In America’s Cup racing, Rule 20 dictates the ins and outs of the four-length boundary zone. Applying some simple math, we can understand where the best position will be for Boat B to set up on the windward hip and attack. An America’s Cup catamaran, for example, will travel at approximately 25 knots closehauled and 55 degrees from the wind in moderate breeze in Bermuda in June. If the four-length boundary is 200 feet wide, it will take a boat about seven seconds to sail the approximately 250 feet to the boundary. Let’s assume it’s 15 seconds to sail to the boundary wall, tack, and completely exit the boundary zone. When splitting with a boat that’s already on starboard, therefore, whether they’ve crossed or ducked to get to the right, the correct play is to always tack at least 15 seconds after the cross to make sure the next time you meet, when you have the starboard-tack advantage, you’ll be able to take full advantage.