Restricted visibility—fog, mist, heavy rain, snow, and similar conditions—cuts how far you can see and can scramble which direction a sound came from. Discover Boating’s fog tips put the main danger plainly: reduced visibility, disorienting acoustics, and the risk of losing all sense of direction even with modern electronics. Inland Rule 3 defines restricted visibility as any condition in which visibility is restricted by fog, mist, falling snow, heavy rainstorms, sandstorms, or any other similar causes (33 CFR § 83.03(l)).
This page summarizes Discover Boating’s “10 Tips for Boating in Foggy Conditions” page; Inland Navigation Rules on restricted-visibility definitions, look-out, conduct in restricted visibility, and fog sound signals in 33 CFR §§ 83.03(l), 83.05, 83.19, and 83.35 (Cornell LII text); and the USCG Boaters Guide lookout / lights / sound-signal sections—only. Those sources do not publish brand radar settings, detection ranges, or invented COLREGS edge cases beyond the cited text—so we do not invent those here. Pair this guide with night navigation basics for recreational boaters, thunderstorms, lightning and severe weather for recreational boaters, navigation rules basics for recreational boaters, radar basics for recreational boaters, AIS basics for recreational boaters, navigation lights and day shapes, VHF marine radio basics, waypoint and route planning basics, the printable Launch Day checklist, and State Rules for state overlays.
When the Rules treat you as “not in sight”
- Inland Rule 3(k): vessels are in sight of one another only when one can be observed visually from the other (33 CFR § 83.03(k)).
- Inland Rule 19(a): Rule 19 applies to vessels not in sight of one another when navigating in or near an area of restricted visibility (33 CFR § 83.19(a)).
Meeting, crossing, and overtaking rules that assume vessels are in sight of one another (summarized in the navigation rules guide) do not replace Rule 19 when you cannot see each other. Read both.
Inland Rule 19 — safe speed, radar, and fog signals ahead
High-level summary of 33 CFR § 83.19 (Cornell LII)—not a substitute for the full Rule or a boating-safety course:
| Paragraph | What the cited text requires |
|---|---|
| (b) Safe speed | Every vessel shall proceed at a safe speed adapted to the prevailing circumstances and conditions of restricted visibility. A power-driven vessel shall have her engines ready for immediate maneuver. |
| (c) Due regard | Have due regard to restricted-visibility conditions when complying with Rules 4 through 10 (§§ 83.04–83.10). |
| (d) Radar alone | A vessel that detects by radar alone another vessel shall determine whether a close-quarters situation and/or risk of collision is developing and, if so, take avoiding action in ample time. When that action is a course change, so far as possible avoid (i) altering to port for a vessel forward of the beam other than one being overtaken, and (ii) altering toward a vessel abeam or abaft the beam. |
| (e) Fog signal / close-quarters ahead | Except where it has been determined that a risk of collision does not exist, every vessel that hears apparently forward of her beam the fog signal of another vessel, or that cannot avoid a close-quarters situation with another vessel forward of her beam, shall reduce her speed to the minimum at which she can be kept on course. She shall if necessary take all her way off and, in any event, navigate with extreme caution until danger of collision is over. |
Discover’s matching practical tip: any time visibility is reduced, slow down—you will not see markers, obstructions, or other boats until they are much closer, and a quieter powerboat is easier to listen from.
Lookout still comes first (Rule 5 + Discover crew tips)
- Inland Rule 5 (Look-out), 33 CFR § 83.05: Every vessel shall at all times maintain a proper look-out by sight and hearing as well as by all available means appropriate in the prevailing circumstances and conditions, so as to make a full appraisal of the situation and of the risk of collision.
- USCG Boaters Guide: Be sure to maintain a proper lookout; scan the water back and forth; stay alert—most accidents involve operator inattention.
- Discover fog: In thick fog, keep at least one pair of eyes—and more is better—looking around; assign crew to zones (fore, aft, port, starboard). Do not bury everyone’s attention in the helm screens.
Radar and AIS are “available means.” They do not turn Rule 5 off. Neither does following a waypoint / route on a chartplotter.
Sound signals in restricted visibility (Rule 35 + Discover tip 4)
The Boaters Guide states recreational vessels are required to use sound signals during periods of reduced visibility and while at anchor. Inland Rule 35 (33 CFR § 83.35) sets the sequences. High-level citations for typical recreational powerboats (read the full Rule for sail, fishing, tow, aground, and length carve-outs):
| Situation (cited Rule 35) | Signal (cited text only) |
|---|---|
| Power-driven making way through the water — § 83.35(a) | At intervals of not more than 2 minutes, one prolonged blast. |
| Power-driven underway but stopped and making no way — § 83.35(b) | At intervals of not more than 2 minutes, two prolonged blasts in succession (~2 seconds apart). |
| At anchor — § 83.35(g) | At intervals of not more than 1 minute, ring the bell rapidly for about 5 seconds (plus gong rules for ≥100 m). May in addition sound one short, one prolonged, and one short blast to warn of position. |
| Vessel <12 m — § 83.35(j) | Not obliged to give the above-mentioned signals, but if she does not, shall make some other efficient sound signal at intervals of not more than 2 minutes. |
| Vessel 12 m to <20 m at anchor — § 83.35(i) | Not obliged to give the bell signals in (g)/(h); if she does not, some other efficient sound signal ≤2 minutes. |
Discover tip 4 restates the recreational powerboat picture in plain language: underway = one prolonged blast about every two minutes; drifting = two blasts; at anchor = short + prolonged + short; ringing a bell about five seconds is also acceptable when you have one. Prefer the CFR wording above when the two summaries differ in detail, and do not invent sequences that neither source states.
