Explanation for Voids in the Rub Rail's Fiberglass

Voids found in Knock Off' #66's rub rail

How was the tug built that allowed these voids to form in the rub rail?  Tommy Chen said that the fiberglass was laid into the mold starting from the top of the bulwark and working down towards the keel (see note below).  The upper turns of the rub rail are particularly difficult to fiberglass as the turns are both sharp and close together.  On top of this, gravity is trying to pull the heavy, wet fiberglass away from the mold.  Adding fuel to the fire is the fact that it's hard for the workers to see into the rub rail's void.   All told these factors made it difficult to get a good tight bond between the gel coat and the fiberglass and also between the layers of glass themselves.  

Void found in Neptune #35

Note: Suspended platforms, attached to beams traversing the top of the mold, were setup inside the hull for workers to stand on.