Chopping a hole in my deck?

i had a caravan which had a 8" x 8" roof vent which could open one side to about 35 deg on any of the four sides allowing great air control depending on wind direction. it would also fully lift.
i have not heard of such a thing being used on a boat but i would fit one in a flash if i could find one and needed one.
 
I have a solar vent fitted in the deck to ventilate my shower/toilet area. I was worried that in the event of the decks being awash it could allow a lot of water below. I have fitted a 5" inspection port directly below the solar vent so that in rough weather I can screw the insert in and stop any inflow.
 
I have a solar vent fitted in the deck to ventilate my shower/toilet area. I was worried that in the event of the decks being awash it could allow a lot of water below. I have fitted a 5" inspection port directly below the solar vent so that in rough weather I can screw the insert in and stop any inflow.

And i bet you never need to use it?
 
Ok, true, but has it let water in up to now in rough weather?

Single I'm still trying to get my yacht in the water!! I have dreamed that because I have so may safety items and because I have overbuilt the yacht, it sinks on launching. (It must be worrying me!!)
 
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