GPS and Electronic Navigation

TL;DR — Any vessel calling at a U.S. port must carry a satellite navigation receiver meeting the requirements of 33 CFR §164.41; that receiver is one tool among several that must be used together to fix position — buoys alone are never an acceptable position fix.

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What the Rule Says

Any vessel calling at a port in the continental United States, including Alaska south of Cape Prince of Wales, must carry a satellite navigation receiver. Two specific performance requirements apply to that receiver: it must provide automatic acquisition of satellite signals after initial operator settings have been entered, and it must provide position updates derived from satellite information during each usable satellite pass. 33 CFR §164.41

The exemption is narrow: vessels owned or bareboat chartered and operated by the United States, by a state or its political subdivision, or by a foreign nation, and not engaged in commerce, are excluded. All commercial vessels calling at covered U.S. ports fall under the requirement. 33 CFR §164.41

For vessels operating on an oceans route, the requirement is stated separately: such a vessel must be equipped with an electronic position fixing device capable of providing accurate fixes for the area in which the vessel operates, to the satisfaction of the cognizant Officer in Charge, Marine Inspection (OCMI). 46 CFR §184.410

How Position Must Be Fixed Underway

Carrying a GPS receiver is not enough on its own. The master or person in charge of each vessel underway must ensure that electronic and other navigational equipment, external fixed aids to navigation, geographic reference points, and hydrographic contours are all used when fixing the vessel's position. No single source is sufficient in isolation. 33 CFR §164.11

Every fix must be plotted on a chart of the area, and the person directing the movement of the vessel must be informed of the vessel's position at each fix. 33 CFR §164.11

The Buoy Rule

Buoys alone are never to be used to fix the vessel's position. The regulatory note explains why: buoys are placed in approximate positions, and strong or varying currents, heavy seas, ice, and collisions with vessels can move or sink them or set them adrift. A buoy may corroborate a fix established by other means, but it cannot serve as the sole basis for a position fix. If no other aids are available, buoys alone may be used only to establish an estimated position — not a fix. 33 CFR §164.11

Marine navigation employs four primary methods: dead reckoning, piloting, celestial, and electronic. Modern voyages combine all four, with electronic navigation serving as the principal real-time reference and the others functioning as cross-checks. Bowditch Ch. 1 §101

Dead reckoning (DR) is the determination of position by applying course steered and distance run from a known starting point. DR accuracy degrades over time and must be confirmed by external fixes whenever possible. Bowditch Ch. 1 §102

Piloting is navigation by reference to landmarks, aids to navigation, and soundings. It is the primary method used in confined waters where dead reckoning alone is insufficient and electronic positioning may be obstructed by terrain or interference. Bowditch Ch. 1 §103

Celestial navigation determines position from observations of celestial bodies. Although no longer the primary navigation method, it remains the backup of last resort if all electronic systems fail. Bowditch Ch. 15 §1501

Wheelhouse Manning and Competency

The wheelhouse must be constantly manned by persons who both direct and control the movement of the vessel and fix the vessel's position. Each person performing those duties must be competent to do so. A person competent to steer the vessel must be in the wheelhouse at all times. 33 CFR §164.11

Compass Errors and Current

The person directing movement of the vessel must know and correctly apply magnetic variation, deviation, and gyrocompass errors. Current velocity and direction for the area to be transited must be known, as must predicted set and drift and the tidal state for the area. 33 CFR §164.11

Standards Referenced for Electronic Equipment

The regulatory framework for electronic navigation equipment incorporates several external standards by reference. For AIS, the applicable IMO resolutions include A.917(22) on operational use and SN/Circ.227 and SN/Circ.245 on installation. NMEA 0400 governs installation standards for marine electronic equipment on moderate-sized vessels. Track control systems must meet IEC 62065. 33 CFR §164.03

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Why It Matters on the Exam

OUPV and Master 100 GT written exams test this topic from several angles. Expect questions that probe:

The carriage requirement and its scope. Candidates must know that 33 CFR §164.41 applies to vessels calling at U.S. ports and that the satellite receiver must auto-acquire signals and update position on each usable satellite pass. 33 CFR §164.41 The oceans-route requirement under 46 CFR §184.410 is a separate provision and may appear as a distractor. 46 CFR §184.410

The multi-source fix requirement. The exam frequently tests whether a candidate understands that electronic equipment alone does not satisfy the position-fixing obligation. The rule requires electronic equipment, external fixed aids, geographic reference points, and hydrographic contours to be used together. 33 CFR §164.11 A question may present a scenario where the navigator relies solely on GPS and ask whether that satisfies the regulation — it does not.

