design ideas needed for a small outboard bracket

Discussion in 'Boat Design' started by lobsterman, Jan 29, 2013.

  1. lobsterman
    Joined: Mar 2004
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    Location: Maine

    lobsterman Junior Member

    I need to quickly make an emergency motor bracket for a tiny 3HP motor, that is going to be used to move a 30' lobsterboat. (I know it will be way under powered !!!, but it will not be going very far at all, and it is outside of the tidal currents).

    This will be just for a one time use, down and dirty, quick boat move, to demonstrate that my boat with a disabled engine, can still be moved under it's own power. Does anyone have any design idea suggestions for a quick and simple outboard bracket ?,
    :?:
     
  2. michael pierzga
    Joined: Dec 2008
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    michael pierzga Senior Member

    Local boat has a swim ladder over the stern that is modified to hold a small OB for emercency power. The little OB lives in the forepeak when not used
     
  3. daiquiri
    Joined: May 2004
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    Location: Italy (Garda Lake) and Croatia (Istria)

    daiquiri Engineering and Design

    Hi lobsterman,
    How about posting some pictures of the transom of your boat?
     
  4. lobsterman
    Joined: Mar 2004
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    Location: Maine

    lobsterman Junior Member

    [​IMG]

    Sorry i don't have pics of the transom, but its the blue boat, (and the yellow boat), both need to be rigged with some quick, simple, and cheap propulsion.
     
  5. lobsterman
    Joined: Mar 2004
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    Location: Maine

    lobsterman Junior Member

    I don't know if that pic worked, all i am seeing is a little box with a red x in it ?. but it is a fiberglass 30' Sisu hull with a semi rounded type stern with a deck rail about 2'x8' across the back.
    If i have to, i may just cut down and fit a couple of 2x4's out the back scuppers, lag screw them to the deck, and go across the protruding ends with a cross peice of 2x'8", then mount the bracket to the correct height off of that.

    I'd rather not drill any mounting holes into the hull if i can help it, but the deck and rails i am not worried about, as they are going to be redone in the spring when i install new fuel tanks.
     
  6. daiquiri
    Joined: May 2004
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    Location: Italy (Garda Lake) and Croatia (Istria)

    daiquiri Engineering and Design

  7. daiquiri
    Joined: May 2004
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    Location: Italy (Garda Lake) and Croatia (Istria)

    daiquiri Engineering and Design

    Ok, here's my 2 cents worth, if someone comes with a simpler idea, so much better...

    One possible solution - a removable transom bracket, made of either wood or (better, imo) of welded steel (or aluminum) pipes. The pipes can be either bent into the desired form, or it can be made of welded straight sections.

    It will be held in place by the gravity and reaction forces, no permanent fixing necessary, imo. Rubber caps and band are important, to ensure a good friction with the transom plate and to protect the hull paint from scratches and wear.

    I have not included any dimensions because I don't have the necessary dimensions of your boat. But I have drawn the direction of the forces involved with forward thrust. Since it is not a particularly demanding piece and forces involved are modest, any artisan will be able to manufacture it just from this rough sketch, by seeing the direction of the forces and by measuring the transom and engine dimensions.

    Two things to watch out:
    - not suitable for reverse thrust
    - depending on the height of the installation, the thrust lever might be difficult to handle.

    Regarding the height of the installation, it could be sufficient to not let the prop aerate. But the prop will not work well if it is placed in the turbulent water behind the transom. In order to get the maximum thrust from your outboard, you'll have to submerge the prop disk below the transom, exposed to undisturbed water. If it is possible, of course

    Cheers
     

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  8. lobsterman
    Joined: Mar 2004
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    Location: Maine

    lobsterman Junior Member

    I am having a hard time picturing what you are describing, also i have no money to pay a welder, i am so low budget that i am probably gonna have to do a Jack the hack carpentry job to make something workable from dimensional wood and screws, as its the material and tools that i have available to work with.

    Yes, the height of it may be a problem, as the engine has no reverse (it a really small old engine), and it must be turned completely around to get reverse thrust. I may have to lay across the stern deck to operate it, (or make up a raised steering control handle for it). I don't think cavitation will be an issue, due to the very low speed that the boat would be moving at.
     
  9. Gib Etheridge
    Joined: Nov 2012
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    Location: BC Canada

    Gib Etheridge Junior Member

  10. midnitmike
    Joined: Apr 2012
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    Location: Haines and Juneau

    midnitmike Senior Member

    I think you've got about the best idea going...just add a gusset and you should be motoring.

    MM
     
  11. lobsterman
    Joined: Mar 2004
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    Location: Maine

    lobsterman Junior Member

    What is a gusset ???.
     

  12. midnitmike
    Joined: Apr 2012
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    Location: Haines and Juneau

    midnitmike Senior Member

    Something like this.

    MM
     

    Attached Files:

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