First decide which kind of boat you want to built, I wanted a light boat (less than 50kg) but it needs to be still large ENOUGH the one I have made is 4 metres long and 1,50 mtres wide and weighs araound 40kg. while building a boat dimensions and shapes are very important. First take a good look at existing boats to get a "feel" of the dimensions used. A good guideline is the next one:
The widest point is at the middle of the lenght.
The bottom has an V-shaped form (stability)
The backside has an wide of approx. 2/3 of the width
the sides will need to have an angle (this has no function at all but it makes your boat look more naturally.
Building an boat is all about curves.
When you have an basic design in mind you can start building.
To choose the matirials you do not need to buy special boat building wood (for which an rain forest is cut down) any cheap plywood and some square wood will do. Take care in your design that plywood will only be bent in one direction. I have used an square 40x40mm 2,70mtrs long for the main strut and 15x15mm for the sides. The diagonal struts were made of 12mm plywood and the side is made from 4,5mm plywood while the bottom is made from 5,5mm plywood.
Make sure you use waterproof glue.
Use screws and NO nails (nails will come out)
How to make it:
1:) make cuttings in the central strut for the diagonal (plywood) struts
2:) fit the central strut on an workbench
3:) Make the bow no fine-tuning or cutting is necessairy yet
4:) Saw the diagonal struts and fix them
5:) Attach the side struts.
5a) Oops the 15x15mm square can not be forced to follow the curves of your design.
5b) laminate some 4,5mm plywood to solve this
6:) now the base structure is ready and you can start finishing it up. I hae used an shaving tool for the central strut and the bow to make sure it makes an perfect fit with the diagonal struts.
7:) now you can start to make your boat waterproof by applying plywood to the bottom and sides.
8:) First start with the bottom make sure the sheet is too large.
8a) &@!*^% The sheet is too small for the lenght and the final curve at the bow is too big for the 5,5mm plywood.
8b) Use some thinner plywood to make the curve and cheat with some polyester
9:) when the glue is dried you can saw off the exes sheet use an belt-grinder or so to make an perfect finish
10:) now you can attach the plywood sides make sure you have enough "cut-off"on the sides
11:) finish the sides again by sawing and sanding
12:) finish your boat by putting sidewalks / flooring / benches etc to it.
What went not completely according to plan.
An floor of 4,5mm was applied directly to the diagonal struts, it was too weak I broke it several times. 5,5mm is fine.
While cruising at full speed (5hp enginge) it goes really fast around 30km/u and when encountering a wave I got a little skared while I have more weight than the complete boat with motor etc. so I finally applied polyester to the bottom side to improve strenght and make sure the plywood will not get wet.
I applied normal outdoor housing paint to the underwater part, DO NOT DO THIS it will come off whitin two days.
While bending the 15x15 square it was not achievable to get the desired curves whitout breaking them, this was solved by laminating plywood to the correct shape an afterwards finishing it up with the belt-sander.
Before you start make sure you have a proper plan and an clear idea of what you want to make