Jet Powered Tiny Mite

About using jet ski motors to power small boats

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Ray Burns
Posts: 2
Joined: Sun May 04, 2008 3:38 pm

Jet Powered Tiny Mite

Post by Ray Burns » Sun May 04, 2008 4:16 pm

Good Evening all,

Terry,Steve,John,Nate Congrats on corrupting another innocent perspective boatbuilder. I have been drooling over your boats for a while now!! beautiful work too all.

So now I am planning on my build for a jet Tiny Mite, I love the look of the gentelmans racers, and am wondering on the hull weights after modification of Squirt and TNT's for the jet (motor stringer, lengthening, etc). As these are things I wont have to do to a Tiny Mite. Did your hulls come close to the Tiny Mites catalog weight of 250lbs. I'm thinking that I could lighten one up by going with a flat deck, no coming. and maybe dropping the motor stringers down in size from 1x6 due to the light weight of the jet ski motor? I plan to build it mid engined with a 2 piece driveshaft and u-joints, to keep the front shaft parallel to the keel, keeping motor low in the hull.

I just picked up a Kawasaki 650sx and am wondering if this will be enough motor for this hull weight, wider beam, and v design.

Well I think that is enough Q's for my first post hehe.
Thanks,
Ray
If at first you DO succeed...Don't look so suprised!

terrymc
Posts: 579
Joined: Wed Feb 23, 2005 11:05 am
Location: San Jose, CA, USA

Post by terrymc » Sun May 04, 2008 5:38 pm

Ray,

Welcome to the deranged...

My hull came it at right around 150. Honest - I think a 650 Kawa might be a little on the small side. The Tiny Mite original design looked at something like 80 HP (a Greymarine 4, and a 650 Kawa is in the 50 Hp range.

The other issue is CG - the 'Mite has the engine forward of the cockpit (and the engine is significantly heavier). I suspect that you would need a modified drive shaft with the jet under the seat.

I'll let the other guys chime in - my initial reaction is this is a challenging mod. Don't let me turn you off - that'snot my intent. Just know what you are getitng into.

Peace,

TRM

Ray Burns
Posts: 2
Joined: Sun May 04, 2008 3:38 pm

Post by Ray Burns » Sun May 04, 2008 7:47 pm

That was the plan. Engine up front with the drive shaft running under the seat to the pump. I like a challenge, besides you guys have the whole jet Squirt thing figured out, so I thought I would do something different.

The note page in the catalog shows the Grey marine install at 45 HP and it states 60 HP as the average for motor installs. I've built my share of 2-strokers over the years and am shure I can get a few more horses outa the 650.

Is there and efficiency difference calculation for props vs. jets? do props give more thrust, or do jets, for the same HP? assuming both are optimized with the correct pitch for there design.

Do you think a light jet ski motor (catalog calls for less that 300) would cause the 'Mite to trim down at the transom excessivly when loaded with driver and passenger, or would I have to worry about handling issues at speed? I thought lighter would be better.

Maybe I'll keep looking for my motor/jet combo for this project, but I could not pass the 650 up for the price. Anyone know if all seadoo pumps have the plastic wear ring in the pump?

Ray
If at first you DO succeed...Don't look so suprised!

upspirate

Post by upspirate » Mon May 05, 2008 4:59 am

I had thought about this same config.

I wonder if there will be enough room on either side of the pump to sit,as I don't think you'd be sitting forward enough to be over the shaft.(anyway,the shaft would be at almost the same height as the pump)
I think that to have the seat over the pump would make it too high as this is quite a small boat.

I believe I'd use a bit larger engine too.

As far as balance,you could always put the fuel tank under the fore deck,& with seating weight aft,it would keep the pump loaded with water I would think.

Denon Osterman
Posts: 554
Joined: Thu Jun 22, 2006 8:58 am
Location: toronto, CAN

Post by Denon Osterman » Mon Oct 06, 2008 10:09 am

heres my 2 cents, if anyones still even following this thread...

1)the 650 will get your boat on plane(though maybe just barely..depends how much you weigh. 35 hp got my TNT on plane with a full tank of gas, 180 pound motor, 150 pound hull, and like 350 pounds of passenger weight...but see question 3). the real question you should be asking yourself is how fast do you want to go :D

2)weight too far back will not be an issue for speed, but rather porpoising...which can be easily fixed either by relocating weight up front or, preferably, adding cavitation plates(or, if youve got a couple hundred lying around, you could opt for trim tabs...but you dont need them)

3)as for which is more effecient, the official glen-l book says they're equal. heres the deal though...props slice through the water, pushing the boat forward and water backwards. jets shoot a ridiculously large amount of water out the back of the boat. top speed and effeciency, in debate, usually go to the v drive. acceleration, without a doubt, will always go to the jet...because as soon as you hammer the throttle, its spinning full RPM and putting out as much thrust as it can, whereas the prop has to spool up, get over the load of planning the boat, etc. jets also have far better manuverability, are far simpler, and much cheaper...what i guess im trying to say is that the difference in speed will not be as noticable, especially at your speeds, to really matter as much as any of the other stuff. once you get up to the much higher speeds, however, such a high volume of water must be shot out the back at such high speeds that jets start to lose out to props, which, for a number of reasons, start to win over.

sorry that was so long, there isn;t really one that's better, they just offer different things. for example, skiing behind a jet is probably not as good as an inboard, because inboards create a much better wake...then again, you cant get a rooster(which, though for cool factor only, is extremely cool) with a v-drive. sounds like you've settled on jet propulsion anyways though, so maybe all that was for nothing :?

Denon

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