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Thread: Brainstorming Jet Powered Cat. Welcome aboard.

  1. #1
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    Default Brainstorming Jet Powered Cat. Welcome aboard.

    I have a 30 hp. Tohatsu Jet and some time on my hands.
    I've been to Boise and looked at the Prototype Powered Traveler, that didn't work that well.

    I've talked to Dick at Outboard Jet about his theories of pushing pontoon boats.
    I've read everything I can find on the 13' Jet Ranger, but want to try something on my own here.

    Proposed plan: purchasing two Aire Tributary 14' tubes, and assorted NRS tubing and fittings, if I don't already have most of what I need laying around here.

    Lash up the tubes with only 20" between them making overall boat width 65"

    Idea is to not give wave coming off inside of tubes enough distance to aerate jet intake. In the 20" between tubes, and infront of intake, fabricate a .125" plate aluminum planing surface angled at about 15 degrees held in place by NRS tubing with it's nose up to raft cross bar, it's tail right at intakes front lip. This might include two side down wings to funnel water into intake, if tubes themselves don't accomplish this.

    OK Jump, in what do you think???

  2. #2
    Moderator AKmud's Avatar
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    I think your idea of a plate to smooth the water will be a necessity. The outboard jet site claims a 10* deadrise is optimal for jet performance. You could even go so far as to shape the plate somewhat (with a slight deadrise) and allow it to funnel the air bubbles away from the intake. I would imagine there will be quite a bit of trial and error to determine the ride height for the motor/plate setup.

    Also, why leave the width between tubes at 20"? You could widen the stance and still have a small plate in front of the motor. I imagine it would accomplish the same task. It may be a bit harder to stabilize though.

    Sounds like a cool project! Make sure and keep us updated with photos as it happens.
    AKmud
    http://i78.photobucket.com/albums/j96/AKmud/213700RMK1-1.jpg


    The porcupine is a peacful animal yet God still thought it necessary to give him quills....

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    Yes, OBJ mentions 6-10 degrees as ideal, however that's for bubbles formed on entire hull bottom rolling back. I wonder if bubbles on small "apron" infront of engine would form that many to need a "V" shape? Most other bubbles formed on tubes will escape to surface before reaching apron, I'd think? I will have to fabricate the transom with adjustments to move engine up and down. My plan of putting tubes close is to keep intersecting pressure waves from tubes, from getting enough time to aerate, causing a lot of froth infront of apron. A concern of this, is pushing confined water in front of apron as speed increases and giving the driver a constant reverse splashing. An underwater video camera would be nice to have. I might have to push hulls with prop first to visualize effect of tube spacing.

    From OBJ:

    "Pontoon boats donít provide a defined height apron of water ahead of the jet intake. The water level between the pontoons varies with speed and load carried. Itís necessary to build an inclined plane ahead of the jet intake attached to the motor mount, about 16Ē wide inclined at about 15 degrees with the leading edge above water level, fully loaded at rest, trailing edge lined up with the leading edge of the jet intake."
    Last edited by 180pilot; 06-12-2007 at 18:17.

  4. #4
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    Default Hydroeye

    Check out... http://members.aol.com/hydroeye/boat.html

    Might help with further ideas.

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    sounds like a good plan. I don't know if 30hp would be enough though. I've seen a few jet powered cats and because of the rounded tubes they arent' the most efficeint boats ever. They all seemed to be just barely on step.
    "When everything seems to be going against you, remember that the airplane takes off against the wind, not with it."
    Henry Ford

  6. #6

    Default Jet Cat

    Also you might want to be thinking about re-enforcing the bottom material of a cat. I don't think a standard raft material will put up with the abuse of scraping across rocks at 20+ mph. Unless you want to be doing a lot of patching I'd be careful. And if you don't want to run it that shallow why use a jet.

    Also think about what it's gonna do in broken water. I think you'll cavitate so much that it wouldn't be worth while.

    Now for ideas. If your really stuck on this idea what about RIGID HULL CAT. Maybe mount a flat bottom out of an old aluminum boat inbetween the tubes. But I think your gonna have a lot of problems with weight. Meaning it will only work well loaded with a certain amount. But maybe you could solve that by increasing and decreasing air pressure in the tubes depending on the load.

    Didn't Mike Strahan try this years ago and couldn't get it to work either. Maybe you could save yourself time and money and see what didn't work for him so you at least don't have duplicate mistakes already made.

    Good luck, if it works you'll probably be a rich man.

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    Your right there. The round shape is definitely not a lifting foil, however the weight of the Aire tubes is only 70# + 105# of engine and what ever I put on it. Since I'm not a marine hydraulic engineer, this will be cut and try. One problem with Aire cat tubes under power, is their upturned ends which can't help lift boat on step as it starts to rotate, like the extended past transom tubes on a inflatable power boats. I might have to extend some transom trim plates to rear. I will also be able to move whole frame forward and back for trim. I'm sure it's enough hp. to get me up. The trick is two, fuel and light weight gear up river...........

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    OH, I forgot the other requirement here,......."Rigid" is not in this project. Boat has to fit in airplane. Yes, I've read about everything Mike and Tracey Harmon have written. They like me, believe there is an answer somewhere.
    Not looking to get rich, just have fun solving a problem. I need the tubes anyway, I have the engine and lots of aluminum, so I'm not out anything but my free time :-)

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    I understand the limitations of the PVC hulls as far as abrasion goes, some extra coats of urethane coating on bottoms should help, and lining or portage will be easy with it's light weight. I've driven an Achilles sport boat up the Coleville with a prop, they told me I couldn't do that either.

  10. #10
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    This really caught my eye, two canoes strapped together with a go-devil between them hmmmmm............


    http://home.earthlink.net/~pilot180/...ures/what9.jpg

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