On the SeaRaider I had a bungee cord loop to hold the board down, I suspect that is the standard procedure for most Swallowboats.
That went well enough through all the races of last year, until we went aground hard (on sand) last week when the bungee cord broke. Instead of replacing that I now fitted a regular downhaul rope, with that rope going through an auto-releasing Clamcleat. Works better than the bungee cord, because we can now finetune the board trim and fasten the board in every angle position.
We were fun racing against another boat last weekend, quite open for some time, only adjusting the board to a different angle finally gave us the edge.
Claus