as far as i know it should be a 1986 model....

that's about the time nacra changed from solid frp to the foam sandwich, which do you have?

as for sail numbers my 1982 nacra 5.2 doesn't have the inverted U symbol either but i have a pic of a 5.2 3089 which does, so i guess it came into use sometime after 1982....

my sail number is J65, which has nothing to do with the hull number as can be seen below but more to do with the fact that it was the 65th 5.2 to be registered? in japan