Steel boats - hull maintenance and longevity

[Brent Swain]

I once flame sprayed a 36 footer. The owner found a Metco gun in a garage sale for $20. Then he found the whole rig for $200. I found it easy to use. First it sprays like a fine sandpaper and stays cool, but as it gets rougher and hotter, you have to take the gun apart and clean it ( for acetylene) or the bond drops off quickly.
He was told that the navy was getting rid of their gas units for arc units, which meant they would end up in surplus stores, very cheap.
Yes, arc is far better, no doubt, but one must weigh the cost of a new unit against the cost of gas.
Friends in Victoria in the 80s were building themselves steel boats. I told them that buying the metco rig was cheaper than hiring someone to do it, especially if they all chipped in on the rig.They did ,and all their boats were flame sprayed.

There is quite a lot of information on the topic of zinc coating in various barge and inland waterway forums. They reckon that electric arc plasma spray does a better job than flame spray and that it's fairly easy as a do it yourself job once the hull has been blasted. The cost is apparently no more than a good epoxy job and can be expected to last 30 years or more.

 

[Brent Swain]

I once had to blast a tank in the back of a fin keel. Getting the sand out would be a major problem. So I cut a 6 inch by 12 inch hole in the back corner of the keel and blew the sand out thru it as I blasted. Then I ground the cutout piece and put 45 degree bevels on the outside edges. Then I blasted it and welded it back in. Then I had only the welds to blast .
That was much easier than trying to blast as the sand piled up .
Cutting a couple of holes at the low points, before blasting, to blow the sand out thru , makes things much easier ,and with 100% strength welds, it has no structural effect on the hull, afterwards.

Not where I am

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[Brent Swain]

There is absolutely no reason a second sand blasting and painting job wouldn't last as long as the first one, given the steel doesn't change, given the same thickness of epoxy.
That defies logic.
Same steel, same epoxy, same results.

 

[Brent Swain]

I use 3/16th plate for a 36 footer ,between 4mm and 5 mm. The same tensile and compression strength as 7 1/2 inch fir ,along the grain! At that rate, strength is not an issue.
After 33 years and several Pacific crossings, the epoxy on 99% of my hull is as good as the day I put it on.
Yes, time HAS told!

Corten is not just about corrosion - which it undoubtedly does better in the more problematic INSIDE - but it is 40% stronger. Meaning a 3mm corten hull is as strong as 4mm mild steel.
I'd be worried about different heat expansion coeffs of steel and the thick epoxy layer, but indeed, time will tell.

 

[Greenheart]

Presumably epoxied ply remains at least as flexible as any elements of a steel hull, yet epoxy isn't known for losing its durability in that application...is it?

 

[Wansworth]

I treated the interior of my steel boat with car underbody liquid

 

[Brent Swain]

Check out
http://groups.yahoo.com/group/origamiboats

 

[Brent Swain]

It is interesting how the "Be reasonable and do it the hard way " advocates, manipulate language to change its meaning. "Crude" is the new perjorative for "Not complicated enough, " the suggestion being that the way to improve an offshore cruising boat is to make it as complicated as possible. I have seen some designers post pictures of the most complicated wiring, framing and plumbing systems imaginable ,and brag about it, while ridiculing much simpler ways of accomplishing the same outcomes, thus suggesting that, that is what makes a boat better for offshore cruising. They seemed to completely miss the Leonardo da Vinci quote;
"Simplicity is the ultimate sophistication!"
They treat "Home made "as an insult , while" Custom Made" and Hand Made" are considered marks of "high quality" when, in fact , they are exactly the same thing.
Amazing how many get suckered into buying their lines, and fail to see the contradictions.

 

[Steersman]

Has anyone ever used 'Chemical Steel' to repair a hole in a steel hull?

 

[Brent Swain]

Has anyone ever used 'Chemical Steel' to repair a hole in a steel hull?

Never heard of it .Elaborate please.

 

[lpdsn]

Has anyone ever used 'Chemical Steel' to repair a hole in a steel hull?

