What typically needs welding
Typical candidates? Cracked brackets and mounts — the spot where a pontoon's cross members meet the tubes, wherever a motor bracket or ladder is bolted on, that rail stanchion people have leaned on for years. A crack like that starts at a stress point and creeps a little further every time the part flexes. Get to it early: small repair. Left, it becomes a broken part.
Lifts and trailers bring the rest: bent or cracked members on an aluminum lift, a broken bunk bracket, a cracked cross member on an aluminum trailer frame. Lift repair and trailer repair are part of the same service.
Why aluminum welding is different
Aluminum's got an oxide skin, and that has to come off before a sound weld will take. It also pulls heat away so fast that thin sections burn through easily. Old, corroded, oil-soaked aluminum? Harder still. Prep is most of the job. It's what decides whether the weld holds.
And the heat changes the metal beside the weld. With some alloys the heated zone comes out weaker, which you can't ignore on a part that carries load. That's why the honest answer is sometimes a reinforcing plate, or a new part instead of a weld.
When welding is the wrong answer
Not every crack should be welded. A riveted hull seam that is weeping usually wants its rivets and sealant addressed, not a weld run along it. A part that has been welded repeatedly in the same place is telling you the design or the load is the problem. And welding near fuel, fuel tanks or fuel lines is not done until they are removed or made safe.
Structural fiberglass is a separate trade and is referred out to a specialist. Aluminum is what gets welded here.
Getting a weld looked at
Call and say what the part is on — pontoon, boat, lift or trailer — and how it failed, plus whether it is an emergency or can be scheduled. That is enough to know whether it is a job for this service.