Powering Pontoon from the Bow

Discussion in 'Boat Design' started by riverman74, Mar 4, 2013.

  1. riverman74
    Joined: Mar 2013
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    riverman74 New Member

    I'm building a 30' pontoon boat for a 2000 mi. river trip. Classic design: aluminum gantry with 8' x 30' deck over four 14' long x 22" Diameter inflatable pontoons arranged in pairs. 40 HP outboard power. I'd like to place the outboard between the pontoons in the BOW of the boat for steering stability. Any info or opinions about bow drive workability?
     
  2. keysdisease
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    keysdisease Senior Member

    It should work fine as outboard power forward is common in specialty vessels like net boats. The pictures are of Florida "mullet skiffs"

    I question your motive as "steering stability" and there may very well be a noise / exhaust / vibration penalty for this installation but it should work. 99.9% of outboard powered boats are powered from the aft end and have no steering stability issues.

    Steve
     

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  3. Petros
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    Petros Senior Member

    for low speeds it should not present any problems. Several issues become problematic at higher speeds, the bow could lift it out of the water, and in a high trust situation, it will be difficult to keep in a straight line (directional stability). Neither of these should be a problem for you I would suspect.

    Also, with the motor forward beaching or putting it on a trailer is more troublesome, unless you have the ability to turn the motor completely around and do it "backwards".
     
  4. gonzo
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    gonzo Senior Member

    If you are placing the motor in the bow for steering stability, (better tracking), it won't work. The only reason special purpose boats, like seiners, have it is to keep the propeller from snagging the nets.
     
  5. SamSam
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    SamSam Senior Member

    You have to steer the opposite. With the motor in the back, when the motor is turned right, the boat goes left. With it in the front, with the motor turned right, the boat goes right.

    Also, in a regular pontoon boat with the motor between the pontoons, integral with the motor mount is a sloping well forward that knocks down waves that keeps the water from getting into the engine cowling, so you'll have to account for that.

    [​IMG]
     
  6. gonzo
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    gonzo Senior Member

    Bow steering makes the boat go sideways but turn heading very little. That is why bow thrusters work. When you are docking or maneuvering the move the boat sideways. With a large skeg or keel aft, bow steering can somewhat work, but not as well as aft steering.
     
  7. riverman74
    Joined: Mar 2013
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    riverman74 New Member

    Thanks, all for the rapid responses! Both Gonzo and Keydisease commented that bow power probably won't improve steering. I would have thought that "pulling" the boat through the water rather than pushing from the rear would work like a trolling motor: it would go fron dynamic instability (having to steer constantly) to dynamic stability (having to only correct steering for wind and current effects). If bow power is no advantage, I won't consider it. Thanks to SamSam for pointing out the need for a wave deflector. I presume that the bow wake from both pontoons could converge near the front of the motor and flood the cowling. Yes? Petros, the outboard has power lift so I hope that beaching problems will be minimal. Thanks for the observation.
     
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  8. keysdisease
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    keysdisease Senior Member

    Yous installation will of course be fixed and not adjustable, but there is how they do it on sailing catamarans.
     

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  9. Submarine Tom

    Submarine Tom Previous Member

    There are more reasons not to do it but if you've already decided not to then, carry on.
     
  10. PAR
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    PAR Yacht Designer/Builder

    Bow mounts will subject the lower unit to a much higher potential for strikes. You'll replace props and gear cases at a much higher percentage than an aft mount.
     
  11. keysdisease
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    keysdisease Senior Member

    You will need a nacelle on the underside of the bridgedeck aft to break the water and give you a place to bolt the outboard to.

    Almost all pontoon boats are powered this way, suggest you head to a local dealership and take a look rather than re-invent the wheel

    Steve
     

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  12. rafter33
    Joined: Dec 2018
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    rafter33 New Member

    Try to google "Searching for Huck in Balkans" - in the book they described a raft with almost identical requirements you are looking for. They may be willing to share plans.
     
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