The reason you put Nicro vents in place is to help prevent boats from becoming moisture pumps. As a boat heats up during the day, the air absorbs more moisture—since hotter air can hold more water. When the sun goes down, and as the air cools, then the additional water can condense out. By keeping the air flowing, the air doesn't tend to act as a moisture pumps, since it keeps the boat from heating up as much and moves the heated air, which holds more water vapor in it, out of the boat.
I agree for the most part. But if the boat is well-sealed, and there are no pools of water to evaporate in the heat (i.e., bone dry bilge), then there is no source of moisture for the air to absorb when it gets hot, and thus no condensation when it cools.
So there are two extremes, both better than the alternatives:
- Good ventilation that prevents condensation when the boat cools
- Seal off the boat and dehumidify the stagnant air aggressively
I agree that option 1 is preferred, but if like me you do not have a good location for a second vent (yet), then option 2 may be a viable alternative
This is a similar argument to the settee locker condensation issue in a separate thread that I started. And by the way, I checked for condensation in my settee lockers last week and they were still completely dry.