What do the I, Z, U and black flags mean at a start?
I · Intermediate · The start and running a race · 4 of 11These flags replace the plain P flag at four minutes and punish boats that are over the line in the last minute. Flag I makes a boat return round an end of the line. Flag Z costs 20%. Flag U and the black flag disqualify. The glossary lists them as starting penalty flags.
How it works
| Flag | Offence in the last minute before the start | Penalty | If the race is restarted |
|---|---|---|---|
| I | Any part of the hull on the course side of the line or its extensions | The boat must sail across an extension so that its hull is completely on the pre-start side before it starts | No carry-over |
| Z | Any part of the hull in the triangle formed by the ends of the line and the first mark | 20% Scoring Penalty, without a hearing | The penalty stays. A second offence in a later attempt adds another 20% |
| U | The same triangle | Disqualified without a hearing | The penalty is dropped |
| Black | The same triangle | Disqualified without a hearing | The penalty stays, and the boat may not sail in the restarted race |
- The 20%: worked out from the score for Did Not Finish, as for any scoring penalty.
- Postponed or abandoned before the start: Z and black flag penalties do not apply.
- Black flag and a recall: the race committee displays the sail numbers of the boats caught before the next warning signal. A boat that sails in the restart anyway gets a disqualification that cannot be dropped from its series score.
- In the results: ZFP, UFD and BFD.
Tricky cases
Under the black flag, a boat was over with 40 seconds to go and the start was then recalled. Can it sail the restart?
No. Its disqualification stands even though the race is restarted, and it shall not sail in the restarted race.
Under flag U, the same thing happens. Can it sail the restart?
Yes. A U flag disqualification does not apply if the race is restarted or resailed.
Under flag I, can a boat dip straight back across the line?
No. It must sail across an extension of the line, which means going round one of the ends.
Does a Z flag penalty stand if the boat got back and started properly?
Yes. The breach is being in the triangle during the last minute, whatever the boat does afterwards.
Why the rule exists
With many boats on a line, some push over early in the hope of a general recall, and start after start is wasted. Each flag raises the price a step, and race committees usually bring them out after a recall. That practice is common usage and not in the rules.
Where it differs
| Where | What changes | Source |
|---|---|---|
| Racing Rules of Sailing | As above | RRS 30.1 to 30.4 |
| Flags used together | Z may be displayed with I | RRS 26 |
From the rule book
World Sailing The Racing Rules of Sailing 2025-2028, rules 26, 30, 36, 44.3 (c) and A10 and Race Signals. In force from 1 January 2025. Checked 14 October 2026. Official document: The Racing Rules of Sailing 2025-2028 (PDF).