This is the yacht 'Fantasy' sailing on Lyttleton harbour not long after she was launched. She was designed by the English naval architect Harrison Butler.
Harrison Butler designed all his yachts to a design rule he created called the Metacentric Rule. The rule was a mathematical equation relating to proportion that was meant to create the most efficient and fast hull for a given length. I think that the rule has now been discredited. Despite this the rule did have the byproduct of producing beautifully balanced hulls. My father who sailed on Fantasy said that she would sail herself to windward for long periods without anyone at the helm.
This characteristic is not something to be taken lightly as anyone who has sailed on an unbalanced boat will tell you. Many years ago I did a trip to the Pacific Islands in a beautiful looking yacht with very very bad "weather helm" i.e. the stronger it blew the more the boat wanted to rip the tiller out your hands and round up into the wind. Weather helm can be exhausting, especially in our case where we had lost our self steering wind vane in a storm and had to steer long watches for many days.
The curiously beautiful balance of Harrison Butlers boats is ascribed to the fact that the lines of the underwater plane of his hulls are symmetrical fore and aft. When you combine this symmetry with an above the waterline hull of non extreme type you have a hull whose balance is perfect when sailed upright and does not alter a lot when heeled.
In the UK many of HBs designs are considered classics and many have been restored and are still sailing.
By modern standards some of these older yacht designs do not give the same amount of accommodation for a given length, but their charm lies in their traditional design and very well mannered sailing behaviour.