US Inland Navigation Rules govern every commercial and recreational vessel operating inside the COLREGS Demarcation Lines. Master the key differences from COLREGS, the whistle signal system, Western Rivers right-of-way, narrow channels, restricted visibility, and vessel traffic services — the most tested material on the USCG OUPV and Master exams.
33 USC
Chapter 34 — statutory authority for US Inland Navigation Rules
33 CFR 80
COLREGS Demarcation Lines — where each rule set applies
33 CFR 89
Western Rivers Special Rules — Mississippi system and tributaries
The United States operates under two parallel navigation rule systems: the International Regulations for Preventing Collisions at Sea (COLREGS, 72 COLREGS) and the US Inland Navigation Rules (33 USC Chapter 34). Understanding exactly where each applies is the foundation of the entire exam topic.
The COLREGS Demarcation Lines are a set of lines drawn across the entrances to bays, sounds, rivers, harbors, and inlets along the entire US coastline. They are published by the US Coast Guard in 33 CFR Part 80 and appear on nautical charts. These lines define the precise boundary between inland and international waters.
The Core Rule
The Inland Rules are not uniform across all inland waters. Three special sub-sets apply in specific geographic areas:
Western Rivers
33 CFR Part 89The Mississippi River, its tributaries, its tributaries’ tributaries, the Red River of the North, and other designated rivers. Includes the Ohio, Missouri, Tennessee, Arkansas, and other major river systems.
Key rule: Downstream vessel has priority over a crossing vessel — regardless of which side the crossing vessel is on.
Great Lakes
33 CFR Part 90The Great Lakes (Superior, Michigan, Huron, Erie, Ontario) and their connecting waters, including the St. Lawrence River to the point where the St. Lawrence enters international waters.
Key rule: Special provisions for vessel traffic, whistle signals, and fog signals adapted to lake conditions.
General Inland Waters
33 USC Chapter 34All other US inland waters not covered by Western Rivers or Great Lakes rules: coastal bays, sounds, harbors, tidal rivers, lakes, and canals.
Key rule: The baseline Inland Rules set that applies everywhere not specifically covered by a sub-set.
Exam Alert
Questions will often ask: "Which rules apply to a vessel operating in [named body of water]?" Know that San Francisco Bay, Chesapeake Bay, Puget Sound, and similar coastal bays are inland waters. The Gulf of Mexico south of the demarcation line is international. The Mississippi River is Western Rivers. Lake Michigan is Great Lakes. Chart 12010 or any standard nautical chart will show the demarcation line at a harbor entrance.
Several provisions exist exclusively in the Inland Rules. These are high-priority exam targets because students who study only COLREGS will miss them entirely. Know these distinctions cold.
On Western Rivers, the standard Inland crossing rule is modified. Under the general Inland crossing rule (Rule 15), the vessel that has the other on its own starboard side gives way. On Western Rivers, that rule is overridden for a specific situation: a vessel crossing the river.
Western Rivers Crossing Rule
Standard Inland Rule 15
When two power-driven vessels cross so as to involve risk of collision, the vessel that has the other on its starboard side must give way and avoid crossing ahead of the other.
Western Rivers Override
A vessel proceeding downstream (descending) has right of way over a vessel crossing the river from either side. The crossing vessel must keep clear of the downstream vessel regardless of its bearing.
Why the Downstream Vessel Has Priority
A vessel moving downstream on a river has limited ability to maneuver against the current. Its effective turning radius and stopping distance are greatly increased by the current pushing it forward. A vessel crossing the river, by contrast, can slow, stop, or retreat to the bank it came from. The rule gives priority to the vessel with the least maneuvering flexibility, which is consistent with the broader maritime principle underlying Rule 18 (the pecking order based on maneuverability).
The most fundamental difference between Inland and International sound signals is the purpose of the signal. This distinction accounts for more exam questions than any other single inland rules topic.
| Signal | Inland Rules (Intent) | COLREGS (Action) |
|---|---|---|
| 1 short blast | I intend to leave you on my port side (pass port-to-port — I will alter to starboard) | I am altering my course to starboard |
| 2 short blasts | I intend to leave you on my starboard side (pass starboard-to-starboard — I will alter to port) | I am altering my course to port |
| 3 short blasts | I am operating astern propulsion (same as COLREGS — no agreement required) | I am operating astern propulsion |
| 5 or more short blasts | Danger/doubt signal — also used to reject a proposed passing agreement | Danger/doubt signal |
| 1 prolonged blast | Leaving a berth or dock; also the bend signal (Rule 34d) | Leaving a berth (no bend signal under COLREGS) |
The Agreement Requirement — Inland Rule 34(a)
Under Inland Rule 34(a), when vessels in sight of one another are approaching each other, the vessel intending a particular passing or overtaking maneuver shall indicate that intent by the appropriate whistle signal. The other vessel, if in agreement, must promptly reply with the same signal. Only after this exchange of signals may either vessel maneuver.
