Trolling Jet Motor?

Discussion in 'Jet Drives' started by howbroker, Jun 5, 2008.

  1. howbroker
    Joined: Jun 2008
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    Location: Missouri

    howbroker New Member

    First Time Post - Looking for advice on the viability of a 12 volt "Prop-less trolling" motor.

    My favorite bass pond gets pretty weedy in the summer, and I spend a lot of time stopping and pulling weeds (Lilly pad stems) off my 55 lb thrust Trolling Motor.

    The Question - Is it viable to build a "prop-less trolling motor?" I have read many of the forums on Jet Drives, and understand the loss of power, poor handling issues at low speeds inherent with the jet drive.

    Most of the posts are discussing ways to generate more power, more efficiency, more speed. I'm looking for some realistic ways to generate enough vector-able thrust, that I could avoid the weedy prop issue and the low draft issue.

    The 55 lb trolling motor easily moves my 10 foot, 2 man "Bass Buddy" boat around my 10 acre pond in my quest for bass. Can a 12 volt pump generate enough power to move this light plastic boat? (100 lbs empty) Does anybody know if there is one commercially available? (I haven't been able to find one) Your thoughts and ideas would be welcome.
  2. charmc
    Joined: Jan 2007
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    Location: FL, USA

    charmc Senior Member

    Hi, howbroker,

    Welcome aboard.

    A jet drive is, essentially, a shrouded prop. I seem to recall that there are some shrouded prop designs out there, some for trolling motors. Here's a guaranteed weedless prop:

    The patented Weedless Wedge is the only 100% weedless prop in the history of fishing. And it delivers full power so there’s no need to carry an extra prop and a wrench. The design behind the Weedless Wedge is both simple and brilliant. The leading edge on each propeller blade is shaped with a swept-back edge that always meets at an angle of less than 45 degrees. “Wedges” weeds away from the hub — even at slow fishing speeds...even through a jungle.

    Another reson for using an electric trolling motor is that they are designed for quiet operation, less chance of spooking the fish. Silent operation is not an attribute of most jet drives, at least those I've seen. :)
  3. redtech
    Joined: Feb 2007
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    Location: suger pine, ca

    redtech Senior Member

    it's nice to have howbroker,
    charmc is right on about noise and jet units but to add a little more jets and weeds don't get along either. small piece of debree plug the intake then no water to the impellers
  4. srimes
    Joined: Sep 2008
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    Location: Oregon

    srimes Senior Member

    shallow draft and unaffected by weeds: Paddle wheel. Not real quiet though.
  5. Guest625101138

    Guest625101138 Previous Member

    I expect lilly pads will just gum up the inlet on a jet.

    This boat is reportedly quite immune to weeds:
    It uses auger type props. These avoid blades that trap weeds. There are amphibious vehicles based on the same concept; been around for a long time:

    One way to beat the weeds is to do what is done in the swamps. Avoid water propulsion and use air. Problem with this is you need a large prop to do anything useful. Something like 2ft diameter on a 10ft boat would get you moving but efficiency only 40%.

    The electric RC stuff you can get for peanuts (or maybe a little more) these days are very powerful. This motor is bigger than you need for power but is the sort of size needed to swing a big prop unless you set up gearing - why bother though:

    Hobbycity have some large CF blades but I have not looked at how they mount. Large RC copter blades would be close to ideal. A couple of kg of thrust is all you need:

    There are Bolly props made for large models but these get expensive:
    The 24X8 would do something useful at reasonable efficiency. Need to mesh to guard it.

    The fundamentals of a water thruster work against your little pump idea being very efficient. If you could set it up to avoid the inlet fouling you have to have quite large power to generate usable thrust. As a first approximation the ideal power as a function of thrust can be determined as:
    Power = (4/pi/9/rho)^0.5 x Thrust^(3/2)/D in Watts

    You will require a thrust of 20N (say 4.5lbf) to do something useful. Rho is 1000kg/Cu.m. D has to be in metres so for a 1" nozzle say 0.025m. Under these conditions the ideal power is 42W. You could double this by the time you account for plumbing and pump losses. A 6" pump would need to spin at 800rpm to do the job. Something off-the-shelf like this would be adequate:
    You would need to nozzle it somewhat to get the best result but it is the sort of size required. Anything smaller would be literally pissing into the wind. Efficiency would be similar to the air prop.

    Rick W
  6. kistinie
    Joined: Aug 2007
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    Location: france

    kistinie Hybrid corsair

    Pump jet

    Does a manufacturer sells pump jet pods or pump jet propeller ?
    ,,,,,,pump propeller to use the good name,,,,

    This for 5 to 10 Kw ?

    Pump jet - pump propellers sous-marins helices.htm

    these are supposed to be very efficient at high speed, but induce a drag at low speed
    the stator is above propeller or after.
  7. apex1

    apex1 Guest

  8. kistinie
    Joined: Aug 2007
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    Location: france

    kistinie Hybrid corsair

    Always a pleasure to ear your sarcasm !
    At least you give a good informations, it is already a positive thing

    French submariner call the dual or triple prop shielded system in submarine "pump jet" or "pompe helice'
    I do not know why they use this name if it is not the good one.

    So what is the name of this shield proppeller with many prop inside ?
  9. apex1

    apex1 Guest

    Ducted Prop or Props
    Rudderpropeller if it can be turned to at least 40° each side
    helice gouvernal in your mothers tongue
    was a pleasure
  10. kistinie
    Joined: Aug 2007
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    Location: france

    kistinie Hybrid corsair

    Ok, good to know

    So even with 3 propeller and a startrek design including water injection in the ducting, name is prop or ducted prop

    No very romantic for such a secret technology :-(

    this picture is a rudimentary pump used in industry for water
    called "propeller pump"

    the other link , a commercial boat pod using submarine technology, gain is supposed to be 10% (on a normal pod i guess)

    Attached Files:

  11. mudman
    Joined: Mar 2007
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    Location: Madisonville, LA

    mudman Junior Member


    Make your own out of a 5 hp engine. You should see what we get through with a homemade 6.5. Easy to make, fuel efficient. Very noisy.
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