Propeller Drive on shallow Draft Boat

Discussion in 'Boat Design' started by steve123, Apr 13, 2016.

  1. Rurudyne
    Joined: Mar 2014
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    Location: North Texas

    Rurudyne Senior Member

    Not entirely.

    Yes, I forgot to mention increased pitch, but the point is that the water race of the second prop needs to be faster than that of the first ... otherwise no benefit is had.

    As for the perpendicular flow thing, I was rather imagining the silliness of a pair of upright wheels facing inward rather than horizontal wheels.

    Now, that said, and now that I think of it, for a trailerable paddlewheel boat wheels that folded in 90 degrees for transport, like retractable wheels on an aircraft only on the back of a boat rather than the bottom of a plane, might be a way to squeeze a bit more boat within the length allowed for trailering without special permit. Maybe have the wheel fold flatter too so it takes up even less length in that position? :?:
  2. Village_Idiot
    Joined: Oct 2007
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    Location: USA

    Village_Idiot Senior Member

    My comments revolve around outboards (with the propeller being outboard, er...aft...of the tunnel). Quite a bit different from an inboard prop, but two key issues are 1) a heavily-cupped propeller will deal with aerated water much better (and acts as a larger-diameter prop, and 2) yes, counter-rotating props work very well for outboard engines also (Yamaha TRP (twin rotating props) are popular on shallow-draft flats boats.

    I run a flat-bottom aluminum tunnel with 115hp 4-stroke outboard, it is about 8m length. On plane, it runs in less than 18cm water. Off-plane, it requires closer to 36cm.
  3. huibes
    Joined: Mar 2010
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    Location: The Netherlands

    huibes Sittin' on the dock of the bay

    Could a large shaft driven tunnel boat be designed to reach 25 knots efficiently?

    Lwl 24 meter.
    Draft < 1 meter.
    Inshore usage.


  4. Joakim
    Joined: Apr 2004
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    Location: Finland

    Joakim Senior Member

    This is an old post, but I just saw it for the first time. I'm wondering how accurate Wageningen B series prediction is for this case. 22" is 0.559 m. With 0.4 allowed draft the tip of the propeller is 0.159 m above the waterline. The vessel would likely have hull draft close to 0.4 m, thus the propeller must in a very deep tunnel. Will the B series prediction be accurate for this kind of arrangement? What about increased resistance (=thrust deduction) due to tunnel and high speed flow in it?
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