Nicro Day/Night Solar Vent
Geoff,
I too installed a Nicro 4" Day-Night Solar Vent in the Veeberth Hatch and set it for exhaust. I used a hole saw (about 4" I think) and cut slow speed.
For air input I cut a slot in the topmost teak pin board at the companionway and installed what W.M had and called a "Venturi Vent". It was about 2" high and about 15" long (cant remember the exact dims.) This was screwed inplace and a bead of silicone rubber around it on the inside. I also cut a piece of fiberglass screening and cemented it on th inside of the installed vent to keep critter out.
As the solar vent runs to exhaust, it draws air in thru the pinboard. This works well. In the winter I have a one piece "winterboard", to replace the pinboards, and have installed a "venturi vent" in that as well. In the winter I remove the battery so it doesn't "die" if it doesn't get enough sunlight in winter to recharge it. This lets it run only during day sunlight during the winter, but that's fine.