. If you have tools and materials available, i would try atvleast :) Are you planning to run your boat trough uk canal system? Looks cool place to boat, i just watched videos of canal boating and i wondered why there were only those weird canal house boat things :D I guess canals have low speed limits?

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sproggy
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Re: CVT scooter motor as inboard?

Post by sproggy »

It's true - chain (or toothed belt, Harley style) off the rear hub would be able to 'correct' the gearing to something more suitable. It would also allow the motor to be mounted more central in the boat rather than offset to one side.

Our canals have a 4mph speed limit so a narrowboat (weird canal house boat thing) is more limited by the speed limit than by its own hull speed. I doubt my Zip will spend much time on canals - doing 4mph in that sort of boat is too frustrating and in locks there is a risk of such a light boat being damaged either by impact with the walls or being crushed by much heavier boats. Even on inland rivers/lakes there's little prospect (legally) of doing more than 10mph - estuaries are the only place it'll be possible to open it up properly on calm days. Hence me not being overly concerned about sustained top speed. At least until I fulfil the dream of moving to Cornwall on the Fal estuary.....

Hercdrvr
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Re: CVT scooter motor as inboard?

Post by Hercdrvr »

Scooter engine in a boat....no

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