To get a truly uniform finish you need to strip all the old wax first. The old gelcoat is oxidised and absorbs wax unevenly. The surface needs to be be cleaned with polishing compound which, over time, makes the gelcoat thinner and more uneven.

And yes, you qualify to hire some young, not too bright but very muscular BMW (formerly known as BN) to wax your hull.

PS. 3/4 of a 40 footer in four hours is pretty damn good.