preparing underwater steel hull

[mikewade]

Hi Guys,
This is my first post after sometime perusing the forum. I have a 20 year old steel van de Stadt 34 which I love. I live in the North of England & its turning cool & damp now, so out of the water she has come for the first time in 3 years, apart from a day of antifouling each year. Her bottom looks tired and I think its time to take her back to bare metal and start again. My questions really revolve around bottom preparation. I believe she originally had epoxy tar on and I would like to do that again. Do I prime the cleaned metal before applying and what is the most suitable epoxy tar (I understand the original "tar" no longer exists) and where do I get it. How much would be needed for a 34' hull and I guess this is only applied as far as the water line then use convetional paint for above? Is it possible to apply in autumn weather (cool & damp) or best to wait until spring?
Any thoughts, comments or guidance would be gratefully received.

[rugludallur]

I would not consider myself an expert by any means but I have read just about everything I can find regarding coating steel boats and perhaps sharing some of what I have read will help.

My first question is do you really need to go to bare metal? Going to bare metal requires blasting and is costly.

I wrote up a little extract from what I learned while doing research for my own boat and put it on my website:

http://dallur.com/index.php?id=16

Perhaps that will help.

Regards
Jarl
http://dallur.com

[gonzo]

If it had tar-epoxy, it should still be mostly OK. You only need to clean and inspect corroded areas. Sandblasting is the easiest and best way to do it.

[rwatson]

Originally Posted by rugludallur

My first question is do you really need to go to bare metal? Going to bare metal requires blasting and is costly.

Confused!

Your web site says

Before discussing the paint itself we need to look at surface preparation which is vital, first off there is no substitute to abrasive blasting, using pre-primed steel or hand cleaning can simply not produce the same quality surface as a good blasting can.

[rugludallur]

Sorry about that, what I wrote on my website is intended for new boats with a welding primer or mill scale no them, the question is whether your current primer/undercoat is still in a good enough condition so that you won't need to sandblast the entire bottom. Perhaps abrading your current paint system and over-coating would be sufficient?

Grinding up damaged areas with a wound wirebrush in an angle grinder can clean them up to a standard compatible with SA 2.5 but it's to much work for more than a couple of square meters.

Does that clean up all confusion?

Regards
Jarl
http://dallur.com

[rustypirate]

If you are upgrading to newer epoxy primers and paints, it may be necessary to blast down to white metal due to incompatibility between the old epoxy tar and newer products. The blasting may be costly, especially as you may not have much in the way of options in locations to have the work done, but for a reliable clean surface, there is no comparison.

For the coating I would contact a commercial marine supplier as they will carry an equally excellent product at about 60% of what a boating store will cost.

[apex1]

Mike
Jarl is right, why going down to bare metal?

Wash her down with pressurized water jet, 500bar, rotating nozzles. That removes all loose paint and marine growth, but does´nt go down to bare metal where the paint (Tar) is still good. DO NOT USE A STRAIGHT NOZZLE! Otherwise you shoot through the hull in the blink of a eye!

You can rent or borrow such equipment asking at any shipyard, they all have it. When you ask to get it for a weekend, you may get it borrowed for a song. Take care, you will need a truck to tow the compressor and equipment.
The common "household" apparatus like the (very good) Kärcher do NOT do the job proper.

There will be some areas where you go through to bare metal. Usually above the prop, where is much turbulence and the oxygen has eaten more of the paint.
Sand these spots to "white" (SA 2,5), before you apply the first layer of Ep primer.

Then follow the pirates advice, buy the stuff where the yard does (or their contractor).

I once did a 200 tonnes ship with a batch of epoxy paint and primer which I got for free, the "best before date" was overdue. The quality was the same, but of course no manufacturers warranty (a big value in commercial applications). It saved me many many thousands of DM and lasted as any "new" stuff would.

Good luck
Richard

[mikewade]

Thanks guys, I appreciate the advice - keep it coming if you think of anything else. I think other than some preventative maintenance I'll wait until the spring as its becoming damper & damper now
Mike