I knew there was a good chance this would happen. I miged a plug into the I/O hole on the back of an aluminum boat. I had nightmare welding issues...mostly because of the swirling winds..and my gas setting was only about 22 . plus it took me a while to get a feel for the process. the verticle surface of the boats transom did not weld anything like my test pieces on the horizontal bench!! the result was i welded a lot longer than i should have... and i ground away a lot of my poor welds, and now the transom sheet aluminum has a serious bow in it. I know there is an art to straightening sheet metal with heat....doesnt anyone have some tips or a GOOD source to read up on it??