2.3 Non-Lateral Aids: Safe-Water, Isolated-Danger, Special & Information Marks
Key Takeaways
- A safe-water mark has red and white vertical stripes, a white Morse 'A' light, and indicates navigable water all around — often a mid-channel or landfall buoy.
- An isolated-danger mark is black with red horizontal bands, carries two black spheres as a topmark, and shows a white group-flashing (2) light.
- Yellow marks are special marks (anchorages, dredging, fishnet, spoil areas) and are not primarily for navigation.
- White-and-orange marks are regulatory or informational: a circle means a controlled area, a diamond means danger, a diamond with a cross means keep out.
- A range is two marks at different heights that you align vertically to stay on a channel centerline.
Non-Lateral Aids: Safe-Water, Isolated-Danger, Special & Information Marks
Quick Answer: Not every aid marks the edge of a channel. Safe-water marks (red-and-white vertical stripes) mean navigable water all around; isolated-danger marks (black with red bands and two black balls on top) mark a small hazard you can pass on any side; yellow marks are special-purpose; and white-and-orange marks give regulatory information.
Beyond the red-and-green lateral system, the aids in this section either mark open water, warn of a specific danger, or convey rules and information. Learn each one's color scheme, topmark, and light.
Safe-Water Marks
A safe-water mark indicates navigable water all around the aid. You will find them at the seaward end of a channel (a landfall or "sea buoy"), at a mid-channel, or marking a fairway. Their appearance is distinctive:
- Red and white vertical stripes (never horizontal).
- Buoy is spherical, or carries a red spherical topmark; beacon versions use an octagonal daymark.
- Light, if any, is a white Morse code "A" — one short flash followed by one long flash (dot-dash), repeated. A long-flashing white (LFl) is also used.
You may pass a safe-water mark on either side. A common use: you approach a coast and pick up the "RW" sea buoy that marks the entrance to a buoyed channel, then follow the lateral marks in.
Isolated-Danger Marks
An isolated-danger mark is placed on or near a small, isolated hazard (a rock, wreck, or shoal) that has navigable water all around it. Its features:
- Black body with one or more broad red horizontal bands.
- Topmark of two black spheres, one directly above the other — the clearest identifier.
- Light, if any, is a white group-flashing (2) — flashes come in groups of two.
Because there is safe water around it, you may pass on any side, but you keep well clear of the mark itself. The two-black-ball topmark is worth memorizing: "two balls, isolated danger."
Special Marks
Special marks are yellow. They do not mark the sides of a channel; instead they identify a special area or feature, such as an anchorage, a dredging or spoil area, a fishnet or aquaculture area, a traffic separation zone, or a military exercise area. If lighted, they show a yellow light, often a slow flash. Because they are informational, you generally do not navigate by them — you consult the chart to learn what the yellow mark signifies. A mooring buoy, a related non-lateral aid, is white with a blue horizontal band and is the only aid you may legally tie up to.
Information and Regulatory Marks
On many U.S. inland and state waters you will meet white marks with orange bands and symbols, part of the U.S. Aids to Navigation System's regulatory set. The orange symbol tells you the rule:
| Orange symbol | Meaning |
|---|---|
| Open circle | Controlled area (e.g., speed limit, no-wake) — the restriction is printed inside |
| Diamond | Danger (rock, dam, shoal, stump) |
| Diamond with a cross | Exclusion / keep-out area (swim area, dam face) |
| Rectangle (square) | Information (directions, distances, locations, marina) |
Ranges and Daybeacons
A range is a pair of fixed marks (beacons) placed on shore at different heights and distances apart. When the front (lower) mark and the rear (higher) mark appear aligned vertically, one above the other, you are on the range line — normally the centerline of a channel. Ranges give an extremely precise steering reference that needs no compass: if the top mark drifts to one side, the channel lies in that direction, so you steer toward the higher rear mark to get back on line. Range lights are often fixed, equal-interval, or slow-occulting and may only be visible within a narrow arc, so a range is used to hold a line, not to fix a wide-angle position.
Daybeacons are fixed, unlighted aids mounted on a single pile, carrying a dayboard: a green square (port-hand) or red triangle (starboard-hand) follows the same lateral logic, while regulatory dayboards use the white-and-orange shapes above.
A Word on Cardinal Marks
The IALA system also defines cardinal marks (North, East, South, West), colored black and yellow with double-cone topmarks, which show the direction of the safe (deepest) water relative to the danger. A North mark (black over yellow) means pass to the north of it; a South mark (yellow over black) means pass to the south; East and West marks work the same way for those quadrants. They are common overseas and are being introduced in limited U.S. locations, but the American system still relies mainly on the lateral system and the marks above. If you see a black-and-yellow buoy with two cones on top, it is a cardinal mark; consult the chart for the side to pass.
Putting the Non-Lateral Marks Together
A quick way to keep these straight for the exam: lateral marks (red/green) mark the sides of a channel and must be passed on a specific side; the non-lateral marks in this section mostly mark a point. Safe-water and isolated-danger marks may be passed on either side (approach a safe-water mark freely; keep clear of an isolated-danger mark but pass on any side). Special (yellow) and regulatory (white-and-orange) marks convey information or a rule rather than a channel side. When in doubt about any unfamiliar mark, its shape, color, topmark, and light together point you to Chart No. 1 and the chart's own notes.
You sight a buoy with red and white vertical stripes showing a white light that flashes short-long (Morse 'A'). What does it indicate?
A black buoy with broad red horizontal bands carries a topmark of two black spheres. This mark warns of what?
On a lake you see a white buoy with an orange diamond containing an orange cross. What does it mean?