This is categorically different from COLREGS, where Rule 34 signals announce actions being taken — there is no requirement for agreement or response before maneuvering. The inland system is a negotiation protocol; the international system is an announcement protocol.
Disagreement — When to Sound 5 Short Blasts
If the vessel receiving a passing signal disagrees with the proposed maneuver, it must immediately sound five or more short blasts. No maneuvering occurs until a new agreement is reached. Neither vessel should proceed with the original maneuver. The disagreeing vessel should hold course and speed while sounding the danger signal. Five short blasts under Inland Rules thus serves two functions: (1) the universal danger/doubt signal under both rule sets, and (2) formal rejection of a proposed passing arrangement unique to the Inland system.
Maneuvering signals are sounded when vessels are in sight of one another. Under Inland Rules, these signals express intent and require agreement. All signals listed here are sounded in addition to any light signals required by Rule 34.
I intend to leave you on my port side
— (one short)
Used in meeting (head-on or near head-on) situations. Proposes a port-to-port passing: both vessels alter to starboard. Must be answered with 1 short blast by the other vessel before either maneuvers.
I intend to leave you on my starboard side
— — (two short)
Used when a starboard-to-starboard passing is proposed. Both vessels alter to port. Less common in meeting situations — requires agreement before maneuvering.
I am operating astern propulsion
— — — (three short)
Sounded when engines are in reverse. Does NOT mean the vessel is moving astern through the water — only that astern propulsion is being applied. Same meaning under COLREGS. No agreement signal required.
Danger or doubt signal / Rejection of proposed agreement
— — — — — (five or more short)
Must be sounded immediately if a vessel is in doubt about the safety of a proposed action or if it disagrees with the proposed passing arrangement. Both vessels should hold position or take defensive action. No maneuvering until new agreement is established.
When an overtaking vessel intends to pass in a narrow channel or fairway, it must signal its intent and receive agreement before maneuvering. Inland and COLREGS overtaking signals differ significantly.
| Intent | Inland Signal | COLREGS Signal | Agreement Required? |
|---|---|---|---|
| Overtake on starboard side of vessel ahead | Long + Short (— •) | Long + Long + Short (— — •) | Inland: Yes. COLREGS: No |
| Overtake on port side of vessel ahead | Long + Short + Short (— • •) | Long + Long + Short + Short (— — • •) | Inland: Yes. COLREGS: No |
| Agreement response from vessel being overtaken | Long + Short + Long + Short (— • — •) | No reply required | Inland: Required. COLREGS: N/A |
Inland Overtaking Agreement Signal — Rule 34(b)(ii)
The vessel being overtaken indicates agreement by sounding the following signal: one prolonged, one short, one prolonged, one short blast (dash-dot-dash-dot, the letter C in Morse code). This agreement signal is unique to Inland Rules and does not exist under COLREGS. If the vessel being overtaken is unsure the pass can be made safely, it sounds five or more short blasts to reject the overtaking maneuver.
Bend or Blind Approach Signal — Inland Only
A vessel nearing a bend or area of a channel where other vessels may be obscured by an intervening obstruction must sound one prolonged blast. Any approaching vessel within hearing range must respond with one prolonged blast. This is an Inland Rule 34(d) requirement that has no equivalent in COLREGS.
Under both Inland Rules and COLREGS, a vessel leaving a berth, dock, or wharf sounds one prolonged blast. This is not a maneuvering signal requiring agreement — it is an informational signal alerting nearby vessels to the vessel's departure. No response or agreement is required or expected.
On Western Rivers, an additional notification requirement exists: a vessel intending to depart from a wharf or bank must sound a similar signal and wait for any approaching traffic to clear before departing, consistent with the downstream priority rule.
Rule 9 is one of the most-tested rules on the captain exam and applies under both Inland Rules and COLREGS, though with some differences in detail. A narrow channel is not defined by a specific width — it is any channel that is narrow enough that two vessels cannot safely pass without one of them using the full width. The rule sets out specific duties for all vessels in narrow channels or fairways.
The Basic Navigation Rule
A vessel proceeding along the course of a narrow channel or fairway shall keep as near to the outer limit of the channel or fairway which lies on her starboard side as is safe and practicable. In practice: stay to the right side of the channel, as close to the right-hand edge as conditions allow.
