Lightly plane the ridges from the octagonal section and adjust until round. Sand and finish.

Smoothing out the ridges

Filling small surface imperfections

It is possible to make a marking tool for the next step-cutting a sixteen-sided cross section-but it isn't really worth the bother. Planing by eye and feel works just as well, and it's decidedly faster. From this point on it's just a matter of planing a bit, checking for straight, rotating the mast, and planing some more until you are happy with the shape. Finish by filling checks and small tear-outs followed by sanding.