Help Making a Steel Flat Bottom Boat

My name is Mike in two months there is gonna be a local Raggota that I would like to be a part of. Instead of using a canoe or kayak I would like to do something different and make myself a 10x4x2 flat bottom boat. I work for a steel plant as a welder. I will be using 22ga steel and bending two pieces together to make the bottom and two sides than I will put on the front and back by riveting them together than I will be putting some support with 1 1/2 x 1 1/2 tube inside the bottom of boat. Everyone at work is telling me it won't float . I was thinking of lining the bottom with some kind of high density closed foam to make it more boyunt seeing it will be in a creek that's not to deep. If anyone could help me in making this boat work it would be greatly appreciated (picture, formulas, sites etc). Thank you for you time

 

What you are attempting is what lots of school kids have acheived, building a sheet tin canoe.

Your size is about
3 mtres x 1.5 metres x .75 metres
= about 3 cubic metres internal size,
or 3000 litres of water
= 3000 kilograms
= 6000 pounds

so it will float ok, if the it doesnt weigh more than 2000 pounds (allowing for a bit of 'freeboard', and your weight)

Save a lot of internal framing by putting bends along the bottoms and side panels (same principle as galvenized roofing iron) and get extra rigidity. use Sikflex at the overlaps where you rivet, to waterproof.

Weld up a frame to fit inside, and, and bolt the 'shell' to this frame above the waterline. If the steel 'shell' is still too floppy, just unbolt the frame, take it out and add a few more cross members and rebolt it. Keep experimenting until its all 'stiff'

Add some wheels to one end like a wheelbarrow, and handles at the other end to make moving it aorund easier.

Go for it - it will work fine.

 

My first boat (more like a canoe) when I was a kid was made from a piece of corrugated roofing. I pounded the corrugations flat at one end, folded it in half, and bent it over. I think I put some nails through, and bent them to hold it closed. I put a piece of 2x8 or 2x10 at the other end for a transom, and nailed the metal to it. I caulked the seams and the old nail holes with roofing tar, stuck it in the water and climbed in. It was tippy, uncomfortable to sit in and leaked like a sieve, and I risked slashing myself on the gunwales and bleeding to death every time I used it.

But it floated....

 

troy2000 thank you so much for your reply this is the first time trying it and I hope it works do you think I would need to line the bottom with Styrofoam or closed cel foam. There is goona be 4 four people on here, the creek in some spots is only like six - 10 inches. also would it make a big deal if it is completely flat bottom with no rigids???

 

rwatson thank you as well also if my sides are 1'9'' how low will the boat go under water???

 

yes, the bottom will need to be supported the most. Thats why I suggested putting ridges in. Flat metal is pretty strong, but it will bend and flex with 3 or 4 people. Polystyrene wont give you much strength by itself, but you could glue it to the floor, and then glue either another sheet of metal or plywood over that. I'd suggest gluing the 'extra floor' to the top of the polystyrene, as well as fasten securely to the sides, this will give you a nice rigid 'sandwich' that might save your life if you ship water.

Also, have a look at aluminium boats, how they bend 'seats' from flat sheets of metal. They give the hull a lot of rigidity as well as providing somewhere to sit.

Think about putting a slight curve on the bottom panel for a big increase in stiffness.

You may also like to make the sides angle out all around ( make the top 6" wider than the bottom). This will mean the sides are not absolutley square, but make a cardboard model, and you will get the idea.

It will me much easier to paddle or motor etc

The floating calcs are easy if you do a bit of kindergarten math. use metric for the least brain pain.

the boat will sink until its weight equals the amount of water it 'pushes aside' (displaces)

eg say the flat 'floor' is 3 metres x 1.7 metres

the sides are 1'9" = about half a metre (.5)

so 3 x 1.7 x .5 = 2.65 cubic metres

1 cubic metre = 1000 litres , so you will be making a hole in the water the size of (2.65 x 1000) = 2625 litres.

By an amazing coincidence 1 litre of water = 1 kilogram (about 2 pounds)

so 2625 kilos (say 5000 pounds) of weight - crew and hull, are required to sink the craft
so 2500 pounds maximum weight should see you safe on calm water and you will sink half of the depth of the sides.

If you have 4 people and gear (120 kilos x 4) = 480 kilos, and say 200 kilos of boat, for a total of 800 kilos max

Since approx 1600 kilos is about maximum safe sinking limit (halfway up the sides)
800 kilos will sink you 1/4 of the way up the sides of the boat (about 7") or .25 metre