Sailboat racing is sometimes lauded for being one of the few sports that is entirely self-policing. There are no umpires and referees on the course. If a competitor breaks one of the rules he is obliged to take a penalty or retire from the race. If he does not do so, another competitor may bring it to the attention of the offender so that he can exonerate himself by taking the penalty. If these two competitors disagree on what happened or whether a rule has been broken or who broke the rule, then a protest hearing is held after racing to determine the facts and who, if anyone, is at fault.
One exception to the self-policing philosophy is that at major regattas there are sometimes judges on the water to ensure enforcement principally of one rule -- the infamous Rule 42. This rule essentially says you are supposed to use the natural actions of wind and water to propel the boat; not sculling, pumping, rocking, rolling, ooching, mooching, smooching or any other unnatural acts. Or something like that. It's actually a lot more complicated (and a lot less fun) than that with detailed definitions of what is and is not legal to do to make the boat go faster. And on top of that the international body of sailing, ISAF, has published some even more complicated "interpretations" of the rule. Most racing sailors have a rough idea of what constitutes illegal propulsion; but the subtleties of the interpretations of Rule 42 are so hard to understand that there is even a training video for judges to help them to learn what to look for.
At the US Laser Masters in Annapolis this month we did have judges on the water looking for Rule 42 violations. They did call about 10 of the 80 sailors for breaking the rule. One very good sailor, a former national champion and renowned coach, was flagged by the judges for doing an illegal tack right next to me on the start line. Illegal one presumes because his tack was so good that he accelerated out of it (into a gap between boats on the start line) faster than he should have done. Another sailor, actually a little old lady from Philadelphia (no kidding), was called for "body pumping".
There was some grumbling among the sailors who had been caught and afterwards there was a spirited debate on the Laser Forum about the issue. Some wanted all Masters regattas to be self-policing. Others felt it was good that the judges kept the racing more fair. Others worried about the competence of judges at some regattas.
Rule 42 tends to be a heated issue because it carries with it an aura of "cheating" If I misjudge an attempt to cross you while I am on port tack and you have to bear away, you may be temporarily angry with me, you may even swear at me, but we both know that I am guilty of nothing more than bad judgment or too much aggression. If you deliberately rock your boat to make it go faster downwind and I ask you to stop, it will seem like I am calling you a cheat. For this reason competitors don't often protest other sailors for Rule 42 violations.
It's a difficult area, not only in interpreting the rule but also in handling the ill-feelings sometimes caused. There has been a festering issue at my summer club for a few years now with some of the old guard believing that one of the newer sailors is winning races through illegal propulsion. But they just grumble; they never call him on it to his face.
Personally I'm for use of judges in major regattas. At other races I think all of us should be prepared to warn a fellow sailor when we think he is breaking the rule and to protest him if he persists. I want the racing to be as clean and fair as possible, even if a few feelings are hurt in the process.