Fish fins made with the standard ProBox base design require that the shapers mark be adjusted so that the box ends up in the correct location. Due to the width of the base for a fish fin the box needs to be placed further forward than normal, but the installation jig cannot accommodate the increased distance from the shapers mark. To correct this the installer needs to adjust the mark forward by 1 3/8" from the original shapers mark. This will place the mark in the correct location so that the installation jig will place the box correctly. These dimensions are all based on the standard ProBox fish fin base, shown above, if you have a custom base you might need to make similar adjustments based on the location of your base.
The key dimension is the 13/16" that is used for standard fins and is designed into the installation jig, this dimension needs to be subtracted from the measurement from the back of the base to the trailing edge to determine the amount by which the shapers mark needs to be adjusted.
In some situations where maximum stability is desired out of the base of the fin, the base could be designed to use the entire length of the slot in the insert. So instead of the normal base length of 2 7/8" the base length could be increased to 3 5/16". This will provide for a stronger base, but will sacrifice fore n' aft adjustment!
If you have any questions please do not hesitate to contact us.