It is possible to get a portlight to seal well , put 1/2 cubic metre of water on them , not so much.
The thought of how many times I've had the bow under and a wave on top of it to the mast just keyed a memory from last year.
Friend in very robust 48 footer leaves a bit late for the pass at the atoll we all were at. Gets lulled by the light wind and sunny day so travels out under motor with the forehatch open and two crew on the bow with cameras. The first 800 metres is fine but the last 50 has stand up waves about 10 M apart or less.( enough to stick the bow right down.) Bow goes under, one crew washed off her feet , camera over the side , a cubic metre of Fijian water down the hatch. Repeat for one more wave. Cost of one leeetle misjudgement , one camera , one scraped leg , a lot of wet bedding , a pump workout ,and people like me ribbing him .
hahaha.
the next day we left as well but an hour earlier relative to the tide and it looked like this , we may have got some on deck but not much and you can bet everything was dogged down, unlike our mate.
anyway , I digress , my point is portholes in a pressure location like the front of a coaming......they will leak!
I'm having trouble finding the magazines because of a house shuffle around , so I'll have a proper go later on, John.