Glass over ply.

[honey badger]

Whilst hacking out some dead plywood on the catamaran I am restoring, a thought sparked from my epoxy saturated synapses.

So with the advances made in modern epoxies thanks to the aerospace/military/and racing worlds.
Could you forego the use of glass cloth for hull sheathing? I realize that there are some jobs that will always require glass.

Asking for a friend...[emoji12]

[UNCIVILIZED]

Strictly speaking, epoxy alone is sufficient for protecting some hulls, yes. But there are limitations. Such as Fir plywood often checks enough so that the only way to prevent it is by using cloth in conjunction with epoxy.
What is it you're looking to do, & why do you want to pass on sheathing the hull in glass?

[honey badger]

Mate, the near on 50 y.o ply hulls on the Narai are glassed to about 3 ft above the keels on each hull.Polyester was the resin.
The rest of the hulls where not glassed at all and are in surprisingly good nick where there has been no corrosion of copper nails pushing up to the surface.
I can confirm your assertion that sunglasses ply does check, especially on the decks.

Would you glass in this instance.

[honey badger]

Ps I will glass the ply that I have replaced on the hulls.

[Captsteve53]

Note in your comment you said Polyester ? Should be Epoxy if going over ply or timber, if for some reason that is out of the question then Vinyl-esters would be better than Poly

Cheers Steve

[Snowpetrel]

Originally Posted by UNCIVILIZED

Strictly speaking, epoxy alone is sufficient for protecting some hulls, yes. But there are limitations. Such as Fir plywood often checks enough so that the only way to prevent it is by using cloth in conjunction with epoxy.
What is it you're looking to do, & why do you want to pass on sheathing the hull in glass?

Yeah, this is exactly my experience, some plywoods check and let in water and rot, others are pretty stable and do well with just a good paint or epoxy system. I tend to think glass and epoxy is preferable to just epoxy especially on hard wearing areas like decks, but it's a lot more work, cost and weight. Even then rot can still start around fittings, or any cracks in the glass.

The key is good basic materials and regular ongoing maintenance. Modern marine plywoods seem to be nowhere near as good as the older stuff. And full epoxy encapsulation does not seem 100% reliable long term, as in over 25-30 years or so.

[Captsteve53]

Ain't that the truth, hard to find real decent marine ply these days

[daletournier]

I've seen a number of Wharrams that have only glassed below the water line for abrasive protection and then epoxy encapsulate the rest. These boats were quite old as stated in a previous post.

[Wotname]

Originally Posted by Captsteve53

Ain't that the truth, hard to find real decent marine ply these days

While this is true in many places, it isn't true in those places where ply is manufactured to AS/NZS 2272 - 2006 and where all veneers are Hoop Pine.

This ply stands head and shoulders above all other marine ply.

Pretty big statement I know but I have used a bit of marine ply over the years from various sources and to various standards; none have proved better than AS/NZS 2272 - 2006.

[valhalla360]

Epoxy and glass do different things.
- Epoxy seals out water but by itself provides little structural or abrasion resistance.
- Glass provides structural (including resisting checking) and provides good abrasion resistance.

On an interior well above the bilge, epoxy by itself may work fine as there isn't a structural issue to solve. In the bilge or on the exterior, it's a lot more iffy to just slap a coat of epoxy on and hope for the best (you may get lucky and have no checking or abrasion but I wouldn't count on it).

[UNCIVILIZED]

When glassing things like hulls, does anyone have experience flow coating, in order to fill the weave of the glass, & minimize sanding & fairing? I've done decks & other horizontal projects with this technique, but never hulls. Though I've always been curious about it since I heard Kurt Hughes mention it in passing.
If you've done it much, it'd be interesting to hear about your experiences doing it. And the info may also help the OP.

[honey badger]

Interesting responses thanks people. I will endeavour to get some pics of 1970's plywood today.It is quite remarkable how good it looks compared to some of today's ply.
On hoop pine plywood I will second the comments on this thread.I did find it heavier than Asian pink plywood though.

[honey badger]

Uncivilized.You asked what my intentions where regarding the hulls. I have access to heaps of epoxy floor coating resin, so will be adding 3 microns per coat.
I will most certainly glass the new plywood i have put on the hulls.

[honey badger]

Originally Posted by Captsteve53

Note in your comment you said Polyester ? Should be Epoxy if going over ply or timber, if for some reason that is out of the question then Vinyl-esters would be better than Poly

Cheers Steve

The original glue used for the hulls would have been polyester/resorcinol/vinylester I am not sure whichever I know nothing about that gear.
All I do know is that where there is no rot the stuff sticks like you know what.

[honey badger]

[ATTACH]152764[/ATTACH. Nigh on 50 y.o. plywood still as good as new. Anybody hazard a guess what timber this is? It smells like pine
.