A Mushroom Vent typically used on boats to provide ventilation for below-deck areas, such as cabins, heads, and bilges. The name "mushroom vent" comes from the shape of the vent, which consists of a rounded dome (the "mushroom") that sits above a cylindrical base that is mounted through the deck.
 
Mushroom vents allow air to circulate freely into and out of below-deck spaces, which helps to reduce condensation, minimize odors, and improve air quality. They also prevent water from entering the boat, as the rounded dome sheds water and prevents it from entering the vent. Mushroom vents come in a variety of sizes 3", 4" and 5" and made from sheet 304 stainless steel. They have a permanent stainless mesh screen inside. They can be used in conjunction with other ventilation systems, such as dorade boxes or air conditioning systems, to provide a comprehensive ventilation solution for your sailing boat.
 
3" 
Deck Cutout 3-1/4"
Height Closed 1-1/4"
Height Open 1-3/4"
Overall Width 4-5/8"
 
4"
Deck Cutout 4-5/8"
Height Closed 1-1/4"
Height Open 1-3/4"
Overall Width 6"