An anchor light is an all-round white navigation light shown by a boat anchored at night, so other traffic can see its position across the full horizon.
It is not a courtesy lamp or a stern light pushed upward. It is legal navigation equipment defined by federal rule, and the wrong lamp in the wrong spot is a violation even if the boat looks bright from the dock. The rules come from the Inland and International Navigation Rules in 33 CFR Part 83, administered by the US Coast Guard, and hinge on one number: your vessel’s length.
When Does Rule 30 Require an Anchor Light?
A vessel at anchor must display the anchor light at night and in restricted visibility whenever Rule 30 applies, and “at anchor” is broader than many skippers assume. A boat made fast to a mooring buoy attached to the seabed counts as anchored for federal purposes and may be lighted accordingly.
Vessels 100 meters or longer must also use available working lights or equivalent deck illumination; other anchored vessels may do the same. Pilot vessels on active duty show their special pilot lights and add Rule 30 lighting while anchored.
In daylight, the anchor shape takes over — one black ball in the forepart of the vessel where Rule 30 requires the shape.
How Many Lights Do You Need for Your Boat’s Length?
Boats under 50 meters may show a single all-round white light where it can best be seen; vessels 50 meters or longer must carry two, with the forward light higher than the after light.
| Vessel Length | Lighting Required | Notable Exception |
|---|---|---|
| Under 7 meters | Single all-round white light where best seen | Light and shape not required outside channels, fairways, anchorages, or normal traffic areas |
| Under 20 meters | Single all-round white light where best seen | Exempt in Coast Guard-designated special anchorage areas |
| 20 to under 50 meters | Single all-round white light where best seen | None |
| 50 meters or longer | Two all-round white lights; forward higher than after | Forward light at least 6 meters above hull; 4.5-meter separation |
| 100 meters or longer | Two lights plus available deck illumination | None |
| Moored barges | Corner lighting allowed under 33 CFR 83.30(h)–(l) | Standard anchor arrangement not mandatory |
| Pilot vessel on duty | Special pilot lights plus Rule 30 anchor lighting | None |
Where to Mount It So the Light Actually Counts
The light must be visible around the full horizon with no mast, rigging, or structure cutting into the 360-degree display, so height matters less than a clean line of sight. Annex I restricts obstruction of all-round lights for exactly this reason. After sunset, inspect the lamp from every angle; a spar blocking it from one direction is a defect, not a detail.
Equipment choice is not specified in the regulations — no model, wattage, or battery type is named. Pick a marine-rated lamp bright through 360 degrees, suited to your electrical system, and meeting applicable Coast Guard approval or certification requirements. For tested options by size and mounting style, see this roundup of the best anchor light for a boat. Full text of Rule 30 is at 33 CFR 83.30.
Common Mistakes That Break the Rule
The most frequent error is substituting a stern light or deck floodlight — neither is an all-round white light and neither satisfies Rule 30. A cockpit lamp or flickering decorative string has the same problem.
Two more traps:
- The “under 50 meters” single-light rule applies only to vessels shorter than 50 meters; a boat at exactly 50 meters follows the two-light arrangement.
- The small-boat exemptions are location-based — the under-7-meter and under-20-meter carve-outs depend on where the boat is, and state rules or marina policies can add obligations the federal rule does not.
Treat any exemption as a legal carve-out, not a judgment that no light is needed for safe navigation. In a busy harbor at night, being seen is the point.
FAQs
Can I use a flashlight as a temporary anchor light?
No. A handheld flashlight does not produce a continuous, unobstructed 360-degree all-round white display and is not a compliant navigation light. Federal rules require a mounted light visible around the full horizon.
Does the anchor shape apply at night?
No. The black ball is a daylight signal. At night the anchor light takes over as the vessel’s anchor signal, and Rule 30 ties each to its own conditions.
Is a boat on a mooring buoy considered anchored?
For federal purposes, yes. A vessel made fast to one or more mooring buoys or similar devices attached to the seabed falls within the definition of at anchor and may be lighted under Rule 30. Local harbor rules can be stricter, so confirm with the marina before leaving the light off.
References & Sources
- US eCFR. “33 CFR § 83.30 — Vessels anchored, aground and moored barges (Rule 30)” Primary text for anchor light and shape requirements.
- US Coast Guard. “Federal Navigation Regulations” Official navigation rules resource and compliance guidance.
- US eCFR. “33 CFR § 83.29 — Pilot vessels (Rule 29)” Covers pilot vessel lighting that combines with anchor lights.