hi patrick, whether 30mm (or 3cm) is sufficient depends the thickness of the leader and braid, on the target fish and in what kind of environment. as a general guide, for light tackle fishing, 8-10 wraps with 5-6 half hitches or middle heavy weight fishing, i'd say about 15-20 wraps with 10-12 half hitches should suffice. for heavy offshore, 25-35 wraps and about 15-18 half hitches should do the job.. half hitches are most definitely necessary in FG knot as it secures your weaves and leader (after cutting off the tag end before continuing with the half hitch). If it's loose, chances are your weaves will give way or unravel, which means the whole knot is gone, when a good fighting fish's at the other end of the line.