This rule applies to all vessels in the channel — not just power-driven vessels. Sailing vessels, vessels engaged in fishing, and vessels constrained by their draft must all comply with Rule 9(a). There are no exceptions based on vessel type for the keep-to-starboard requirement.
A vessel less than 20 meters in length or a sailing vessel shall not impede the passage of a vessel that can safely navigate only within the narrow channel or fairway. "Not impede" is a stronger duty than "give way" — a vessel required not to impede must take early, positive action to stay out of the way, not merely yield at the last moment. If a vessel less than 20 meters in length is on a course that would require a larger vessel to leave the channel, the smaller vessel is in violation of Rule 9(b).
A vessel engaged in fishing shall not impede the passage of any other vessel navigating within a narrow channel or fairway. This is a significant departure from Rule 18 (the pecking order), which normally gives fishing vessels right of way over power-driven vessels. In a narrow channel, fishing vessels cannot use their Rule 18 priority to force power-driven vessels out of the channel.
A vessel shall not cross a narrow channel or fairway if such crossing impedes the passage of a vessel which can only safely navigate within the channel. This rule does not prohibit crossing — it only prohibits crossing when doing so would impede a vessel that is constrained to the channel. A vessel wishing to cross when such traffic is present must take all necessary action to make the channel vessel's passage safe.
Under COLREGS, if a vessel is in doubt about whether its crossing will impede channel traffic, the doubt itself should resolve in favor of not crossing. Under Inland Rules, the crossing vessel must actively ensure that it does not impede.
When overtaking in a narrow channel or fairway, the overtaking vessel must use the whistle signals specified in Rule 34(b). The vessel being overtaken must be consulted and must agree before the overtaking maneuver begins. This applies under both Inland Rules and COLREGS.
Under Inland Rules: the overtaking vessel sounds the appropriate signal (long + short for starboard overtake, or long + short + short for port overtake). The vessel being overtaken must sound the agreement signal (long + short + long + short) before either vessel maneuvers. If it disagrees, it sounds five or more short blasts.
A vessel nearing a bend or an area of a narrow channel or fairway where other vessels may be obscured by an intervening obstruction shall navigate with particular alertness and caution and shall sound the appropriate signal prescribed by Rule 34(d). Under Inland Rules, this is the one prolonged blast. Under COLREGS, Rule 9(f) requires the signal but does not specify the sequence — COLREGS Rule 34(e) requires the same one prolonged blast bend signal. Note that both rule sets require the bend signal, but the Inland Rules codify it more explicitly and it is more frequently tested as an Inland-specific rule.
A vessel shall, if the circumstances of the case admit, avoid anchoring in a narrow channel. This applies under both Inland Rules and COLREGS. Anchoring in a channel reduces the navigable width available to other vessels, particularly those constrained by their draft. In emergencies, anchoring in a channel may be unavoidable — but in all other circumstances, the vessel should seek anchorage outside the channel limits.
Traffic Separation Schemes (TSS) are a system of one-way traffic lanes, separation zones, and inshore traffic zones established by the International Maritime Organization (IMO) in busy or dangerous waterways. They are depicted on nautical charts and appear wherever vessel density creates collision risk. Rule 10 governs how vessels must use them.
Key TSS Locations (US Waters)
Vessels using a TSS shall proceed in the appropriate traffic lane in the general direction of traffic flow for that lane.
Vessels shall join or leave traffic lanes at the termination of a lane if possible. When joining or leaving from the side, do so at as small an angle as possible.
Vessels shall avoid crossing traffic lanes. If crossing is necessary, cross on a heading as nearly as practicable perpendicular to the general direction of traffic flow.
Inshore traffic zones shall not normally be used by through traffic. Vessels less than 20 meters, sailing vessels, and vessels engaged in fishing may use inshore traffic zones.
A vessel other than a crossing or joining vessel shall not normally enter a separation zone or cross a separation line, except to avoid immediate danger or to engage in fishing within the separation zone.
A vessel engaged in fishing shall not impede the passage of any vessel following a traffic lane.
A vessel less than 20 meters in length or a sailing vessel shall not impede the safe passage of a power-driven vessel following a traffic lane.
TSS and the Rules of the Road
Using a TSS does not suspend or override the other rules of the road. A vessel in a TSS still must maintain a proper lookout (Rule 5), proceed at a safe speed (Rule 6), take action to avoid collision when risk exists (Rules 7 and 8), and observe the crossing, overtaking, and meeting rules (Rules 13–15). The TSS establishes the traffic pattern; it does not establish right of way between specific vessels.
