Jet Bullet

About using jet ski motors to power small boats

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DSR
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Joined: Mon Mar 21, 2016 8:11 pm
Location: Allegan, Michigan

Re: Jet Bullet

Postby DSR » Sun Jun 10, 2018 11:43 am

Hi Kyle,

The flattened area in front of the pump intake is referred to as a "delta", and it helps on jet boats and skis to create additional hydrodynamic lift to the v-bottom hulls, and normally the deltas have a couple degrees of rocker to help lift the bow of the boat up for a better running angle at speed since a lot of skis don't have any trim adjustment and the thrust line is above the bottom of the hull instead of below, like the prop boats. So adding it to the keel of the Bullett would be a good thing.
You wouldn't want to flatten the bottom of the hull to match it, instead treat it like it would be "cut" into the bottom of the hull with a decent radius to eliminate any sharp edges to the transition between the two surfaces.

Hope that helps :D

Dave
DSR Performance - Home of yet another jet TNT build :D
Codename "Just A Little....."
viewtopic.php?f=23&t=29753

DSR
Posts: 263
Joined: Mon Mar 21, 2016 8:11 pm
Location: Allegan, Michigan

Re: Jet Bullet

Postby DSR » Sun Jun 10, 2018 11:50 am

This is a decent example........
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DSR Performance - Home of yet another jet TNT build :D
Codename "Just A Little....."
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Captain
Posts: 15
Joined: Wed Jun 01, 2016 4:39 pm
Location: Salisbury, North Carolina

Re: Jet Bullet

Postby Captain » Sun Jun 10, 2018 12:52 pm

Thanks Dave that definitely helps I wasn’t sure if I needed it or not now I will make sure I put a delta into the bottom of the bullet hull very nice model. Good luck on the TNT build.
Kyle
Jet Bullet 1200 Triple 2 Stroke Build
If You Want To Go Fast You Have To Mix Oil And Gas

DSR
Posts: 263
Joined: Mon Mar 21, 2016 8:11 pm
Location: Allegan, Michigan

Re: Jet Bullet

Postby DSR » Sun Jun 10, 2018 7:51 pm

Thanks Kyle, I'm hoping that life slows down pretty soon so I can get back to the fun stuff
And the model I posted was just a Google image I found to illustrate the delta pad I was referring to. :D

One thing I just thiught to ask, have you measured the length of the Polaris powertrain yet? I'm guessing that you'll want to mount the pump as far back as possible for the length and to get the weight in the proper location in the hull (I ended up putting the pump a foot behind the transom in the TNT to get the CofG right with the Honda setup I'm using, but I know your 2-stroke triple is lighter and I imagine it's shorter also.....)
DSR Performance - Home of yet another jet TNT build :D
Codename "Just A Little....."
viewtopic.php?f=23&t=29753

Captain
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Joined: Wed Jun 01, 2016 4:39 pm
Location: Salisbury, North Carolina

Re: Jet Bullet

Postby Captain » Mon Jun 11, 2018 6:05 am

I will get measurements tonight I’m not sure of the total length of the engine to the pump. I was planning on putting it as far back as I could just to make it fit. I’m sure I will have to stretch bullet to the 12’ 1” version. The weight isn’t to bad the Polaris only weighed 585. I would like to keep the bullet as light as possible to make this thing fun to drive I’m hopeing the bigger hull won’t kill the skis performance. I really wish I could tig weld in order to reproduce the needed parts for the back tunnel engine and pump mounts. I thought about making everything out of steel. I know I could do that but I’m worried I get carried away end up with a lot of weight. I’m still doing some planning. I like to over think things and complicate the hell out of them.
Kyle
Jet Bullet 1200 Triple 2 Stroke Build
If You Want To Go Fast You Have To Mix Oil And Gas

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hoodman
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Re: Jet Bullet

Postby hoodman » Mon Jun 11, 2018 6:18 am

I bet it won't end up with much more weight than the original ski. Glen-l claims 140 lbs for the hull! Plus you'll have a wider flatter planing surface. I don't know the power output of the engine you're planning on installing but I'm guessing it's at least double the recommendation. You're braver than I am!

