preparing underwater steel hull

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.

 

Advice on coating a steel hull below the waterline

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

 

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.

 

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.

 

Sorry about the confusion

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

 

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.

 

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

 

preparing underwater steel hull sections

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

 

Bare steel and prepping a steel boat

Thanks for posting. If you see a bunch of small blisters with shiny metal under them then this is the sign that the paint has to come off and start at steel again.

You can sandblast or simply chip (if your fast). See How to repaint a steel boat without sandblasting report that can be bought (4 dollars-pays for the website) here-
http://www.tongacharter.com/book-sandblast.htm
or
http://stores.lulu.com/store.php?fAcctID=1427396

I think I also posted it for free somewhere on this site.

Also you might view "Metal boat repair and maintenance" found here-
http://stores.lulu.com/store.php?fAcctID=1427396
or
http://www.tongacharter.com/book-repair.htm

lastly be sure to do a corrosion survay on the boat. The instructions can be found here-
http://www.tongacharter.com/report-corrosion.htm

I think that is a free download and will save you thousands if you have any leaks going on.

Good luck.

Scott

 

Hello Scott
Thanks for the interesting reply. I will be sure to ask for the book from santa Claus this christmas. Interesting about stainless steel. On my boat the previous owner had drilled a hole in the steel and passed the pulpit light cable through sealing it with sikaflex. Of course it has rusted badly. I was due to have this welded up this week and instead have a tapped in stainless gland for the cable routing. can I stop any resulting corrosion with duralac or something?
Mike

 

How to pass a cable onto deck

Great question-How to pass an electrical cable onto deck. First thing is a DC cable is easyier than a AC cable. That is cause AC has the posibility of "inducing" voltage into the hull, while DC only can leak through a real connection. I would guess your using a DC light so this is not a problem.

Next is the galvanic action between the stainless and the steel. The steel will corrode away under the SS. You can weld a bit of steel pipe onto the deck in lue of the stainless. This is not a bad solution and lasts for about 20 years. You can weld a piece of stainless to the deck to pass the cable and that still lasts about 20 years. You can put a plastic "Gland sealer" and bolt it with the plastic nut, only these tent to make a 3/4" hole in the deck.

In my book Metal boat maintenance (http://www.tongacharter.com/book-repair.htm) I tried to cover this but there is no easy answer.

Lastly the big thing is to be sure the wire pass does not leak or drip. The drip will ruin the inside of the steel hull in a short (5-10 years) causing a trail of destruction toward the bildge.

Thanks again for asking.

Scott

 

Thanks Scott - appreciate it! . It is DC current and I think the best is to weld the gland in place rather than drill & tap.

ps down in New Zealand, Auckland & christchurch in March 2010. might see you there!!!!

Mike

 

Interesting read, Scott. Is that a Colvin Witch design I see in the book?

WRT deck penetrations for cables etc, we always used a pipe with a U bend at the top - a snorkel. The wire then had a drip loop and went vertically up into the pipe, so the tendency was for water to run away from the cable gland, not towards it.

PDW