Crossing a TSS — The Perpendicular Rule
When a vessel must cross a traffic separation scheme, it must do so on a heading as nearly as practicable at right angles (90 degrees) to the direction of the traffic lanes. This does not mean the vessel's track over ground must be perpendicular — the vessel's heading must be perpendicular. Current and leeway may result in a different track over ground. The key is the heading: the vessel must point across the lane, not at a diagonal. This minimizes the time the vessel spends in the lane and presents a clear, predictable path to other vessels.
Rule 19 applies when vessels are not in sight of one another — meaning in fog, mist, heavy rain, dense precipitation, sandstorms, or any other condition that reduces visibility to the point where vessels cannot see each other. It is a special rule that supplements, rather than replaces, the other rules. When in restricted visibility, vessels are no longer in a meeting, crossing, or overtaking situation in the traditional sense — because they cannot see each other. Rule 19 provides the framework for safe navigation when visual contact is lost.
Proceed at a Safe Speed
Rule 19(b): Every vessel shall proceed at a safe speed adapted to the prevailing circumstances and conditions of restricted visibility. A vessel shall have her engines ready for immediate maneuver. Safe speed in restricted visibility is significantly slower than in clear conditions. The vessel must be able to stop in less than the distance of visibility — in fog, this may mean bare steerage speed.
Comply with Rule 6 Safe Speed Factors
When operating in restricted visibility with radar, additional safe speed factors apply: the characteristics and limitations of the radar equipment; constraints of the radar range scale in use; the effect of sea state and weather on radar returns; the possibility that small vessels or floating objects may not be detected at all. These are Rule 6(b) factors specifically listed for radar-equipped vessels.
Use Radar — Assess Risk of Collision
Rule 19(d): A vessel that detects another vessel by radar alone shall determine if a close-quarters situation is developing or risk of collision exists. If so, it must take avoiding action in ample time. Avoiding action should not consist of an alteration to port for a vessel forward of the beam (other than overtaking). Course alterations to port for a vessel ahead are specifically prohibited unless overtaking.
Hear a Fog Signal Forward of the Beam
Rule 19(e): If a fog signal is heard forward of the beam (anywhere in the forward 180-degree arc), the vessel must: (1) reduce speed to the minimum at which it can be kept on course (bare steerage), and (2) navigate with extreme caution until danger of collision is past. The vessel may also stop entirely. This is a mandatory requirement, not discretionary.
Sound Fog Signals — Rule 35
In or near restricted visibility, all vessels must sound the appropriate fog signals at required intervals regardless of time of day. Power-driven vessel making way: 1 prolonged blast at intervals not exceeding 2 minutes. Power-driven vessel underway but stopped (not making way): 2 prolonged blasts with 2-second interval, at intervals not exceeding 2 minutes. Sailing vessel underway: 1 prolonged + 2 short blasts (dash-dot-dot), at intervals not exceeding 2 minutes.
| Vessel Type | Fog Signal | Interval |
|---|---|---|
| Power-driven, making way | 1 prolonged blast | Not more than 2 min |
| Power-driven, underway but not making way | 2 prolonged blasts (2-sec interval between) | Not more than 2 min |
| Sailing vessel, vessel towing, vessel NUC, RAM, constrained by draft, engaged in fishing | 1 prolonged + 2 short blasts (— • •) | Not more than 2 min |
| Vessel being towed (if manned) | 4 blasts (1 prolonged + 3 short) — • • • | Not more than 2 min |
| Vessel at anchor (20m and over) | Ring bell rapidly for 5 sec | Not more than 1 min |
| Vessel at anchor (100m and over) | Bell (forward) 5 sec + gong (aft) 5 sec | Not more than 1 min |
| Vessel aground | 3 bell strokes + rapid bell + 3 bell strokes | Not more than 1 min |
| Pilot vessel on duty | 4 short blasts in addition to regular signal | At intervals |
Critical Rule 19 Exam Points
The following table covers all major sound signal differences between Inland Rules and COLREGS. This is the most comprehensive comparison of these two systems and covers every major scenario tested on the USCG exam.
