I was first exposed to this through an early (80s, 90s?) issue of (bodyboarding magazine) Riptide. There was a picture of Mike Stewart and a caption to the effect of 'Mike Stewart [underwater surfing] inspecting the reef at teahupoo.' Or maybe my memory is failing me and I am combining two stories into one (according to
http://www.surfline.com/surfaz/teahupoo.cfm he was one of the first (3 people) to surf that place).
Mike Stewart was leading the way in those days, he wrote about duckdiving when stuck inside. That was very interesting because he described a breaking wave as a series of diminishing n shapes and working against this a series of diminishing U shapes. These U shapes suck you out beyond the breaking waves (n shapes). Although I use this on a bodyboard I find with bodysurfing/underwater surfing you can get out the back with very little effort using this approach.
My experience:
1. I've never needed a mask (but I've not surfed huge waves but I have surfed very fast waves). When freediving I always use a mask so maybe this is just a learning habit (I learnt about freediving in a dive pool (chlorine) and underwater surf in the ocean).
2. Strong awareness of where I am in the wave (I don't feel lost or out of control or close to hitting the reef)
3. Wary of surfers because you're invisible even when you're visible. I'm more wary of surfers paddling out (duckdiving through the wave you're on) than surfers dropping in
4. Ease. It's very easy to lock into (catch) the wave, much more so than surface surfing. It's easy to get out the back (see above) and it's easy to exit waves
5. Fins, the short fins we use in bodyboarding don't seem particularly good for catching waves underwater (but may be better for positioning). It's like you've got more time to catch the wave and need more prolonged power (longer fins). Not sure about this, I'd be interested to hear other's opinions
6. Stand up surfing you use an edge, bodyboarding you use and edge and a leg (extension of that edge), bodysurfing you use a surface and under water surfing you use your whole body. It doesn't make it better, it's just different. I like surfing on the surface for the sounds, the vision the shifting of weights at speed. Underwater surfing offers different sounds and that shifting of weight (weightlessness due to speed) is constantly there but quite a different sensation
7. I'm happy to do it by myself
8. but I think it would be possible to share individual waves in a way which is not possible for surface surfing (because underwater there's a greater area of power and I don't think one person in the wave would impact another person's power/position in the wave). Surfing culture is typically about one person on the wave (or finding a site and not telling people about it) but when you see dolphins, there's often five or six inside the one wave
9. Although it's easy to underwater surf I'd recommend people learn to surface surf first because there's a whole language in reading waves and conditions. It's not that one is better than the other but I'm not sure that overall awareness is developed underwater. People die by placing themselves in the wrong position in surf and they don't need to be riding waves to do so
10. lifeguards surf underwater to catch waves but in a utilitarian manner (to get to shore) maybe one day they will stay down and turn left or right
11. WA's fat waves mean there is a great power in the wave. I don't mean the height of the wave I mean how fat it is when viewed from above. This generates the push we use when underwater surfing. I've not surfed in Hawaii but I guess the waves are fat there (Waimea shore break is fat)
12. My sponsors? I ride a 1974 model with arms, legs and few dings where it has hit various reefs (from surface surfing).
Migs