Rule 18.1(a) states that rule 18 does not apply between boats on opposite tacks on a beat to windward. For the purpose of rule 18.1(a), when are boats 'on a beat to windward'?

For the purpose of rule 18.1(a) which is only needed in multi-boat situations when at least one boat is in the zone, two boats on opposite tacks are considered to be ‘on a beat to windward’

Consider the following four situations, each involving boats on opposite tacks in the zone of a mark to be left to port. The mark could be a windward mark, a finishing mark at the port end of a finishing line, a windward gate mark, or a limit mark that is not a rounding mark. In each of these situations, the boats shown are ‘on opposite tacks on a beat to windward’ and, therefore, rule 18 does not apply between them.

Rule 42.3(c) states that a single pull on any sail when surfing or planing is possible is permitted except on a beat to windward. For the purpose of rule 42.3(c), when is a boat 'on a beat to windward'?

Rule 42 addresses each boat in a race individually. For the purpose of rule 42.3(c), a boat is ‘on a beat to windward’ provided that, in the absence of all other boats, the course she would sail to sail the course and finish as soon as possible is close-hauled or above.