Module 16 - Pilotage
Other Marks
What you will learn
Distinguish isolated danger, safe water, special and emergency-wreck marks, then connect each limited message to the correct cautious action.
These families can look superficially similar while conveying different information: danger at the mark, navigable water around it, a chart-defined feature, or a newly reported danger.
An isolated danger mark is black with one or more broad red horizontal bands, carries two black spheres when practicable and shows white Fl(2) if lit. It is on or near a danger with navigable water around it, but IALA explicitly requires the chart and publications to establish the danger's extent and safe passing distance.
A safe water mark has red-and-white vertical stripes, may carry one red sphere and uses a white isophase, occulting, one long flash every 10 seconds or Morse A rhythm. It may mark a fairway, mid-channel, landfall, channel entrance or useful bridge passage. 'Navigable water around' is not a guarantee of uniform depth or absence of traffic.
A special mark is yellow, may carry a yellow X and uses a yellow rhythm that does not conflict with the reserved white-light families; the chart or local notice gives its purpose. An emergency wreck marking buoy instead has blue-and-yellow vertical stripes, a yellow upright cross when fitted and an alternating blue/yellow light to warn of a new danger.
Two spheres and two white flashes reinforce the danger-at-the-mark message.
| Mark | Day cue | Light if fitted | Operational message |
|---|---|---|---|
| Isolated danger | Black/red bands; two black spheres | White Fl(2) | Danger at or near the mark |
| Safe water | Red/white vertical stripes; one sphere | White Iso, Oc, LFl.10s or Mo(A) | Navigable water around the mark |
| Special | Yellow; yellow X if fitted | Yellow, non-conflicting rhythm | Chart-defined area or feature |
| Emergency wreck | Blue/yellow vertical stripes; upright cross | Alternating blue/yellow | New danger requiring updates and avoidance |
Do not turn a safe-water cue into a guarantee
After a night landfall the crew identifies a white Morse A light at the charted fairway position and proposes steering directly beside it at full speed.
1. Confirm the family
Morse A is one permitted safe-water rhythm; compare its position and any visible red-and-white body.
2. Read the limited message
Navigable water exists around the mark, but the mark does not promise uniform depth or clear traffic.
3. Use the plan
Take the charted fairway track with planned speed, depth checks, lookout and buoy clearance.
Sense check: A safe-water mark supports a route; it does not cancel the chart, sounder, traffic picture or uncertainty in a floating mark's position.
Common mistake or limitation
- Isolated danger and safe water both mention navigable water around a mark, but one warns of a hazard at the mark and the other identifies useful water.
- A yellow special mark has no universal pass side; its local meaning must be read from the chart or notice.
Recap
- Use stripe direction, topmark and rhythm to separate these families.
- Translate each name into its limited message before choosing a route.
- Check current publications, depth and traffic after correct recognition.
Optional quick check
Section 8 of 12
What is the essential difference between isolated danger and safe water marks?
Sources and factual review
Reviewed 2 September 2026 - Compass Revision editorial review.
Continue studying Pilotage
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