GPS is a SpeedPuck mounted on the spin pole.

I measure total time on the tack - from just before I reduce speed to where I get back to roughly the same speed. Then I measure the actual time the boat is tacking (just the turn portion).

Subtracting the boat tacking time from the total time on tack, I get a metric on time spent decelerating/accelerating. By far, most of the time is on the accleration end. Many times the point just before deceleration is at the same time as the tack begins, so all the time is on acceleration.

"Turn times" are slightly slower going to port, but decelerate/accelerate times are 30% slower. So I looked at the track and sure enough, there's the hook on the end of each port tack. I analyzed the other race and sure enough, its there too.

I don't know if anyone else measures this stuff, but tacks, jibes and mark roundings are consistently 19% of my total time during the race. I'm picking that figure apart to see if I can find where the improvements can be made.