Outer Reef, a 36 trawler with sails, has a sea chest. The sea chest is 13 D X 26 L X 24 H. The bottom of the chest is the boats hull. There are 66 holes 7/16 in diameter, in 6 rows each with 11 holes, drilled through the hull. All sea cocks , except the air conditioning sea cock, come out of the top cover of the sea chest. Each has a PVC pipe that extends from the top of the chest to the bottom of the chest, almost touching the bottom. The a/c sea cock comes off the side of the chest. The water line is about 6 below the top of the chest. There is an access plate on the top of the chest that provides access inside. I am not sure about a vent. I had never thought about the need for a vent and had never looked for one until this discussion on T&T. If there is one, it has to be a part of a deck washdown system supplied by a pump on the generator. The sea chest provides saa water for the main engine, generator, water maker, aft head, a/c, and wash down system. The forward head and depth sounder are the only underwater thru holes. Larry Outer Reef Port Aransas, Texas