Module 12 - Visual Aids to Navigation
Lighthouses and Other Structures
What you will learn
Distinguish fixed, floating and paired aids and use their charted structure and rhythm as corroborating identification evidence.
The physical structure helps identify an aid by day and sometimes by night, but its charted position, light character and surrounding marks remain essential. Fixed does not mean infallible, and floating does not mean positionally exact.
Lighthouses and major fixed lights may be identified by charted structure, daymark, light character and sometimes a fog signal. On paper charts a light flare indicates a lighted feature; use the applicable chart-symbol reference rather than treating one symbol description as universal across every product.
Beacons are fixed structures and may be lit or unlit. Light vessels and large light floats are floating aids at charted stations; mooring radius, weather or an off-station condition means they must not be treated like fixed survey points. Current charts and warnings remain authoritative.
Leading marks are a charted pair. When the front and rear marks are in line they provide one leading line or line of position along the intended alignment, not an exact fix by themselves. Lit buoys add the colour and rhythm prescribed for their mark type, while the buoy's shape, topmark and charted position complete the identification.
Choose the stronger identification
At dawn, a flashing white light and tower are visible, but the bearing disagrees with the expected lighthouse while a charted lit buoy lies close to that line of sight.
1. Compare structure
Use binoculars from a safe situation to distinguish the fixed tower from the floating mark.
2. Check the rhythm
Time the complete character and compare both candidates.
3. Retain position margins
Do not use either as a fixed point until bearing, character and surrounding evidence agree.
Sense check: A familiar-looking structure on the wrong bearing is a warning to reopen the identification, not adjust the chart mentally.
Common mistake or limitation
- Two aligned leading marks provide one line of position; a second independent line is needed for a fix.
- A lit buoy is not a fixed surveyed structure and may be displaced or off station.
Recap
- Separate fixed structures, floating aids and paired leading marks.
- Use structure and daymark together with charted light character.
- Keep floating-aid and single-line position limits explicit.
Optional quick check
Section 5 of 6
What position information do aligned leading marks provide?
Continue studying Visual Aids to Navigation
This public lesson is part of Revision Module 12. Full revision access adds the guided Learn, Practise and Test flow, flashcards and revision progress.