Each penalty applies in the last minute before your starting signal. Three of them use the triangle formed by the two ends of the line and the first mark; the I flag uses the line and its extensions.
30.1 I Flag Rule
If any part of your hull is on the course side of the line or its extensions in the last minute, you must sail around an end (cross an extension back to the pre-start side) before starting. Diving back through the line does not count.
30.2 Z Flag Rule
Be in the triangle in the last minute and you get a 20% scoring penalty (ZFP) without a hearing, calculated as in rule 44.3(c). It stays even if the race is restarted or resailed, but not if the race is postponed or abandoned before the start. Do it again in a later attempt at the same race and you get another 20%.
30.3 U Flag Rule
Be in the triangle in the last minute and you are disqualified without a hearing (UFD). If there is a general recall, or the race is restarted or resailed, the penalty falls away and you can sail the new start.
30.4 Black Flag Rule
Be in the triangle in the last minute and you are disqualified without a hearing (BFD), and that stands even after a general recall or restart (but not a postponement or abandonment before the start). After a general recall your sail number is displayed, and you may not sail the restart. If you do, your disqualification becomes non-excludable.
Common situations
Black flag and general recall
Check the board before the next warning. If your number is on it you are out of that race even if you think you were behind the line. If you disagree, request redress; do not sail the restart.
Changed in 2025
The 20% in the Z flag rule now uses the 2025 scoring-penalty rounding: nearest tenth of a point, with 0.05 rounded up.