TOPIC: FIBERGLASS REPAIR QUESTIONS

I cut the seat top out of my boat so I can remove the old foam and do some repairs. Now it's time to rebuild them and I'm not sure of the best way to go about it. The original ones had problems like cracks and dips from sitting on them for 50 years. I had a few ideas so tell me what you think. Idea 1 was put thin plywood in place and then start building layers of fiberglass on top of the wood and meeting up with the original side fiberglass to create a totally sealed compartment. The second was to fiberglass in a sheet of cloth and let it dry so it's tight and flat then layer it with 2 layers of 3 oz mat to build it up a little and finally top it off with a final sheet of cloth to give it a smooth finish. Please let me know if any of these will work and if not let me know the best way to go about do it. Thanks in advance for all the help.

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I also found this picture and thought about doing something like this to give a little more support.

boozer,

that last pix LOOKS sturdy to me. = IF i was doing it, i would epoxy coat those new seat frames, too, to SEAL them from water.
(i like to fix things ONCE!)

yours, satx

Amen to fixing it once. Looks like a plan to me.

To cut down on weight and not have to worry about wood rot you could frame it with the pink or blue slab foam from Lowes or Home Depot and then Lay 3-4 layers of 1700 Biaxial cloth over it with epoxy and it would be strong as heck and NEVER rot.

A couple of stringers across that box, spaced at 1/3 increments would be a very good idea. It will stiffen up the top and you won't have anywhere near as much of a sagging problem. You could go with foam and glass, but my preference is epoxy coated wood.

Also, I would make sure there is some kind of drain. Perhaps an opening in the stringers and a drain hole at the low point. Otherwise, if water gets in, it is there permanently. I'm not sure if this was designed as a floatation tank, but if it is, use a stern plug similar to what they use on small sailboats. An easy get at West Marine or similar store.

Larsons have drain tubes that run through the seat boxes. I have circled the end in the attached pic. I am not seeing the body of the tube through the inside of the box. Did you grind it out? The problem is that in cold climates water is some times left in the drain tubes in the winter and ice expansion opens cracks into the seat boxes and drain water soaks the foam the next summer. I have also seen cases where the application on the fiberglass by chopper gun over the tubes is very thin and it looks like water found ways to infiltrate into the seat boxes.
I made a tool to go through the drains to make sure they are not plugged and are full diameter and then I add glass to the drain tubes inside the boxes.
This leads to the "do you want it water tight versus do you want the box to drain discussion". If you keep the foam blocks in the seat box, putting drain holes in the box will lead to soaked foam. If you decide to not replace the foam, drain holes would probably work.
I reseal the tubes and use the foam blocks. The I drill a couple of one inch holes in the seat top and seal the holes with plastic cap plugs. As I install the foam I make sure to drill holes in each block to align with the inspection holes. If you ever want to check for water in the seat box, pull the cap plug, wrap a piece of paper towel on a dowel and check the bottom for moisture.
As for the dips in the seat tops every Thunderhawk seems to have them. I use 5/8 plywood for the seat cushion bottoms when re-upholstering and that bridges the dip in the seat top.
I also attached a pic showing the drain inside the box and a pic of the seat cushion in a Thunderhawk.

@flying fish - re:your bottom photo of the interior - curious what you used as a coating/paint color. Really like the flat gray look for my rebuild...thanks