reinforcing transom

Discussion in 'Fiberglass and Composite Boat Building' started by darrell4wd, Jul 31, 2012.

  1. darrell4wd
    Joined: Jul 2012
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    darrell4wd Junior Member

    I want to put a heavier four stroke and a small kicker on my Mac 22 and need to strengthen the transom. Will I have to remove the gelcoat to layer up the resin and cloth or can I rough up the gelcoat and resin over it? Inside is covered with a rubber coating. Any help appreciated.
     
  2. tunnels

    tunnels Previous Member

    Anything to do with strength and getting a really good bond grind off the gelcoat and get back to the raw glass again and build on and up from there . The rougher the better . All bonding where you want to get things strong shoulf be 100mm to 120 mm wide bonding surface to old glass and even new !!:D:p
     
  3. PAR
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    PAR Yacht Designer/Builder

    To address this we need to know what you boat currently has for a transom core and what you'd like to add. So, make, model and year, plus hows it's equipped, the HP you'd like to install, etc.
     
  4. darrell4wd
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    darrell4wd Junior Member

    It's an 84 Macgregor 22 ft. The motor I'm adding is a Honda 4 stroke Power Thruster and a 2hp Honda air cooled for backup. I'm looking at 150+ lbs. I will use some kind of back up from the inside. The previous owner did some gelcoat repairs, not a very good job on the transom. This boat will be used strictly for river motoring long distance. Thanks for your input. Here's a pic, not my exact boat but identical. picmacgregor22na.jpg
     
  5. PAR
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    PAR Yacht Designer/Builder

    How may HP on the 4 stroke?
     
  6. darrell4wd
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    darrell4wd Junior Member

    It's a Honda 9.9 High Thrust model, the backup will be an air cooled Honda 2 hp. 150 lbs total I'm told
     
  7. PAR
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    PAR Yacht Designer/Builder

    The transom needs to be 1 1/2" thick. Typically this is 2 pieces of 3/4" plywood, covered in 'glass. You could get by with 1" for just the HP of the 4 stroke, but the additional weight of the 2 HP suggests a heftier transom.

    The plywood should be bonded to the inside of the transom and tabbed to the hull shell as well. It's likely you already have a single piece of 3/4" already there, so an additional piece, bonded to the inner skin will likely do just fine.
     
  8. darrell4wd
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    darrell4wd Junior Member

    I'm pulling the original motor mount so I'll be able to see the layering better. It makes sense to reinforce the inside. I did find a guy who does boat restoration, fiberglass, gelcoating and the such local. I think I'll get him to come look at it and hopefully come up with a plan. Thank you guys very much for the info. I'll let you know how it turns out.
     
    Last edited: Aug 2, 2012
  9. darrell4wd
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    darrell4wd Junior Member

    I pulled the motor mount and the thickness is 7/8" inch and it doesn't look like plywood. I crawled back under cockpit and found that what I thought was rubber coating is actually black tinted resin over heavy roving. The transom is rounded making it difficult to add plywood. How much strength would I get by adding more layers of roving and tabbing it 12" or so sides and bottom? I have pretty good room to work so in that I'm lucky. Please tell me I don't have to grind the inside surface for the new material to adhere....I contacted a guy who does fiberglass and gelcoat repair, $100 per hour plus materials....ouch. Thanks
     
  10. PAR
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    PAR Yacht Designer/Builder

    Yes, you have to grind the surface for a good bond with any material you install, preferably down to good mat or fabric (through the gel coat). This is normal practice with 'glass repairs/modifications.

    The transom curve on your boat isn't very deep, though bending in 3/4" stock will not be possible, so you'll bend in thinner stuff. It's likely 3/8" will take the bend, though you cuss a bit, while 1/4" will easily bend, but you'll need more layers. For your needs, two layers of 1/4" will do, if well bonded and tabbed.

    A few layers of roving and tabbing will not offer the stiffness you need. If you bulk up (fabric) to the stiffness necessary, it'll be much heavier then plywood and you'll make a career out of this type of lamination.
     
  11. darrell4wd
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    darrell4wd Junior Member

    Shucks, I knew you were going to say that about the grinding. I took some samples of plywood pieces out to check and the 3/8" is going to be tough but I think the 1/4" will be very doable. Also, I watch some West System videos laying cloth, it would be a long term committment to build up some thickness using resin and cloth. I really appreciate your help. I'll take some pics of the work in progress and post them later.
     
  12. rasorinc
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    rasorinc Senior Member

    Someone get rid of this crap, please..........................
     
    Last edited by a moderator: Aug 11, 2012
  13. PAR
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    PAR Yacht Designer/Builder

    Stan, I got a reputation knock from this spam, so be nice to her or she might spank you too. Seeing as what she's pushing, she might be pretty good at spanking, in which case . . .
     
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  14. Boat Design Net Moderator
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    Boat Design Net Moderator Moderator

    This spammer has now been banned and their posts removed. (I think the post feedback may have been a member clicking on the wrong post thinking the blue bar went with the post above instead of the post below - I've removed that as well. Sorry about that.)
     
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  15. rasorinc
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    rasorinc Senior Member

    Thanks much Jeff, Stan
     
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