STEEL HULLS with Composite Superstructure / Topsides

Watch out for "Point and Shoot Applicators"

Substrate Prep and ambient conditions are first on list of any coating job, no matter what the coating chemicals are. first think to check applicators out on.

Remember the polyurea applicator is the manufacture of the finial product, its just chemicals in 55 gallon drums till he makes it a polyurea.

There may well be more Point and Shoot applicators out there than the other kind and watch out for pickup bed lining applicators.
There is a world of difference in surface prep than what they do compared to industrial applicators, like sand blasting and coating to NACE & SSPC standards, salt testing, moisture reading, other contaminants testing and PDA standards.

 

Polyurea Bonding Question

So you agree with Wynand that epoxy coating the inside surfaces of the steel hull is better protection than the numerous older methods involving zinc?

You've made comments with reference to Polyurea materials. Have you had much personal experience with these products? Of course the first basic question to ask if one was even going to consider such a coating is, 'How well does it bond to steel??' Could it really be relied upon to not let moisture between itself and steel....over the long term?

When I first watch this video of a particular Polyurea formulation developed for Iraq.....Dragonshield brand
http://www.youtube.com/watch?v=DGlMK0KWOJ4
...my thoughts were, 'how about a real damage proof hull plating backed-up with this material'....WOW?

You mentioned it was tough to remove the coating in order to effect a repair. I submit that in a number of cases you might not have to remove this inner hull coating as its elasticity might just keep it bonded to the steel plate that is damaged, and that steel plate might even be 'pressed' or hammered back out into shape. I realize this would take some torch heat to the outer steel skin, but I have seen reference to a fire-resistant version of Polyurea??

 

Composite I-beams for Framing Structure

...this subject came up on another forum, and I introduced this other idea tha's been floating around in my head.

Several other steel builders have all identified this 'fully welded' or 'standoff gap' as an important considerations when trying to get the perfectly clean bare steel surface to apply an anti-corrosion primer to.

To this I would also add the problems with trying to get a fully-blasted underside to any 'T' shaped ribs, frames, stringers, etc that might be utilized.

What I want to more fully examine is the possibility of using I-beams constructed of composites (core-sandwich construction) in the place of many of the 'minor' (and possibly major) internal framings of a steel hulled vessel. The I-beams could be cut from a big 'panel' of specially layed-up sandwich core with specific skins to meet a desired strength in the I-beam. These I-beam reinforcements would likely be bonded to the inside of the steel shell with the latest methacrylate's.

This would significantly eliminate a lot of welding of the internal framing, and it would be much easier to prep for a really good anti-rusting of the bilge areas.

This might or might not be all oversprayed with a custom blend of polyurea ?

 

Till now I found that 2pk epoxy is the best finish for any hull bilge, steel or aluminium or timber (some boat builders think that bilge timber should breath, I believe having owned several timber sail yachts that if I can seal it end grain or long sawn edges I will).

As Ace mentioned prep is the main issue, I prefer spray epoxy coating the blasted steel when its bright silver grey rather than rotary wired brushed plus I give a lot of attention to the edges of hull penetrations, sea chests. Roller application is okay if all those hidden areas among stringers and frames, limber ports are well coated.

The PU polymer coating sticks really well to steel if it is clean and free of flaks rust, paint etc, the all important factor is the skill of the applicator to set up the blender/heater equipment. Only use low pressure system on hulls for thickness control, the high pressure system is ok for big areas like concrete basement floors or rotary mineral mills.

 

The fastest way to answer is samples.

send me your mailing address and I will send you a sample on thin steel plate.
You can have fun trying to destroy the coating.

 

I assume that is directed to me?

One thing you brought up and needs consideration is the need to preprep some of the smaller gaps, etc that might not get filled completely down deep prior to it 'setting-up'. It other words the coating might bridge over some gaps, slots, etc without fully bonding to ALL of the surface area,...particularly as it appears to be a rather 'thick fluid', and it sets up so fast??

 

Polyuera that is sprayed will fill 1/16 inch gaps.

Yep, there are all kinds of polyureas, some you can even roll or brush on. The lower the pressure of application the weaker the coating.
The strongest one I manufacture was discovered while they were trying to make the Dragon Shield you mentioned.
We operate over 3000 psi and use a spray gun that allows the chemicals to mix even more making the finial product even stronger.
In the spray polyurea world of products, I list a pickup bed liner as the weakest and Dragon Shield as the top of the list.
Tack dry time is around 9 sec. so yep, not much time to run down a crack.
No limit as to how thick we can apply polyurea - 60 mils is a thin coat for us.
125 to 250 mils is very common for a rough / high wear service. A bilge area of a boat (if no iron being thrown around while working on engines or such), I do not see needing more than 125 mils.
Polyurea as you may by now know is a plastic, so there is one out there that would hold up well.
We spec'ed out a Salt Water Tank lining for ConocoPhillips in their Kuparuk oil field and should be applying in next June- not our strongest coating.
As I mentioned some were, ConocoPhillips is testing polyureas for lining their tanks under 1000 or 2000 psig.
Other companies have tanks lined with polyurea coating for the past 6 years and I hear an inspection was done after the 6 years and the coatings looked new.
We will be switching our reactor back to the tough polyurea chemicals after tomorrow and could shoot some 7 inch x 7 inch samples in next few weeks.
I think seeing is the surest way to answer so many questions. Brian, If you wanted to get a sample welded up with a framing material on a plate and ship it to us, we would apply our coating to it. You could then cut it up and beat on it - it would answer a 100 questions for you.

