Inland Navigation Rules
Everything you need to know about Inland COLREGS for the USCG captain's license exam — whistle signals, Western Rivers right-of-way, bridge-to-bridge VHF, and the key differences from International Rules that show up repeatedly on the exam.
Exam Threshold — Rules of the Road
Rules of the Road (which includes Inland Rules questions) requires a 90% passing score on the USCG OUPV exam. You can miss only 5 of 50 questions. Inland vs. International differences are among the most heavily tested topics. Know every difference in this guide cold.
The Inland Navigation Rules Act of 1980
What the Act Did
Before 1980, inland waterway navigation in the United States was governed by a patchwork of three separate rule sets: the old Inland Rules (for harbors and rivers), the Western Rivers Rules (for the Mississippi system and its tributaries), and the Great Lakes Rules. Each had its own numbering, logic, and signal conventions — a recipe for confusion for mariners who operated across multiple waterway systems.
The Inland Navigation Rules Act of 1980 (Public Law 96-591, codified at 33 U.S.C. 2001-2073) unified all three sets into a single Inland Rule set that mirrors the structure and numbering of the 1972 International COLREGS. It took effect on December 24, 1981. The unification made the Inland Rules far easier to study alongside International Rules — the rule numbers align, the structure aligns, but specific provisions in certain rules differ.
Where Inland Rules Apply
Inland Rules apply in U.S. inland waters — generally the waters inside the COLREGS Demarcation Lines established by 33 CFR Part 80. These lines roughly follow the mouths of harbors, bays, and rivers. Seaward of the demarcation lines, International COLREGS apply. Shoreward of the lines, Inland Rules apply.
Key Waters Governed by Inland Rules
- U.S. harbors and ports (inside demarcation lines)
- Bays, sounds, and inland lakes
- The Mississippi River system (Western Rivers)
- The Intracoastal Waterway (ICW)
- The Great Lakes and their connecting waters
- All rivers, canals, and other inland waters of the U.S.
Codification and Authority
The Inland Rules are published in 33 U.S.C. Chapter 34 (Sections 2001-2073). Supplemental regulations — including bridge-to-bridge radio requirements and demarcation lines — appear in Title 33 of the Code of Federal Regulations (33 CFR). The USCG enforces these rules and publishes the official text in Navigation Rules: International-Inland (COMDTINST M16672.2D), the blue book mariners carry aboard.
Whistle Signals Under Inland Rules
The Proposal-and-Agreement System
This is the single most important conceptual difference between Inland and International whistle signals. Under Inland Rules, a whistle signal is a PROPOSAL — it states what the signaling vessel INTENDS to do, and it requires agreement from the other vessel before the maneuver is executed. Under International Rules, a whistle signal is INFORMATIONAL — it states what the vessel IS DOING and requires no reply.
If the other vessel agrees with the Inland proposal, it replies with the same signal. If it disagrees or is uncertain, it sounds the danger signal (five or more short blasts). No maneuver should be made until agreement is established. This proposal-and-agreement mechanism is what the exam calls the "whistle signal exchange" and it applies to meeting, crossing, and overtaking situations where vessels are in sight of each other.
The Four Core Inland Signals
"I intend to leave you on my PORT side." The other vessel is to your starboard — you propose to pass each other with both boats moving starboard of the channel centerline. Reply: same signal (1 blast agreement).
"I intend to leave you on my STARBOARD side." An unusual arrangement — typically only when waterway geometry or traffic requires it. Reply: same signal (2 blast agreement).
"My engines are going astern." Same meaning under both Inland and International Rules. This is NOT a proposal signal — it is informational in both rule sets.
Doubt, disagreement, or uncertainty about a proposed maneuver. Either vessel may sound this when in doubt. All maneuvering should stop until the situation is resolved. Same under International Rules.
The Bend Signal
Inland Rule 34(e) (mirroring International Rule 34(e)) requires that a vessel nearing a bend or obstruction in a channel where another vessel may be hidden from view must sound one prolonged blast. Any approaching vessel around the bend must respond with a prolonged blast of its own. This is the bend signal — distinct from the meeting/passing signals — and it applies in both rule sets.
Bend Signal: 1 Prolonged Blast
- Sound when approaching a bend where visibility is obscured
- Reply vessel responds with 1 prolonged blast
- Both vessels then proceed with caution
- Applies under both Inland and International Rules
- Not a passing proposal — it is a warning/announcement signal
Overtaking Signals Under Inland Rules
Under Inland Rules, an overtaking vessel proposes its passing side using the standard 1-blast (pass to overtaken vessel's port) or 2-blast (pass to overtaken vessel's starboard) signal. The overtaken vessel agrees with the same signal or sounds the danger signal. This is different from International Rules, where the overtaking signal in a narrow channel is 2 prolonged + 1 short (intend to overtake on your starboard) or 2 prolonged + 2 short (intend to overtake on your port).
