I was going to share a simple way to turn your venturi into a one way valve, that stops water rushing in when you first get in or are sitting around waiting to catch waves. Unfortunately every time I go to load some photos I took my mac wipes the text, so I'll try and describe how to do it.
It takes less than 15 minutes, has a minimal effect on boat drainage and cost virtually nothing.
I simply cut a bit of 1mm EVA, or rubber or some of that white packing foam that comes with everything you buy, to the shape of the hood that covers your venturi hole. The idea is to create a flap that covers the venturi hole but fits snuggly under the hood. I usually glue it at the front edge of the flap to the hull using some 5 minute epoxy.
It is such a simple idea and makes cold mornings, race starts where you are sitting around, catching waves a much dryer proposition.
As the water tries to rush in the hole the flaps seals the hole. When the cockpit fills it simply drains as normal.
If you have a bullet it is easier to remove the bullet first. Then re attach the bullet later.
Sorry the photos didn't work. Hope you get the gist of how to do it.