All who make the voyage south in the Aurora Australis are familiar with the bridge deck, which provides shelter and the best views and, unlike other ships, is open to the passengers. But it doesn't resemble a bridge so why the name?
Sailing ships were originally steered from aft, close to the rudder, making both the steering gear and monitoring the ship's movements relatively simple. This time-honoured arrangement remained until the emergence of mechanically propelled vessels.
The first method of mechanical propulsion was by paddle wheels, one on each side of the vessel. These large wheels towered above the height of the deck and impeded the view of the helmsman down aft.
So planks were laid between the top of each paddle box, and with an iron railing on each side, this 'bridge' provided a viewing platform for the watch officer who was then able to shout his orders back to the helmsman.
This arrangement evolved and soon the ship was steered from the bridge itself, providing both watch officer and helmsman with a clear view.
As paddle wheels disappeared in favour of screw propulsion, the bridge remained and, as superstructures of ships developed, became what we call the bridge deck of today.
Peter and Basil Greenhill First Atlantic Liners: Seamanship in the Age of the Paddle Wheel, Sail and Screw