Steel Boats and Welding

[Outlawed]

Hello all. After reading all these good post on this topic I would like to add my notes.There alot of factors involved that alot of people dont look at when it comes to steel. Salt water is any metals worst enemy.If proper care is not done you will just watch your love just rust away. But this can be kept at bay to some degree with the proper care. The proper use of OSFO(oxidizer),Steel seal and good primer will keep the rust down.The oxidizer dries moisture and kills the rust.The steel seal acts like a moisture barrier and the primer is somewhat the same.knowing how to weld is just a small part of this.Having a needle gun(for paint chipping),chipping hammer,deck crawler(good for stripping decks of paint and rust)but a needle gun will work for this too) and a high speed grinder with a wire wheel are tools you must have.I have worked on inland and offshore towboats for 10 years now and have alot of experience with this matter.I hope I have contributed to this topic...good day all.

[SaltyMonkey]

Thanks Outlawed.

So, what would be the ideal coating for a steel sailboat? Anyone want to contribute? There is the epoxy barrier coat layer (west or paint?) in the mix. Would it be something like:


OSFO
Steel seal
Epoxy barrier coat
Paint primer
Paint (bottom paint or on deck/topside some epoxy topcoat?)

[hpeer]

I see some boats have "flame sprayed aluminum" on the hull.

Any thoughts or comments on that practice?

Also, where to get it done?

[GordMay]

Thermal (Flame) Spray Fundamentals
➥ http://140.194.76.129/publications/e...2-3401/c-2.pdf

Google Thermal Sprayed Coatings for more info'

[hpeer]

Thanks Gord,

As it turns out the boat we just bought has "flame sprayed aluminum" on the steel hull but we have some spots where there were repairs.

I was wondering if we should go back and get it recoated.

In the meantime I use a two-part zinc epoxy with a two-part top coat.

[Yachts66]

Happy to oblige Miller. Gordon already responded to the Ultrasound/Audio gauge question, so I won't repeat that except to say they are the same. The more sophisticated machines will read through coatings, so they are truly non-destructive, where as the $995 specials require you to remove the coatings to bare metal in order to get a reading. Imagine doing that at several hundred locations on your hull and you'll see why the $2,000 machine pays for itself in one use. The machines are not hard to use, they come with a great deal of documentation, some even with training videos. Some of the manufacturers also offer training classes. So, do you need to be a "professional?" I guess it depends on how you look at it and how well you can read. The process itself is very simple. You put the probe/transducer against the hull and get the reading. With a less sophisticated machine you can write the reading on the hull in chalk. The more sophisticated machines will store the location and reading in memory then give you a nice Excel spreadsheet formatted printout. Some of the newer machines allow you to drag the probe over the hull and take continuous readings! Very cool I think. Hard to use? No not really. Hard to set up the machine? I guess that depends upon your level of literacy. I've used them, I don't think it's all that difficult. I guess some folks are hesitant to "do" and would prefer to read and talk abut things as opposed to actually getting their feet wet so to speak. For them, perhaps a "professional" is money well spent. Certainly it's safer and frees one up to continue their dreaming.

Core-Ten. Is a steel created for architectural applications. My personal feeling is it has no place in boat building. It's harder and more brittle and a lot more expensive. The common misconception is that it's "rust-proof" and thus the ideal steel for boats. Very wrong misconception. The way core-ten works is it quickly develops a thin oxidation layer that in effect "seals" the underlying steel preventing oxygen from getting to it. Without oxygen you can't have rust. In architectural applications it's frequently unpainted for this reason. On a boat, it has no advantages, does not like salt water any better than mild steel and as I said, is more brittle. I would never build a boat out of it. Would I consider buying a boat built out of it? Maybe.

As Brent pointed out and as I pointed out many posts back, the proper way to build a steel boat is to start with bright metal and start laying on a good epoxy paint. I really like Ameron products. Ameron 235 is the old standby in the marine industry. Ameron 240 is I think intended to phase out 235, but I may be wrong on that. In any case, it cost more, but it's also approved for tanks. It makes a lot of sense to paint the inside of a steel diesel tank and that would be the product to use. If when building a boat you start with steel that's pre-blasted and primed (weldable primer) you don't need to sand blast the hull. If you don't use the pre-primed and blasted paint, you do. Steel purchased this way is usually not actually sand blasted, it's done with a mechanical abrasive process, but the end result is the same. Sand blasting is very messy and very expensive and increasingly ever more regulated because the blasting medium can be toxic. Which is why I think a person is much better off starting with pre-primed steel. You can get a small sand blasting unit at Harbor freight for touching up small areas which I think is the way to go.

As Brent said, foam on bare steel is a nightmare waiting to happen. That said, foam really sticks when it's sprayed on, so it's not easy to remove. There is the added complication of having to remove the interior joinery in order to get to the steel to sand blast and paint as well. If I find a boat that's been foamed but not painted first I'd walk away. It would just be too much trouble and expense to remove the entire interior and do the job right in my opinion. Of course, if you didn't like the interior the boat came with and get all hot and bothered at the thought of tearing everything out and doing it "right," that might be a boat for you. In my view this is one of the major problems with steel boats. You get people who either through ignorance or dishonesty don't do the job right and what's left isn't worth buying.

I spent two years looking for Star (my Roberts 65) before I found her. Now that I've lost her, I've pretty much come to the conclusion the only way to replace her is to build a new.....but that's just me.

