A= 1/2 to 3/4" depending on how easy you want it to be to get the spray skirt on and off. on my last boat 3/4"

B= 3/16" to 3/8" depending on A and the type of wood used. On my last boat 3/16"

C= 1/2 to 3/4" depending on dimension of bungie of spray skirt. On my last 5/8"

D= 3/16 to 1/4" depending on thickness of vertical strips. Latest: 3/16"

None of these dimensions are carved in stone you have leeway to adjust to meet your materials and desires.