Steel Hull Painting Problem in France

[Pasarell]

The strip of exposed steel made me ask if it was an electrical cause but boatyard Manager (who is a qualified engineer of somesort) said he didnt think so, that perhaps it was a rushed paint job or something not done properlywhen it was sitting in a cradle, that he would sort it out. I'm not sure if I was convinced as I mentally memorised where it is so that we could investigate further at a later date.

The sling or support hypothesis can't explain how the strip runs vertically up the inside of the two keels.

Or are you saying that the paint has come off because of a painting problem and that the steel hasnt then become damaged because it is being protected by an electrical current and that is not a bad thing but once the boat is out of the water it is a bad thing?

Passarel - How quickly would the steel deteriorate while out of the water? It's only been out and exposed for two weeks maximum.

Meanwhile, boatyard has sanded back to our original undercoat, added lots of coats of stuff on top of that and are waiting for proper drying inbetween and boat should be back in the water next week. OH has stood over them and says that they are being thorough (now!)

I dont want to be sexist but really my part of the deal is supposed to be sorting out the curtains and stuff but I do love our boat and I am very interested in its welfare, can't help but get dragged into OH's remit.

I would be very interested in contacting Lt Cdr Oulds, certainly worth a phone call.

Thanks again all. I hope other steel boat owners are getting something from this.

Thanks again everyone

If the problem is caused by electrical systems (including too many anodes) there is not necessarily a paint problem. It is impossible to say without proper investigation.

Electrical faults in a steel boat can cause the paint to blow off the surface, and when it does so the steel usually stays shiny clean until exposed to oxygen - when it is lifted from the water.

Steel will not deteriorate more quickly once exposed to air but the appearance will be of fast rusting because it was so clean when it came from the water.

Steel is routinely blasted and left for several hours before painting in commercial situations but it is correct to say that the longer it is left the more it will deteriorate. A holding primer is all that is needed to maintain the condition, not armies of painters and especially not rushed thick coatings. Speed of rusting will depend a lot on weather conditions. Dry and low humidity is obviously better than rain!

My point about getting someone who knows what they are doing involved is that there is no point in recoating the steel and hoping the problem will go away. While you have the boat out of the water it makes sense to find the cause and correct it as it will just recur if not sorted. If it is an electrical problem it is because something has gone wrong with your systems - and that means they are likely to get worse in the future - possibly causing much more damage. This is the time to sort it!

Going back to the boatyard activities, if the steel was exposed for 2 weeks and they just sanded it then it will corrode again even if the electrical probelm is resolved. In earlier post I said that sanding steel is one of the worst forms of surface preparation. On a small strip blasting may not make sense but they should at least grind the surface. The purpose of surface preparation is to remove corrosion products so that they will no longer be active when painted. Sanding does not remove them - it just makes them look nice and shiny so the layman thinks all is well.

Hope this helps!

 

[ean_p]

question for Pasarell please

Hi pasarell
With your experience what would be your best prefared coating for the underwater sections of steel craft given that it will be sand blasted back to clean metal and how long would your pre fared system last as a rule of thumb and is the system reasonably robust/ repairable following small scale damage. And what is the generally expected life span of an epoxy system that has been reasonably well applied if not the same as above please?

 

[Pasarell]

Hi pasarell
With your experience what would be your best prefared coating for the underwater sections of steel craft given that it will be sand blasted back to clean metal and how long would your pre fared system last as a rule of thumb and is the system reasonably robust/ repairable following small scale damage. And what is the generally expected life span of an epoxy system that has been reasonably well applied if not the same as above please?

Hi Ean P
Firstly, what do you mean by clean metal and what conditions will the job be done under? I've worked with various systems over the years but now I'm biased and prefer urethane systems, especially if the conditions are less than perfect or coatings applicators are not professionals able to work quickly and to a high standard.

If conditions are perfect there is little difference between a good epoxy and a good moisture cured urethane system.

The major factor that will affect longevity though is surface preparation. There are tight definitions of what clean metal means and, in my experience, most blasters and expecially those in the yacht business, have no idea of those standards. They do half a job and tell you, with great authority, that it is perfect. In fact I can't remember seeing someone who is responsible for surface preparation checking for salt contamination after blasting etc.

A good coating scheme applied properly onto well prepared steel can last for 20+ years unless treated badly. Yesterday I was talking to the Kuwait Standards authority and one of their people told me of a recent job they were called in to look at where the coatings failed after 2 weeks! Of course, not a coatings failure at all - a surface preparation failure.

I'm travelling today but will send a PM when I get back to the UK at the weekend to answer your question properly

 

[sk8rboy]

Sorry to be slow to update. Boat is now back on the canal. It was pretty much taken right back and started again. Shiny metal done with grinder. Small discount for inconvenience. We still have to try and ascertain what caused that strip to peel but overall we are happy with the eventual result. Time will tell.

Thanks again for all the great advice.