Lights, electronics, and “being seen”
- Lights: Boaters Guide and navigation lights and day shapes—show navigation lights from sunset to sunrise and during restricted visibility (fog, rain, haze). Discover: turn running lights on whenever visibility is reduced (or the anchor light if at anchor)—not only after dark. Broader after-dark lookout / safe-speed habits: night navigation basics.
- GPS / chartplotter: Discover—helps you stay on course in fog but does not see through fog. Practice before you need it. Pair with waypoint and route planning.
- Radar: Discover—valuable if fog is likely on your waters; practice interpreting the screen in clear weather. Rule 19(d) governs radar-alone detection. Details and licensing high-level: radar basics. No brand Gain/STC/FTC settings or invented detection ranges here.
- AIS: Complements radar for equipped traffic / broadcasting your identity—see AIS basics. Neither replaces a lookout or VHF Channel 16 / DSC.
- Depth: Discover tip 8—watching the depth finder against the chart can help you stay out of busy shipping channels and warn of shoals when visual cues disappear.
Discover “stay put / wait it out” tips (high level)
From Discover’s fog page (practical tips alongside the Rules—not a rewrite of the CFR):
- Preparedness: If the forecast includes fog or fog already obscures the view at the dock, leave the lines tied until conditions improve.
- Anchor only when traffic is low: Stop and drop anchor if you cannot comfortably proceed and you are in a low-traffic area; fog often lifts later. In a busy channel or inlet, stopping is often the worst choice because other boats will come upon you. Even at anchor, make the appropriate sound signals.
- Focus and listen: Prefer the fog/water “horizon” as a focus rather than staring into blank fog; near land, listen for echoes of your sound signals.
What this page does not cover
- Brand radar install, antenna height, Gain/STC/FTC tuning, or invented detection ranges in nautical miles.
- Full International vs Inland fog-signal differences beyond what the Boaters Guide already notes for inland sound-signal intent vs international action (see also the navigation rules guide).
- Sail / fishing / not-under-command / restricted-in-ability-to-maneuver / tow / aground signal variants beyond the table rows we quoted from Rule 35—read § 83.35 in full.
- A substitute for a state-approved boating-safety course or for carrying a copy of the Rules when required (Boaters Guide: ≥39.4 ft / 12 m on U.S. inland waters).
Honest gaps
- No brand picks, price tables, or invented fog gadgets.
- We paraphrase only the cited Inland Rules and Discover / USCG pages—no invented edge cases.
- State overlays and local waterway rules: State Rules.
- Lights, radio, radar, AIS, and chart-checked routes remain separate duties even when you know Rule 19.
Book a free Vessel Safety Check with the Coast Guard Auxiliary. Put a quick confirm that everyone at the helm knows fog lookout, lights-on-in-reduced-visibility, and the basic Rule 35 powerboat signals on the same pre-departure pass as the printable Launch Day checklist. Budget situational-awareness gear alongside radio and distress beacons in the True Cost tool if you are still outfitting.
Sources
- Avoid launching into forecast/obscuring fog; slow down; anchor only in low traffic + sound signals; powerboat fog-signal tip (prolonged / two blasts / short-prolonged-short; optional bell ~5s); GPS does not see through fog; radar valuable if fog likely; practice electronics; crew lookout zones; lights on in reduced visibility; depth vs chart; focus at fog/water meet; listen for echoes: Discover Boating (NMMA), "10 Tips for Boating in Foggy Conditions" (updated Mar. 26, 2024). https://www.discoverboating.com/resources/boating-in-fog
- Restricted visibility defined (fog, mist, falling snow, heavy rainstorms, sandstorms, or similar); in sight = visually observed: 33 CFR § 83.03(l), (k) (Inland Rule 3). Cornell LII. https://www.law.cornell.edu/cfr/text/33/83.03
- Look-out by sight, hearing, and all available means: 33 CFR § 83.05 (Inland Rule 5). Cornell LII. https://www.law.cornell.edu/cfr/text/33/83.05
- Conduct in restricted visibility: safe speed; engines ready; radar-alone avoiding action with course-change caveats; hear fog signal / close-quarters forward of beam → reduce to minimum, take way off if needed, extreme caution: 33 CFR § 83.19 (Inland Rule 19). Cornell LII. https://www.law.cornell.edu/cfr/text/33/83.19
- Sound signals in restricted visibility (power-driven making way / stopped; at-anchor bell and optional short-prolonged-short; <12 m and 12–<20 m efficient-signal alternatives): 33 CFR § 83.35 (Inland Rule 35). Cornell LII. https://www.law.cornell.edu/cfr/text/33/83.35
- Proper lookout; lights sunset–sunrise and in restricted visibility (fog, rain, haze); sound signals in reduced visibility and at anchor; Navcen amalgamated Rules pointer: U.S. Coast Guard / USCG Boating, A Boater's Guide to the Federal Requirements for Recreational Boats (Nov. 8, 2023 PDF). https://www.uscgboating.org/assets/1/AssetManager/Boaters-Guide-to-Federal-Requirements-for-Receational-Boats-20231108.pdf
- Amalgamated Navigation Rules / handbook pointer (as cited in Boaters Guide): USCG Navigation Center. https://www.navcen.uscg.gov/
- Free Vessel Safety Check: U.S. Coast Guard Auxiliary. https://www.cgaux.org/vsc/