Transom Design for Outboards

Discussion in 'Boat Design' started by Xyberz, Jun 3, 2014.

  1. Xyberz
    Joined: May 2014
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    Xyberz Junior Member

    I tried doing a search and couldn't find anything specific.

    Is there a standard for designing transoms for mounting outboard motors? This obviously is very important when designing a boat or any watercraft that will be using a powered motor. I just want to make sure I have the correct width, height, thickness, etc to be able to hold an outboard motor.

    Originally I was going to make the sponsons, (yeah I found out what they're called! LoL) on my cat only about 6 inches wide but since it'll be powered, I'm thinking that is not wide enough to support and mount an outboard.

    Would I find out the mounting requirements on the outboard maker's website in the technical specs?
     
  2. Ike
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    Ike Senior Member

  3. Xyberz
    Joined: May 2014
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    Xyberz Junior Member

    Thanks for this link. That post is over 1100 days old and won't let me post anything new to it. I still do have some questions though I'd like to ask since the link to the PDF file is no longer valid.

    I'm currently trying to draw out the design for my cat but I'm currently stuck at the back of it where I have to design in 3 separate transoms, one for each sponson and one right in the middle of the cat. What is the minimum width that the sponson would need to be in order to support an outboard? The total length I'm shooting for will be between 12-16 feet and about 6ft wide.
     
  4. DCockey
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    DCockey Senior Member

    Outboard dealers have the "rigging guide" for the line of outboards they sell which will include mounting dimensions for the outboards in that particular line.

    Standard nominal transom angle for outboards is 12 degrees from vertical.

    Link to section of 2008 Yamaha rigging guide with engine and clearance dimensions: http://www.aquaservices.net/pdf/yamaha/dimension_yamaha.pdf

    2002 Yamaha rigging guide: http://mx.durdom.pro/moto/manuals/YAMAHA/WaveRunners/Yamaha_RIGGING_GUIDE 2002.PDF

    2012 Yamaha rigging guide: http://www.riverteam.ru/price/Rigging guide 2012.pdf
     
  5. Xyberz
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    Xyberz Junior Member

    Awesome! Thanks for those PDF links. I'm assuming that if you build your transom to hold one type of outboard, then it's highly likely that it'll be ok for other brands too right? I have still yet to decide what sized outboard to use but I'm thinking right now that maybe twin 9.9HP. I'm wondering if one will be enough to start and later buying the second one to add on.
     
  6. JSL
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    JSL Senior Member

    ABYC has dimensions & specs
     
  7. Xyberz
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    Xyberz Junior Member

    Wow, you either have to have a paid membership just to view their stuff online which seems to be a minimum of $255 per year or buy each individual document separately for $50. Well at least that's how much the S-12 costs.

    I guess I'll just go off of other designs that are already out there, I'm thinking that they're following the correct guidelines.
     

  8. sprit
    Joined: Jul 2013
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    sprit Junior Member

    Long and short shaft engines are different.
    Nominal vertical height from the transom cutout to the bottom of the boat is typically 20 inches, but some engines require 22.
    Don't assume that what is right for one engine or boat is right for all!
    Design the transom for the engine.
     
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