When you're racing upwind, it's important to sail in clear air!! On starboard tack, a good way to protect your lane of clear air is by using a “blocker.” A blocker is another boat on starboard tack that’s to leeward and bow out on you (one-half to one boatlength ahead of you in the race). You want to have this boat in a position to intercept incoming port tackers that otherwise might lee-bow you (and force you to tack out of your lane). With a blocker in place, the incoming boats will either have to lee-bow the blocker or duck behind the blocker and go behind you too. This will leave you free to continue sailing in your lane. One good way to get in the proper position with a blocker is to duck behind a starboard tacker (while you're on port), go two or three boatlegths and then tack on their windward hip.