The sea appears through the floor of the boat. I accept that water would splash into the boat but not through the floor directly.
This is similar to another issue relating to the wake of the boat appearing unrealistic.
Not sure if this issue has been reported - could not find it in search.
Which boat is affected? Or is it all of them for you? I've just been trying to replicate the issue and haven't been able to. The closest I've come is doing a tight turn in the gunboats where the angle is high and the water 'floods' the rear deck.
Cool. You might have to wait for a dev, but it may be a fixed issue (unless it ends up being specific to your setup). Your report says you're using the stable alpha build. I was testing in the latest dev build (updated only just prior to me seeing your issue and testing) and it didn't seem to happen. I've done tests in all weather conditions and choppy seas but it's not happening on this end.
Problem is still present in the latest dev build as of 25/9. Spray and water appears through the floor when viewing in 3rd person.