I never had a problem with the loose-fitting boards on my 5.5u, but if it bothers you, it's easy to carpet the inside of the bottom of the daggerboard trunks, either with designated self-adhesive carpet or with almost any relatively thin carpet epoxied in. The most important area is the aft half or third of the lower opening, and maybe the front radius of the upper opening.


good luck


Andrew Tatton Nacra 20 "Wiggle Stick" #266 Nacra 18 Square #12