Ferrocement Corrosion

I occasionally get a ferro to survey and most often I find a piece of crap waiting to find a coral bed to live on. Great for rebuilding reefs and offering places for little fishes to survive, but damn near imposable to survey properly, without full build documentation, even with an xray machine.

 

From the description already given, it is unlikely it would survive the trip to the coral bed.
It sounds like a death trap to me.

 

I agree with most of the above, except that even though you, or anyone else for that matter are unable to survey the hull and that it looks like crap cosmetically due to poor plastering and/or armature fairness , does not necessarily make it structurally a piece of crap, one of the unfortunate things about FC construction. As far as reefs go when I first moved here 35 years ago there was a guy building a Hartley South Seas and he had actually done a decent job of the FC work but then went and built the cabin with OSB, the boat did get finished but im not sure if it went in the water but the guy died and it sat in the marina yard until the cabin disintegrated and they pulled the 6cyl ford diesel and sunk it for divers to dive on.
I agree, without documentation and photos I couldn't survey one and ive actually built one and been involved with other build. Thing is though the same goes with glass hulls, you can tell a lot of things when surveying but you don't know if it has all the laminate it is supposed to have or the fiber fraction without delving deeper than a typical survey. Its really not that much different except that we tend to trust that because they are production boats that they were built right wheres the FC boat is typically a home build and we assume the opposite.

Steve.

 

Some related threads . . .

-- http://www.boatdesign.net/forums/boat-design/we-love-ferro-cement-but-beware-21436.html

-- http://www.boatdesign.net/forums/sailboats/ferro-cement-yacht-49919.html

 

A ferro boat with these 'symptoms' is DOA or at the very best, a DNR. Donate it to an artificial reef society and make sure you get a waiver.

 

Steve W. Do you have any opinion on trying to repair the boat I posted about?

 

The problem is, even if you repair the current problem areas you will likely have the same problem somewhere else very soon. Some one screwed up plastering this one, no real way to fix that after the fact. Especially now that water has gotten into the mesh.

 

Im afraid i agree with all the others, water just does not get into a properly plastered fc hull. Even if all the armature is in there it would be impractical. Interestingly, in the latest issue of professional boatbuilder magazine there is a story of a pro built aluminum boat where the manufacturer of the plate screwed up and a number of boats were built by various west coast builders, short story, big lawsuit, boat totaled, builder ended up with the boat and over a period of years stripped the entire skin and replated it, the point being bad things can happen to to good boats regardless of what material it is built of, the difference is the aluminum boat, after replating had value, the fc boat, not so much.

Steve.

 

It wasn't the aluminum manufacturer really. ALCOA took over ALCAN and there was some difference in the nomenclature.

 

Yup. right alloy -5083 H321, but not marine grade. About $200 million worth of boats in US northwest & Alaska. I looked over a 40' commercial boat that had been parked outside (near salt water but never launched) for about 6 months and the hull was so rough it hurt to run your hand over it.
Lots of postings on the Metal Boat Society 'forum' under 'Faulty Aluminum Plate'

 

Ok, I had just skimmed the article but i just went back and re read it and it clearly states that " alcan had manufactured 775000 lbs of the bad 5083" which would indicate to me that it was something other than 5083. But its not important for this thread as i was only using it as an example to point out that the often used statement that you cant properly survey a ferro boat, while true, is really the same for any build method with the possible exception of some forms of wood construction. Most glass boats do not come with documentation to prove that it was built to the laminate schedule that the designer specified or what the fiber fraction is etc, so, unless a surveyor finds a red flag such as high moisture readings or blisters he will just take it at face value that the boat is sound and often it is. In reality a ferro boat that is not displaying any problems should also be assumed to be sound, especially as most ferro boats are now 30+ years old.

Steve.

 

Thanks for all the advice. I had another question about the boat that I have gotten mixed opinions on. There are 2 I believe copper grounding plates through bolted to the hull. I have heard this is ok and on the flip side that it is detrimental to the boat. What do y'all think? All other issues aside.

 

I believe that you have copper grounding plates attached to a hull that is structurally in terrible shape. It is unsafe and not worth putting any money into. However, if you are determined to restore it, all the boat needs is a lot of money and labor. I have never seen any object that can't be restored, provided the owner has the time and finances to afford it.

 

If properly installed any thru-hull penetration should have the mesh completely sealed to keep water out of the mesh. If these plates where done right (not so likely on this boat) there should be no electrical contact between the mesh and the copper so the plates should have no effect on the mesh.

If the copper is somehow connected to the mesh (no idea why anyone would do this) the zinc on the mesh and the steel could get eaten by the copper since both steel and zinc are less noble than copper.

But Gonzo is right, worrying about the copper plates is pretty much re-arranging the Titanics deck chairs given the condition of the hull.

 

haha good analogy .. thanks for explination. I was just wondering for clarification sake since I was told 2 different things.