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Old 05-03-2015, 10:15 PM   #1
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mig welding

What would be the general consensus on using a mig welder when welding up a steel hull. I have herd different theories on the idea and would like those who have built with mig to chime in.
Some say the weld is too porous. Is this true, or is this the result of inexperienced welding technics?
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Old 05-03-2015, 11:50 PM   #2
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mig welding

There is nothing wrong with MIG welding a steel or aluminum boat. I assume by "too porous" you are describing a failure condition called porosity. Porosity can happen in any welding process for a variety of reasons. In MIG welding porosity is typically caused by shielding gas not being used or blown away by breeze etc. Common rookie mistakes.

I will go out on a limb and state with almost total certainty that every single welded steel or aluminum boat, ship, barge or tug produced in the last 30+ years has been constructed by MIG welding or one of its variants.
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Old 05-04-2015, 12:03 AM   #3
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Mig welding is the welding method of choice when welding heavy and some not so heavy gauge steel. Generally thickness lighter than 0.060" is difficult. It is the method of welding very heavy plate since it is less labor intensive than stick. It is good enough for welding an excavator bucket in quarry service, so I can't see why a boat is more critical. Skins in boats tend to be relatively light gage but not in the problematic range. One draw back of Mig welding outside is wind. It can blow away the shielding gas, but it has to be blowing pretty hard. I think one big advantage of Mig is the lack of slag to chip away afterward. This pays a big dividend in terms of paint adhesion, The big bugaboo with steel construction is corrosion. A bit of unchipped slag in a difficult to see location is a rust issue sooner than later. As to weld quality, Mig welding is relatively low skill compared to stick welding. Stick has many ways to produce poor welds in the hands of of a low skilled welder, Mig, far fewer. Manufacturers wouldn't weld heavy equipment wit Mig if they were concerned with porosity. Prorosity is the result is the result of contamination, improper weld machine settings, poor technique, or some other fixable issue. Stick welding has the same issues.
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Old 05-04-2015, 06:53 AM   #4
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MIG is the only way to go. Stick welding will take too much time, and the weld you get will not be as good as MIG.

A 200 amp machine is ideal, and I would use gas vs flux core wire. I welded my boat with mostly .035 wire, and a 15' lead. If you want a longer lead, you'll have to up size the wire to .045 so the wire pushes through easier. The wire comes in 35 lb spools.

Lincoln and Miller make good machines. I use a Lincoln 250.

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Old 05-05-2015, 08:44 AM   #5
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mig welding a steel hull

Thanks for the replies. You have set my mind at ease. I shall forge ahead and take the advice of the nay - sayers with a grain of sea salt.
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Old 05-05-2015, 10:16 AM   #6
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Have you heard of the Metal Boat Society(MBS)? Welcome to the Metal Boat Society
They might be of help to you if you are looking to build a metal boat.

If you are in the US, many local community colleges have welding classes that are very affordable. My local school has welding classes for stick, MIG, and TIG. The classes also will test you for certification after the class is finished. The common advice I see to learn welding is to take one these classes, not only to learn the process, but also to get practice. The cost of the class covers materials and consumables and it is cheaper to take the class compared with learning on your own.

Later,
Dan
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Old 05-05-2015, 10:24 AM   #7
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Have you heard of the Metal Boat Society(MBS)? Welcome to the Metal Boat Society
No. But thanks!

Bookmarked.
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Old 05-05-2015, 01:28 PM   #8
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MBS is only $30 a year and has a quarterly newsletter/magazine. There website does not get a lot of traffic, which they are trying to change, but the site has quite a bit of useful information.

MBS has a meeting in Anacortes WA, which I think is in August this year.

Later,
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Old 05-05-2015, 01:33 PM   #9
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For other good information on boats, lightning, welding, metal boats, etc, visit Michael Kasten's site, Articles by Michael Kasten - Kasten Marine Design, Inc.

Kasten was the editor for MBC for many years.

Later,
Dan
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