I was driving my 4x4 yesterday in heavy snow shower, thinking of that Crow’s Nest Canvas. The light snowflakes were naturally driven by the airstream created by the generated wind. At low speed, the snowflakes were deflected upward by the front end, flying over the hood but falling and melting on the windshield. At higher speed, the airstream was driving the flakes totally over the top of the truck, keeping the hood and windshield dry and clean. But I can assure you that if I would’ve taken the windshield away, I would’ve needed goggles to watch the cockpit being filled. Since «Nothing is lost, nothing is created, everything is transformed»; due to a plan against a breeze, the airstream is compressed, accelerated and is partly transformed by a void turbulent airflow.
At low ship’s speed, the air flow was driven upward and above the nest in the exact same manner. You just had to back up in the nest to not feel the wind too much. But at higher speed, backing in the nest was not sufficient. The lookouts had to rig a canvas air deflector at the rear of the nest. It would then bring the air flow higher and produce a larger void that gave better protection against the breeze. On a ship’s bridge wing not equipped by wind deflector, you just have to back up a bit if you don’t want to feel the wind too much; far from rocket science.
Light shade canvas would’ve been unnecessary since a lookout didn’t have to scan the horizon more than 2 points abaft the beam. Any type of vessels approaching from a direction of more than 2 points abaft the beam is considered by the Rules of the road as an overtaking vessel, which befalls as the giveaway vessel and must keep clear from the stand-on vessel.
Sorry but, I personally found the lookout duties as the most boring job on earth and steering a vessel by hand on a straight course not much more exiting; but an experience required if you wish one day to command a vessel.