The only info I can find for Australian cats in the 50's were 20 foot Yvonnes (which from day one flew spinnakers), designed in 1951 by lindsay cunningham of little americas cup fame they were sailing in good numbers by 56, go here for their history.
http://www.geocities.com/Colosseum/Arena/9449/#YVONNE20%20CATAMARANby the early 60's there were numerous very fast cats like the Arrow and arafura cadet sailed at clubs everywhere.
I remember the film being done because my father worked at the shell refinery at geelong in Victoria where the sub was filmed docked at the pier. He was told if employees were filmed as they worked, to stand still as they would be deleted from the film stock by hand. My dad also built a 14 foot ply cat with a solid deck at this time and the first time he took it out couldn't turn it around as the rudders smashed, typical of cats at that time. He had an oar onboard, dropped the sail, sculled the cat around, rehoisted the sail, got to shore, and left it there never to sail it again. A big storm came through later and washed it away which he was rather grateful for as he said the cat scared the hell out of him.
