Searched the forum and cannot find an answer. What keeps the vents (not the dorade itself) from barring entry of rain water.
Now that is a perfect explanation...why didn't I think of wikipedia??? Thank you Loren...nothing like a visual...now I understand!
Note that the 'Dorade' scheme does let rain (and spray) enter along with air, and then routes the water back out to the deck.
Some older sailors might recall the Matec vent from 20 or 30 years ago with its flexible interior flap that was supposed to close under the force of solid water but remain open to provide minimal restriction to air flow the rest of the time. Long gone from the market, and remaining examples in use probably have the vinyl becoming hardened and inflexible due to age.
History and Trivia.... maybe or maybe not helpful.