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Old 05-12-2005, 10:08 PM   #1
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Why not use an motorcycle engine?

Hi, im pretty new at this forum, so this will be my first post.
Im coming from Sweden, so you'll have to exuse my bad english.

Im thinking of using an suzuki gsx-r 1100 engine in an, as small a possible, sportboat. Reasons are great power to weight ratio.
The only really problem i can see, is the transmission (dont know the correct word for it, but in sweden we call it "drev") since the engine runs at quite high rpm's.

Have this been done before?
What do you think, is it a bad idea? I really cant see why.
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Old 05-12-2005, 10:17 PM   #2
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I've always liked the idea of a motorcycle engine (or two) in a small cat!
Although the engine rpm is likely to be very high, could you not use the motorcycle transmission (gearbox) to reduce this to a usable speed? maybe even use different ratios for different sea conditions.
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Old 05-12-2005, 10:23 PM   #3
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Coorrr!!! sounds like a good idea to me! Imagine trying to get props for it though! You'd ring the friendly prop salesman and say "My engine revs to about 15'000rpm can you help me out at all?"
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Old 05-12-2005, 10:26 PM   #4
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what about a small 125 engine??
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Old 05-12-2005, 10:31 PM   #5
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No No No Mr rob! Its half the fun to have an engine thats to big for the size of the boat! Like john said maybe a 16-18ft cat with a BIIIGGGG Revvy engine !
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Old 05-12-2005, 10:40 PM   #6
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Gav has a little boat for his nipper. Its about 10ft I think. Would be cool with a small engine like a 125 for running around on the river.
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Old 05-12-2005, 10:45 PM   #7
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Good response on this forum!

15.000rpm is a lot, that's what most 600cc rev, the 1000+ cc bikes usually rev about 10.000.
The 1100r engine produce 155hp@9500rpm.
The hayabusa, about 175hp@9500rpm.
Not to mention turbocharging theese engines, they'll be weicked with a little modifications!

It cant be too hard to find a solution for the gearing.
Have anyone seen this in a boat before?
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Old 05-12-2005, 10:47 PM   #8
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oh no got a 650 jetski engine to in that unless we can talk our mate into letting us fit his 1300 jet bike engine in it
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Old 05-12-2005, 11:01 PM   #9
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Quote:
Originally posted by s.strömbäck
It cant be too hard to find a solution for the gearing.
Have anyone seen this in a boat before?
There was a small cat racing here a few years ago with a pair of Norton Wankel rotary motorcycle engines mated together, but they never really got the drive system (surface drive) set up right and it had a little too much stern lift. Made plenty of power tho'!

I can't see why the motorcycles' own gearbox wouldn't work, at least as a economical way of getting it going for testing.
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Old 05-12-2005, 11:11 PM   #10
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One of these motorcycle engines would be ideal.
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Old 05-12-2005, 11:12 PM   #11
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Yeah, i agree with you. The gearbox from the bike would perhaps work.

But what i wonder, is at which rpm's i want my prop. to run? I guess that depends on what propeller I use? What is reasonable?

Once i figured out that, i know wich gearing i need in the "gearbox".

I'll post a link to a swedish project, where the guy is bulding his own transmission from a volvo gearbox (from a car).
http://forum.savarturbo.se/viewtopic...ighlight=b%E5t
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Old 05-12-2005, 11:19 PM   #12
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Quote:
Originally posted by s.strömbäck
But what i wonder, is at which rpm's i want my prop. to run? I guess that depends on what propeller I use? What is reasonable?
I would say, in the region of 4000rpm at the prop, but if you employ the motorcycle transmission, you can select whatever gear you like, at least for testing/setup purposes. It would make prop selection easier.
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Old 05-12-2005, 11:27 PM   #13
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IMVHO the key to efficiency is getting the prop tip speed down (drag proprtional to square fo speed and all that). So the rpm and prop diameter are the 2 key points. So I know where you're coming from with 4000 rpm, but I reckon if you could tweak that and the prop diameter down (without increasing appendage drag) it "should" be possible to get efficiency to go up - unless you underdo the blade area so slip goes up too much.

All idle speculation of course - but the motorcyle engine & box idea looks like a good one.
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Old 05-12-2005, 11:39 PM   #14
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thanks for your replies, which boat- and the weight of it, should be taken in concideration too i guess.

I realize that "someone" has to learn once or two things about prop. sizing. hehe
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Old 05-12-2005, 11:54 PM   #15
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Re: Why not use an motorcycle engine?

Quote:
Originally posted by s.strömbäck
Im coming from Sweden, so you'll have to exuse my bad english.
Better than most of them from Up North.....
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Old 06-12-2005, 08:19 AM   #16
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I agree a motorcyle motor in a cat , purrrrrrrfect.
But at the end of the day it's cost effectiveness. the shear expense of having a transmission built is scary. I'd plum for the Suziki or the Kawasaki, aint even touched on getting it into reverse yet, that presents another set of problems if the original box is retained.
I'm know there are several firms in the US that can build to suit but $$$$$$$$$$$$
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Old 06-12-2005, 08:39 AM   #17
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Re: Re: Why not use an motorcycle engine?

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Better than most of them from Up North.....
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Old 06-12-2005, 09:53 AM   #18
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Quote:
Originally posted by Matt
IMVHO the key to efficiency is getting the prop tip speed down (drag proprtional to square fo speed and all that). So the rpm and prop diameter are the 2 key points. So I know where you're coming from with 4000 rpm, but I reckon if you could tweak that and the prop diameter down (without increasing appendage drag) it "should" be possible to get efficiency to go up - unless you underdo the blade area so slip goes up too much.

All idle speculation of course - but the motorcyle engine & box idea looks like a good one.
Anyone know what ratio the lower unit on a F1 motah has?


trouble with going for lower prop speed is, you wind up with bags of pitch and it's subsequent troubles, if you intend going fast.
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Old 06-12-2005, 10:07 AM   #19
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Agreed-good point.
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Old 06-12-2005, 10:55 AM   #20
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What about a 2 cylinder "ducati"-style engine?
Lots of Torque and HP at low revs???
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