Regards,

Thomas

[Yachts66]

Oh, Miller, forgot to say most surveyors don't do the audiogauge(ultrasound if you will). That is generally done by a separate contractor or if you're up to it, yourself.

Regards,

Thomas

[SaltyMonkey]

Originally Posted by Yachts66

Core-Ten. Is a steel created for architectural applications. My personal feeling is it has no place in boat building. It's harder and more brittle and a lot more expensive...

But my understanding from reading is that Cor-Ten is stronger than mild steel.

Originally Posted by Yachts66

I really like Ameron products. Ameron 235 is the old standby in the marine industry. Ameron 240 is I think intended to phase out 235, but I may be wrong on that...

Is this used only internally, or externally as well?

[Yachts66]

High tensile steel is "stronger" than mild steel, but it's not used in boat building either. Strength is a relative term. Cor-Ten is not meant to be used in boat or ship building.

You can use it on the outside of the tank, but it's more expensive. Were it me, I'd use 240 on the inside and 235 on the outside. Condensation results a water getting inside the tank. Coating the interior of the tank will protect the steel. The old wives tale held that the diesel fuel itself would protect the steel, but that is not true.

Thomas

[SaltyMonkey]

So let me understand (confused) since we are focused on tanks...

The interior of the hull, before foaming, should be coated with 240? Bilge and above?

The exterior of the hull should be coated with 235? Deck, above the water line, below the waterline?

If not, what would you recommended as a coating?

e.g. can you lead us through a complete recommendation of all the layers internally and externally? e.g...

OSFO
Steel seal
Epoxy barrier coat (whatever that is?)
Paint primer (Needed??)
Paint (bottom paint or on deck/topside some epoxy topcoat?)

I still don't get a picture of what the complete hull layers are for best practices on steel...internally vs externally...above vs below water line.

[Yachts66]

Go back many pages and read my post on coating the interior of the hull. As I remember it you didn't like my suggestions then, maybe reading it again will help.

240 is approved for tank coatings, 235 is not. You can use 240 where you would use 235, but it cost you more money. If money is not a consideration, use 240.

Except for the interiors of tanks you can use 235 everywhere on the boat inside and out. It's an excellent undercoating product.

Thomas

[SaltyMonkey]

Ok, just to bring it up to date, here is what I think is the recommendation by Y66. Honestly, it's difficult to come up with a best practice from all the suggestions from different people. If anyone has one please chip in to align this confusion. Also, the exterior which is not mentioned.

Originally Posted by Yachts66

I realize I'm jumping in here late, c'est la vi. Brent's the man when it comes to building steel boats on the cheap. He's also got a pretty good book on the process he'll be happy to sell you. I made the mistake of loaning my first copy out, so I had to buy a second one from him, but he didn't seem to mind at all. Imagine that?

Ok, first, always remember steel boats rust from the inside out. 2 part epoxy paints are wonderful for protecting steel, but lousy if the steel is not prepped properly. For the little more it costs, I think you're way far ahead to buy your steel pre-primed, where they will mechanically abrade the steel to remove the mill scale and paint it with a weldable primer. This eliminates the need of sand blasting which is very messy and not inexpensive. Once the boat is finished, I would want to put at least two coats of expoxy primer on the interior. Actually, I think I'd use the following painting scheme: 1. Coat of epoxy primer lime Ameron 235; 2. Sound damping paint like Mascoat Delta dB; 3. Another coat of 235; 4. Yet another coat of 235; 5. A coat of Mascoat Delta T insulating coating above the water line; 6. At least 2" of fireretardent closed cell polyurethane foam over the Delta T; 7. A coat of flat latex house paint on the foam because Brent says that will really make the foam inflammable and I believe him!

Yeah, I know that sounds like a lot of work, and it won't be cheap, but look at it this way: Once you've installed the interior a goodly portion of your hull will be inaccessible unless you're willing to tear out the interior! Do you want to worry about rust behind the bulkhead or under the overhead? I don't, so I would follow the above painting scheme to the letter. I like the Delta dB because some designs, particularly Roberts radius chine boats are flatish on the bottom and when the pound into the waves the hull has a tendancy to "ring." Delta dB would stop that. Of course you will want additional sound proofing in the engine space.

On my boat, the builder put a stainless (316) crash plate wrapped around the bow about a foot on either side. I wish he'd have made that plate wider and ran it down to the keel. Why? When the inevitable happens and you run into something, or as happened to me a drunk fisherman ran into me, the stainless crash plate gives extra protection to the hull and if the paint is damaged, there won't be any rust.

That said, if the boat is painted properly with multiple coats of high quality epoxy paint, it will be very tough and you won't get much rust anyway. What little does come up is easily dealt with.

Finally, after saying all the above, if I had the money I'd build an aluminum boat and not worry about rust at all! LOL

Regards,

Thomas

[Yachts66]

235 would be the base coat on the exterior, over which you would place your color coat above the water line and your anti-fouling below the water line. Some folks like to use a zinc rich primer under the 235 on the exterior some seem to think it's not necessary.

Thomas

[Yachts66]

Ohhh to that I might add it's hard to have too many coats of paint. I think Brent told me once he has many, many, many coats of paint on his boat.

Thomas

[SaltyMonkey]

Ok things are getting clearer...this is good.

Exterior:
- Zinc rich primer (optional)
- 235 (I guess this acts as a traditionally applied epoxy barrier coat)
- Then either colour coat or anti-fouling.

Is there any place for the additional suggestion of...

- OSFO
- Steel seal

before applying the primer or 235 either on interior or exterior?