The open end is for draining while sailing, not while at the dock And, it is also the reason there are scuppers placed at what was (at one time) the low point along the rail. As the trim of the boat changes, so does the location of the low point. Usually, the low point moves aft as more weight collects in the stern third and the boat no longer rides on its design lines.

As for water on the cockpit seats, I use cushons. Bottom Siders are great and they give me the inch I need to see over the coachroof.