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In strong winds the dorade box is the first line of defense against water trying to enter the ventilation systen.
It should have a big volume be deep have a small inlet and a big drain. To prevent the incoming air going out the drain instead of coming into the living area I use a U-tube, familiar from the common verity of WC where it prevents bad smells from entering the house.

The picture of the finished doradebox shows that the boat is now also painted on the inside. The black handhold from the corner of the box also functions to prevent my delicate head from hitting the corner.

In Archive July 2008 I describe how the rest of my heavy weather ventilation system prevents water from entering the boat even if its upside down.