it's nylon webbing and the Capricorn uses it for the boards.

In many cases (on the a-cats anyway) there is a recess in the daggerboard trunk to allow clearance for the knot end of the line. If that recess/slot isn't there, I have seen some folks run the thin nylon webbing straight through board and tie back onto the deck (it gives you 2:1 purchase on lifting the board). Probably need to glue in some sort of nylon hard spot in the board to prevent sawing through the laminate.

Granted, I'm shorthanded on the A - but I wouldn't sail without it there. Its a great system on any boat.