Inland vs. International Comparison Tables
The exam consistently tests your ability to distinguish Inland from International Rules. These tables are your fast-reference for the differences that appear on the USCG exam most often.
Sound Signal Comparison
| Signal | Inland Meaning | International Meaning |
|---|---|---|
| 1 short blast | I intend to leave you on my port side (proposal — requires agreement) | I am altering my course to starboard (information only) |
| 2 short blasts | I intend to leave you on my starboard side (proposal — requires agreement) | I am altering my course to port (information only) |
| 3 short blasts | I am operating astern propulsion | I am operating astern propulsion |
| 5 or more short blasts | Danger signal — doubt or disagreement with proposed passing arrangement | Danger/doubt signal — no specific passing context |
| Bend signal (1 long blast) | Required when approaching a bend or obstruction where another vessel may be hidden | Required same — Rule 34(e) |
| Passing agreement | Required — other vessel must reply with same signal to confirm | Not applicable — signals are informational, no reply required |
General Rules Comparison
| Topic | Inland Rules | International Rules |
|---|---|---|
| Whistle signal system | Proposal-and-agreement (signals are intentions requiring acceptance) | Informational (signals state what the vessel is doing) |
| Special flashing light | Yes — yellow, 50-70 flashes/min, for certain towing configurations | Does not exist |
| Western Rivers right-of-way | Downbound vessel has ROW; proposes passing side | No Western Rivers provision |
| Bridge-to-bridge VHF | 33 CFR 26 requires VHF Channel 13 in most U.S. waters | No equivalent federal mandate at rule level |
| Overtaking signal | 1 or 2 blasts as proposal; other vessel agrees or signals danger | 2 prolonged + 1 short (starboard) or 2 prolonged + 2 short (port) in narrow channels |
| Traffic separation schemes | Applicable in certain inland areas designated by USCG | Governed by COLREGS Rule 10 for TSS on high seas |
| Demarcation lines | Applies inside COLREGS Demarcation Lines (33 CFR Part 80) | Applies seaward of Demarcation Lines |
| Enacting authority | Inland Navigation Rules Act of 1980 (33 U.S.C. 2001-2073) | 1972 Convention on the International Regulations for Preventing Collisions at Sea |
Western Rivers Right-of-Way
What Are the Western Rivers?
The Western Rivers are defined in Inland Rule 3 as the Mississippi River, its tributaries, South Pass, Southwest Pass, Tennessee-Tombigbee Waterway, Tombigbee River, Warrior River, Alabama River, Coosa River, Mobile River above the Cochrane Bridge, Flint River, Chattahoochee River, and the Apalachicola River above its junction with the Chipola River. This is not just the Mississippi — it is a defined statutory list.
The Downbound Rule
Downbound Vessel Has Right of Way
On the Western Rivers, a vessel proceeding downriver (with the current) has the right of way over a vessel proceeding upriver (against the current). The downbound vessel proposes the side on which to pass by sounding the appropriate whistle signal. The upbound vessel must acknowledge and maneuver to accommodate the downbound vessel's chosen passing side.
The rationale for this rule is practical: a vessel going with the current is harder to control — it has less steerage response relative to the water bottom, longer stopping distance, and is more subject to current forces. Giving right of way to the downbound vessel acknowledges this physical reality.
Western Rivers Passing Procedure
- Downbound vessel initiates contact and proposes passing side (1 blast = pass port side; 2 blasts = pass starboard side)
- Upbound vessel responds with same signal to agree, or sounds 5+ blasts to disagree
- Both vessels execute the agreed-upon passing maneuver
- If the upbound vessel disagrees, the downbound vessel may propose the other side or stop
- The upbound vessel has no right to override the downbound vessel's proposal without the danger signal
Exam Tip — Western Rivers vs. Narrow Channel
Exam questions often mix up Narrow Channel rules (Inland Rule 9, where both vessels alter starboard in a head-on) with Western Rivers rules (where downbound has ROW). If the question specifies a river in the Western Rivers list — especially the Mississippi — think Western Rivers ROW first. If it just says "narrow channel" without specifying a Western Rivers waterway, apply Rule 9 (starboard-side passing).
Bridge-to-Bridge VHF Communications (33 CFR 26)
The Bridge-to-Bridge Radiotelephone Act
The Bridge-to-Bridge Radiotelephone Act (33 U.S.C. 1201-1208) and its implementing regulations (33 CFR Part 26) require certain vessels to carry and use VHF radiotelephone equipment for navigational safety communications. This is separate from the Inland Navigation Rules themselves but closely related — VHF bridge-to-bridge radio is the modern complement to whistle signals for vessel-to-vessel coordination in confined waters.
