Does the vent have a shutter or seal … ?
Does the vent have a shutter or seal allowing the user to close it from inside the boat to shut out both air and water (e.g. in storm conditions where a roll-over is likely, can one just shut them from inside)?
There is the shutter marked by red crosses on pictures. The user can close it completely or just reduce inflow passage (4 positions).
You do not need to close the shutter in storm conditions.