1974 20' sceptre transom replacement and i/o to outboard bracket conversion

[Big fish]

Sorry but another question. After grinding the inside of the outer skin I didn't grind it down evenly and there is some wavy spots. Will this uneven surface be a problem when bonding the core to it? Thanks again for all your help and I can't wait to see more of your progress.

[flyingfrizzle]

Originally Posted by Big fish

Sorry but another question. After grinding the inside of the outer skin I didn't grind it down evenly and there is some wavy spots. Will this uneven surface be a problem when bonding the core to it? Thanks again for all your help and I can't wait to see more of your progress.

Most of the time when you do a laminate you always start with csm (matt) and that will help hold more resin to fill in the voided areas. If the voids are real bad you may want to add 2 layers of 10oz matt to give more thickness to fill them in.

There are two ways I usually do a transom to the original skin. The first is if I use Poly or vinyl-ester. I start by adding a layer of 10oz matt then a layer of 1708 over that then 2 layers of matt over that for the inside laminate between the skin and core. That will give you skin-matt-matt(on back of the 1708)-biaxel (top of 1708)-matt -matt. This gives you two layers of matt to fill the voids between the skin and the layer of biaxel. Then the two layers of matt on top of the biaxel will help fill the voids to the core material. This creates a good bond to the hard surfaces that you lay up on or to. This leaves the biaxel in the middle which is for strength mainly. The core gets soaked with thinned resin before it is installed and then I will add several layers of 1708 between the two 3/4" wood plys. Always put the matt side towards the bare wood. At this point I will clamp it inn place and wait for it to set up. Once dried I will add the fillets around the edges and then start laying up the outter layers of glass. Matt should be used always as a first layer up against old glass or wood to gain bond strength by holding more resin and filling voids. Most people like the 1708 because it has the matt glued or (stitched for epoxy) to the back of the biaxel fibers. You can lay it as one layer and it is faster maybe easier to do than two layers separate.

The second way I may install a core into the transom is with epoxy. I then use just a thickened epoxy resin with cabosil then trowel it directly onto the surface of the skin. The trowel I use will be notched with 1/4" teeth and I get it thick enough it will stay in place and not run down the skin. The thick resin should fill most voids and dips. Once this is applied I stick the core to the skin and let it bed down into the thickened resin. I try to get all the air out if possible and clamp it in place to set up. Dont squeeze the resin out from to much pressure. Try to keep as much in as possible but at the same time bed it well enough to get all the air out. The epoxy has a strong enough secondary bonding strength that it can be used with out matt and will bond the core in well. It will not provide much strength as that comes from the cloth. You need to make sure the original skin is plenty thick to do it this way. This is how I did the 74 20' sceptre. The skin was super thick already and I added more bixal to the inner section between the core wood plys and the front side of the core to give it plenty of strength. If I bond it in this way I will also will fully seal the wood core with two layers of matt first so that it will be completely seal from any possible water intrusion. I scuff it real well with 36 grit to give the surface some "tooth" for the epoxy to bite to. The thinned poly or ve will absorb into the wood better than the epoxy. I usually thin with styrene or you can use acetone. (The first method I described to you I just bond the wood in without enclosing the core first. It gets enclosed as it is laid up.) Once the epoxy sets up you can add all the fillets around the edges and then laminate the front side of the core to the boat.

There are many ways to do a transom but that is the two main ways I do them. Hope this helps, Mike

[Big fish]

Can I use poly resin and mat on skin to build some thickness? Then do what you did with epoxy for the core.

[flyingfrizzle]

Originally Posted by Big fish

Can I use poly resin and mat on skin to build some thickness? Then do what you did with epoxy for the core.

