Fiberglass over steel hull boat

I am looking at purchasing a trawler (80,000# displ)50+ ft that when built (1975) had fiberglass skin applied over steel hull to avoid corrossion. 3 Years ago the below waterline application was stripped and new epoxy formulation applied. Has anyone else heard of the original application and can I expect to strip the rest of the vessel in years to come?

[gonzo]

To answer that question it is necessary to know the kind of resin, reinforcing firbers and treatment of the metal.

[RCardozo]

I have a 73' Dutch Sailing Barge that was built of rivetted iron. I was told when the rivets started to weep the previous Owner glassed the hull. That was in the 70's. I was told there were two layers of 5200 sealant applied. When the second was tacky they embedded fiberglass mesh in it the added fiberglass. The exterior had either bottom paint or epoxy. It is till good. I have one crack that I need to fix but the balance of the hull is fine.

[alan white]

"...but the balance of the hull is fine."

What would indicate the hull's condition? Is there an easy way to inspect it? Just curious, since that method is new to me (but I know very little of metal boat technology).

Thanks, Alan

[RCardozo]

Therin my friend lies the problem. Ultrasound testing wont work because you have two different materials and the readings get all fluky. I talked to a couple companies that do this. I am an Architect and know some testing firms who told me it is really difficult to find companies that would be able to do it if at all. They would need to get a reading on the steel solo and the the 5200 and fiberglass to get a baseline. Any surveyor you hire will tell you there may be all sorts of horrible things happening but he can't say what. You are left with the fact that you have to inspect at haul out and if there are any problems with the glass to remove and repair. Keep me informed on what is up. I have a crack caused by hitting a piling and need to do a repair. I will have more data when I grind down the glass and inspect.

[alan white]

Originally Posted by RCardozo

Therin my friend lies the problem. Ultrasound testing wont work because you have two different materials and the readings get all fluky. I talked to a couple companies that do this. I am an Architect and know some testing firms who told me it is really difficult to find companies that would be able to do it if at all. They would need to get a reading on the steel solo and the the 5200 and fiberglass to get a baseline. Any surveyor you hire will tell you there may be all sorts of horrible things happening but he can't say what. You are left with the fact that you have to inspect at haul out and if there are any problems with the glass to remove and repair. Keep me informed on what is up. I have a crack caused by hitting a piling and need to do a repair. I will have more data when I grind down the glass and inspect.

Yes, you will, I'm sure--- in that location. That will either cause you to sleep better or stay up all night pacing and muttering.
Iron would expand a lot and so it would show that expansion in a bulge, but what is bulge and what is a normal rivet, or an odd overlap in the iron or the glass layup?
I suppose one could drill to a set depth in suspect areas and check for rust in the flukes of the bit, then epoxy the holes, but nothing's easy, huh?
And all along, that hull could be as sound as the day it was built!
Only the failures get analyzed (Why did the corrosion happen? Ah, yes... let's rip this side off the old girl and see!).
And how easily could water migration under the skin follow a seam? Either a testamonial to the longevity of 5200, or an example of its ability to contain iron oxide.

A.

[RCardozo]

I ended up replacing a chunk of plating in my forward hold. It appears a past fiberglass patch exhibited cracking in the joint and the water corroded the steel plate. Other areas had the glass still bonded solidly to the hull so that you had to use a hammer and prybar to pop off the glass. Damage was easy to identify by tapping on the hull. Any leak creates corrosion which corrodes the steel and causes it to expand thus breaking the bond with the glass. If you have a large hollow sound then replace the glass. The key is you must watch and maintain the glass. Any cracks need to be patched. Most of my problem was that the inside was concreted which makes it impossible to monitor the inside of the steel. Once water gets thru the hull it gets trapped in the concrete and all hell breaks loose.

[masalai]

As it could still be between the concrete and steel! I was invited to manage the operations of a coastie in the Solomons. A converted Chinese fishing vessel of some 80 ft. What a disaster of rust and concrete patching (more cement than ferro) originally built in steel. "When the rats desert so should the crew."

[RCardozo]

Right. The hull was riveted iron. Luckily it can be welded. Some areas showed almost no rust. When water gets in its all over.