I was checking out “swied”'s thread on his HWS Project and was interested by some planshape generation discussion there.

I thought I would share the method I have just used on a HWS project of my own which has worked well for me.

Most uninterrupted planshape curves (exluding the first and last 12 inches of the board) can very nicely approximated by a large radius (normally somewhere between 4 and 6 metres for a shortboard).

So, for example, if I want to generate a curve for a 6’8" (2032mm) board with a 13" (330.2mm) nose, a 20" (508mm) widepoint 1" (25.4mm) behind centre, and a 15" (381mm) tail. I do the following.

Using a point on the stringer 12" back from the nose as the zero point with the x direction down the stringer and the y direction at 90 degrees to this we end up generating the following coordinates.

1st point coordinates (x,y)=(0,330.2/2)=(0,165.1)

2nd point coordinates (x,y)=(2032/2+25.4,508/2)=(1041.4,254)

3rd point coordinates(x,y)=(2032-304.8,381/2)=(1727.2,190.5)

Plug these coordinates into:

http://home.att.net/~srschmitt/script_circle_solver.html#top

This particular example returns an answer of a radius of 4891mm (with a centre point of X934 and Y-4636).

Now mark your template with a centreline and measure and mark your three points above onto the template.

Put a free standing vise on the floor or ground, pull your tape measure out to approximately your radius (4891mm in this case) and put it in the vise at this dimension. Tape a pencil to the other end of the tape measure, position your template at the correct location which the pencil will scribe through your 3 marked points (this can take a little trial and error) and then scribe your curve. The Circle Solver program coordinates of the centre point of your circle can help cut down the trial and error of positioning your template to get the pencil passing through all 3 points.

Now you only have to complete the curve for the last and first 12 inches of the planshape, which can almost be done with steady hand and good eye, or french curves, etc.

Sorry if I have made this sound more complicated than it is as it’s not nearly so complicated as I’ve made it sound. Hopefully it will make some sense to someone.

Cheers

Rohan