Nice looking boat.
I wouldn't say my previous comments were a "recomendation"! - more simply trying to kick out a few ideas......
Ok, I see what you are talking about - I would still not use starboard or Acrylic
as the "blank" - either steel or fibreglass sheets
, with the "filler" (under the straight "blank") for the curvature made out of epoxy and wood (and through which the bolts for the "blank" go into the existing holes) and the new opening port bolted simply to the flat "blank" (if the blank is beefy enough I don't think will need any reinforcement behind to hold the new opening port in place).
My feeling is that trying to accomadate any curvature with a gasket
would make the result prone to leaks
- I think better to stick with flat on flat for that seal.
Also, have you thought about replacing the round portholes with opening versions? Photo
a little unclear, but also seems a bit short of deck
vents. What about putting a hatch
(or 2!) into the cabin top (heat likes to rise) - don't have to be full size hatches, indeed for security
reasons useful not to be.....obviously not a 5 minute job!, but using wood frames and fibreglass might be able to get away without any welding.
Late thought! - appreciate that you probably can't get a new opening port that exactly fits the existing hole (at least not off the shelf), but instead of fitting as per the photo what about getting something that fits at least one dimension (or as close as) - either height or width and bolting through the cabin sides. The idea being that at some point you may fancy getting the welder out to fill in the existing hole so you can recut to an exact fit (obviously will still need a "filler" to cope with the curvature).