I suspect you mean something like this:

http://www.loctite.co.uk/loctite-4087.htm?nodeid=8802657107969

I remember helping my dad to repair a rusty wing on our old banger using it when I was a kid - bit of an annual job. If you want to slowly morph your rusty steel boat into a plastic one it is one way but you might get a stronger repair with glass and resin or even a weld. I wouldn't really want to rely on it to keep the boat on the surface of the sea.

 

[Brent Swain]

What a total crock! My paint job is 34 years old and shows no pitting.The trick is o get a super thick buildup on clean steel from the outset.Mine was 30 gallons of epoxy tar on shotblasted and cold gavanizing primer, on a 31 footer. Most paint problems are either not so clean steel or lack of buildup to an adequate thickness.
No, steel under the paint doesn't change it's molecular structure, to be more prone to corrosion with time. Well protected, it remains the same stuff.That claim is laughable.

 

[Brent Swain]

Interesting thread! I built my hull with 3mm steel, and will launch soon. My plan was to go with flame sprayed zinc, but I could not find anyone to do it. Tom Colvin in his book on steel boat building feels modern epoxy coatings are so good that it is not worth going for sprayed zink. There are zinc rich coatings, and aluminium/zinc coatings you can spray on which sound fantastic, but the price is also quite something, and application requires some expertise. I eventually took the advice of industrial experts and went for an epoxy undercoat intended for the inside of tanks, which is so hard you can cut thread into it.

I would think the secret is proper preparation, and then internal construction so that you can remove panels and inspect the inside of the hull often. Mine has removable panels, but it is hard not to build furniture over it. We will see once she is in the water how it holds up.

I met a sailor in the Pacific who built a steel hull in France, and scrimped on the paint. Five years later he was desperately looking for somewhere to do sandblasting and repainting outside. Inside was his biggest worry and he was facing the prospect of stripping out everything and blasting, then re-painting.

I used hot galvanized steel for my decks, cabin, cockpit and wheelhouse ,not much more expensive than shot blasted and zinc primed steel.

 

[Brent Swain]

Most steel boats rot away from the inside.

Only because most are not adequately epoxied inside.Many have no paint at all under the spray foam insulation, a big ,very common mistake, which costs a lot of boats. Foam is not adequate protection for steel ,period.

 

[Brent Swain]

Nope.


Unfortunately I cruise in the real world

Even finding somewhere that does blasting is getting harder.

I hear Tunisia is doing a booming business in that which is no longer legal in Europe.

 

[AndrewB]

Has anyone ever used 'Chemical Steel' to repair a hole in a steel hull?

I assume you mean Plastic Padding "Chemical Metal", a two-part polyester filler. It's good for car body repairs, but when I tried it on a steel yacht, it didn't grip well, rust soon formed underneath and it cracked off. Suspect it doesn't cure properly in damp, dirty, rusty or oily conditions.

Epoxy filler works better, specially when used with glass-fibre mat. There are several brands of 'under-water epoxy putty' which could be used as an emergency temporary patch to the hull, but I wouldn't rely on it as a permanent fix in a critical area. One application where it worked surprisingly well for me was for replacing a stripped thread on an engine.

 

[Brent Swain]

Not where I am

[/IMG]

So nice to get all my steel shot blasted and primed from the source.

 

[Brent Swain]

I hear Tunisia is doing a booming business in that which is no longer legal in Europe.

Are other neighbouring countries , non EU an option there?

 

[davidlhill]

When I saw the thread I thought - oh, here we go again.

Now I see BS seems to have been neutered. Is that right?

 

[rotrax]

When I saw the thread I thought - oh, here we go again.

Now I see BS seems to have been neutered. Is that right?

I certainly hope so...................................

He appears so desperate to let us all know how clever he is that now he appears to have lost credibility on the other steel boat thread he has resurrected this old one.

To give credit where credit is due, my steel Hartley, built in NZ in 1986 from corten steel, would have derived great benifit from some of his anti corrosion features.

But, like ALL steel boats, unless these ideas are incorporated during build it requires far more work than the vessel is worth to do them later, when rust and corrosion are manifesting themselves.

IMHO, of course.