Just reading back what I wrote earlier, I should clarify, that the filler is used to produce a fair and even curve, so it belends the hull sides with keel line, because the fibreglass tape leaves a flatish surface from the outside edge of the keel tapes to the keel line.

I hope I'm saying what I'm try to say. When doing this it would make it more bouyant I would have thought, but I guess its more a cosmetic fairing of the hulls.

Regards