Ventilator when the Rescue Boat is to be upseted/capsized.

[pipingnam]

Would you please let me know how to prevent water flow in Rescue boat by Ventilator way when it is to be upsetd/capsized.
And please let me know the name of the Watertight Ventilator if you can. Thanks a lot!

 

[MintJulep]

A floating ball in a tube with a seal.