Calling Steel Boat Experts

[BigART]

Hello Folks

Need a bit of advice. Having purchased a steel boat last year and put a significant amount of personal effort (or my wife did anyway) into scraping, prepping for and applying antifouling we are disappointed with the results 17 months later. I particular, there is loads of peeling around the anodes (pic below). What is going on? Too much protection? Nigel Calder descibes this effect on impressed galvanic protection systems but we don't have this and never connect to shore power.

 

[claudio]

I can't tell from the photo, is that's antifoul on the anode itself. If it is then the anode won't work at all and I would expect local galvanic reactions as water gets in. The anode needs to be exposed to the sea water and connected to the hull via the steel bolts.

 

[Ships_Cat]

Could be:

1. Improper preparation. Unless sandblasted back to grey steel (not sanded or ground) you are likely to have adhesion problems with paint underwater. If the boat is a high quality one faired with epoxy filler look carefully for areas where the sanding board has cut through both the fairing and the base primer to the steel and cut away the sandblasting bite - a potential trouble area on faired steel boats.

2. Inadequate paint system. The only way to go is with two pot epoxy primers made for immersed marine service - if you have used anything else then that is very likely your problem.

3. A zinc rich primer was used. They should not be used on underwater steel on small vessels, as is likely to cause adhesion problems once sea water has leached through the coatings above (which it will do).

4. It is said that over protection (too many anodes) can cause paint adhesion problems, but have never seen it myself nor know anyone that has seen a proven case. However, if you have many anodes and the damage is only around them, then maybe that is it. If you use a proper coating system you do not need anodes to protect the steel, only the exposed metals (and that only if they are not naturally corrosion resistant in seawater or if in contact with another incompatible metal)

It has been said by another that it may be because it looks like you painted the anode - although it looks to me as if the photo has the anode removed - however, regardless, even if you painted the anode or the anode is not making a low resistance path to the steel, there is no way whatsoever that the paint damage you show would have been caused by that (for non believers, if the claim was true then the paint would be falling off all underwater parts of any steel boat with "insufficient" (sic) or no anodes - it doesn't! You could only get damage on exposed metal - as you possibly know, a steel boat requires no different protection to a plastic boat as long as its coating system is not breachecd).

John

 

[ytd]

where is the anode? Has it been removed. If not it looks like it has been completely eroded. From my experience of a steel boat, that looks normal for 17 months. If it hasn't been taken back to bare metal in the last 5 years it will be hard to get paint to adhere. Ours used to lose most of its paint around the prop area due to sandblasting by sand sucked up by the prop when freeing ourselves fom numerous groundings. that's the moral hazard with steel boats. Because you can run into anything with minimal damage you tend to run aground a lot more.

 

[Ships_Cat]

If the grey bits and the shiny bits are bare steel, and it certainly looks so, then this, despite your own experience, is definitely NOT (with lots of exclamation marks after it) normal for a steel boat with any proper coating system on it.

I know there are poorly built steel boats out there (especially amateur built and maintained ones) that have such coating problems but in the end it is a quality problem not a problem that is natural to steel boats. The proper way is easy - blast, epoxy prime, epoxy fair (if wished), epoxy prime/undercoat, antifoul to the paint manufacturer's specification; epoxy coats preferably professionally sprayed to ensure the correct minimum coating thicknesses - albeit more expensive than the doityerself scrape, or sand/grind, and paint.

John

 

[BigART]

Sorry, sorry, sorry. I didnt explain very well.

The picture shows the two studs welded to the hull AFTER the anode had been removed. The anode(s, there are 16 of them) were all used, some slightly, others about 30%. Only the top layers of antifouling has come off revealing various layers of primer, etc. No steel, rusty, bare or otherwise has been revealed. The local advice has been put neoprene pads under the anodes which I seem to remember my last plastic boat had. I think I will try that.