Captain
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Re: Jet Bullet

Postby Captain » Mon Jun 11, 2018 6:34 am

The stock 1200 puts out 130 hp I am doing a few things to squeeze out a little more power.
Kyle
Jet Bullet 1200 Triple 2 Stroke Build
If You Want To Go Fast You Have To Mix Oil And Gas

Captain
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Re: Jet Bullet

Postby Captain » Mon Jun 11, 2018 10:33 am

I have convinced myself aluminum is the way to for the pump I believe I need to construct this first then build it into the bottom of the boat.
Kyle
Jet Bullet 1200 Triple 2 Stroke Build
If You Want To Go Fast You Have To Mix Oil And Gas

DSR
Posts: 263
Joined: Mon Mar 21, 2016 8:11 pm
Location: Allegan, Michigan

Re: Jet Bullet

Postby DSR » Tue Jun 12, 2018 3:35 am

I like to over think things and complicate the hell out of them.


LOL! Welcome to my world Kyle.......

I don't think you'll have much to worry about with the 1200s performance in the Bullet. Fiberglass is a heavy building material for boat hulls. The Honda donor ski that I got for the TNT build had a dry weight of 798 lbs. with only 250 lbs. of it being engine and pump, so the hull with the hardware weighted almost 550 lbs by itself (it was freakin heavy to push around when I was cutting it up to dispose of it...). In comparison, the original TNT plans lists hull weight at 125 lbs. and with the mods I'm doing (stretching the hull 1.5 feet and turning it into a tunnel hull), the new bare hull is estimated at 200 lbs. and dry weight of the completed boat of about 600 lbs. (almost 200 lbs lighter).
Adding to that are the facts of the Bullet being a more efficient planing hull design than the ski, with less deadrise, or V, to the bottom, and being wider than the ski hull, you have a very real possibility of the Bullet actually being faster than the ski originally was (as an example, the Honda donor I got had a top speed around 65-66 mph. When I plugged the numbers for the Honda's engine and pump into my hull design program for the TNT, I ended up with almost 90 mph in the tunnel hull using the same horsepower..... :D )

As far as installing the Polaris power into the Bullet goes, there's several ways it can be done. The easiest way is to graft the center of the ski hull into the Bullet design, which allows you to use the original pump intake tunnel, pump mounting and engine mounts for powertrain alignment. I didn't go that route due to the hull design, and because I wanted to be able to install and remove the jet pump with intake as one piece (like the full-size jet pumps), so I found out that the older Yamaha GP and XL1200s actually use a cast aluminum pump intake duct inserted into the hulls instead of being part of the hull mold like most of the skis (still have to fab a billet aluminum mount flange and adapter to install the Honda pump to it, but that's part of the fun....). There are also companies out there offering cast aluminum pump intakes for the aluminum mini river jet boats that people are building, but those intakes are PRICEY!!
One thing I learned a long time ago, since I'm not a welder, is that a lot of the cost of getting stuff fabricated and welded is the fabrication part. Getting aluminum welded is a LOT cheaper if you do all the fab work yourself and all the welder has to do is welding the pieces together.....
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DSR Performance - Home of yet another jet TNT build :D
Codename "Just A Little....."
viewtopic.php?f=23&t=29753

JasonG
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Location: Camilla GA

Re: Jet Bullet

Postby JasonG » Wed Jun 20, 2018 10:59 pm

This is how I shaped the hull on my dynojet. The boat had a 12 degree deadrise. I started about 2' in front of the leading edge of the intake to smooth out any water flow into the pump.
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Captain
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Location: Salisbury, North Carolina

Re: Jet Bullet

Postby Captain » Sun Jul 08, 2018 6:17 am

That’s a very nice looking dynojet hull thanks for sharing. I have been trying to finish up a my truck build before I start another project I have a bad habit of jumping between projects. So the bullet is still in the planning stages but definitely on the list. I got my father interested in this build now as the boat will spend its life at his lake house so that will help to get this build going and finished in a reasonable time our goal is to have it in the water next summer.
Kyle
Jet Bullet 1200 Triple 2 Stroke Build
If You Want To Go Fast You Have To Mix Oil And Gas


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