Things You'll Need
Instructions
Plan out how many boats you intend to carry on your trailer. If you are looking for a flatbed trailer to start out with, search for one with as wide of a wheel-base as possible since the canoes and kayaks have the potential to make the trailer top-heavy.
Measure out the dimensions of your trailer and mark those same dimensions on 2x4 tube steel. This will be used to construct a frame resting on top of the trailer. Lay out the pieces and weld them together.
Measure uprights for your boat trailer by marking out 3 feet of 2x4 tube steel for every storage level that you want. If you only plan on transporting four boats, then measure out 3 feet of tube steel. Cut the tube steel and weld it in the middle of the width pieces of the boat trailer's steel frame from step 2. Use a level to make sure that the uprights are exactly perpendicular to the trailer and frame.
Measure the distance between the two uprights and cut a 2x4 tube steel section to span the length of the uprights, connecting them into a box. Weld the 2x4 section between the uprights.
Use the cutting torch to cut the 1/8 steel plate into small triangular gusset plates that can be welded as reinforcements for the uprights. Weld the steel plate triangles to the 2x4 steel tube sections so that the length and height of the steel triangles are connected to the tube steel.
Measure out trusses from the 2x2 tube steel that will extend perpendicular from the uprights for your boats to rest on while traveling. The trusses should be at least 4 to 5 inches longer than the width of your boats. Cut the trusses and weld each arm to the uprights. Returning to our example, if you are building a trailer for four boats, you will need four trusses, two for each upright.
Measure and cut another upright and pair of trusses if you are using the trailer to haul kayaks. Weld the upright to the middle of the cross beam which already connects the two installed uprights. Having an extra upright in the middle of the boat trailer's frame will allow you to tie in kayaks on the trailer. Due to the rocker design of canoe's the mid sections of the canoes will not be in contact with the middle upright and trusses.
Weld steel triangle gusset plates to the trusses and uprights as additional supports.
Use a drill and tap and dye set to drill bolt holes into the trusses and uprights if you want to add additional reinforcements by bolting steel brackets to the boat trailer.
Lift the boat hauling frame onto the trailer with the help of a couple of friends. Drill into the wood platform on the trailer and use U-bolts to connect the trailer platform to the boat hauling frame.