This duct taped vent on the foredeck of a new 80 footer caught our eye, and got us to thinking about the subject of keeping water out of the interior when vents are used. The design principles are quite simple, if somewhat costly to execute.

We’ve covered this subject in detail in Offshore Cruising Encyclopedia, so here are the basics:

• The vent needs to lead to a substantial containment structure, either above or below deck with sufficient volume to allow water to drain before it overflows into the interior.
• Vent box drains need t o be substantial in size.
• Air into the interior needs a downpipe that sticks well above the deck, into the vent box.
• The vent cowl and downpipe should have a baffle between them to minimize spray being carried into the down pipe with the air flow.
• Finally, a system of regulating air flow and sealing the downpipe from inside the boat needs to be incorporated.