Further to the above:
I have excluded all terrain elements using a covering polygon
I have replaced with a "HydoPoly_Ocean_Perennial" tag to cover the QMID square
The island terrain is supposed to be specified using a Polygonhole in the replaced HydroPoly - but I can't get this to select.
The poly I'm trying to use as a hole is now Poly#3 , the poly I'm trying to use as a parent is Poly#2 (SBuilder seemed to swap the descriptive names when I changed the order of the polys BTW).
I have tried inside/ouside right edge/left/edge vertices. The Parent Poly (#2) won't select as a parent poly.
Hope that clarifies the situation.