Tropical flooding rivers... please help me.

Discussion in 'Propulsion' started by Darien, Aug 14, 2015.

  1. Darien
    Joined: Aug 2015
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    Darien Junior Member

    Hi. I´m new here and need help, please. My family and I work on the river systems in Panama towards the Colombian border collaborating with indigenous communities to build potable water systems. Everyone here uses dugouts with outboards. Those are great for carrying huge loads, but slow and expensive even when unloaded. And they get damaged if you make a mistake and clip a submerged log.

    I started investigating after seeing the guys in New Zealand zooming up skinny rivers in their jet boats on youtube. Our rivers are typically fairly "flat" with gentle shoals that get down to 4-6" deep in the dry season. In the wet season, we have to deal with lots of debris and super dirty water (jets don´t like that, right?) There are also hidden obstacles in the river, mostly logs.

    It is quite far to many communities, so I´m hoping to scrap together something I can sit down and drive with a wheel, handlebar, or whatever and carry another guy, a toolbox, bedrolls, and machetes. It needs to be dependable, fixable, stable, fixable, and fast... in that order (sorry, that´s a mess of compromise I know). Oh, and cheap :) Getting on plane quick is more important than top speed (the rivers are curvy, obviously)

    I found a sturdy Al hull from canal surplus that resembles a little what the New Zealand guys build which I am considering and would appreciate input, 11ft. picture attached. ?? What propulsion system would be best for my situation? DSC_000.jpg

    Ok. So I have no boat building experience, so feel free to rake me through the coals for my ignorance. I can build things. I would like to ask if it would be ridiculous to consider dual surface piercing props on CV axles (largely for redundancy when one breaks) with a lower fin so they slide over rocks and logs? I found a Rotax 787 which I figured would be good for weight. Could this be used for boat props?

    Thank you so much for any help you can offer.
     
  2. rasorinc
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    rasorinc Senior Member

    I WOULD WANT to have an aluminum boat say 15' in length and powered by an outboard engine that has shallow water running ability. (operate while tilted up) Carry extra props
    inexpensive ones. Simple to change and to work on. Also light in weight compared to inboard engine with jet. Keep every thing as simple as possible. Fit rowing ores for emergencies. Provide good seats and adequate flotation. One cubic foot of rigid Styrofoam will float 55 pounds.
     
  3. Darien
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    Darien Junior Member

    Thanks for the reply. Maybe I overstressed reliability. I want to get away from the outboard because I´ve seen the violent lashes that even experienced boaters suffer when their outboard catches a snag. And for ponies to weight, can a Rotax and accompanying parts not compete with an outboard?:confused:
     
  4. markstrimaran
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    markstrimaran Senior Member

    swamp motor

    I am no expert, but any thing is do able. Have you looked into swamp motors. I assume that you want to build vs buying.
     

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  5. Darien
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    Darien Junior Member

    Yes. I was hoping to keep the weight down in the boat to lower the CG and as you mentioned, build it myself. Also, I want to avoid tiller driven and have something like the New Zealand mini jet boats with a steering wheel and sit up front to see obstacles better.
     
  6. markstrimaran
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    markstrimaran Senior Member

    Rotax vs Briggs and straton

    Dollar for horspower. The Rotax is very pricey. The Briggs is a simple piston. The Rotax is a rotor motor. That will fail if overheated.
     
  7. markstrimaran
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    markstrimaran Senior Member

  8. Darien
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    Darien Junior Member

    I understand that the Rotax like from Seadoos was a pretty conventional piston and cylinder setup and the valve is the rotary aspect. Of course any setup melts at some temp.:D
     
  9. Darien
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    Darien Junior Member

    Thanks. Yes, I looked at these, the long being like a thai long tail and the short more akin to the mud motor. That is basically the prop action and protection I´m looking for but with the weight of the power plant snug in the bottom of the boat... I was thinking of having a pedal or something to raise the "surface drives" from the comfort of my seat to avoid the snags I´m fortunate enough to see.
     
  10. Darien
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    Darien Junior Member

    Oh... and I found the 2002 Rotax 787 in a junkyard. I think I could get it for $300-$400. I didn´t do a compression check, but it turned smooth without the plug and I couldn´t budge it with the plug.
     
  11. rasorinc
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    rasorinc Senior Member

    I would still go with an outboard with remote steering and trim. Mount a fin or a pare of fins at the transom. Mud motor would be my 2nd choice.
     
  12. markstrimaran
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    markstrimaran Senior Member

    stump jumper.

    Thanks for the education. Rotax rotor vavles. I should have remembered from working on snow mobiles.
    OK your plan is to mount a 110 hp at ? 8000rpm
    In a aluminum ? 16' vee hull. Tentatively of course.
    you need a thru hull cuttless bearing. With the end being coupled to old jeep u joint or cvc With the propeller shaftshafts supported with hydraulic shocks to the transom?
    It will be easier with a lot less shaft RPM's.
     
  13. Darien
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    Darien Junior Member

    hmmm. yes... I think. That is what I would like to ask. Is that a bad idea? Can I account for the high rpm with a gear ratio? Would I be better off with an aluminum engine from a little car? If dual props, should I do pulley, gears? Should I even consider a jet? Thank you so much everyone for your help.
     
  14. markstrimaran
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    markstrimaran Senior Member

    20 hp will get you going.

    An in board 20 - 30 hp. Would be plenty of power. A 110 hp about 55 mph. On a aluminum hull would stress crack.
     

  15. Darien
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    Darien Junior Member

    Thank you. That is very helpful. The aluminum boat in the picture is quite heavy duty. It´s not like a jon boat that you could just toss in a truck bed. The crazies in NZ often put way more than 110hp in their homemade aluminum puddle jumpers with UHMW PE on the bottom to slide over rocks. welded, not rivet, construction. I think 40-45mph WOT with a quick hole shot would be a good balance for me.

    We do access a couple of rivers via a trek across the ocean, but I want to optimize for the river conditions and probably can´t afford to marinize the vehicle right now.
     
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