Laying chopped strand over ENTIRE boat hull?

So I'm considering something which I've not really seen done before (though I'm sure it has been done, many times). I'm considering grinding away all of the gelcoat from a small 16' skiff, getting down to bare glass and laying new CSM down on the entire bottom of the hull.

The stringers on the skiff were blow out and I think it was ran for years with virtually no structural support. There are hairline cracks throughout the bottom of the hull that go INTO the laminate (i.e. all the way thru the original gelcoat and into the glass).

I've already rebuilt the stringers and the boat is flipped over now for bottom repair. I was only planning on laying new glass on the sections directly below the stringers (this is where the cracks are the worst), but upon seeing that there are cracks all over the hull I am considering adding large sheets of 1.5 oz chopped strand with poly resin down over the entire hull bottom to stabilize the stressed skin layer, and sealing with gelcoat.

A couple questions/concerns about doing this.

1) (most important question, obviously) Is this a stupid idea?
2) Should I be concerned about the new CSM delaminating down the road?

I know typically this is NOT something you'd do when re-gelcoating/painting a hull bottom. But like I said, given the hairline stress cracks that go into the fiberglass I feel the hull could use some stabilization/re-enforcement.

Thanks in advance to any responses and advice

 

It isn't a wacky idea.

It isn't often done because the cost usually exceeds the boat's value. The repairs you have preformed probably already surpassed this threshold.

If you use 60 grit or coarser delamination shouldn't be an issue.
BUT
-Internal cracks left in the existing FG will eventually telegraph thru the new layer.
-one layer of 1.5 oz matt won't suffice.
SO
Grind more off and add more back on.
OR cut your losses.

 

A shame you didn't put that mat inside the boat, before redoing the stringers, I certainly would not be putting that outside. I would fill the entire void under the deck as you call it, with pouring foam, till it oozes out of the ports you cut, that will firm things up, you can paint the outside with a high solids epoxy primer, brushing it into all the cracks, then sand and give it a coat of gloss. If the boat cracks up, you'll still get home safe.

 

Thanks for the great replies and advice everyone by popular consensus I’m opting not to lay new glass. I figured it was very excessive, guess I just needed some additional opinions to verify this.

I will probably still lay narrow strips of new glass over the worst parts of the cracks, but this is only along the outer edges of the hull bottom and keel. Rest of the hull I will just sand down like normal with 80 grit and reapply about 18 mils of fresh gelcoat. In any regard, the new stringers and repairs on the inside should stiffen up the hull tremendously to prevent further stress and cracking. That’s the hope anyways.

 

If you are adamant about laying narrow strips of new glass on the cracks, instead of using CSM you could use a woven glass cloth instead - you can even buy it in rolls of different widths (eg 2, 3, 4" wide).
And if you go down this route it might be worthwhile using epoxy rather than polyester resin, as epoxy will be much 'stronger'?

 

Polyester is an appropriate resin for this repair.

Epoxy on a few layers of cloth won't appreciably strengthen the existing thick poly hull.

Epoxy will interfere with the OP's desire to re gelcoat.

Hundred dollar bills have superior purchasing power than a five spot. But two $5s is adequate for my lunch, and doesn't run the taco truck out of change.

 

Beautiful

 

I probably will use 4 oz cloth with a layer of 1.5 oz CSM overtop for easy sanding. I've got loads of usable glass in the garage so I'll just use that.

 

Thank you all tremendously for the great responses and advice.. everyone's opinion is very much appreciated. As is the case with most things, it appears there are numerous ways to skin the cat here. Completely forgot to mention in my 1st post that the inside of the hull is already reinforced with 1708. There are three layers 1708 with epoxy resin over top the cracks that were below the busted outboard stringers. Stringers themselves are fully tabbed in with 1708 and epoxy, and I layed an additional layer of 1708 over top the entire stringers (foam cored) and extended the glass all the way to the center stringer on both sides. So, there is essentially an entire layer of 1708 overtop the entire inside of the hull bottom, plus two additional layers over the cracks. If this is not sufficient, I'll be damned.

The plan going forward from here is this: I've already got the hull sanded down nice and flat with the RO sander (I know you don't have to go down to bare glass to reapply gelcoat.. just got a little overzealous with the angle grinder when I was removing all the pretty "new" Awlgrip that was there (a piss poor job that looks like it was sprayed with zero prep). I will grind a 4" strip down to bare glass on the port side (starboard side is already done), as well as the keel, and add new glass. Probably a layer of 4 oz and then 1.5 oz CSM on top. This will all be faired out nice and flush. Then gel the entire hull bottom. Should come out nicely (*should*).

Again thanks to everyone for the wonderful advice and all the responses. And THANK YOU all for talking me out of laying new glass over the entire hull... I think it would've worked no problem, just (as many of you pointed out), wayyyy to much work than what is probably necessary.