Red,
Building an AL boat is a serious endeavor and it takes quite a bit of equipment to form the metal up. Also designing the structure correctly will be the difference between the boat that holds the weight and gets thru the water well and the one that is unbalanced and pushes its way around the water. I am not trying to be discouraging but just to give you a few things to think about....
Myself like many on this forum built aluminum boats professionally for many years so if you don't mind I will interject a few pointers to help out with your project.
Weight: You can get books directly from the Coast Guard with all the formulas and guidelines for figuring out your beam, length, transom height, capacity etc. for figuring your overall weight, water displacement, and flotation needed. Because of the thickness of the materials your using forming and shaping the structure will be much harder...but worse yet you really need to know your weight and water displacement ratio.
Are you going to press keels into your bottom and sides? You can do a lot of forming with some simple hydraulics and a bit of I-beam. Most AL boat manufactures equipment is homemade. This will help keep weight out by strengthening your major hull parts and preventing you having to compensate with a lot of reinforcement inside. Those ribs you see in Al boats without floors or sides are very necessary. You want your floor ribs to continue up the sides almost to your gunnel rail. Mig welding is fine for all your internal structure inside the hull, decks, ribs, live wells, gun boxes, seats. TIG your hull seams and do so with 100% pen....do not wire weld ANY of your hull. When boats are built they are build upon flat jigs that press all the ribs and other structure in tight whilst its welded...I recommend coming up with a plan to simulate this. A bottle jack and firm table come to mind...your trailer frame could make a good jig table!! You definitely need to come up with either a braked piece or a welded structure for a Knee brace and corner brackts on your transom as well as a cover in which to put some marine treated wood.....you could use some rectangular AL tubing instead but that will complicate it and drive up your costs. Just take a closer look at the boats at some dealers and you will get the idea at what I am driving at....don't try to redesign it just copy it in the size you need. For durability Weldcraft, Southfork, and Weldbuilt are all people I know that build LARGE wide boats that hold up....have a look at how they do it.
Not necessarily thicker material but much more structure (ribs) then others...lots of light stiffeners. At any rate its not complicated...but its like an aircraft...it must endure a lot of force with a light structure.
Weld your hull up first (upside down on sawhorses works well), sides, transom, and center seam (if you have one). Flip it over and form your bow in the front and finish her out. Then it needs to go to your jig....welding out on the floor is going to be tough...you need the capability to pull/push the entire hull straight and hold it that way while you add structure. Whilst building boats it always needs to be on a flat level surface so you can sight/eyeball from the line of the transom to the bow and make sure its staying in line and square after you add each piece of structure. Rubber hammers and long clamps will be your best friend.
Just my $.02
Tommy
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