01 / Why it mattersWhy nav lights aren't optional

Navigation lights are one of those things every boater knows about and almost no boater fully understands. The rules are written in nautical miles and arc degrees, scattered across two overlapping rule sets (International COLREGs and U.S. Inland Rules), and the boat dealer who sold you the boat may or may not have installed lights that actually meet the spec stamped on the label.

Here is what's true: between sunset and sunrise — and during reduced visibility — the U.S. Coast Guard requires every recreational vessel to display the correct configuration of lights for its length and propulsion type. Failing to comply isn't a small thing. If you're involved in a collision and your lights aren't compliant, you can be found at fault regardless of who hit whom. Insurance carriers know this, and so do maritime attorneys.

The good news: for most boats, the rules are simpler than they look. By the end of this guide you'll know exactly what your boat needs, what to look for on the box, and how to avoid the three or four mistakes that catch most owners.

02 / AnatomyThe four lights every boat needs to understand

Whatever the size of your boat, the rules are built from a vocabulary of four lights. Memorize the arcs and you've memorized 80% of the regulations.

Sidelights — port (red) and starboard (green)

Each sidelight covers a 112.5° arc, beginning at dead-ahead and sweeping outward to 22.5° abaft the beam on its respective side. Red is always port (left), green is always starboard (right). The mnemonic that's stuck in every sailor's head: "Red right returning" — but for nav lights, the simpler version is "port wine is red."

Stern light (white)

Mounted aft, the stern light covers the 135° behind the boat — picking up exactly where the two sidelights leave off. Add the three arcs together and you get 360° of horizon, with no overlap and no gaps.

Masthead light (white, forward)

Despite the name, this one isn't necessarily at the top of the mast. It's a forward-facing white light covering the same 225° arc as the two sidelights combined, and on a power-driven vessel it must sit above the sidelights. On boats under 39.4 feet, you're allowed to combine the masthead light and stern light into a single 360° "all-round white" light — which is what most outboard-powered runabouts have.

All-round white light

A 360° white light, used either as a combined masthead-and-stern on small powerboats (mounted above the sidelights), or as an anchor light when you're not underway. These two roles are completely different, and confusing them is one of the most common mistakes — more on that in section 06.

03 / VisibilityHow far each light has to be seen

This is where most owners get tripped up. The arc is one part of the rule. The other is the minimum visibility distance, measured in nautical miles, and it scales with boat length. The numbers below come from USCG Navigation Rules, Rule 22.

The light's box or label will state the rated range — typically "USCG 1NM" or "USCG 2NM." Buy lights rated at or above the requirement for your boat's length. A 1NM-rated bow light on a 42-foot vessel is non-compliant even if it's the right shape.

04 / PowerboatsPowerboat configurations

Under 39.4 ft (12 m) — the most common case

You have two compliant options:

1. Combination bow light + all-round white pole light. A bi-color (red/green) light at the bow, plus a single 360° white light on a fixed or telescoping stern pole, mounted at least 1 m (3.3 ft) above the sidelights. This is what 90% of bass boats, runabouts, center consoles, and small cruisers use.
2. Separate masthead + sidelights + stern light. More common on cabin cruisers where a forward-facing 225° light can be mounted on the cabin top and a 135° stern light goes on the transom.

39.4 to 65.6 ft (12–20 m)

The all-round shortcut goes away. You must have a separate forward 225° masthead light, separate sidelights, and a separate 135° stern light. Visibility requirements increase: sidelights must be visible at 2 NM and the masthead at 3 NM.

Boats under 23 ft (7 m) and slower than 7 knots

An exception worth knowing: vessels under 7 m that won't exceed 7 knots may display a single all-round white light only. Sidelights are recommended but not required. This covers a lot of small jon boats, dinghies, and tenders — though sidelights are cheap insurance.

05 / SailboatsSailboat configurations

Sailboats are where most of the confusion lives, because the lights you display change depending on whether you're under sail, under power, or motor-sailing.

Under sail only

Sailboats under 20 m (65.6 ft) have three legal options:

• Deck-level lights. Sidelights (or a bi-color bow light) plus a stern light, same as a powerboat — minus the masthead light.
• Masthead tri-color. A single fixture at the top of the mast that combines red (port sector), green (starboard sector), and white (stern sector) into one 360° light. This is the offshore favorite because it draws less power, sits high enough to be seen above wave tops, and won't be blocked by an eased headsail.
• The classic option. Standard deck-level lights plus optional all-round red over green at the masthead. Rare today, but still legal.

Under power (or motor-sailing)

The moment you fire up the engine and put it in gear, your sailboat is treated as a powerboat — which means you must add a steaming light (a forward-facing 225° white light, mounted partway up the mast) and switch from the tri-color to your deck-level sidelights and stern light. During the day, motor-sailing also requires a black "steaming cone" with apex pointed down, hoisted where it can be seen.

At anchor

An all-round white anchor light, at the masthead or wherever it's most visible. This is not the same as a stern light or a tri-color. See section 06.

06 / Anchor lightsAnchor lights — a separate animal

Three lights at the masthead are commonly confused: the masthead (steaming) light, the tri-color, and the anchor light. They are not the same.

• The steaming/masthead light is white, faces forward 225°, and is used only when under power.
• The tri-color is a single fixture combining 360° of red, green, and white sectors — used only when under sail alone.
• The anchor light is a 360° all-round white light — used only when at anchor, never when underway.

Many modern combination fixtures roll the tri-color and anchor functions into a single mast-top unit with an internal switch — that's fine. The rule is that only the correct light for your current state may be illuminated. Lit anchor light while underway = ambiguous to other vessels = potentially at-fault in a collision.

07 / CertificationSpotting a USCG-certified light

The Coast Guard has issued formal warnings about uncertified imports — typically inexpensive fixtures sold online that don't meet the chromaticity (color), luminous intensity, or cut-off angle requirements. Use one of these and you're not legal even if the light looks correct.

Look for the following on the packaging or the fixture itself:

• A clear marking such as "USCG 2NM" (or 1NM, 3NM as appropriate)
• Compliance with 33 CFR 183 (the certification regulation)
• Compliance with ABYC A-16 (electric navigation lights standard) — common on quality fixtures
• A reputable manufacturer: Attwood, Perko, Hella Marine, Lopolight, Aqua Signal, Innovative Lighting

If a $14 nav light on a marketplace listing makes no claim to certification, assume it isn't.

08 / Decision guideThe 60-second decision guide

If you read nothing else, read this:

This guide is a starting point — for the full rule text, the USCG Navigation Rules are freely available online and required onboard for vessels 12 m (39.4 ft) and over.