Alternative power plant for inboard jet boat

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Nick - 19 Jun 2006 10:31 GMT

I'd like a few thoughts on this seemingly crazy plan.

I've come into possesion of an inboard jet boat with no engine, around 16ft
long.

The idea is this, purchase an outboard engine (just the top part or one with
broken gearbox or something, you get the idea)
and use it as an inboard engine, it would be around the 220hp mark that I'm
looking for.

It'd be a lot smaller and more fuel efficient and easier to maintian as far
as I can see, but would like to know if there are any issues with:

-Turning the engine 'on its side' so to speak
-Would a 220 hp outboard engine be powerful enough to drive the impeller?
-I'm assuming with a custom frame or something it shouldnt be too hard to
actually mount it in the boat, the engine space is massive for it.

Rgds,
Nick

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tschnautz@gmail.com - 20 Jun 2006 04:39 GMT

it can be done. but there's too many impractical issues to deal with.
on about any outboard, they have a water pump in the lower unit. your
idea would take some interesting thinking concerning cooling, not to
mention exhaust which also is pushed through a lower unit as well.

funny you should mention the idea of a horizontal 2 cycle engine,
Evinrude did that in the mid 60's up to the early 70's (?) making their
first I/O out of a 90 hp. V-4 two cycle.

http://hhscott.com/evinrude/images/480_production.jpg

> I'd like a few thoughts on this seemingly crazy plan.
>
[quoted text clipped - 16 lines]
> Rgds,
> Nick

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MMC - 20 Jun 2006 17:07 GMT

Looks like an overgrown BMW motorcycle engine!
BTW, aren't (most) ourboards horizontal? Is this related to the crankshaft
orientation or the cylinders?
MMC

> it can be done. but there's too many impractical issues to deal with.
> on about any outboard, they have a water pump in the lower unit. your
[quoted text clipped - 27 lines]
> > Rgds,
> > Nick

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Nick - 20 Jun 2006 17:49 GMT

> Looks like an overgrown BMW motorcycle engine!
> BTW, aren't (most) ourboards horizontal? Is this related to the crankshaft
> orientation or the cylinders?

With respect to a car engine etc the cylinders are horizontal, shaft
vertical. My main concern is the carbs if you turned the engine around
etc....

Rgds,
Nick

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Nick - 20 Jun 2006 17:47 GMT

> it can be done. but there's too many impractical issues to deal with.
> on about any outboard, they have a water pump in the lower unit. your
[quoted text clipped - 6 lines]
>
> http://hhscott.com/evinrude/images/480_production.jpg

Thank you for the words of advice,

I do realise I'd have to fabricate some kind of cooling and exhaust output,
but I don't think it's outside the realms of possibility given a few
tools/bit of knowledge.

My thinking is it'd make the boat a lot lighter/faster, use less fuel and
simply be an interesting thing to try above all else. Does an 80hp mercury
have an sump etc btw, I think it's a 2 stroke but I'm not sure.

Rgds,
Nick

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Boat Forum / Building / June 2006

Alternative power plant for inboard jet boat