| Situation | Inland Rules | COLREGS (International) |
|---|---|---|
| 1 short blast — meaning | Intent to leave you on my port side (propose port-to-port passing). Requires agreement reply. | I am altering my course to starboard. No reply required. |
| 2 short blasts — meaning | Intent to leave you on my starboard side (propose starboard-to-starboard passing). Requires agreement reply. | I am altering my course to port. No reply required. |
| 3 short blasts — meaning | I am operating astern propulsion. (Same as COLREGS.) | I am operating astern propulsion. |
| 5 or more short blasts | Danger or doubt signal; also used to reject a proposed passing arrangement. | Danger or doubt signal. |
| Agreement reply to 1 or 2 blasts | Same signal echoed back by the other vessel. Required before maneuvering. | No reply required or used. |
| Disagreement with proposed passing | 5 or more short blasts sounded immediately. | Concept does not apply — signals announce actions, not proposals. |
| Overtake on starboard of vessel ahead | 1 prolonged + 1 short blast (— •). Requires agreement signal. | 2 prolonged + 1 short (— — •). No agreement required. |
| Overtake on port of vessel ahead | 1 prolonged + 2 short blasts (— • •). Requires agreement signal. | 2 prolonged + 2 short (— — • •). No agreement required. |
| Agreement reply to overtaking signal | 1 prolonged + 1 short + 1 prolonged + 1 short (— • — •). Required. | No reply signal. No agreement process. |
| Bend signal | 1 prolonged blast required by Rule 34(d). Other vessel replies with 1 prolonged. | No equivalent bend signal rule. |
| Leaving a berth or dock | 1 prolonged blast. | 1 prolonged blast. |
| Power vessel making way — fog | 1 prolonged blast, not more than 2 min intervals. | 1 prolonged blast, not more than 2 min intervals. |
| Power vessel not making way — fog | 2 prolonged blasts with 2-sec interval, not more than 2 min. | 2 prolonged blasts with 2-sec interval, not more than 2 min. |
| Sailing vessel — fog signal | 1 prolonged + 2 short (— • •), not more than 2 min. | 1 prolonged + 2 short (— • •), not more than 2 min. |
| Purpose of maneuvering signals | Express intent; agreement required before maneuver. | Announce action being taken; no agreement required. |
Master Exam Strategy
Every question about the meaning of a whistle signal on the captain exam requires you to first identify which rule set applies. If the vessel is in a harbor, river, bay, or other inland water: apply Inland Rules. If the vessel is on the high seas or international waters: apply COLREGS. The number of blasts may be the same, but the meaning can be entirely different. When in doubt, look for the phrase "in sight of each other" — that triggers maneuvering signals (Rules 34 / 34a). "In or near restricted visibility" triggers fog signals (Rule 35).
Vessel Traffic Services (VTS) are shore-based systems that monitor and manage maritime traffic in specific ports and waterways, similar in concept to air traffic control. VTS centers use radar, VHF radio, and AIS tracking to maintain situational awareness and provide traffic management services. In the United States, VTS is operated by the US Coast Guard under 33 CFR Part 161.
San Francisco VTS
San Francisco Bay, San Pablo Bay, Carquinez Strait, Sacramento River, San Joaquin River
Puget Sound VTS
Puget Sound, Strait of Juan de Fuca, Rosario Strait, Haro Strait
New York/New Jersey VTS
Port of New York and New Jersey, Hudson River, Kill Van Kull, Newark Bay, Raritan Bay
Houston/Galveston VTS
Houston Ship Channel, Galveston Bay, Texas City Ship Channel, Clear Lake
Prince William Sound VTS
Prince William Sound approaches and Valdez Narrows (Alaska)
Louisville VTS
Portions of the Ohio River including the McAlpine Locks area
Vessels required to participate in a VTS (33 CFR 161.16) include: power-driven vessels of 40 meters or more in length; vessels certificated to carry 50 or more passengers for hire; vessels towing where the length of the tow exceeds 76 meters; and certain vessels carrying hazardous cargo. These vessels must check in with the VTS center when entering the VTS area and report at designated reporting points.
Recreational vessels and commercial vessels below the threshold are not required to participate, but may voluntarily contact VTS for traffic information. Many mariners choose to check in with VTS voluntarily in congested or restricted waterways even when not legally required.
Required when entering the VTS area and at each designated waypoint or reporting line
If nothing to report, a negative report is still required at each reporting point
Required when departing the VTS area
Any deviation from the planned route must be reported to VTS
Mechanical deficiencies affecting the vessel's maneuverability, steering, or propulsion must be reported
Compliance with VTS instructions does not relieve the vessel master of the duty to comply with the Inland Navigation Rules. VTS may issue vessel movement suggestions, advisories, or in some systems mandatory directions, but the master retains full responsibility for the vessel's safety at all times. A VTS instruction that would require a vessel to violate the Navigation Rules must be questioned — the Navigation Rules are the primary legal authority governing collision avoidance.
The Vessel Movement Reporting System (VMRS) is used in some VTS zones. Under VMRS, vessels must report at designated reporting points along the waterway. Compliance with VMRS reports does not replace the general VTS participation requirements — both systems may apply simultaneously in a given waterway.
