The boat and others like it were kept in slips lined with heavy plastic sheeting that dropped down on the end for entering and exiting. When re-entering, about a gallon of bleach was poured into the enclosed area and the bottoms stayed slick.
Yep, those were called "Boat Bath" or such and they did work
. Alternative to the bleach method was to use a shore powered pump
to get most of the salt water
out of the bath and then to re-fill with fresh from the dock
. Also seemed to work
But then, reality would strike: the boat bottom stayed clean but the plastic sheet didn't, and growth would form rapidly there, and grow and grow and grow, until eventually the added weight of the growth would overcome the buoyancy of the flotation collar around the bath and it would sink. So, folks would drag the bath and its attendant ecosystem over to the launching ramp
(and that wasn't easy) to scrub it a couple of times a season. What a mess and what a stench would ensue. Yuck! And over the years, the method has become less popular.
Here in Tasmania a few boats use them... mostly the Etchells fleet here in Cygnet... so its not dead yet!