Surfing Waves

Any ideas? My plan is just to swim three days a week. I have about half an hour during lunch, and my goal is 800 yards in that time. (currently 600 yards, with about a 50/50 swim and rest ratio) I was a pretty good competitive swimmer, but my conditioning SUCKS. Otherwise, I already lift and run pretty religiously.

I ask because I'm going on a three week trip, and I've never surfed consecutive days before. Those few times I did my shoulders were SORE the next day.