From the American magazine “Modern Mechanix” – Feb 1929 – Found at Modernmechanix.com
There is a knack to keeping one’s balance on a single runner coaster which you may acquire quickly, or maybe not.
The coaster requires a 16’’ 4-by-4 and a 1-by-4 board 6 feet long for runner and brace. The Runner must have a slight curve to it’s bow, as Fig 1 shows. To warp the wood, steam it or soak it in hot water, then place the bow end in a vise, and block up the other end until a curve a trifle greater than the one shown is obtained.
Detail of single-runner coaster.