You could do that, and it might be fine, but that kinda defeats the purpose of using epoxy to get the good secondary bond to the old skin. If I was to fill all the voids and dips with matt and poly or VE I would just continue to work with that same resin and lay the core into the boat while the resin was still green. You get a better bond when you do a green or chemical bond. The peel strength is much higher and you will get less delamination problems. The part of the lay up that will be the weekest is the bond to the older orignal poly glass. The point of using the epoxy is it will give you better secondary bond strength to the old poly skin. If you lay poly on the old skin it wont have the same peel strength. You would be just as good or better off to continue with the poly and do a full wet chemical lay up all the way out vs letting it fully cure then doing a secondary bond on top of the new glass. The window for a lay up is best if it cures all together but you still have hours to a day or two to reapply more resin and glass and still get a good green chemical bond. If it was me I would do one of two things, First- use epoxy to to fill the voids and build it back up with 1708 stitch cloth and then lay the skin in place so it is all epoxy from skin to core. Then you can switch to poly or ve to do the rest on the outer core to save some money if you must. OR secondly- use VE or poly to fill the voids and dips with matt and 1708 and do a full green or chemical bond from the start to finish all the way out. You just need to take more time prepping the surfaces on the old skin before you start. Scuff it up well so it has plenty of tooth for the new resin to bite into and clean it very well and get the best bond you can out of the resin. I think as long as you prep the surface well and use enough biaxel cloth for strength you will be plenty strong and you wont have any problems with delamination or such. Just take your time and make sure you get all the air out of the laminate and leave no air pockets or spots for water to get into the core and it will last for years with out issue. There have been many boats rebuilt with just plain old poly resin that last years. The epoxy and VE are much better products and will give you more strength but at a cost. If you are trying to get the most strength out of a light lay up for performance high end resin systems is a must but just for a pleasure fishing vessel where weight is not a issue you can over build it with poly a little for peace of mind and be fine.

[Big fish]

Thanks a lot for the great info. That explains it all. When are you planning on finishing your boat? What color will it be? Keep us posted.

[flyingfrizzle]

Originally Posted by Big fish

Thanks a lot for the great info. That explains it all. When are you planning on finishing your boat? What color will it be? Keep us posted.

I'm waiting on some warmer weather right now. I don't want to spray it due to the weather. It will get cold at night even if I pick a good warm day to do it. Here in NC were still get a few days above 70 this time of year but it can be 85 today and then a high of 20 tomorrow.

Right now I am working on another 20' (this one a cc) in my heated shop. I hope to have both ready by time it warms up so I can spray both of them once it warms up out side.

I could spray them in my shop but I don't want over spray every where. I do have a friend with a paint booth. I did the electrical wiring on a while back for him when he installed it so I might reach out to him for a favor if the spring doesn't hurry up and get here.

Color? Not sure but probably the popular seafoam green or Carolina blue.
(UNC Tarheel Blue)

[Big fish]

I understand. Do you do any glass work when it's cold out? Here in Hawaii weathers the same almost year round. Also I'd go with Carolina blue. It's a very nice color. And that's my favorite basketball team. Go heels.

[flyingfrizzle]

I do glass work year around but when it gets much below 60 degrees I do it inside of my heated shop. I will lay the glass then crank the heat up a bit to help it cure out well. I have done small repairs outside on larger boats that wont fit in my shop this time of year. If I do I need to pre-heat the area with a blow drier or heat gun and then do the lay up. I get the glass laid then I hit it lightly with the heat gun till it starts to kick. Once it kicks off it generates enough heat on its own to cure on out. There are plenty of good warm days where I can do work out side and then there are some like last week where it was in the 20's. We have cold to mild weather here in NC mainly for just a few months. It can be 85 degrees on Monday and then have a high of 30 on Wednesday. They have a saying "If you don't like the weather here in NC just wait a day or two and it will be different". Sounds much nicer where you are this time of year.

[Big fish]

After glassing ply core to outer skin do you do tabbing first or do you glass entire core first? What is the next step?

[flyingfrizzle]

Originally Posted by Big fish

After glassing ply core to outer skin do you do tabbing first or do you glass entire core first? What is the next step?

I usually cut the glass cloth large enough to cover the whole core with 6" of extra on each side and bottom so it will Tabb to the sides. It is much stronger as a continuous piece. Then I add extra tabbing over top of the wing tabs off of the larger full piece. Make sure you do fillets on the corners first before you add the cloth.