Thread: Mini jetboats with Jetski engines

What jet unit you putting in it?

Haven't sorted that jet.
Maybe big ski or used boat?
Don't know much about the boat ones at this stage

Id be lookin at a real big ski one or maybe bore the nozzel.
Also look at max working rpm of both motors, the 4 strokes (skis) usually run a reduction box to get pump rpm back down to 6 or 7k.

Bigger nozzle more out of the hole. Smaller more top speed.

With the extra weight and drag of a boat compared to a ski i imagine a bored nozzle and higher pitch impeller would make the most of it.

No doubt it would work just straight swapsi but might as well optimise pump for engine and boat.

4st skis are direct drive - 8k rpm ish factory.
I've rebuilt a couple if supercharged seadoos and was looking for a NA one when got put onto the Suzuki engine - which is lighter also, let alone so bloody cheap!
My only worry is car engine doesn't go that far rev wise. 7k ish but Scott and others have done the M15a no probs.
The boats actually end up weighing LESS that a ski
Less hull in water also with the boat due to reduced dead rise angle.
100hp through a 6" ski jet with suzuki will net around 70km/hr which is enough
The biggest thing is price of Suzuki engine, heaps quieter and uses about 1/4 fuel - huge number of plus's but would be nice to have another 20hp which the 2st has - even though not needed and the exhaust needs to be watercooled.
Then again - $4k less outweighs downside.
Will prob wire factory ecu in and have engine and running gear for under $1k vs going to a Haltech or similar which ecu alone is 1300 at cost let alone mapping time etc

Ah ok. When i had mine the 4st were just coming out and were pulling over 10 to get the hp.
I doubt the boats would be lighter than the one i had but yea could be lighter than the mega ship skis coming out now.
As far as speed its basicly surface area in the water that holds ya back, and you need x amount to feed the pump and be able to turn not slide.
Way back when i was into skis the world record for speed from a factory ski hull and worked factory pump and motor was 86mph.
Mine did an indicated 78 and gpsed 80mph.
15 min from the cut to Kiateritery beach in anything less than 2 foot chop

Seadoo RXP 2 seater is about 180kg
Guys are building ski motor 3m boats under that.
The dead rise angle on a boat is a lot less than a ski
Typically a boat will be faster than the ski the engine is out of.
There is some gopro footage somewhere from the transom showing about 300x500 of the Intake area touching the water and the rest of the hull 'floating' - pretty cool shot and a lot less than I thought

I still think I need to 'rent' you for a weekend to stitch the origami set together.
Prob work out best hr rate ever for you.
Will talk about it later

K

Im trying too get a M15a running with a Toyota 4af hei off the back of the cam and a carb set up. If it works (cant see why it shouldn't ) it should be cheap as hell.
If your boat weighs under 300kg its going too be too bloody thin IMO.
We have weighed 4 or 5 complete ready too go little boats , properly marinised with engine covers . only the little 8 and 9 footers (550 /750 kawa ) came close to 200 kg.
Mines 3mtr x 1180 with 5&10 mm bottom and 2-2.5 every where else and its 320 with a 100kg motor.

Just going off what mates have built and their indicated weight.

If you get stuck with the ignition/ecu side of things let me know and ill do what I can.
I did conversions etc for about 5 yrs and have it down pat IMO
It's pretty straight forward when you understand how it works as a package

Who's gonna be ya crash test dummy that test pilots this thing?

Originally Posted by savageshooter

Who's gonna be ya crash test dummy that test pilots this thing?

Me!

My hull 95% done : )



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Your actually going to put a motor and unit in this time and not use you Fred Flintstone feet thru the bottom like the last one eh?
Looks the berries mate!

Originally Posted by R93

Your actually going to put a motor and unit in this time and not use you Fred Flintstone feet thru the bottom like the last one eh?
Looks the berries mate!

It's the norm on the coast ain't it? Box of piss and float down the river lol. This one will be sold after test run would change things on the next one in the hull.

Have torn off the front wind shield now didn't look right before straight, going for curved look.

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What motor and pump are you going to use?

The square ugly screens work on a boat that's under 1.4 beam from what I've seen in my research. wrapped which looks good and you lose the corners so to speak