A good Surfski watch

Is there a waterproof sports watch where you can turn off the smoothing algorithm? My Suunto Ambit shows little speed variation when I'm on a downwind. I can be whizzing down a wave one second and completely stall out the next and yet the speed readout hardly changes.

My old Fenix 5 is pretty good at showing speed accurately and I guess the newer 6 or 7 models would be equally good if not better.

I like my old Garmin eTrex 20 for that very reason, the readout is quite granular and quick, unlike a Forerunner I once used, that was pretty misleading due to averaging.
It also has a screen larger than a watch and it's legible in most daylight conditions without a backlight.
Fancier GPS units are bulky, less legible in sunlight and eat lot more battery. eTrex is about perfect for a rigid Nelo strap with an adaptor to attach it to a GoPro mount Nelos come with. I don't even remove it for transport.

I have a cheap garmin instinct that works well, though it does smooth things a little more than some of my friends’ fancier models of garmin.

Check the different activities on your watch. Even cycling has a smoothing algorithm that I found annoying on the boat.

‘Cardio’ is one of the few activities that gives me raw gps data. In an ideal world you would be able to choose a smoothing rate equal to the accuracy of your gps.