can i go over the transom rating ?

Discussion in 'Powerboats' started by den44057, Oct 14, 2010.

  1. den44057
    Joined: Oct 2010
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    den44057 Junior Member

    i have a 1961 15ft aluminum star craft runabout with all aluminum transom and i just bought a 1980 55 hp Johnson that i would like to put on it.
    now my question is my boat is rated for a 50 hp would the extra 5 hp matter ? or should i brace the transom with wood ? thanks for any info

    den
     
  2. WestVanHan
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    WestVanHan Not a Senior Member

    Even if the 30 year old 55 horse motor likely isn't putting out 55hp,on a 50 year old boat-to be safe-I would strengthen it somehow.

    Even if you're not getting on the gas much.
     
  3. PAR
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    PAR Yacht Designer/Builder

    You should post photos of your boat, the transom should already have a core, usually of plywood in 15'ers.
     
  4. den44057
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    den44057 Junior Member

    i can post pics tomorrow i was just trying to find out if its worth puting the motor on the boat or will it damage it, i bought the the starcraft from a one owner and it came with everything he got with it in 61.

    its a very clean boat and has a 61 18 hp johnson that runs great but is slow
     
  5. den44057
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    den44057 Junior Member

    trying to post pics so everyone can see what I'm talking about but it keeps saying one security token is missing ?

    i am going to try and describe the transom the best i can.
    the transom is 16'' high and 5' wide it has and board going across the top 6'' wide and then there is a aluminum shelf going across under that.
    now from the shelf down its just aluminum no more wood but there is a couple braces going from the floor to the transom and to the shelf.
    no there is no holes drilled into the back of the boat as the 18 hp on it is clamped but the 55 hp i bought does not have these clamps.
    hope this helps some and if i can figure out the pics i will get them up
     

    Attached Files:

  6. Jeff
    Joined: Jun 2001
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    Jeff Moderator

    I resized and attached the photos above. (the original file size of 23 MB seems to be too large to upload in one go, causing the upload to take too long and get truncated; as cameras are getting higher and higher resolution we'll need a better mechanism for dealing with larger and larger files without slowing down the server. Sorry for the hassle.)
     
  7. den44057
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    den44057 Junior Member

    you got them up thanks for the super fast help
     
  8. gonzo
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    gonzo Senior Member

    The problem in not just the transom but the rest of the boat too. You will be going faster than it was designed for and slamming harder. The failure may be in the bottom and framing rather than the transom.
     
  9. den44057
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    den44057 Junior Member

    there is that much differance in just 5 more hp to cause that ?
     
  10. PAR
    Joined: Nov 2003
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    PAR Yacht Designer/Builder

    5 HP is a 10% increase over the maximum rating for your boat. I suspect your boat could handle it, but that transom looks in terrible shape and needs rebuilding, before hanging a motor on it.

    The first thing I would do is get the old motor off there, and strip out the half a century old core and supports. Replace the wooden pieces, possibly consider using a full plywood core, then reassemble with new fasteners, bedding etc. Even once this is done, you'll be torquing your transom with a 55 pretty good, but with a new core and fasteners you'll have some life span. If you bolt the 55 on there as it is, you'll probably tear out most of the fasteners on the support structure, the first time you slam the throttle open. Then you'll have a whole lot more work and repairs to do then just replacing the transom core and some fasteners.
     
  11. den44057
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    den44057 Junior Member

    its just the paint here is no rot or anything else wrong with the transom
     
  12. PAR
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    PAR Yacht Designer/Builder

    You have to remove the fasteners to check their holes and to check the flanges and the areas under the heads, for stress cracks and breaks. I can guarantee there will be cracks on some of the supports, where the fasteners go through after 50 years. The only way to check is spend an afternoon and remove each fastener, clean and inspect the area under the head, around the hole, the fastener itself and of course how tight it is in it's hole.
     
  13. den44057
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    den44057 Junior Member

    so even if the boat was only used with a trolling motor except for two times in the 50 years its still going to have stress cracks ? the man i bought it from lived by a lake that only used 9.5 hp so he used a trolling motor he said all but two times he took the boat to the next county over and used the 18 hp on it.
     
  14. WestVanHan
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    WestVanHan Not a Senior Member

    Put it this way-hang the boat by it's bow with a cable,and throw 1000-2000 pounds of lead on the now horizontal transom.
    Would you put your kid,niece,grand kid under it???

    Don't think it's worth it? Well then clamp it on and go for it.
     

  15. den44057
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    den44057 Junior Member

    illl go for it lol what the heck
     
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