These things were used at fairground attractions - bumper cars, merry go-arounds etc. - until at least the 1980's. They tended to come in the shape of a wooden

These things were used at fairground attractions - bumper cars, merry go-arounds etc. - until at least the 1980's. They tended to come in the shape of a wooden barrel with a hinged lid which had a number of shark fin shaped metal plates on the bottom. There was a rope attached to the lid which was used to raise and lower it. The water got quite hot in use which led to steaming barrels later in the evening.