VHF Channel 16 is the calling and distress channel and is monitored by VTS at all times. Each VTS center assigns specific working channels for traffic reporting — common channels include 12, 13, 14, 20, and 65. The specific channel for each VTS is published in Coast Pilot and on nautical charts.
Rule 2 is the foundational "responsibility rule" that underlies the entire Navigation Rules system. It applies equally under both Inland Rules and COLREGS, and it is the rule that courts and the Coast Guard apply when assessing fault in a collision.
Rule 2(a) — Owner and Master Responsibility
Nothing in these Rules shall exonerate any vessel, or the owner, master, or crew thereof, from the consequences of any neglect to comply with these Rules or of the neglect of any precaution which may be required by the ordinary practice of seamen, or by the special circumstances of the case.
Rule 2(b) — Departure from the Rules
In construing and complying with these Rules due regard shall be had to all dangers of navigation and collision and to any special circumstances, including the limitations of the vessels involved, which may make a departure from these Rules necessary to avoid immediate danger.
Rule 2(b) is the "escape valve" of the Navigation Rules: when strict compliance with a rule would create immediate danger, deviation is permitted and may be required. This does not give mariners general license to disregard the rules — it applies only to genuine emergencies where following the rule would cause the very harm the rule is designed to prevent.
Proper Lookout — Rule 5
Every vessel shall at all times maintain a proper lookout 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 risk of collision. This means eyes, ears, radar, AIS — all available tools must be used. Lookout is continuous, not periodic.
Safe Speed — Rule 6
Every vessel shall at all times proceed at a safe speed so that she can take proper and effective action to avoid collision and be stopped within a distance appropriate to the prevailing circumstances. There is no universal safe speed number — it must be evaluated against visibility, traffic density, maneuverability, and navigational hazards.
Early and Substantial Action — Rule 8
Any action taken to avoid collision shall, if the circumstances of the case admit, be large enough to be readily apparent to the other vessel, either by visual means or by radar; a succession of small alterations of course or speed should be avoided. Early action prevents close-quarters situations; small alterations confuse the other vessel.
Risk of Collision — Rule 7
Every vessel shall use all available means to determine if risk of collision exists. If there is any doubt, risk shall be assumed to exist. Radar bearings must be taken: if a steady compass bearing to an approaching vessel indicates it is not drawing ahead or astern, risk of collision almost certainly exists.
Crossing Ahead of Stand-On
Rule 16 instructs the give-way vessel to avoid crossing ahead of the stand-on vessel. If possible, the give-way vessel should slow and let the stand-on vessel pass ahead. Crossing in front of the stand-on vessel under engine power, even with clearance, violates the spirit of Rule 16 and increases risk.
Avoiding Collision with All Means
Rule 8(e) requires that if necessary to avoid collision or allow more time to assess the situation, a vessel shall slacken speed or take all way off by stopping or reversing means of propulsion. Speed reduction is always available and is always good seamanship when doubt arises.
Under US admiralty law, a vessel that violates the Navigation Rules is presumed to have caused any collision that occurs — this is the "Pennsylvania Rule" (The Pennsylvania, 86 US 125, 1873). If your vessel is in violation of any navigation rule at the time of a collision, you bear the burden of proving that your violation could not have contributed to the collision. This burden is very difficult to meet.
The practical consequence: strict compliance with the Navigation Rules is not merely a regulatory requirement — it is essential legal protection in the event of any incident. A vessel operating at excessive speed in restricted visibility, failing to sound required signals, or improperly using a traffic lane has already established a presumption of liability before any other facts are examined.
The Navigation Rules are a minimum standard, not a ceiling. Good seamanship often requires more than strict rule compliance. Examples:
The phrase "ordinary practice of seamen" in Rule 2(a) encompasses all of these habits. A vessel that technically complies with every rule but fails to exercise good seamanship may still be found at fault under maritime law.
These are the highest-frequency exam points on the Inland Navigation Rules. Know every item on this list before sitting for the USCG captain exam.
Q
Where do Inland Rules apply?
A
Inside the COLREGS Demarcation Lines (33 CFR Part 80)
Q
What does 1 short blast mean Inland?
A
Intent to leave you on my port side (port-to-port passing proposed)
Q
What does 2 short blasts mean Inland?
A
Intent to leave you on my starboard side (starboard-to-starboard passing proposed)
Q
Is an agreement reply required Inland?
A
Yes — same signal echoed back before either vessel maneuvers
Q
What does 5 short blasts signal Inland?
A
Danger/doubt; also rejection of a proposed passing arrangement
Q
Western Rivers crossing rule?
