JohnLincoln:
Yes, that is correct.I was assuming that the swimmer started at zero initial velocity.
The OP implied that he had a three axis accelerometer, so it would be possible to measure horizontal acceleration in the direction of travel.
The measurement would become complicated when the swimmer went from being upright on dry land to being horizontal in the water as the axes get flipped around. Also the largest acceleration may be during this period if the swimmer dives into the pool.
Hi:)
Beacuse of the fact that this project is not a google's project, I can define that the swimmer starts in the water when his head is straight with the swim diraction but my main issue here is the noise this sensor creates. I realy consider to change to a pressure sensor and put them on the end of the pull