Lesson previewFour Other-Mark Families, Four Different Messages1 section shown
Preview lesson
Four Other-Mark Families, Four Different Messages
What you will learn
Distinguish isolated-danger, safe-water, special and emergency-wreck marks by the navigation question each family answers before using colour, topmark or light detail.
These four IALA families can sit in the same pilotage area but communicate different relationships: local danger, navigable water, a charted special purpose or a newly marked wreck.
Begin with family rather than a memorised side to pass. An isolated-danger mark is placed on, moored on or above a local danger with navigable water around it. A safe-water mark states that navigable water exists all around and may be used for a fairway, centre line, mid-channel position, approach or landfall.
A special mark indicates a special area or feature whose nature is found in the chart or another nautical publication. It is not normally used for a channel or obstruction when another IALA family is more suitable. An emergency-wreck buoy instead gives conspicuous temporary warning of a newly marked wreck or danger while information and permanent marking develop.
The family changes the next question. Isolated danger requires the danger's extent and a safe passing distance. Safe water requires confirmation that the charted route, depth and traffic suit this vessel. Special requires the local purpose, boundary or restriction. Emergency wreck requires current warnings, the marked pattern and a conservative route clear of an incompletely surveyed hazard.
Colour alone is insufficient. Black can combine with red or yellow, yellow can mean special, cardinal or part of an emergency-wreck pattern, and white lights serve several families. Combine body pattern, permitted shape, topmark, complete light, charted position and current information before acting.
Family first
Similar-looking aids answer four different navigation questions
Isolated danger
Danger at or near the mark
White group Fl(2)
Safe water
Navigable water all around
White Iso, Oc, LFl 10s or Mo(A)
Special
Charted special area or feature
Yellow, non-reserved rhythm
Emergency wreck
Newly marked wreck or danger
Blue 1s · dark 0.5s · yellow 1s · dark 0.5s
Family identity changes the decision: avoid a local danger, interpret navigable water, investigate a special purpose or protect the vessel from a newly marked wreck.
| Family | Question it answers | Immediate follow-up |
|---|---|---|
| Isolated danger | Where is a small local danger with navigable water around it? | Find its extent and a safe passing distance from current information |
| Safe water | Where is navigable water all around this aid? | Confirm the route, depth, traffic and vessel margin |
| Special | What special area or feature is charted here? | Read the symbol, notes, notice, lettering or authorised pictogram |
| Emergency wreck | Where is a newly marked wreck or danger? | Use current warnings and keep a conservative distance from the marked pattern |
Sort four reports before changing course
During an unfamiliar approach, the crew reports a black-and-red buoy, a red-and-white buoy, a yellow buoy and a blue-and-yellow buoy. None has yet been related to the chart.
1. Name each candidate family
Use pattern, shape or topmark and any complete light character rather than assigning a route from colour alone.
2. State its question
Say local danger, navigable water, charted special purpose or new wreck before discussing a manoeuvre.
3. Locate the charted feature
Match position, symbol, notes, surrounding aids, depth and current warnings to the candidate family.
4. Choose a vessel-specific response
Control speed and sea room, then plan a track using actual depth, traffic, restrictions and margin.
Sense check: If the plan still says only 'yellow buoy' or 'water all around', it has not identified the purpose or proved a suitable route for this vessel.
Common mistake or limitation
- Treating every non-lateral mark as an instruction to pass on one fixed side.
- Using one colour without corroborating body pattern, topmark, light and charted position.
- Assuming correct family recognition supplies depth, clearance, restriction or safe passing distance.
Recap
- Isolated danger, safe water, special and emergency wreck answer four different questions.
- Identify the family from several coherent cues before deciding what it means.
- The chart, current information and vessel constraints turn recognition into a route.
Optional quick check
Section 1 of 1