Maneuvering signals are given on whistles, no matter what their physical construction.
The only "horn" is the fog horn which is usually the same as the maneuvering whistle. Go figure.
Departing a berth is a maneuvering situation. On US "Inland" waters this requires a prolonged blast before getting under way. International Rules don't require the prolonged blast, but it is permitted for vessels not in sight of one another. In both sets of rules when astern propulsion is used three short blasts are used. So, the hodge-podge of Hollywood whistle grunts, groans, toots and shrieks are just the imagination of the sound mixer.
Even so, I must point out that until the coming of magnetic stripe sound film after WW-2 it was a real chore to shoot "synched" sound. The cameras and recording gear were beyond clumsy. It was possible to shoot something similar to what we call a "sound bite" in those days, but only at great expense. The sound was always recorded on a separate machine from the camera in a process known as "double system." Shooting silent B roll continued right through the film era in news coverage and is still common today. It took only a single cinematographer and his camera and tripod. "Wild," or unsynched sound was recorded on a disk, wire, or (later) 1/4-inch tape.
Because putting natural sound to picture on location required a lot of work, studios tended to collect libraries of sounds which were used over and over from feature films to documentaries. The same big, throaty steam whistle sound might blast from Olympic on this picture and from Berengaria on the next. Economics rule.
So, don't believe you are hearing the real McCoy when you see an image of steam spewing from a whistle. The sound could have been recorded years apart and miles away from the picture.
-- David G. Brown
