Hi Tim,
I know this is a late reply, but I happen to see your question while searching for something else. I have used my Apple Watch Series 2 while surfing on 3 occasions. In my case, I always wear protection on my arms from the sun and temperatures, so my watch is either under my rash guard, or my wetsuit. I do this to protect the glass on the watch from an occasional knock on my surfboard, but I don't think it's necessary. I'm using the sport watch band, I keep it a notch tighter during surfing. I would recommend placing the watch in "water mode". This limits the touch screen usage. I found that when the water beads up on the watch face, this can lead to unexpected "taps" or unexpected response to "taps". In water mode, I've found that the watch responds to crown press or watch face tap pretty well. The watch face tap in water mode, if there's not a bead of water on the face during the tap, just shows you the current time, or if you have the workout feature enabled, your stats for workout. I have the "show watch face on arm raise" disabled on the watch. During surfing, your arms go through a lot of motion, so having the watch face illuminate all the time, will probably just lead to loss of battery life, with minimum benefit. That's just my opinion. The watch actually does a good job of monitoring my heart rate, and give me some good "exercise" credit minutes during my surfing, even though I haven't activated any type of workout activity. I haven't tried to enable an outdoor exercise activity, which enables the GPS, but I'll try the next time we get a good swell. I think using some sound judgement based on the size of the waves, and conditions probably make sense, as to whether you should wear your watch while surfing. If your in double overhead conditions, and likely to take heavy wipe outs, I would probably recommend a less expensive watch, but that's just my recommendation. Good luck, and hope you get some good waves...