Propulsion removing solutions?

Discussion in 'Boat Design' started by Lietuvis, Oct 7, 2018.

  1. Lietuvis
    Joined: May 2011
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    Location: Lithuania

    Lietuvis Junior Member

    Hi. Sooo its about 4 meters long catamaran boat with small electric motor propulsion. Hull (see attached picture below) is with aft tunnel to prevent air suction due to small draught and protect thruster from external "objects" and vice versa. The problem occurs when electric propulsion needs repair, maintenance or cleaning from "jamming". We need solution for easy propulsion removal, swapping or cleaning without lifting boat out of the water. As i understand propulsion itself is designed as outboard but used as inboard and is part of the hull construction. So any ideas how it can be done without compromising hull construction?
     

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  2. BlueBell
    Joined: May 2017
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    Location: Victoria BC Canada

    BlueBell Ahhhhh...

    It's only a small, 4m cat.
    Why can't it be lifted out of the water for service?
    Even just at the stern?

    What is it you're showing in the last two pictures?
     
  3. messabout
    Joined: Jan 2006
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    Location: Lakeland Fl USA

    messabout Senior Member

    The third picture shows what appears to be a clamp mechanism such as the ones on ordinary trolling motors. That would imply that it is removable. The next picture shows some elwctrical components that apparently deliver regulated power to the motor. The leg of the motor obviously extends through the top of the tunnel.

    Is there a panel of some sort that can be removed in order to raise the motor and propeller into the hull? There must be a method that allows the motor leg to go through the top of the tunnel. Or is the top of the tunnel open sufficiently to remove the entire motor?

    I see no rudder or other steering device in the pictures...............How is the boat steered? If the boat is a cat, then does each hull have a propulsion unit?
     
  4. Lietuvis
    Joined: May 2011
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    Location: Lithuania

    Lietuvis Junior Member

    The last two pictures is current design (propulsion installation). Yes, as you said its probably "trolling motor" and both cat hulls have one. But it,s installed into the hull and is not removable. Well, it can be removed, but only from underwater side. Owner/builder of the boat recently had lots of problems with maintenance/repairing of the motor and wants easy solution for swapping, repairing and cleaning propulsion unit without pulling boat out of the water or diving :) I want to know is there any design solutions used in practice, maybe some removable panels as you said etc.
     
  5. Heimfried
    Joined: Apr 2015
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    Location: Berlin, Germany

    Heimfried Senior Member

    If I understand it right, the hull given in the sketches is not yet built and the last pics show an even bottom of a different hull.
    A possibility would be to build a kind of motor well as a part of the hull and connect the motor to a tightly fitting plug which would be inserted vertically. The bottom side of the plug would be shaped like the respective part of the hull tunnel, so hull and tunnel are fair. In case of e.g. weed in the propeller it would be possible to lift the complete plug with motor to get access to the propeller. The walls of the well would prevent the water coming in.

    The shape would be similar to the top parts of a kitchen mill (well, tunnel, plug):
    k019.jpg k021.jpg
     
  6. Lietuvis
    Joined: May 2011
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    Lietuvis Junior Member

    No, its already built. Its just like "sandwich" construction with double walls, that's why it looks flat from inside because you can see only inside shell. Plan is to build series of these boats, and next version should be with improved construction (next probably will be with only one outside shell). Never used kitchen mill, so i'm not familiar with it's construction :D But i think i understood your idea and I thought about it, but it i bet it would bee pain in the *** to make it very "clean".
     
  7. BlueBell
    Joined: May 2017
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    Location: Victoria BC Canada

    BlueBell Ahhhhh...

    Is the boat steered by differential thrust?

    Who designed the boat?
     
  8. JamesG123
    Joined: Mar 2015
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    Location: Columbus, GA

    JamesG123 Senior Member

    Okay so this is like a prototype of what they/he/you want to produce?

    Ducted props don't lend themselves to easy movement and serviceability. And not even podded ones if you don't want to get wet. Simplest solution is of course a hatch in the top of the duct, bottom of the hull (!) A more water tight alternative is to make the whole mounting part a block that slots into the top or back and then bolts down, or make the upper bracket that the top the tube is clamped to pivot rearward with a sealed slot in the hull/tunnel so that the motor/prop can swing up and back. Any of which adds complication and a precision of fabrication that is not evident in the pictures you've posted.
     

  9. portacruise
    Joined: Jun 2009
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    Location: USA

    portacruise Senior Member

    You might need frequent access with two motors when one, but not the other of the two motor props tangles in weeds- affecting steering control. Outboard mounting which allow swing up and back is probably the only way without compromising/reconstructing the hulls. The motor mount could be moved further into the tunnel if the hulls are reconstructed by adding a slot constructed so no water gets into the hull (a la James above). A wild idea is needed if using 2 outboards and keeping the motors within the tunnels and not behind them. Maybe the motor downshaft can be constructed at sharp angles around the outside and include a pivot so the motor can be flipped up- but don't know if the angles and the bent downshaft disturbance to flow would work out.

    OE
     
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