Measuring the flex in surfboard fins during surfing

In this paper, we describe the fitting out of a surfboard with inbuilt measurement system and a set of fins instrumented with flex sensors. The inbuilt measurement system consisted of GPS, accelerometers, and gyroscope. Telemetry data were collected during characteristic surfing maneuvers on ocean waves at a sampling rate of up to 80 Hz. Our results indicated that our surfboard with instrumented fins can be used to measure the flex in fins during surfing. Our data showed that both fins flex while on waves (at surfing speed), but not during paddling (at low speed). The commercial sensors recorded fin flex values of up to 10% as the fins are loading and unloading at surfing speeds of up to 6 m/s (from GPS data).