Here, the north 'shadyside', (that facing toward the structure, away from the horizon), margin of a (truncated) sail #1 has been widened to allow a water-skirt, (not shown), to be attached .

The set-back face will allow the assembly to (largely) maintain toroidal geometry through this section, (a part of the 'core' or 'apple core' that centers each set of sails) .

The skirt seating slot, seen extending across the margin, may be routed after casting,

but the form would be stronger, (though the work more complicated), if it were a part of the casting itself ~ as this would allow reinforcing fibers to travel unbroken to the bottom of the margin .

Doing it this way would require an independent insert in the casting mold which would need to be removed before the mold itself was opened .

All but one of the proposed holes for securing the skirt are visible, (these could be drilled and tapped after the form had hardened) .

Although a wider margin adds mass to the rotating assembly, skirts seem the most effective way to keep water, debris and insects out of the housing .