The buoy prohibition. This is a classic exam question. Buoys alone cannot fix a position. They may corroborate a fix. If no other aids are available, they may support only an estimated position. 33 CFR §164.11 Know the distinction between a fix and an estimated position.

Dead reckoning limitations. DR accuracy degrades over time. Bowditch Ch. 1 §102 A question may ask what must be done to confirm a DR position — the answer is to obtain an external fix.

Piloting in confined waters. Piloting is the primary method in confined waters where DR is insufficient and electronic positioning may be obstructed. Bowditch Ch. 1 §103 Expect questions that ask which navigation method is most appropriate in a harbor or channel.

Celestial as last resort. Celestial navigation is the backup of last resort when all electronic systems fail. Bowditch Ch. 15 §1501 The exam may ask about the hierarchy of navigation methods.

Compass error application. Variation, deviation, and gyrocompass errors must be known and correctly applied by the person directing movement. 33 CFR §164.11 This connects to chart work and compass correction questions that appear throughout the exam.

Speed considerations. The person directing movement must set speed with consideration for visibility, proximity to structures, squat and underkeel clearance, channel proportions, traffic density, wake damage, current, and local speed limits. 33 CFR §164.11 These factors appear in both Rules of the Road and navigation general question sets.

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Common Pitfalls

Confusing "fix" with "estimated position." A fix is established by two or more independent, reliable lines of position. An estimated position is less certain. The regulation explicitly states that buoys alone may support only an estimated position, not a fix. 33 CFR §164.11 Candidates who conflate the two will miss questions on this distinction.

Assuming GPS alone satisfies the fix requirement. The regulation requires multiple sources — electronic equipment, fixed aids, geographic reference points, and hydrographic contours. 33 CFR §164.11 GPS is one input, not the complete answer.

Misidentifying the applicable carriage regulation. The satellite receiver requirement in 33 CFR §164.41 applies to vessels calling at U.S. ports. 33 CFR §164.41 The oceans-route electronic position fixing device requirement in 46 CFR §184.410 applies to vessels on an oceans route and is subject to OCMI satisfaction. 46 CFR §184.410 These are distinct provisions with different applicability.

Overlooking the auto-acquisition and update requirements. The satellite receiver must auto-acquire after initial settings and must update on each usable satellite pass. 33 CFR §164.41 A receiver that requires manual satellite selection or that only updates on demand does not meet the standard.

Forgetting that DR degrades over time. Candidates sometimes treat a DR position as equivalent to a fix. Dead reckoning accuracy degrades and must be confirmed by external fixes whenever possible. Bowditch Ch. 1 §102

Neglecting current, set, drift, and tidal state. These are not optional considerations — the person directing movement must know current velocity and direction, predicted set and drift, and tidal state for the area to be transited. 33 CFR §164.11 Exam questions on electronic navigation often include a current or tidal component.

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Quick Check

Q1 — What two performance requirements must a satellite navigation receiver meet under 33 CFR §164.41?

The receiver must (1) automatically acquire satellite signals after initial operator settings have been entered, and (2) provide position updates derived from satellite information during each usable satellite pass. 33 CFR §164.41

Q2 — Can buoys alone be used to fix a vessel's position?

No. Buoys alone cannot be used to fix a vessel's position. If no other aids are available, buoys alone may be used only to establish an estimated position. 33 CFR §164.11

Q3 — What sources must be used when fixing a vessel's position underway?

Electronic and other navigational equipment, external fixed aids to navigation, geographic reference points, and hydrographic contours must all be used when fixing position. 33 CFR §164.11

Q4 — Which navigation method is the backup of last resort when all electronic systems fail?

Celestial navigation, which determines position from observations of celestial bodies. Bowditch Ch. 15 §1501

Q5 — What is dead reckoning, and what is its primary limitation?

Dead reckoning is the determination of position by applying course steered and distance run from a known starting point. Its primary limitation is that accuracy degrades over time; DR positions must be confirmed by external fixes whenever possible. Bowditch Ch. 1 §102

Q6 — Under 46 CFR §184.410, what is required of a vessel on an oceans route regarding position fixing?

A vessel on an oceans route must be equipped with an electronic position fixing device capable of providing accurate fixes for the area in which the vessel operates, to the satisfaction of the cognizant OCMI. 46 CFR §184.410

Q7 — What must the person directing movement of the vessel know regarding compass errors?

Magnetic variation, deviation, and gyrocompass errors must be known and correctly applied by the person directing movement of the vessel. 33 CFR §164.11

Q8 — Which navigation method is primary in confined waters where dead reckoning is insufficient?

Piloting — navigation by reference to landmarks, aids to navigation, and soundings — is the primary method in confined waters where dead reckoning alone is insufficient and electronic positioning may be obstructed by terrain or interference. Bowditch Ch. 1 §103