Fiberglassing over wood

[coopec43]

My resin is "A low styrene emission, orthopthalic polyester resin, thixotropic and pre-promoted." (So now you know)

Acetone Vs styrene thinner? It seems if I do enough googling I can get whatever answer I want!

"Adding styrene to new resin to get a better bond to wood seems like a good idea up front, but the chemistry starts working against you rather quickly. Adding more than a very small amount of styrene (2% or so) can have a big effect on physical properties, this includes water resistance and crack resistance, plus the penetration into the wood is only marginally better".
https://www.boatdesign.net/threads/p...styrene.57039/

Anyhow I used acetone and I've moved on! (Sorry I started the thread!)

[coopec43]

Sometimes I read an online opinion on (say) thinning resin with styrene (or acetone) and my immediate thought is "Does this guy know what he is talking about?"

I can't find it now but he doesn't approve of thinning with acetone either. He says to let the resin coating cure and then add the lay-up. "If it is not cured it will draw the resin out of the wood"

I just looked at the guys' background who advised against using more than 2% styrene to thin resin (See previous post) and I'll take his word as gospel

[Fore and Aft]

I hardly see any glass tabbing failures on plywood bulkheads. But when it comes to polyester/fibreglass on plywood that’s on the exterior of a boat I have seen some shocking failures.
Cheers

[coopec43]

Originally Posted by Fore and Aft

I hardly see any glass tabbing failures on plywood bulkheads. But when it comes to polyester/fibreglass on plywood that’s on the exterior of a boat I have seen some shocking failures.
Cheers

I won't argue with that.

[Chotu]

Originally Posted by coopec43

Sometimes I read an online opinion on (say) thinning resin with styrene (or acetone) and my immediate thought is "Does this guy know what he is talking about?"

I can't find it now but he doesn't approve of thinning with acetone either. He says to let the resin coating cure and then add the lay-up. "If it is not cured it will draw the resin out of the wood"

I just looked at the guys' background who advised against using more than 2% styrene to thin resin (See previous post) and I'll take his word as gospel

This guy is the gospel. You should always take his word. He is brilliant with polyester.

[Benz]

Originally Posted by coopec43

There's plenty of 50 year old polyester yachts with marine grade ply bulkheads still sailing.

What production epoxy/glass boats are there? I am not aware of any but that is not to say there aren't any.

"That most boats have plywood bulkheads tabbed in does not make it good practice: it is simply cheap practice."

What is the alternative used in production boats? (Maybe they use a product called G10? What is the cost of that? I shudder!)

"How long till someone adds a through hull and doesn't prep the hole correctly?"

If someone is stupid/careless enough to do that then damage may result but it doesn't matter whether polyester or epoxy gas been used.

You are stuck on the production boat idea. Production boats are cheaply built, some more than others, but even if they all are doing it, that doesn't make it a good idea. Sure, some older boats dodged the bullet and haven't had bulkhead rot, but many, many others have suffered catastrophic water intrusion. Surely that is impossible even for you to deny.
My point is, knowing the chances of failure on wood-cored polyester structures, it doesn't make sense to keep doing it.

[coopec43]

Originally Posted by Benz

My point is, knowing the chances of failure on wood-cored polyester structures, it doesn't make sense to keep doing it.

I'm not discussing wood cored polyester structures.

I'm talking about tabbing bulkheads to the hull, making up a 'shelf" for an autopilot (or toilet), securing a timber cabinet to the side of a hull with polyester/glass, using encapsulated ply for deck fittings - sheet winch mounts, anchor winch mounts, stanchion mounts, hand holds, cleats.

Maybe it's time we moved on

[Benz]

Originally Posted by coopec43

I'm not discussing wood cored polyester structures.

I'm talking about tabbing bulkheads to the hull, making up a 'shelf" for an autopilot (or toilet), securing a timber cabinet to the side of a hull with polyester/glass, using encapsulated ply for deck fittings - sheet winch mounts, anchor winch mounts, stanchion mounts, hand holds, cleats.

Maybe it's time we moved on

All of these things are bad practice. Bulkheads should never be plywood, nor should winch pads and deck fittings. In short, there is no excuse in our day to use plywood anywhere in a boat's structure. Settee locker lids? sure. Counter top? OK. But never, never in the structure, nor with holes coming through it from outside.

[Chotu]

Originally Posted by Benz

All of these things are bad practice. Bulkheads should never be plywood, nor should winch pads and deck fittings. In short, there is no excuse in our day to use plywood anywhere in a boat's structure. Settee locker lids? sure. Counter top? OK. But never, never in the structure, nor with holes coming through it from outside.

