Welding a steel boat while she is in the water?

[Honey Ryder]

Hi there, we intend to do some welding while the boat (steel trawler) is in the water....but we haven't done it before...to quote Laurence Olivier
in "The Marathon Man" (a must see movie with Dustin Hoffman), "Is it safe?"

The welder will be plugged into shore power, am intending to use a gasless MIG welder, and I need to weld some steel supports to a ceiling which we have beefed up, and some steel section to some hull stringers. It is up to 6mm steel, so will be using a 150 amp welder.

My concern regards the earth clamp from the welder to the piece I am welding. As it is an earth clamp, does this mean that the piece being welded takes any stray current, and if so, does this make the hull live?

Many thanks for your suggestions and advice on this,

David

[Hotboy]

Hi David,
I have welded internally and dockside on a steel vessel without any problems. Just a couple of things to remember, and perhaps others can add to it, keep all leads away from water and be mindful of neighbours nearby. Ensure spatter doesn't fall on their boat and, welding can produce stray current that will contribute to electrolysis/corrosion of metal (underwater) on other boats nearby. At least that is my experience.

[Hotboy]

P.S. David. Also disconnect your batteries to protect your alternator from possible damage.

[Honey Ryder]

funny you should mention that about the batteries. i read somewhere (only one other place) that this was a very good idea, to protect the batteries (rather than the alternator). many thanks for the advice!

[GordMay]

Originally Posted by Hotboy

P.S. David. Also disconnect your batteries to protect your alternator from possible damage.

Indeed.

Originally Posted by Honey Ryder

... My concern regards the earth clamp from the welder to the piece I am welding. As it is an earth clamp, does this mean that the piece being welded takes any stray current, and if so, does this make the hull live? ...

Not if you ground to the piece being welded.

[Wotname]

Big ships do it all the time

[lorenzo b]

If you are welding something to the boat, use the boat itself as a ground. If your ground lead is short, just grind the paint off anywhere and clamp to it. If the piece is free standing, run a ground wire from the piece to the boat. I recently did a lot of welding on my boat installing paravane booms and used a 12/3 romex bundled, all three wires tied together, as a ground and it worked fine on a 250 amp diesel welder. Typically, my welder is mounted in the shop room and permanently grounded to the hull so I can weld anytime to the boat itself. Not to worry, steel is real. Love the stuff. Make it bigger, make it smaller, cut it in half and put it back together backwards, the medium to totally plastic.

[S/V Alchemy]

Good advice here!

[GordMay]

Originally Posted by lorenzo b

If you are welding something to the boat, use the boat itself as a ground. If your ground lead is short, just grind the paint off anywhere and clamp to it ...

As near as practicable to the weld location.

[anjou]

Make sure your space is ventilated and that you dont get a tan from reflected light, including your eyes, and have an extra fire extinguisher on hand.

Make sure sparks cant fall or roll into inaccesable spaces and start a fire.
Keep asking yourself

What if

[Honey Ryder]

A big Thank you to everyone who has responded with such good advice. A big relief!

[Hotboy]

Re:batteries. I know most would be aware of this but just in case you've forgotten to remember, many batteries vent off hydrogen. Please ventilate before welding.

[Boracay]

The big no-no with welding is not the welding, it's the grinding.

Those red hot small steel bits can travel amazing distances and embed themselves in someone else's pride and joy. Then they rust and leave marks everywhere...

It might have been my imagination but with a 10 amp power supply to my welder I had trouble getting a good arc. My suspicions fell on the long run of the mains power down the jetty and I might have had the earth a bit too far from the job. Close as possible may be better.

[bangkaboat]

Hotboy & Anjou have pretty much covered things. I'd suggest you pick up a couple of fire blankets or cover areas with wet towels(at least). As mentioned, sparks travel a long distance & can get through the slimmest of crevices. If you're using self-shielding flux core, the spatter is much more so than gas shielded wire or stick(SMAW).

[lorenzo b]

Had a slight leak in one of my fuel tanks and the yard sent over a welder who welded it over with the fuel in the tank. Them Cajuns is crazy.