I have used hot wire cutters before and decided that this was how I wanted to get the rough shape of my foam. the picture below is my homemade wire cutter: The design is very simple: There is a thin guitar string stretched between the two wooden arms. this is powered with a variable power supply. The blue rope is used to tension the wire.

I bought some foam sheet from Wickes in Brighton.

I used the hot wire cutter to split this sheet in half.

This made it easier to handle and cut down to the surfboard shape. Tracing the outline of the board from my card template. I designed the board in AKU shaper and then fusion 360.

I then hotwired the outline making sure I stayed on the outside of the line. To give the board some curve lengthways (rocker) I glued some foam on the nose and tail. I used the hot wire again to rough in the curve. I then used a surform and apiece of wood with some 80 grit sandpaper stuck to it to make the shape to the template and symmetrical. I then traced some lines on the top of the board to give me an idea of how much to round off the rails with the sandpaper.