Strange how you can work through all sorts of challenges in building a
boat and then get stumped by a simple problem. I am working on the aft
head sole. I built a nice teak grate, carefully fitted it to the shower
drain opening and epoxied support battens underneath. The original idea
was to fabricate an FRP pan with flanges to hang from the battens below
the grate but soapy water could run under the flange and into the bilge.
The next idea was to epoxy the pan under the battens but that would
eliminate access to the bilge below the head and there is no space for a
separate access hatch.

I suggest that the edge of the pan extend up alongside the grate and be
screwed and bedded against the sole planking.
It might have ledges within it on which the grate would rest. It'd be more
complex, but stronger, to make the sub-sole opening smaller to provide
support for the pan and the grate.

Could you put a lip on the pan that overlaps the sole, inset the grate,
and finish the lip with a small (1/2") rounded cofferdam? Make sure the
shower curtain hangs inside(ish) the cofferdam and you should have most
of the problem licked.

The issue seems to be driven by maintaining bilge access. It would be
easy to solve without that constraint. In most production boats that I
have seen, the entire head sole is the "pan" even where there is a
grating inset. Could you use that approach and install a 6" or 8" access
plate in the pan under the grate to get the necessary access?

The newer IPs have a grating at the bottom of the companionway with a
removable drain pan below for access to the (lighted!) bilge. If I
remember, I'll take a picture at the Annapolis boat show and e-mail it
to you.

dave