The development of the steam engine figured in yacht design. In England, the practice was to use fire-tube boilers wherein the hot gases of combustion ran through parallel tubes surrounded by water; a design that required as slow process of heating the water to avoid damaging the boiler before making steam. In the United States, the practice was to use water-tube boilers, wherein the water is surrounded by the hot gases of combustion, allowing for making steam more rapidly. While the boiler was the source of steam, the marine steam engine is where the steam was converted to mechanical power. With smaller, more rapidly spinning propellors engines comprised cylinders with pistons, connected to a crank shaft, driven by steam.