Sidelight: Nav Lights Trainer

Practice the lights, shapes and sound signals of the U.S. Inland Navigation Rules before your next lesson or trip. Start with Night Watch: identify a vessel from eight viewpoints and check the rule behind every answer.

START WITH THE FREE CONTENT
The full lights and shapes reference, the arc explorer and all sound signals are free, along with a Night Watch drill on 8 core configurations. No account is needed.

Sidelight Pro is an optional one-time purchase that unlocks Night Watch on all 30 lit configurations, the Day Shapes and Fog Signals drills, and future content updates. No subscription.

NIGHT WATCH
A vessel's lights change as you move around her. Sidelight draws each configuration from eight viewpoints — head-on, on the bow, abeam, on the quarter and astern — and asks what you are looking at. Every answer shows the rule it comes from. After each answer Sidelight names the lights showing from your position, tells you what your choice would have shown instead, and quotes the rule text.

LIGHT ARCS
Walk around a vessel on a plan view and watch the masthead light, sidelights and sternlight hand over at 22.5° abaft the beam. The geometry is computed from Rule 21, not hand-drawn.

LIGHTS & SHAPES REFERENCE
31 configurations under Rules 23 to 30: power-driven vessels, sail and oars, towing and pushing (including the Western Rivers), trawling and fishing, not under command, restricted in ability to maneuver, dredging, diving, mine clearance, pilot vessels, anchored and aground. Each one includes the lights with their arcs, the day shapes, the fog signal where one applies and a short excerpt of the rule text.

SOUND SIGNALS
Hear maneuvering, warning and restricted-visibility signals, generated to the timings in Rule 32: a short blast of about one second, a prolonged blast of four to six seconds. Includes the bell and aground signals, plus a list of the Annex IV distress signals.

DRILLS THAT ADAPT
Spaced review brings back what you miss and spaces out what you know. Answer choices are checked so two configurations that look identical from your viewpoint are never offered against each other.

BUILT FOR STUDY
• Lights, day shapes and sound signals in one app
• Scenes drawn in code from eight viewpoints, sized for phones and tablets
• Works fully offline
• No account, no ads, no tracking
• Light and dark mode, large text and screen-reader descriptions of every scene

ABOUT THE CONTENT
Rule text is quoted from 33 CFR Part 83 as published on the Electronic Code of Federal Regulations (eCFR). Sidelight covers the U.S. Inland Rules; the International Regulations (COLREGS) differ in places and are not covered in this version.

If you think an answer is wrong, tap "Think this answer is wrong?" under the question or email support@tyasi.io with the rule number. Confirmed errors are corrected in an update.

Sidelight is a study aid from Tyasi LLC. It is not an official U.S. Coast Guard publication and is not endorsed by the Coast Guard. Always follow the current official Navigation Rules and good seamanship.

Recent changes:
First release of Sidelight: learn U.S. Inland Rules navigation lights, day shapes and sound signals, with every answer citing its rule.