80 Mastercraft transom replacement

[80Mastercraft]

I've looked over the form and decided to post a question. I'm replacing my transom on my 1980 Mastercraft, inboard, and could not find information on the couple of subjects I'm stuck on so I turned to all of you. First the transom in my boat is not so much a structural support as in an outboard or IO, I'm sure it does however help with lateral loading and of course the swim platform.

I have removed the old board and grinded down the leftover wood and fiberglass down to the hull. Please see the attached pictures of the before and after grinding. The original transom was wood wrapped in fiberglass and I'm going back with that. I am using marine grade plywood the same thickness as the original, if I remember correctly the thickness is 3/8". The original wood layup was cut into small pieces, about 8" tall and 4" wide. I'm duplicating the manufacture process because the original transom lasted 30 years and I'm hoping I can at least match what they did, so if I get another 30 years that will be plenty. See the pictures for the pieces and how I'm going to lay them up.

My questions:

1 How would you suggest to hold these pieces in place as the peanut butter dries? I was thinking vacuum bag but this is expensive and I'm only going to do this once. I don't really want to screw thru the hull, this would add more work.

2) Will polyester resin work for the peanut butter? Someone told me that the poly would not work because it will not dry. Is this true or has anyone used poly in this type of application and had good results?

Thanks for the help

James

 

[Woodonglass]

Polyester PB will work. Epoxy would prolly be better for this application. Poly sets up quick and I think you're gunna need time to get everything in place and get it clamped up. You'll need to mix the PB, Spread it on each individual piece of Plywood, set them in place, make final adjustments and then clamp. This all takes time and you won't have that much with Poly. Epoxy will give you that time. How much space is there between the stringers and the stern skin once the new transom skin is in place. You can build a bracing platform inside the boat to effect your clamping from using a piece of 1/4" plywood if you have enuf space between the stringers.

 

[80Mastercraft]

The space after the wood has been installed will be somewhere around 1/4"-1/2". I plan to tab in the stringer so the water cannot get between the end of the stringer and the transom. When you talk more time, is it 1-2 minutes or are we talking 10+ mins? I plan to do a little section at a time, yes more time consuming but I hope to have less waste in resin. I talked to the local wholesaler of the resin who informed me of times and mixes so I can slow down the cure, but I'm in TX and it's hot so time will be short. I may wait until temps cool some before attempting this project, for the resin and me.

 

[Woodonglass]

Poly resin kicks off in anywhere from 10 mins to 25 mins depending on how "Hot" you mix it. Epoxy usually give you 30 -45 mins unless it's extremely hot and in direct sunlight. There are ways to Trick both but epoxy will stll be slower. I guess if you do a few pieces at a time you could get it done but keeping it all straight true and level may be an issue but then again maybe not. It would be much like laying ceramic tile I guess. So in a way the Poly quick set ability might just be a Plus.