Best Aluminum for Boat Building

I am seriously interested in learning to weld aluminum. In the interest of future projects I fugured I would buy some scrap aluminum froma local metal worker to practice on. So...which alloys should I get. These are for freshwater projects, but a small bay boat or small skiff for bay fishing may be in the works for the future so saltwater applications are not totally out of the question.

-First - Do you know how to weld (any type)right now? If you do not, go find a community college or local technical school and get some instruction. They may ever have an advanced class that will get you closer.

Second - You should reseach which alloys you will work. There are a number of choices and some limit the effective welding process that can be used. I have not worked in this field in years, so I do not choose to suggest without knowing the actual application and doing some study on my own.

Third - There are are multiple processes for welding aluminum available. All are different and some are very different. Some alloys are best welded with TIG (expensive) others can be handled with SMA (looks like welding rod and the easiest is MIG (has a gun that lays weld).

Most of your practice should be laying beads on flat stock so don't buy new metal. After you learn to weld and pick up some good used gear, go find a scrap metal dealer that get flat stock from some where and make a deal to buy some from him with the understanding that you can sell it back to him as larger pieces for not much less than you bought it for.

Build yourseld some forms and holders to let you weld uphill down hand and overhead and try to assemble soem structures that are really difficult and hard to manage and you may be close to boat building.

-Ive been a full time welder for about 5 years now, and a tinkerer most of my life before that. I spent a year doing contract work stick welding trawlers but in the last year and a half most of my work has been aluminum; big tip trailers, and aluminum plate boats.

Here's my 2 cents worth... I dont think it really makes too much of a difference what alloy you go with, particularly for fresh water. Just go with something that isnt too hard. We use 5083 marine alloy, but a lot of the 5000 series alloys are suitable. You'd do well to decide early on if you want to go for a 'plate' boat or a 'pressed' boat. Plate boats use relatively thick sections (1/4" or more) of aluminum and hold their shape well. The boats my company makes are of this variety, take a look at the web page if you like (note, this is not a plug)


Typical dinghys and runabouts use much thinner sections, sometimes 1/8" or smaller. The smaller sections wont keep shape without being formed a bit, and the most common way of doing it is by pressing the sheets to give them a sort of a clinker look. You can get the same sort of effect by buying a rolling wheel, marking the lines on the sheet then rolling them on the wheel.

The heavier boats are much more solid and easier to weld, but you're probably looking at around $6,000 to build a 20" with a cuddy cabin - not including fitting it out or an engine. Aluminum prices are going up and up. If you're going with plate, you're pretty ok, you should get away with yusing your small mig. You'll need a plastic liner for your gun, and different tips. If you're using flux core, you'll need to swap to a non-grooved roller set.

If you're going to go with pressed, you'll probably need a lot of skill, or a better welder - preferrably both. The welders we use at work are about $20,000 Fronius units with all the options (push pull gun, water cooled leads) that do a synergic pulse mig, and have adjustable current *on the gun* in the form of a dial or buttons in one amp steps. This gives extremely fine control over heat and its adjustable while you're welding, so you can turn it up as you get to a corner, or down if you start to burn through. They also have 4 step options (hot start, run, crater fill) to get a tig-like experience in a fraction of the time. The synergic pulse is truly excellent for overhead and vertical up welding and gives a minimum of spatter.

In truth, like me, you will probably never be able to justify buying a unit like this, but thats what it takes to compete at that sort of a level when it comes to aluminum. All the players have them. If you're going to go ahead with your (im guessing single phase, off brand) welder, start by getting some reasonable size sheets 1/4" or so. If there's a boat maker in your area hit them up for scrap. You'll probably get a box full for a six pack.

Aluminum is great in some ways - unlike steel you'll never get a pretty looking weld that doesnt do anything. For this reason alone, i think the standard of aluminum welding is generally higher than steel. It has to be spotlessly clean, or you're wasting your time. use a stainless wire wheel, or a flap disk. Temperature and root gap are critical. Filling gaps is not easy. Unlike steel, it doesnt give any signs the weld pool is too hot, so you'll be quite surprised to see the puddle drop right through the plate every time it happens. Dont sweat it too much; it still happens to me ;-)

you may find that setting the welder is hard, partly because it doesnt make that good sound you get with steel, and partly because you may only have 5 voltage settings on your unit. Hotter is better, so start by just 'tack' welding until you get the hang of it. You'll see that just before it drops out, the pool goes from greyish to a bit shiny, then it sinks a little, then very quickly disappears. Once you can control the puddle to the point you can 'sink' it level with the plate and not drop it out, you're doing well. butt welds are tricky, so progress to a fillet. a 'step' in your gun movement of around 1/4" will give a pretty looking weld.

The most critical things are probably cleanliness of material, correct heat, consistent gun angle and consistent stick out, in that order. If you get a lot of grey/black discoloration around your bead it means you're not getting enough gas coverage - move your gun closer.

If i were in your position, Id see if there is a local boat builder who would take me on part time on weekends if i worked for free. In return you'll learn how to do a professional looking weld, probably pressure testing, have access to heaps of scrap, and they'll usually let you use the equipment after hours.

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