I know this is not directly RIB related, However I am hopeful that the GRP RIB build knowledge on RIBNET will help.
The Portsmouth Victory Class are currently in the process of getting RCD approval for their prototype GRP replacement hull (see pics at http://www.woozle.co.uk
) and need to seal two hatches approx 400mm square to the bouyancy tanks (example in pic attached). The fittings that have been proposed so far seem very bulky and overkill, designed for much larger yachts / commercial applications than a 7m Sailing Dayboat.
I seem to recall a Company that make stainless steel fitting for many of the RNLI RIBS, but cannot seem to find them- I hope that this company may have something. Alternatively - any other pointers?