Ski jet in boat

Just a thought!

Would it be doable to install a ski jet in a small boat?
Am thinking about using a motorbike engine..
V2 1000cc from Suzuki 4-stroke. 132 hp
A normal Seedoo jet(with reverse bucket) use a 2-stroke engine developing some 130 hp.
A gear will have to be made, to compensate for the higer rpm of the 1000cc.

Does the 1000cc have the ba... to swing the jet??
Do you think I need more torq?

Moreover is a jet a poor performer, compared to, say a bravo drive on the same boat?

Any info is appriciated

Morten

You might find this site interesting: http://jetjon.homestead.com/page1.html - this is a small site about using jetski engines and drives in jon and other small boats.

Moreover is a jet a poor performer, compared to, say a bravo drive on the same boat?

Yes - a prop is more efficient than a jet. But the advantages of a jet - shallow water capability, safety for people in or getting into and out of the water near it, turning characteristics, etc. might make it worth while.

The 130 hp jet drive could probably be replaced with a 75 hp outboard and get about the same speed. Definitely a 100 hp outboard would get the same top speed as the 130 hp jet drive.

Thanks alot guys..

Nice link!

Are jets really that bad, performance wise??
I mean 75-100 hp on the same boat, as a 130 hp jet?!

Fuel costs are bad enough as it is, don't want to waist fuel on 30 hp not putting in "any" work!

Is it just ski jets that are that bad, or would a real jet(hamilton or what ever) be better?

Morten

[Portager]

The performance comparison of jet drive to propeller drive varies with speed. Assuming a properly integrated drive and a properly sized jet, the jet will generally be more efficient (defined as maximum speed versus horsepower) at speeds above 20 to 25 knots. Because of the lower efficiency below 20 knots it typically takes jet boats significantly longer to get up on plane giving the impression that they are slower.

The jet pump unit must be carefully sized to the engine power and torque curves. The intent is to fully utilize the available power without ever overloading the engine. Overpowering a jet is similar to overpowering a propeller, you will cause cavitation which will waste power and eat blades. You wouldn't increase the power in an inboard without changing props and you can't increase the power to a jet without changing the jet pump. The trick is you can't just change an impeller you need to increase the flow area, so you need a new housing and impeller (i.e. different pump).

Cheers;
Mike Schooley

Now you have me splidt!!

But I am thinking, if jets are used on big fast ferryes, they can't be that bad.
I mean they are used for houres on end, and even just 5% better effecienty from a prop would translate into big $.

Can't you just up or down the RPM of the impreller to match the engine to the jet. (within reason!!)

MOrten

[Portager]

In the speed range of 25 to 45 knots jets are more efficient than submerged props, therefore they are a good choice for craft that operate in that speed range. Craft that operate at the low end of that speed range may not have the excess power required to get up on step and could take a long time to get up on plane. Could I interest you in a "Rocket Assisted Takeoff (RATO)" propulsion option? I always wanted to design a gasoline burning, air breathing rocket engine.

Unless the jet drive was originally oversized (and they all are oversized a little due to the production pump granularity and to allow for altitude effects), it would be close to the cavitation limit at maximum design power. You can increase power up to the cavitation limit, but if you go beyond the cavitation limit you will not get more thrust, you will just be throwing the excess power away and reducing impeller life.

Cheers;
Mike Schooley

[tom28571]

There is an article in the July issue of the trade journal Maritime Reporter that describes tests of jets and Sea Rider surface drives on the same boats (49ft x 20 tons). The surface drive outperformed the jet by a big margin at all speeds up to 40kts.

Tests were run by the Tiawan Coast Guard.

[Portager]

I specifically stated that jets were more efficient than submerged drives. I didn't want to cloud the issue with surface drives, but you are correct a that speed range a surface piercing drive should be more efficient that a jet.

Cheers;
Mike Schooley

What happends after 40 knots??

I'm guessing a surface drive would be better??!

Morten

[lockhughes]

Wonder if the Tiawan Coast Guard folks were trying these?

Marine JET Technology Corp
innovative technologies improve jet performance by up to 80% at low boat speeds, while also increasing top speed, fuel efficiency and cruising range. These patented methods mark the most significant advance in marine propulsion systems in many years

http://marinejettech.com/welcome.html