Who Must Comply
Vessels Required to Carry Bridge-to-Bridge VHF (33 CFR 26)
- Power-driven vessels of 26 feet or more in length while navigating
- Every vessel of 100 gross tons or more carrying one or more passengers for hire
- Every towing vessel of 26 feet or more in length while navigating
- Every dredge and floating plant while in or near a channel or fairway
VHF Channel 13 — The Bridge-to-Bridge Channel
Channel 13 (156.65 MHz) — Bridge-to-Bridge Navigation
VHF Channel 13 is the primary channel for vessel-to-vessel navigational safety communications in U.S. inland waters. Vessels covered by 33 CFR 26 must monitor Channel 13 and use it for all bridge-to-bridge communications — meeting arrangements, passing intentions, and vessel identification. One watt is the maximum transmit power for Channel 13 (to minimize range and prevent interference across wide areas).
VHF Channel 16 (156.8 MHz) remains the international distress, urgency, and safety calling channel — every vessel with a VHF radio must monitor Channel 16. But Channel 16 is not the bridge-to-bridge navigation channel for inland waters (except on the Great Lakes, where Channel 16 is used for bridge-to-bridge in some contexts).
VHF vs. Whistle Signals
VHF radio does not replace whistle signals under the Inland Rules — it supplements them. When vessels agree via VHF to a passing arrangement, they may still be required to exchange whistle signals to confirm the arrangement visually/acoustically when in sight of each other. However, 33 CFR 26 does establish that a VHF arrangement that includes all the required elements (vessel identification, position, proposed passing side) satisfies the intent of the bridge-to-bridge communication requirement.
Exam Focus — 33 CFR 26 Key Points
- Channel 13 = bridge-to-bridge navigation channel for U.S. inland waters
- Channel 16 = international distress and calling channel (monitor always)
- Required for power-driven vessels 26 feet or more, towing vessels 26 feet or more, 100+ GT passenger vessels
- Maximum 1 watt transmit power on Channel 13
- VHF bridge-to-bridge communications must identify the vessel and state position and intended action
- VHF agreement does not eliminate the whistle signal requirement when vessels are in sight of each other
Meeting, Crossing, and Overtaking Under Inland Rules
Inland Rules 13, 14, and 15 govern overtaking, meeting, and crossing situations. The structure mirrors International Rules, but the whistle signal mechanics and Western Rivers modifications make the Inland application different in practice.
| Situation | Rule | Inland Action Required |
|---|---|---|
| Meeting head-on | Inland Rule 14 | Both vessels alter course to starboard; exchange 1-blast signals; each vessel passes port-to-port |
| Crossing (power-driven vessels) | Inland Rule 15 | Vessel with the other on its starboard side is give-way; stand-on vessel maintains course and speed |
| Overtaking | Inland Rule 13 | Overtaking vessel is always give-way regardless of type; signal intent and get agreement; pass on agreed side |
| Western Rivers meeting | Inland Rule 9(a)(ii) | Downbound vessel has ROW and proposes passing side; upbound vessel must agree or signal danger |
| Narrow channel meeting | Inland Rule 9 | Keep to starboard; signal and agree before passing; sailing/fishing vessels do not impede channel traffic |
| Restricted visibility | Inland Rule 19 | Safe speed; sound signals by type; radar contact alone does not determine give-way/stand-on |
Inland Rule 14 — Head-On Meeting
When two power-driven vessels meet head-on or nearly head-on — a situation where collision risk exists — both must alter course to starboard and pass port-to-port. The whistle signal exchange is mandatory: both vessels sound 1 short blast to propose and agree to the port-to-port passage. If the meeting occurs in a manner where a port-to-port passage is not practical (an unusual waterway configuration), 2 blasts can be proposed, but this requires explicit agreement and is not the default.
Inland Rule 15 — Crossing
In a crossing situation between two power-driven vessels, the vessel that has the other on its starboard side is the give-way vessel. The stand-on vessel maintains course and speed. The give-way vessel must take early and substantial action to avoid collision — ideally by altering course to pass astern of the stand-on vessel. Under Inland Rules, whistle signals are exchanged in crossing situations the same as in meeting situations when vessels are in sight of each other.
Inland Rule 13 — Overtaking
A vessel is considered to be overtaking when it approaches another vessel from a direction more than 22.5 degrees abaft her beam — the overtaking arc. The overtaking vessel is ALWAYS the give-way vessel, regardless of type (a sailing vessel overtaking a power vessel is still give-way in the overtaking situation). Under Inland Rules, the overtaking vessel proposes the side of passage with whistle signals and the overtaken vessel agrees. Once committed to the overtake, the relationship continues until the overtaking vessel is clear.