A
Downstream vessel has right of way over any crossing vessel
Q
Bend signal (Rule 34d)?
A
1 prolonged blast; reply is also 1 prolonged blast. Inland only.
Q
Overtake to starboard, Inland signal?
A
1 prolonged + 1 short (— •); requires agreement
Q
Overtake to port, Inland signal?
A
1 prolonged + 2 short (— • •); requires agreement
Q
Agreement to overtaking, Inland?
A
1 prolonged + 1 short + 1 prolonged + 1 short (— • — •)
Q
Rule 9(b) — vessels under 20m?
A
Must not impede a vessel that can only navigate within the channel
Q
Rule 9 — fishing vessels in channel?
A
Must not impede any vessel navigating within the narrow channel
Q
Rule 10 — crossing a TSS?
A
Cross on a heading as nearly as practicable perpendicular to lane direction
Q
Rule 19(e) — fog signal forward of beam?
A
Reduce to bare steerage; navigate with extreme caution
Q
Rule 19(d)(ii) — restricted visibility radar?
A
Do not alter to port for vessel forward of the beam (except overtaking)
Q
Power vessel fog signal?
A
1 prolonged blast, not more than every 2 minutes
Q
Power vessel stopped fog signal?
A
2 prolonged blasts with 2-sec interval, not more than every 2 minutes
Q
Sailing vessel fog signal?
A
1 prolonged + 2 short (— • •), not more than every 2 minutes
Q
Vessel at anchor fog signal (20m+)?
A
Rapid ringing of bell for 5 seconds, not more than every 1 minute
Q
Key Western Rivers authority?
A
33 CFR Part 89 — Western Rivers Special Rules
The captain exam presents situational questions that require applying multiple rules simultaneously. Work through these scenarios to develop decision-making fluency before exam day.
Scenario 1 — Meeting in San Francisco Bay
Facts: You are operating a 50-foot power-driven charter vessel in San Francisco Bay, heading eastbound in the main ship channel. A 300-foot container ship approaches heading westbound. You are in sight of each other.
You wish to pass port-to-port. What signal do you sound? What must happen before you alter course?
San Francisco Bay is inside the COLREGS Demarcation Lines — Inland Rules apply. To propose a port-to-port passing, sound 1 short blast. The container ship must respond with 1 short blast to agree. Only after both signals are exchanged may either vessel alter course. If the ship does not respond or sounds 5 blasts, do not maneuver — hold your course and sound 5 blasts yourself.
Scenario 2 — Western Rivers Crossing
Facts: You are on the Mississippi River at St. Louis, operating a small passenger vessel. You intend to cross the river. A tow boat pushing 8 barges is descending the river (moving downstream). The tow is on your starboard side.
Under the standard Inland Rules crossing rule, you would be the give-way vessel because the tow is on your starboard side. Does Western Rivers change this?
No change — you are still the give-way vessel, but for a different reason. Under 33 CFR 89.25 (Western Rivers rules), a vessel crossing the river must keep out of the way of any power-driven vessel descending the river, regardless of which side the descending vessel is on. Even if the tow were on your port side, you would still be the give-way vessel because the tow is the downstream vessel. Wait for the tow to pass before crossing.
Scenario 3 — Narrow Channel, Fishing Vessel
Facts: You are operating a 45-foot recreational vessel in a narrow channel leading to a harbor. A commercial fishing vessel with gear deployed is stopped across the channel ahead of you. The fishing vessel is larger than you.
The fishing vessel is normally above you in the Rule 18 pecking order. Does it have the right of way here?
No. Rule 9(c) requires that a vessel engaged in fishing shall not impede the passage of any other vessel navigating within a narrow channel or fairway. The Rule 18 pecking order does not apply in this specific situation. The fishing vessel is obligated to move or clear gear from the channel. If it fails to do so, you may sound 5 short blasts to signal doubt, and contact the vessel on VHF Channel 16 or the designated working channel.
Scenario 4 — Restricted Visibility, Radar Contact
Facts: You are in dense fog in Chesapeake Bay. Visibility is less than 200 yards. You are proceeding at 8 knots. Your radar shows a vessel dead ahead at 1.5 miles, apparently stopped or making way slowly. The bearing is steady.
What immediate actions are required under Rule 19?
Immediately reduce speed — 8 knots is almost certainly not a safe speed in 200-yard visibility. The steady bearing indicates a risk of collision. Under Rule 19(d), take avoiding action in ample time. Do not alter course to port for a vessel forward of the beam — if you must alter, alter to starboard or slow to a stop. Sound the appropriate fog signal (1 prolonged blast, not more than every 2 minutes). Listen for fog signals. If you hear a fog signal from forward of the beam, reduce to bare steerage immediately under Rule 19(e). Consider stopping entirely until the situation is resolved.
