Picture of Balancing a trimaran model
Making a model boat with pop-pop motor has a difficulty, when you fasten the motor on the boat.
If the boat is quite an ideal construction, with the same acute angle at stern and bow, and minimal displacement, the boat can be unstable. So it is practical to make e.g. a trimaran.
First guess is to calculate the immersed volume from the weight. For instance the motor weight is 120 g, burner 50 g.
The rated weight of the main hull (LWL=40 cm, B=4 cm laminated wood) is about 150 g, outrigger hulls (30x3 cm cardboard) 80 g.
The draft (T) can be about 2 cm.
So the displacement is 400 cm3. 
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Step 1: Main hull

Picture of main hull
The main hull would be strongre for the motor and the burner, made with the Baselint Method, from laminated wood planks, and fastened with epoxy resin adhesive. Near the burner it can have an aluminum sticker.
On the picture it has a windshield too.

Step 2: Outrigger hulls

Picture of outrigger hulls
The outrigger hulls have simple geometry, the sides are rounded, but the bottom is only cut at the bow and stern. The cardboard is painted waterproof. The sticks can be fastened after balancing.
boat-sketch (author) 2 years ago
The trimaran is made