I built the Stuart Launch engine from castings. High pressure cylinder is 3/4 inch. Low pressure cylinder is 1 1/4 inch. A compound steam engine uses the exhaust steam from the high pressure cylinder to flow through an exchange pipe to the low pressure cylinder. Allows the engine to run longer using less water. Reversing gear is Stephenson Link. Cylinder drains have tubes to direct hot water and steam downward. Suitable for boats from 4 to 6 feet. Video shows engine running on compressed air.