I agree about the pads, but you are way off about bulkheads. Plywood bulkheads are probably the smartest thing you could do. That’s exactly the type of force plywood is designed to handle. They are incredibly strong, they are lightweight, They are faster to build, and there is absolutely no reason not to do it.

I’m not talking about garbage plywood, I’m talking about true waterproof marine plywood encapsulated in epoxy. But there’s absolutely no reason to create foam composite fiberglass panels for bulkheads.

[Benz]

Originally Posted by Chotu

I agree about the pads, but you are way off about bulkheads. Plywood bulkheads are probably the smartest thing you could do. That’s exactly the type of force plywood is designed to handle. They are incredibly strong, they are lightweight, They are faster to build, and there is absolutely no reason not to do it.

I’m not talking about garbage plywood, I’m talking about true waterproof marine plywood encapsulated in epoxy. But there’s absolutely no reason to create foam composite fiberglass panels for bulkheads.

I disagree with all my heart, but that's what the internet is for: opinions. Then you just have to decide whose opinion carries more weight.

[Chotu]

Originally Posted by Benz

I disagree with all my heart, but that's what the internet is for: opinions. Then you just have to decide whose opinion carries more weight.

This is good for a discussion. I need to know why. Why would you think that plywood is not the perfect material for a bulkhead?

And if not, what are you making it out of? Foam and glass? Foam and carbon?
What are the specific engineering qualities of those materials that make them superior to plywood in tension?

I’ll admit, for a box beam across a catamaran, I don’t see plywood as the right material. The forces are a little bit more complex in that case. But a simple bulkhead in a single hull? That’s just tension.

I promise I won’t get testy. I’m curious what you are thinking.

[coopec43]

Originally Posted by Benz

I disagree with all my heart, but that's what the internet is for: opinions. Then you just have to decide whose opinion carries more weight.

I've tried to find out what your experience is with boat building materials and construction by looking at your CF profile but it is completely blank

What does Marine Service Provider mean in your case?

Is there any chance of updating your profile so we can assess the weight of your opinion?

[Benz]

Originally Posted by coopec43

I've tried to find out what your experience is with boat building materials and construction by looking at your CF profile but it is completely blank

What does Marine Service Provider mean in your case?

Is there any chance of updating your profile so we can assess the weight of your opinion?

In this case, Marine Service Provider means I have a rigging business, but sometimes branch into boatbuilding when necessity compels. My experience is with first, long ago, fixing up a 1967 Irwin 27 with rotten plywood bulkheads and spongy compression beam. That behind me, I built a Cape George 31 from a bare hull, using no plywood for any structure (foam/glass/polyester). Sailed it from CA to Newfoundland (still sail it), and now live in Rhode Island, where I initially did captain work in the summer (80' steel schooner) and boatbuilding in winter. Built several different boats--some polyester/vinylester/gelcoat production boats, some epoxy/foam core custom jobs, worked on several others. No one I've worked for around here uses plywood or balsa in the structure: it's all about cored foam or the various flavors of honeycomb (Nidacore, etc). I'm not fond of grinding fiberglass or carbon, so I edged out of that and into rigging, which I've enjoyed playing with since I first went to sea in 1995. I have a few clients, but my primary one is RigPro, where I work as a subcontractor doing most of their splicing work.
I admit I know very little of composites compared to the vast experience of the lifelong boatbuilders around here, but I've seen enough to know that even the cheapest production boatbuilder I've encountered will not use wood in his boats' structure, nor will he use encapsulated plywood as pads or core.

[Fore and Aft]

I originally built boats before becoming a marine surveyor and of all the thousands of boats I have surveyed (1964 or 67 was the oldest production yacht) glass tabbing and plywood bulkheads are not really an issue. Sure there is the occasional failure but nothing that warrants outright condemnation.
I built our plywood yacht and where there is a drain hole I glued a peice of PVC pipe in, then glassed over the top of it. That way the end grain is 100% sealed.
Cheers

[Benz]

Originally Posted by Chotu

This is good for a discussion. I need to know why. Why would you think that plywood is not the perfect material for a bulkhead?

And if not, what are you making it out of? Foam and glass? Foam and carbon?
What are the specific engineering qualities of those materials that make them superior to plywood in tension?

I’ll admit, for a box beam across a catamaran, I don’t see plywood as the right material. The forces are a little bit more complex in that case. But a simple bulkhead in a single hull? That’s just tension.

I promise I won’t get testy. I’m curious what you are thinking.

My bulkheads are foam and glass, made on a flat table. I haven't the engineering know-how to compare them to plywood, I only know that water intrusion is death to plywood, and having dealt with that before, I never wanted to again. Laminating foam/glass panels on a flat table is dead easy, using whatever system suits you best.