G'day 'Bismartin', the portholes are 'orrible things for sure, so you can imagine drilling what seemed like thousands on the 'AMATI TITANIC', anyway, similar problems existed with this model, they cracked, rough edges etc, but 'brass eyelets' were supplied to finish these off. I used them , but did it in a completely different way, but that's another story!
I had 'eyelets' spare, but none big enough, so I thought,"what else is there I can use for these buggers?"
So I came up with a humble and a readily available source,and cheap!(raid the bathroom) cotton buds!!, not the fluffy bit, the plastic tube!. If you drill out your portholes to a size that these fit tightly, insert the ends, push it fair in, then trim with a new blade, or cut them to about a 1/4 of an inch and push them with the 'other end' of a drill, (anything round that is wider than the tube)
I've did all mine in this way and it looks quite 'realistic', each porthole looks like a 'separate fitting' and not just a hole!. Give it a go on a spare bit of wood and see how you go, just a thought to spread around, but it worked for me!!...Dave.
P/s, if you are sailing her, you could 'crimp' or use something to 'fill' the 'inserted' end, not too hard a job to keep it watertight and still have a clean looking porthole!!??