Need help with small jetski powered boat

Hello everyone,
I am wanting to build a small (10 feet ) boat using a jetski engine and drive I have. Is there anyone elso doing this that could help me out. I need help with the design of the bottom of the boat so the jet drive works right.
Also looking for help with the balance of the boat. I know the 1/4 scale weedeater powered boats I have built work best with the cg at 30% from the rear. Not sure if this would be the same case as full size boats.
Any help would be greatly appreaciated.
-Tony

 

You want the inlet as far aft as you can get it and depending on inlet design you may have to create a FLAT spot. The front of the engine will end up where ever. You can then determine CG and can put weight forward if needed or small trim tabs on the transom. On a larger 10' boat frame just put in the power unit and adjust later after trials. Stan

 

Stan,
Thanks for the info. I would like to put the engine mid mount ( in front of the drivers seat ) and extend the drive shaft to the jet drive.
Do you think I would have problems with that?
-Tony

 

Would really need to see your boat plan to give advise on that. Howerer, putting the engine in a central position is a good idea. I thought it was a complete unit jet and engine locked together. After you flip the boat over you can find the CG as it is not a heavy boat. 3 friends and an attached strap will give you the balance point. Placing the engine there or slightly forward is usually OK and balance weight with fuel tanks, battery etc. After trials you may need trim tabs or more weight fore or aft. It is not a major problem. A center engine boat is a good design--So get started............Put a protective sleeve around your shaft in case it blows.
What plans are you using?

 

I am using a complete jetski unit. I don't have it out of the jetski yet so I am not exactly sure how they are hooked together, but I am a good fabricater (I scratch built a single seat helicopter, among other things) so splitting the engine and jet drive and building a drive shaft shouldn't be too tough.
As far as plans- I don't have any yet, but I really like the Tiny Might. A little longer than 10 feet, but thats ok.
https://www.boatdesigns.com/products.asp?dept=262
http://www.glen-l.com/designs/inboard/dsn-tnm.html

Do you know of any others that would work good?
Also if anyone has a set of Tiny Might plans that they are not using I would be interested in them.

Thanks again you have been a big help.
I am ready to get started.
-Tony

 

Tony
If you want to do some analysis of the expected performance then this link will be useful for your proposed hull:
http://illustrations.marin.ntnu.no/hydrodynamics/resistance/planing/index.html
You could check out how your model performs against this data. It is quite simple to use. If you hild the curses over figure it opens a sketch that shows how the various parameters relate to the hull.

I think you will find the 30% figure for your lcg is in a good range. Bringing it aft can usually reduce to end drag but you get higher low speed drag.

It is possible to optimise the outlet and inlet size for your jet but I do not know if you have this included in your scope.

Rick W

 

sharpie

look at hamilton jets new zealand.

 

Hey man i have a rough design for a 12' boat i can shoot you

 

Grantus,
Sorry it took so long to reply. I have been away from my computer for awhile.
I would be interested in that rough design your were talking about.
12 foot is about the length I was shooting for.
Thanks,
Tony