Exceptions overruled. The judge directed a verdict for the defendant on the following undisputed evidence: The plaintiff, a prospective participant in an outboard speedboat race on the Connecticut River in the South Hadley Falls vicinity, with which he was totally unfamiliar, arrived at the launching site where there were about fifty speedboats and seventy-five people, "just went ahead and put his boat in the river," made no inquiry of anyone where the race course was located or laid out, proceeded upstream (where in fact the race was to be run) to adjust the motor and test the propeller, reversed his direction and went downstream at fifty miles an hour or more, meanwhile adjusting the carburetor while in a kneeling position, glanced back and saw another boat behind him, and then saw the flashboards of the dam about thirty feet ahead, and, at fifty miles an hour, went over the dam operated by the defendant under legislative grants of 1848 and 1859. The only rational inference is that the plaintiff's preoccupation with the motor to attain maximum speed was the sole active and producing cause of his accident. Clough v. New England Tel. Tel. Co. 342 Mass. 31, 36.