This is a relatively simple, lightweight hollow tube with a ridge on the outside, designed for routing a ventilation hose through the deck. Use a hole saw, insert the adapter, caulking around the outside, attach the appropriate size vent hose with a hose clamp, and cover the outside opening with a clamshell vent. Do a good job on the caulking. No internal baffling, so there is no protection against wind-blown rain or waves entering the boat.
For use with Beckson C1, C5, and CS7 vents