When at a boat’s starting signal any part of her hull, crew or equipment is on the course side of the starting line or she must comply with rule 30.1, the race committee shall promptly display flag X with one sound. The flag shall be displayed until all such boats are completely on the pre-start side of the starting line or one of its extensions and have complied with rule 30.1 if it applies, but no later than four minutes after the starting signal or one minute before any later starting signal, whichever is earlier. If rule 30.3 applies this rule does not.
Rule 29.1 illustrated
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This rule may appear at the start of a Match race. It is sufficient for the recalled boat to dip below the start line. It is not necessary to sail around one end of the start line.