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Repairing Coosa Transom

Old 07-06-2018, 05:18 PM
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Default Repairing Coosa Transom

My 1991 C-Hawk 245 has a 1 year old coosa transom I installed with the help of the Hull Truth. I struck a floating log offshore and did considerable damage to the transom where the motor mounts. Any advice on how to repair would be appreciated.



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Old 07-06-2018, 05:21 PM
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The splashwell walls are 1.5" coosa with a couple layers of 1700 biaxial over them, and tabbed into the transom as well as connecting to the main stringers, making them large gussets or knees. I don't think the transom took any damage outside this center area.


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Old 07-06-2018, 06:49 PM
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With the core sheared like it is, I'd say it needs to come out and start from scratch.
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Old 07-07-2018, 01:48 AM
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Sorry to see this. You may be able to scarf in new core in the center, but you will need to extend the new material well into the undamaged transoms. 12 to 1 is standard, meaning 18” in your 1 1/2” core. It’s major surgery​​​​​ whether you do this or replace the entire transom,
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Old 07-07-2018, 03:48 AM
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I was considering replacing the core between the two large knees, tabbing and glassing it to the existing knees. Then doubling their width to hold the new piece on place. I know in home construction a design like this would work. I don't know if it would create a hard spot or not.



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Old 07-07-2018, 05:25 AM
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You already have a hard spot. That’s why the damage was contained between your knees. The problem is that in your proposed repair, your placing your joint at a hard spot. What about filling in the space between the knees as you propose, but then adding a kick out to the rear transom face that spans across your knees into clean transom. I looked for pictures of boats that have the kick out that I’m thinking of, but couldn’t find any and couldn’t think of the boats that had them. You would end up with a 5’ wide area with extra transoms thickness.
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Old 07-07-2018, 05:51 AM
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Wow! So sorry to see. I'd be sick over that. I don't really have anything to offer, unfortunately. I think for peace of mind I'd take a day and some alcohol to mourn the loss of my time (and money), and then just replace the whole thing.
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Old 07-07-2018, 06:11 AM
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without knowing how well the rest was glassed this could be worse then you can see
time to take out the grinder and see whats there, you may be able to scar the glass and attempt to pull it from the core to get an idea how badly it got damaged

I get guys hit some good stuff at high speeds and have not seen a transom fail that bad, especially a new one.
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Old 07-07-2018, 06:17 AM
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Just curious... what happened to your Suzuki's lower unit with that impact?
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Old 07-07-2018, 08:11 AM
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Sorry for your loss. Makes me feel good about my marine plywood transom.
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Old 07-07-2018, 08:47 AM
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Raybo it was like getting in a head on collision, the boat came to a dead stop. I think if I had run it aground that fast it would have been much less damage, as the impact would be spread out over a full second or two vs the instant impact. I am going to cut the whole core out between the knees at a minimum. Do you think it was a poor design or workmanship from when I built it the first time? The layup schedule was thinner than standard, but I thought it would be stronger. I realize the strength of the total laminate depends on the thickness, but I didn't think 2 inches of chopped strand, woven roven, and plywood would be stronger than 1 7/8's inches of coosa, biaxial glass, and epoxy.

Fly- The suzuki lower unit almost looks untouched, all the force was transmitted to the transom.

Caper-Plywood is looking good.


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Old 07-07-2018, 09:58 AM
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the choice of materials doesnt instantly make for a superior product, the job still relies on technique.
those c-hawks usually built with mahogany plywood which is a darn good strong wood.

that last pic the glass doesnt look well saturated and a good amount of air, did you roll it better after that picture was taken?
I also feel the edge of the cutout should have had more of a bevel its really hard to wrap 1708 around a hard edge with epoxy reson- but I dont think that would have made that much of a difference
what brand epoxy resin did you use
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Old 07-07-2018, 10:07 AM
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I have read Gerald and others opinions of working with epoxy vs vinylester vs poly. I don't have any beliefs in the superiority of one material over another, sorry if it sounded like I did. I don't remember when exactly the picture was taken but in person the glass looked very translucent and wet out. I used Raka brand 127 series laminating resin and slow or non-blush hardener. Thank you for taking the time to look at this.
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Old 07-07-2018, 10:29 AM
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i would carefully inspect the rest and then come up with a plan
its not uncommon for boats to have different thickness transoms with engine areas being thicker, this is common in high performance boats

not to kick you when you are down but I see a 300 suzuki and a boat that you put some work into you should really think about insuring it
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Old 07-07-2018, 10:55 AM
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Thank you. It is/was insured. I enjoy the work, I enjoy learning about it, and I get a sense of pride from doing it. I could drop it off someplace and have it fixed, insurance will cover it. I would rather take some time off from fishing and rebuild it myself. Ask me in a week when I'm covered in fiberglass dust and it's 90 degrees with 90% humidity and I might change my mind on the enjoyment part.
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Old 07-07-2018, 11:22 AM
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Have your insurance fix it and be fishing in 2 weeks.
Fix it yourself and hope to be fishing next spring.
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