Scenario 5 — Traffic Separation Scheme, Crossing Vessel
Facts: You are a 30-meter power-driven vessel approaching the New York Traffic Separation Scheme from the south. You need to cross the southbound lane and the separation zone to enter the northbound lane.
How must you cross the TSS? What are your obligations to other vessels in the lane?
Under Rule 10(c), you must cross the lane on a heading as nearly as practicable at right angles to the direction of traffic flow. Aim your bow perpendicular to the lane — your track over ground may be diagonal due to current, but your heading should be 90 degrees to the lane. You must not impede vessels following the traffic lane (Rule 10(f) and 10(g)). As a vessel under 40 meters, you are below the mandatory VTS participation threshold, but contact New York VTS on Channel 12 voluntarily for traffic information. Cross when a gap in traffic permits safe passage — do not force vessels in the lane to maneuver for you.
Where exactly do US Inland Navigation Rules apply versus COLREGS?
The US Inland Navigation Rules apply on all US inland waters inside the COLREGS Demarcation Lines published in 33 CFR Part 80. Seaward of the lines: COLREGS. Inward of the lines: Inland Rules. The lines appear on nautical charts at the entrance to every major bay, harbor, river, and inlet. The Western Rivers rules apply on the Mississippi River system and other designated rivers under 33 CFR Part 89. The Great Lakes rules apply on the Great Lakes and their connecting waters. A vessel transitions from one rule set to the other precisely at the demarcation line.
What does one short blast mean under Inland Rules compared to COLREGS?
Under Inland Rules, one short blast means I intend to leave you on my port side — it is a signal of intent that requires an agreement reply before either vessel maneuvers. Under COLREGS, one short blast means I am altering my course to starboard — it announces an action already being taken and no agreement is required. This intent-versus-action distinction is the most tested difference on the USCG captain exam.
How does the Western Rivers crossing rule differ from the general Inland crossing rule?
Under the general Inland Rules crossing situation (Rule 15), the vessel that has the other on its own starboard side is the give-way vessel. On Western Rivers (33 CFR 89.25), a vessel crossing the river must keep out of the way of a power-driven vessel descending (going downstream) regardless of which side the crossing vessel is on. The downstream vessel always has right of way over the crossing vessel, whether the crossing vessel approaches from port or starboard.
What are the five short blasts used for under Inland Rules?
Five or more short blasts is the danger or doubt signal under both Inland Rules and COLREGS. Under Inland Rules it serves a second function: when one vessel proposes a passing arrangement and the other vessel disagrees, the disagreeing vessel must immediately sound five or more short blasts to reject the proposal. Neither vessel maneuvers until a new agreement is reached. Five short blasts can also be supplemented with five short flashes of a light signal.
What precautions does Rule 19 require in restricted visibility?
Rule 19 requires every vessel to proceed at a safe speed adapted to restricted visibility conditions. A vessel using radar must determine if a close-quarters situation is developing and take avoiding action in ample time. Course alterations to port for a vessel forward of the beam are prohibited (unless overtaking). If a fog signal is heard forward of the beam, the vessel must immediately reduce to bare steerage speed and navigate with extreme caution. Vessels must sound the required fog signals under Rule 35 regardless of time of day.
What is the bend signal under Inland Rule 34(d) and when must it be sounded?
Rule 34(d) requires that a vessel nearing a bend or area of a channel where other vessels may be obscured by an intervening obstruction must sound one prolonged blast. Any approaching vessel within hearing must reply with one prolonged blast. This is an Inland-only requirement with no COLREGS equivalent. The signal must be sounded early enough for approaching traffic to hear and respond before vessels come into sight of each other. It applies in any river, harbor, or channel where terrain, structures, or other obstructions limit sight lines.
When are vessels required to participate in Vessel Traffic Services?
Under 33 CFR Part 161, vessels required to participate in a VTS include: power-driven vessels 40 meters or more in length; vessels certificated to carry 50 or more passengers for hire; vessels towing where the length of the tow exceeds 76 meters; and certain vessels carrying hazardous cargo. Smaller recreational and commercial vessels are not required to participate but may contact VTS voluntarily for traffic advisories. Compliance with VTS instructions does not relieve the master of responsibility under the Navigation Rules.
NailTheTest has hundreds of Inland Rules practice questions covering whistle signals, Western Rivers, narrow channels, restricted visibility, and VTS — matched exactly to the USCG exam format.
Practice Inland Rules Questions