Special Flashing Light and Inland-Only Provisions
The Special Flashing Light
The special flashing light is an Inland Rule-only light that does not appear anywhere in International COLREGS. It is defined in Inland Rule 21(e) as a yellow light, flashing at a rate of 50 to 70 flashes per minute, visible all around the horizon for at least 2 miles. It is placed at or near the stern of certain push-ahead towing vessels.
Special Flashing Light — Quick Reference
- Color: Yellow
- Flash rate: 50-70 flashes per minute
- Arc: All-around (360 degrees)
- Placement: At or near the stern of the towing vessel
- When required: Certain push-ahead and towing configurations on inland waters
- International equivalent: None — Inland only
On the exam, any question that mentions a "special flashing light" is testing whether you know it is Inland-only and yellow. If a question asks which light exists under Inland Rules but NOT International Rules, the answer is the special flashing light.
Inland Rule 9 — Narrow Channels
Inland Rule 9 closely mirrors International Rule 9 but incorporates Inland-specific whistle signal mechanics. Key provisions:
- Vessels must keep to the starboard side of a narrow channel when safe and practicable
- Vessels less than 20 meters (65.6 feet) or sailing vessels must not impede vessels that can only navigate within the channel
- Fishing vessels must not impede vessels navigating within a narrow channel
- A vessel may not cross a narrow channel if doing so would impede a vessel that can only navigate safely within the channel
- When overtaking in a narrow channel, the whistle signal proposal-and-agreement system applies
- Western Rivers provisions for downbound ROW interact with Rule 9 on designated Western Rivers waterways
Traffic Separation Schemes Under Inland Rules
Traffic separation schemes (TSS) in inland waters are established by the USCG under its authority and follow Inland Rule 10 (mirroring International Rule 10 in structure). Vessels in a TSS must proceed in the appropriate traffic lane in the general direction of traffic for that lane, keep clear of separation zones, normally join or leave a scheme at the terminations of the lane, avoid anchoring in a TSS or near its terminations, and use inshore traffic zones only for local traffic or entering/leaving adjacent ports.
The USCG has established traffic separation schemes in high-traffic areas such as the approaches to major ports. These are published on NOAA charts and in Coast Pilot publications. The Inland Rule TSS provisions align closely with International Rule 10 — exam questions on TSS may apply either rule set depending on the location specified in the question.
Inland Rules Exam Strategy
Identify the Trigger Words
USCG exam questions almost always signal which rule set to apply. Look for these trigger words:
Apply Inland Rules When You See:
- "Inland waters"
- "Inside the demarcation lines"
- "The Mississippi River"
- "A U.S. harbor"
- "The Intracoastal Waterway"
- "The Great Lakes"
- "Western Rivers"
Apply International Rules When You See:
- "On the high seas"
- "International waters"
- "Seaward of the demarcation lines"
- "COLREGS"
- "In international waters"
- "Outside the demarcation lines"
The Most Tested Inland vs. International Differences
1. Whistle signal meaning
Inland = proposal. International = informational. This distinction drives at least 5-10 exam questions.
2. Special flashing light
Exists only in Inland Rules. Yellow, 50-70 flashes/min, 360-degree arc. No International equivalent.
3. Western Rivers downbound ROW
Downbound vessel has right of way on Western Rivers. No equivalent in International Rules.
4. Bridge-to-bridge VHF Channel 13
33 CFR 26 requires Channel 13 for bridge-to-bridge navigation in U.S. inland waters.
5. Overtaking signal format
Inland: 1 or 2 blasts as proposal. International (narrow channel): 2 prolonged + 1 short or 2 prolonged + 2 short.
Quick-Reference Sound Signals Card
Inland Rules — Sound Signals Quick Reference
In Sight of Each Other
In Restricted Visibility (Fog)
Frequently Asked Questions — Inland Navigation Rules
What is the difference between one blast and two blasts under Inland Rules?+
What is the Inland Navigation Rules Act of 1980?+
Which vessel has right of way on Western Rivers under Inland Rules?+
What is the special flashing light under Inland Rules?+
What VHF channel is used for bridge-to-bridge communications under 33 CFR 26?+
How does Inland Rule 9 (Narrow Channels) differ from International Rule 9?+
What does three short blasts mean under Inland Rules vs. International Rules?+
Ready to Test Your Inland Rules Knowledge?
NailTheTest has hundreds of Inland Rules practice questions drawn directly from the USCG question bank — including whistle signals, Western Rivers, bridge-to-bridge VHF, and Inland vs. International comparison questions. Study smarter and hit that 90%.
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