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.
