expoxy pad on top of gelcoat

[Colbud]

Hi all,
I'm about to assemble a solar gantry on the back of the coach roof of my Lagoon 450. my design involves 4 vertical posts along the back of the roof to which I will attach a one inch stainless tube.
the two middle posts are easy to install as the roof is flat. out towards the sides of the roof it curves down slightly(6 degree tilt) and I'm considering making up pads out of thickened epoxy or fibreglass on top of the gell coat ( it is non skid patterned) to create a level base for post base.
I would appreciate any prep advice or other solutions.

[Spot]

If it were mine to do, I would start with a prelaminated G10 or FR4 type board and cut it to shape and bevel it with a 7 inch sander or a flap disk on a 4 inch angle grinder. Or if I had extra time and materials maybe mold them with resin and cloth in a mold made from a deli type container. I would not try to build up in place. To bond to deck I would clean with acetone, sand, clean again, and tape or mask off the surrounding area. I would add a little fumed silica to the epoxy so it is less runny and/or use a fast hardener but not the 5 minute stuff as it seems to turn yellow faster. If you had white pigment you could add 2 or 3 percent to better match existing.

[tkeithlu]

Spot's answer is beautiful, but there is another question. Would your gluing the solar frame to the gelcoat supply a strong enough bond when a gale wind gets under the panels, or a wave sweeps the cabin top? You are relying on the fiberglass/gelcoat bond and the strength of the gelcoat itself. That stuff is meant to be pretty, not structural. If it were mine, I'd through bolt it to the cabin roof, and put any backing on the inside.

[Bill O]

Two excellent responses by Spot and tkeithlu.

Would strongly agree w/thru bolting the fittings.

[Gary Mc]

If you are going to thru bolt , which I strongly agree with, then you could use a piece of Starboard cut to the required shape. Easier to work with then G10 etc. and would look fine.
Good luck

[Bill O]

If you have access to Coosa or HDU board, the tooling process would be even easier to make pads to level out the coach roof crown/camber.

[s/v Jedi]

All good tips above

As for thickening epoxy in high compression applications, it is best to use the high density filler as main component, then add some colloidal silica (fumed silica, cabosil) as a thickener to prevent running). You can make successful castings with that.

[Spot]

Thanks for the thanks.
I guess I was thinking bolted through as well.
6 degrees of deck slope is significant if you like things square/flat/tight.
Maybe two tapered pads are needed, one internal one external?
Drawing showing top pad only. I would also do the drill-fill-redrill thing on the mounting holes if there is a core material on the deck that could get mushy from water intrusion.

Another thought...have bases made up with the taper included?

[Spot]

Originally Posted by Spot

Another thought...have bases made up with the taper included?

Something like this, still could use a backer, nuts, and fortified through holes...

[s/v Jedi]

Originally Posted by Spot

Something like this, still could use a backer, nuts, and fortified through holes...

I have it like this: it is a source of leaks. I like a pad underneath and actually made 1/8” ones for me in the form of split washers (there’s wiring through it) but need to install them still.