Hi, John,
The 4" will do noticeably better than the old 3". The cowl size (as mentioned above) is the limiting factor.
For underway in hot, steamy places, I'm a greaty fan of fans, strategically placed, for making life below decks better.
Also, for at
anchor where it rains a lot, we made a
hatch dodger that works on the dorade principle, and can leave the
hatch open up to about 25 knots, after that, the
wind blows the bouncing rain drops in, below that, it allows a lot of air in.
Ann