 

there is another way to see first hand is find an applicator close to you and see if they will do a little spraying for ya. Warning, it take us an hour to heat our equipment up to spec, so he might want some money, but if your serious it could answer a lot of your question. Go to the Polyurea Development ***. They have a list of people that have passed their advanced applicator class. At least those people have been taught the right stuff, now if they do correct substrate prep.
I deal with companies that have rooms full of lawyer waiting to sue so I better be doing it right.

 

We prefer the low pressure applicator because it allows more control plus slightly slower tack off time so workers can tidy up gullies with a palet knife.

The thickness that proved most successful for our PU foam fenders was max 4mm thick top side and underside with 6mm at the waist. The idea is the coating must be flexible to allow a hinging movement top and bottom, allowing the foam fender to compress without cracking the coating joint line.
The vessels weigh 20tonne, coming along side container ships under way, off shore terminals platforms holding position in all sea states so the fenders are under constant impact with severe abrasion.

For a bilge water proofing anti corrosion and insulation coating (plus impact protection) I think low pressure application @ max 2-3 mm thick coat would suffice. It's not like coating a dump truck shell for rock protection.
Thickness equals weight so unnecessary thickness is just fuel burning deadweight.

 

Fenders sounds like an interesting project

Yep, hard to spec out a coating and thickness without knowing a little more about the service of the boat. Our commercial fishing boats would require a tough coating of 125 mils to last a life time. If it's a sail boat with no foot traffic or physical activity, it would be a thinner coating.

Titirangi, what chemical compound company did you use? Also, how long or how much service life has the fenders lasted?
All polyuria's that I know of are flexible, some a lot more than others. We are spec'ing out for -60 deg. F to +70 deg. F. Even my rough service coating will meet that.

The compression of your fenders is a very interesting application. That is why I am interested in what chemical company you used.

 

It may not be relevant but:

I am told that airliners are painted with polyurethane coatings because of it being flexible.

Polyuria is a different composition?

We painted a alloy work barge with etching primer, 2-pack epoxy undercoat, polyurethane. It got a hammering. The top coat is scratched and peeling in some locations but the undercoat is extremely robust - unaffected after 10 years.

The scary thing about new products is that we don't know how good they are until 10 years down the track. I am very interested in 2-pack epoxy tar. Any negative reports on this?

 

Hot zinc spraying and then painted over the zinc with epoxy is a great coating system for the interior if you can afford it. Most steel boats I have worked with that were treated this way stay pretty much pristine inside. I have one 65 footer treated this way too.

But a steel craft should also be properly designed and constructed with a view to longevity. Hatch coamings for example should project through the steel decks amply.

If you just epoxy the inside well and keep the water out ( including condensation) you'll find it will outlast you anyway. As for the gaps between frames stringers and the hull, don't fret about them, for starters the paint goes into the gap and secondly these days we often use a bead of sikaflex polyurethane sealant to fill any gap. It works a treat and I can guarantee the sikaflex works we've been doing that for 15 years. We even use sikaflex underwater to seal riveted steel vessel plate boundaries after sandblasting.

I would use steel frames and I'd look for a design that can be built from flat plate. Looking at your design types you will have a lot of leeway for structural weight anyway.

A lot of successful steel craft have steel decks and plywood deck houses often that plywood is fiberglassed with a thin layer to completely weather proof the ply. A lot of earlier steel hulls have a deck shelf overlapped with plywood and then teak decks, there's a 1935 Dutch classic nearby that's still in great condition built this way.

 

Quick turn around or put in service is normal for polyurea.

Environmental & Substrate condition requirements for polyurea applications is very short compared to other coatings. Polyurea does not require certain temp and humidity conditions for curing. All they require is conditions to be correct at time of application. This normally means a reduction in over-all application cost when compared to other coatings. That is why ConocoPhillips is looking at (third party testing now) polyurea for immersion tank linings.
True, there is a cure time after application, but this does not require a certain condition. It just means it will take longer to reach 100 % cure.

 

Third party engineering firms have estimated 50 to 75 year service life on different projects.
U.S. Military has been using polyurea for several years now, even replacing armor plating and some polyurea on subs top hull.

 

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We found the compression ability is critical for fender to function properly protecting alloy hull.
The first boats operating around NZ waters had fenders coated with RHINO TUFF STUFF that has not performed well. Several fenders had coating with metre long splits, or lumps torn out strangely enough caused by timber pilings. We ensure coats are smooth, will slide of steel no problem but it grips timber.

The second & third fleet were built for operations in winter ice conditions water 0dg, ambient air -30dg with small floes and slush. I used Bayer product that was good but application was difficult, too sensitive to ambient temps/humidity.
For second fleet I found a new better applicator, we did many tests and found this product very superior for toughness and flex compared to RHINO or Bayer. Unfortunately I don't have the chemical details, I left file at the yard but in 2yrs the second fleet fenders have performed very well.
One boat lost radar in a heavy night fog and managed to hit nearly every obstacle possible including a sea wall & head on into anchored up 3000tonne CG ship while returning to port. The fenders showed multiple grazes but no splits or tear. I'll contact the yard for my file.

Bayer performed well but spray conditions must be perfect - Baytec® 52BC001 is combined with Desmodur® K630 to produce high-grade polyurethane elastomer for spray application.

The photos show weakness and delamination result of poor application method by spraying in below 15c temps/90% humidity