All modern surfing contests are based on the Heat concept.
A Heat is basically a competition on water between surfers to determine who surfed better. Heats have a fixed period of time. Two up to four surfers may compete in a Heat.
For each surfed wave, each judge gives a single score between 0-10. The mean of all judge scores is assigned as the wave score.
At the end of the heat, the top 2 waves scores of each surfer are summed up and compared between the others. The surfer with the better total score wins the heat ("not winners" are not necessarily eliminated from the contest).
Surfing contests generally use backets of Heats to determine the winner of the tournament.