That's just the ticket for interior circulation to keep the lockers dry Tom.
You also need to bring fresh air in and out of the boat.
I found some notes I made from the book:
You should work toward a complete exchange of air hourly so your ventilation system should be designed to flow
15 CFM per crew member (900 cubic feet per hour) plus the volume of the empty boat.
A 30 foot sailboat contains about 1000 cubic feet of air on average.
An occupied boat obviously requires more ventilation than an unoccupied boat. (We found our boat did just fine, unoccupied, in winter conditions with just one 4" solar exhaust vent running. We never close the intakes except in VERY heavy weather.)
Additional vents over the galley and head to carry away water vapor and odors are a good idea.
A 3 " Nicro Day/Night Solar Vent flows 600 CF per hour. The four inch model flows 1000 CF per hour. The exterior cover is the same size. Get the four inch model. They come with two fan blades and can be set up for intake or exhaust. On our boat, we think the intakes can be passive.
The problem we have had with these is that in high latitudes there is just not enough sunlight to keep them running in the winter when you need them most. Unfortunately, Nicro has discontinued the 12V model so we are looking for an alternative. (We have decided we need one more active exhaust vent)
Comment: When we talked about this with people in the Pacific Northwest they always asked if we hadn't had a problem in Hawaii where it is supposed to be so humid. The answer is "No". In Hawaii, we always set up a full length awning over the boat and opened the hatches (Pictures and article
). The trade winds flowed through the boat and she was always bone, dusty dry. The mold and mildew problem we found in the high latitudes caught us completely by surprise. We were astonished at how wet the inside of our boat was when we closed her up to keep warm. As always, we learn as we go however. We bought dehumidifiers, we insulated and, finally, we ventilated. Now we are better prepared and more comfortable...
...even with the cold rain that is beating down on the coach roof as I type this.