Anyway, this isn't my first boat build, and it's far from my first metal fabrication project. But it is my first metal boat project. I've previously done some welding of aluminum, but that was almost all TIG of very light material (.050"-.060"). I am pretty new to the MIG welding of this heavy gauge aluminum. I am using an HTP Revolution 2500 multiprocess welder. I am currently using the standard 9' graphite lined whip and mig gun that it ships with for welding aluminum, but I am planning on buying a spool gun with a 25' whip soon, as constantly moving the power supply around the boat to reach where I am welding is a PITA.
https://www.specmar.com/aluminum-boat-p ... raft-1520/
This is the boat. The picture at the above link sucks, but there is a pdf drawing which is more useful. I can't find on any of the drawings they sent where an empty hull weight is given, but the weight of the raw aluminum prior to cutting (so, including the pallet of scrap that shipped with it, plus whatever the router removed as kerf) was just over 2500 pounds. So not more than that for hull weight, and they seem to indicate that the weight of the boat with systems, the 130hp Honda they show, and full fuel is 2880 pounds. Max displacement is 3880 pounds. So give or take 1000 pounds of cargo and passengers, depending on what motor I choose.

They don't call for a jig due to the accuracy of the CNC cut parts; rather they just say build it across 4x4s leveled on the shop floor. In order to be able to move it around a little bit, and to create a better working height (we'll see if I still think it's better after I get the sides on), I made a frame out of 2x10 lumber,and leveled my 4x4s across that. It's sitting on 4 chinese made machine skates (allegedly 6000# capacity each) that I bought for moving my big shear (which is great for aircraft material, but alas too light duty to be of use on this project).

This was a little frightening. .190" (3/16) aluminum doesn't really like to bend like this, and several ratchet straps gave their lives forcing the shape into the bottom panels. I am currently welding stringers into this area, treating it with caution since I had tacks "unzip" on me several times while putting these into shape. I probably won't relax working on this until after I get the ribs and the chines tacked in place.

Keel, "ski" (pad, etc), transom, bottoms, and the first longitudinal stringers tacked in place. With my aviation background, I keep referring to the stringers as "longerons" which has confused the hell out of my more boaty friends when I have talked to them about the project.

How it sits presently. The frames are not tacked in; I am just using them to help in aligning the remaining stringers. Once those and the forward girders are in place, then I can start tacking in the frames.
Anyway, probably the real purpose of this post is to solicit feedback on choices for motor, trailer, etc. since there will be a lead time for those items. I probably need to order a trailer soon if I want it here this summer. I could build my own but I have my hands full already building the hull. I have been relatively happy with the EZ Loader that I bought for my jon boat, so I was thinking of one of their tandem axle units meant for a 4000# boat (so about 5K gross weight). The goal is to be able to drop the bow door and load up in my driveway using ramps (for loading my quad, etc). It may be desirable to build a little extra weight capacity in, but the models I am seeing with heavier capacities are also meant for longer boats. I'm open to suggestions... Trailering distance is about 170 miles from my house to the boat launch, up and down several mountains. So durability and capacity are important, but extra weight is just that. Current tow vehicle is a 2017 crew cab half ton ram with the hemi V8, but I may want to occasionally tow it with the wife's Durango which IIRC has just over 6000# max tow weight.
I have bounced around a bit on the motor. When I first began considering this boat, I was thinking just a regular 80hp outboard to stay within the design limit for tiller steering, to keep it simple as possible. After a season traversing the lakes to and from my property with the jon boat and a prop outboard, it became obvious that I need a jet unit because both the approach to my property and the channel between 2 lakes that I have to transit are very shallow, and there's lots of other shallow spots too. I had just about talked myself into a 115hp jet outboard (which with the jet loss gives 80hp at the pump, and thus meets the design limit for tiller steering). But after more thinking, and seeing the size of the boat coming together, I am leaning more towards a 150hp jet (so about 105 at the pump), and hoping that will be enough. There's a jump of about 100 pounds motor weight going to the 150 so for the extra 25hp at the pump I'd lose 100# of cargo capacity. I don't really care about top speed that much; 95+% of the time I will be crossing the same two freshwater lakes the approximately 15 miles from the boat launch to my property. Probably with the occasional run on a river for moose hunting, and maybe once in a while in saltwater for halibut or deer hunting on the islands out in the sound. But mostly it will be back and forth on the lakes.
If I were ordering a motor right now, I would pick Yamaha's 150 jet. I asked my friend who used to work at the outboard shop in our hometown if he recommended Yamaha or Mercury (they both make a 150/105 jet), and he said between those two, Yamaha all day, every day. The local Yamaha dealer is also the EZ loader dealer so I may be able to get a better deal if I buy both the trailer and the motor from him. Mercury support in Anchorage seems spotty... There's the Bass Pro, and one shop down on Old Seward that usually has overpriced boats for sale on Craigslist. Vs the Yamaha dealer that I have already bought a jon boat and trailer from. But I am open to ideas.
I did look into buying a prop outboard and one of the jet conversion units, but those all appear to have a 6+ month lead time on orders. That would open up the option of a Suzuki outboard.... They seem to be a good deal, but they don't appear to offer a factory jet. The local choices for used motors don't appear to be great either. Anyway, thanks for reading this far.