This is a raft that I built during a 4 hour Hackathon. It has yet to make it's maiden voyage but it was built to leisurely float down a river and carry several passengers along with fishing supplies and beer.

Step 1: Materials and Tools

To build this raft in these proportions you will need the following materials:

2x6x12ft x4
2x6x8ft x2
5/4x6x8 x24 (decking planks)
55 gallon plastic drum x6-8
pipe strap x25ft or so
plenty of screws
silicone caulk

along with the following tools:

miter saw
caulk gun
drill
heavy duty wire cutters (or something else to cut the pipe strap, we used an angle grinder).

The barrels are very easy to get by calling local car detailers. They get these barrels full of soap (hence the name) and will sell you empty ones for around $5 in my area. Make sure you get the plugs with the barrels! We used six barrels because that's what we could get ahold of at the time but the raft is long enough to have 8 (not sure if this is necessary though). Make sure to use pressure treated lumber and outdoor screws or galvanized nails. The total cost of the project was around $250 which is pretty cheap for a boat!

Step 2: Seal Your Barrels

The first step is to seal the barrels to prevent them from taking on water. Just plug your barrels with the plugs and go around all the seams with silicone caulk or whatever waterproof adhesive you have.

Step 3: Assemble Your Frame

Build your frame by making a 8ft x 12ft square with your 2x6 pieces. Then set your barrels in the frame and attach your other pieces of 2x6 so that they fit snugly up against the barrels. You are making channels for your barrels to rest in so that they can't move. We used three screws per joint. Bolster your frame by putting supports in the middle. We put two pieces of our decking horizontally in-between our 2x6s. We then cut 1ft sections of some of our scrap decking at angles and used them to brace our supports.

Step 4: Apply Your Decking

After you have assembled your frame, attach your decking to your frame. Make sure to lay out your decking before you start screwing them down so that you know they fit. We did not have quite have enough decking boards so we left a 1in gap in-between each one. This ended up looking alright and making the raft lighter although it is not quite as firm as it would have been. We used two screws in each board on the outside piece of frame and one screw per board on the inside piece of frame.

Step 5: Attach Your Barrels

The final step to your raft is to attach the barrels. To do this you use the pipe strap and screws. Use at least two pieces of pipe strap per barrel and you want to screw the pipe strap into the frame on the inside of the frame. You must not have the barrels laid in the channel to do this. Screw the pipe strap to the inside of the outside frame piece then lay the barrel in the channel and tighten down the strap by screwing it into the inside piece of the frame. Repeat this with all of your barrels.