If not able to make one in GRP I think you would be better to make one
from ply as they are quite thick. I do have one to measure but it is
not here at the moment it is at a holiday destination. If no one else
comes up with the info send me a text next week on my mobile and I
will measure it for you. The shape is a parallelogram, the angle can be
obtained from the hull as the top and bottom are parallel with the hull
surface. The foil profile can be roughly taken from the slot it fits
into. There is quite a load on the trailing edge as it is fairly thin,
especially if you touch bottom so you would need to beef up the edge
with grp.
I would be tempted to make one in ply and clad the whole thing in
glasscloth and then a layer of flow coat ( gel coat with a small amount
of wax added to prevent surface tackiness ) and profile it after.
Ian