In the dawn of the industry, horse power was assigned by guesstimation. Some companies used a pound scale tying the boat to the dock to measure motor thrust. It was found to be more of a propeller efficiency test than a measure of horse power. As outboards became popular a test propeller with a flat outer rim was put on the prop shaft and an adjustable band which was attached to a pound scale was put around it. (Thus the term "Break Horse Power".) The first dynomometer. When it was found horsepower sold motors, engineers went to great lengths to be sure there carefully hand built prototypes put out the most horse power possible. The production line could not afford to be as meticulous. The casting and machining of that time produced motors of varying horse power. Few achieved the rated power, and a few were downright lemons.
Things came to a head in the early thirties when customer complaints and charges by rival companies caused Steve Briggs to get together with other manufactures (Evinrude, Elto, Lockweed, plus Caille, Johnson, Scott Atwater, Muncie Gear Works and others) formed the National Outboard Association. It was agreed that representatives of rival companies would randomly pick three models off the line to be sent to the Pittsburgh Testing Laboratory and the average horsepower of the three would be the certified horse power of that model. They measured the electrical output of an electric motor attached to the propeller shaft. It is considered more accurate. Overnight some Evinrudes lost 2 or 3 horse power.
Later Champion and Martin joined. When Mercury was asked to join, they got a "No, thank you" from Mr. E. C. Kiekaefer. His wildly inaccurate horsepower ratings coupled with increased sales spelled the doom of the NOA. Evinrude always bought rival manufacturers outboards for Engineering to examine. I wish I still had the horse power curves they produced for Mercury outboards. Today the brass NOA certification medallions that hung on all Evinrude and Elto outboards of the late 30s and 40s are considered collectors items. The horsepower of the classics of the 50s we love were the best estimates of the engineers at the time the owners manuals and advertising campaign were laid out. . . 😀
