thanks for the criticism, it is useful remark.
hard to compete with professionals like you, but I will say in defense:
- The border of the upper lid to be lower than the central, through this, even when the slope of the yacht with a full deck water popodat water will not be in the central part of
- To ensure the integrity of a rapid lateral flow can be predumotret face, as one of my models from sheet metal (rubber seal)
- Instant soul will not, if the water and hit the central part, it will meet in the middle and the bottom of the shoulder would not allow her to pour out at once when you open

ready to listen to any criticism!

Sorry man, I sort of get what your saying but if you get water to a depth above the cap on the deck wouldn't water flow up and over the inner ring and fill the chamber?

Thanks for the extra image dassault! Now I see, this is quite clever, you have to make sure that when the vent is closed it is 100% air tight and in an ideal situation it would work fine, I just don't know on a yacht that is swaying in all directions with water splashing everywhere, I really like the thinking though :)