Hi Adrian,

The standard plans provide two options.

One is to use a standard surfboard finbox. The other is to build a socket to take a self made fin.

If you have weed where you are another option is a self made fin like a mini dagger centreboard in a case so you can pull it up to remove the weed then reinsert.

Best wishes
Michael

Note to North Americans – Centerboard means it is in the centre of the boat, as opposed to a leeboard which is off to the side to some extent. The action of any location of board can be described dagger or swinging.