Jet designs

[Skoontz]

This is a Jim Rich or jet guy type question, so here goes....

I was out doing some windshield time today and my brain got to going....Jets typially take in water through what I will call a hole in the bottom and squirt it out.. Now as we all know, the faster you go, the greater the friction, thus the need to get more boat out of the water to reduce the drag....Since the jet sucks itself into the water, there is only so much boat you can remove from the water without wrecking the amount of thrust it can give....So, the question....

Has anyone ever tried building a jet that bolted entirely behind the transom? You would use an intermediate drive like a lower unit boat does, then connect the jet? I know, that sucker would be hanging over the back a ways...But, it could get boat out of th water, whilst allowing the sucker to suck so it can squirt water..... Same basic design as a through the bottom jet, but this would mount kind of like a lower unit boat, the intake just behind the transom, then the thruster behind that to make the boat go....You could even get kind of crazy and add trim to the whole thing....

Has it ever been done, and is this too warped to even concieve, or does it have possibility? I'm thinking with as hard a a jet comes out of the hole, it could raise the top end for dragging....

[Mark75H]

Jet drive stern drive? Cool idea, never seen it done or proposed.

Couldn't you just put an aftermarket jet for some big outboard on a similar stern drive?

[Skoontz]

Sam, as I'm thinking through this thing (sometimes I take breaks from work to get a break and end up thinking about working on things) I belive jet intakes sit under engines and through the bottom they go....Then, the driveshaft to the pump, and the droop snoot type pump which Jim showed me at Bakersfield....So you have some type of affair that theorectically is 4' long and runs sort of at an angle, because the boat bottom is lower than the thrust hole....

I'm envisioning this thing would almost have to have the intake mount just under the thrust hole/pump. A big two stroke outboard could be a fun toy on this bad boy like a 3.0 Merc or even an old V-8 OMC...If only I had to money to put some of these brain farts I get into models....The Skoontzenator comes to mind.....

Jim, where you at on this??????

[Mark75H]

Have you seen an outboard jet? Seems like that is what you are describing??:confused:

[Skoontz]

Not up close and personal, but in pictures, yes....The signifiant difference here is the outboard would have alot more hanging in the water. Ideally, the intake would be right at the surface, perhaps even using some type of very shallow sterring fins to funnel water into the hole. I'm after reducing drag here, which, I think mounting the unit after transom would allow the boat to hang........Trim would give us bow lift...I could see the danger of a blow over in the horizon....Maybe large afterplanes could handle that.....

[iwanajohnson]

Save a hole lot of time and effert and get a outboard jet. they mount behind the transom, they have tilt/trim, no need for ruders, the shoe (sucker) sets down in the water but the pump dosn't so it has no drag and they make fins to direct water in but it looks like it would create more drag than their worth. go to www.outboardjets.com this might help. Hope this helps some.

[ePerformanceMarine]

Sam, as I'm thinking through this thing (sometimes I take breaks from work to get a break and end up thinking about working on things) I belive jet intakes sit under engines and through the bottom they go....Then, the driveshaft to the pump, and the droop snoot type pump which Jim showed me at Bakersfield....So you have some type of affair that theorectically is 4' long and runs sort of at an angle, because the boat bottom is lower than the thrust hole....

I'm envisioning this thing would almost have to have the intake mount just under the thrust hole/pump. A big two stroke outboard could be a fun toy on this bad boy like a 3.0 Merc or even an old V-8 OMC...If only I had to money to put some of these brain farts I get into models....The Skoontzenator comes to mind.....

Jim, where you at on this??????

I was wondering what that smoke was !:eek:

As I think I showed you we run loaders and shoes under the boat to grab more water while reducing the drag with hull lift. We also run set-back pumps thus letting you air the hull out more to reduce drag, while running a shoe and loader.

[RichardKCMo]

You guys lost me when you moved that 500+# iron behind the transom cause 2 strokes sure makes more of what is is, and they didn't even ask that cigar girl , i guess like Roger Miller said way in the back.!!!
RichardKCMo

[Skoontz]

Yes, Jim. I remember. The jet technology of today is light years ahead of the days when every day cruiser under the sun had a 455 Olds hooked to their Berkley....

But, condsider that if there was some way to put all that stuff behind the boat, and the ability to lift, or trim the pump, with nothing under the boat sucking you in. It would all be behind you.

Have you ever heard of such a thing, and/or does it sound like knit wittery, or might this just be a way to gain more speed?

[Moneypit]

Look over on hotboat. There is a thread about a 95 MPH "Eagle" cruiser type with the jet stuck way out the back.....Looks just like what you are discribing........MP

Search "95 MPH boat"

[Skoontz]

That's what I'm talking about...I guess someone already thought of it....

[Michael J Gwaltney]

Not up close and personal, but in pictures, yes....The signifiant difference here is the outboard would have alot more hanging in the water. Ideally, the intake would be right at the surface, perhaps even using some type of very shallow sterring fins to funnel water into the hole. I'm after reducing drag here, which, I think mounting the unit after transom would allow the boat to hang........Trim would give us bow lift...I could see the danger of a blow over in the horizon....Maybe large afterplanes could handle that.....
I am not clear on your goal using a jet. Hard to match propeller speed unless you use gobs of hp and fuel.
US Military has used Varney jet units on military outboards for many years. The varney looks simular to a production gearcase and must be pretty durable. Military likes them for deploying and retreiving troops at high speeds reducing possible prop rash and shallow water (beach) operation.

[Skoontz]

Michael:

I'm not really sure what any gain would be, except that concept of getting more boat out of the water for speed. Jets come hard out of the hole, and if one could supply enough power, could be a petty hard combo to beat in a drag. Say take Plan B's motor, not sure of all the hard parts, but appears to be about a 500cu in motor, 12/71 blower, enderlie bug catcher...He comes out of the harbor at a low throttle and the engine speeds up then down up then down, just like a nitro motor in a dragster.... KT and my favorite GN, they're all good, but that ones got class... so hook that thing up and squirt come water.... You would have to strap in in order to punch that thing, then pray your organs don't get bruised from the thrust....

Never been a big jet fan, until Jimm his wife, and Amanda Rich pitted next to us and he gave me the grand tour of all the updated goodies jets are running these days....Then my mind wandered, just like with the 6 cylinder sort of radial outboard. There's some pretty fun possiblities, especially when you are drivng down the road, the music on the radio at the time stinks, with nothing better to do...