Why do ski boats have 2 speedometers ?

Question

Why do ski boats have 2 speedometers ?

Answer 1

Dual speedometers date back to the days when competion slalom water skiers aimed for the "perfect" speed of 36 mph. Because boat speedometers are fairly inaccurate, and most use a water pickup tube to measure water pressure, manufacturers started  making boats with two speedometers with the pickup tubes mounted on both sides of the hull as a way to help assure the speed is fairly accurate as long as both readings are the same.