terrific question... it is standard operating equipment on my boat, aka OEM.
The vent leads inboard to an opening in the the quarter berth just above a cut out box for personal items and the engine alternator controller with analog amp meter.
When personally installed or stowed in the quarter berth (me) with both the porthole opening to the cockpit at my feet and dorade scoop installed and facing in the right direction a slight breeze appears. The dorade/cockpit porthole combination might just be installed as a methane gas eradicator, but who knows the design intent for certain>\?
A warning placard can be located in the cut out box for personal items (mine is filled with flares and emergency bungs). A pvc valve is also located in the box. The placard reads the "pvc valve should not be closed without the dorade vent removed and a deck cover placed in the opening in case water should enter through the scoop during extreme heeling of the vessel and water entry into the dorade vent result without manner of escape into anything other than your electrical panel" or words to that effect.
Three thoughts on that:
1.) the deck plate is long gone, an odd diameter and thread, and a three year search for a replacements has proven futile. If you happen to own this piece of equipment and want to sell it please contact me via pm and I will send you my first born child in return.
2.) the dorade scoop is the perfect dust and dirt collector to trap dust and dirt to plug the so called dorade vent drain. When proudly clearing the dorade scoop drain of dust and dirt with a wire coat hanger do not flood the dorade venting box with fresh water from a hose to clear or test the drain as you will likely either a.) flood the personal item box or b.) flood your electrical panel.
3.) Why would you install an opening (hole with tube attached) to the exterior of your finely handcrafted saltwater resistant fiberglass/resin hull and locate it directly behind your electrical panel? This is the thought that sticks with me the most...
4

If you are experiencing so much vessel heeling that salt water is entering your perfectly directed dorade box vent you are perhaps not balancing your vessel to the best of its potential.
In the interum... consider opening the pvc valve in the personal stowage cut out box, lightly introducing a small amount of fresh water into the dorade vent while observing water evacuation from the hole in hull behind your electrical panel, clearing the accumulation of dirt and dust from the drain with a wire coat hanger if clogged, and once clear, stuffing a carefully rolled up t-shirt tightly into the dorade vent while searching for an appropriate deck plate for the next three years.
IMHO,
Max