Radar Principles and Terminology
The USCG exam tests fundamental radar physics. Understanding how a radar works — and why each parameter matters — makes it far easier to reason through exam questions rather than memorizing answers in isolation.
Pulse Length (PL)
Pulse length is the duration of each transmitted microwave burst, measured in microseconds. It directly controls two critical performance factors: range resolution and minimum detectable range. A shorter pulse gives better range resolution (ability to separate two close targets in range) and a shorter minimum range, but transmits less average power. A longer pulse transmits more power for greater maximum range but sacrifices resolution. Modern radars automatically select short pulse on close range scales and long pulse on longer scales.
Exam tip: shorter pulse length improves range resolution and minimum range.
Pulse Repetition Frequency (PRF)
PRF is the number of pulses transmitted per second. Higher PRF means more pulses per second, which improves close-range sensitivity and produces a brighter, more stable image. However, higher PRF limits maximum unambiguous range because a second pulse is transmitted before the echo from a distant target returns, causing range ambiguity — the radar cannot tell which pulse produced the echo. Lower PRF allows longer maximum range. PRF is expressed in pulses per second (pps) or kilohertz (kHz).
Exam tip: high PRF limits maximum range; low PRF allows longer maximum range detection.
Horizontal Beam Width
Horizontal beam width is the angular width of the transmitted radar beam in the azimuth plane, measured in degrees. It directly determines bearing discrimination — the ability to resolve two targets close together in bearing. A narrow horizontal beam gives better bearing resolution. Typical marine X-band antennas have horizontal beam widths of 0.8 to 2 degrees. Wide beam width causes bearing smear: a compact target appears as an arc on the display. Two targets separated by less than the beam width in bearing will merge into a single echo.
Exam tip: narrow beam width provides better bearing discrimination.
Vertical Beam Width
Vertical beam width controls how the radar handles ship movement in a seaway. A wider vertical beam keeps the target illuminated even as the vessel rolls and pitches. Too narrow a vertical beam causes targets to disappear during heavy rolling. Vertical beam width also determines the extent of sea return near the vessel — energy striking nearby wave surfaces at low elevation angles is returned as sea clutter. Typical vertical beam widths are 20 to 30 degrees.
Exam tip: wider vertical beam reduces target loss during rolling.
Radar Horizon
Radar waves follow the earth's curvature slightly more than light, so the radar horizon extends beyond the optical horizon. The formula: D (nm) equals 1.22 multiplied by the square root of antenna height (h) in feet. Maximum detection range equals the radar horizon from own antenna plus the radar horizon from the target's height. A 64-foot antenna has a radar horizon of 1.22 times 8, or 9.76 nautical miles. A cliff 100 feet high has a radar horizon of 12.2 nm, so the cliff can be detected at up to 22 nm.
Exam tip: maximum range to target equals own horizon plus target horizon distance.
Optical Horizon vs Radar Horizon
The optical horizon distance formula is D (nm) equals 1.15 times the square root of height in feet. The radar horizon coefficient is 1.22 rather than 1.15 because radar waves refract more strongly around the earth's surface than visible light. The difference is approximately 6 percent. On exam questions about radar detection range, always use 1.22 for radar calculations. Do not confuse with dipping distance calculations for lights, which use the 1.15 coefficient.
Exam tip: radar uses 1.22 coefficient; lights and optical horizon use 1.15.
S-band vs X-band Radar Specifications
Most exam questions about radar bands focus on the tradeoffs between frequency, wavelength, resolution, and weather penetration. Know the numbers and what each characteristic means operationally.
| Characteristic | X-band | S-band | Operational Impact |
|---|---|---|---|
| Frequency | 9 to 9.5 GHz | 2.9 to 3.1 GHz | Higher frequency = shorter wavelength |
| Wavelength | approx 3 cm | approx 10 cm | Shorter wavelength = better resolution |
| Navigation use | Primary navigation | Supplemental / large ships | X-band is standard for small to medium vessels |
| Resolution | High — sharper targets | Lower — larger target echoes | X-band distinguishes closely-spaced targets better |
| Rain penetration | More affected by rain | Better rain penetration | S-band preferred in heavy precipitation zones |
| Sea clutter | More sea clutter | Less sea clutter | X-band needs more STC adjustment in rough water |
| Antenna size | Smaller antenna practical | Larger antenna needed | X-band suits smaller vessels with limited space |
| Detection range | Good to excellent | Excellent — longer range | S-band suited for ocean watchkeeping |
| Blind zone | Shorter — better close targets | Longer minimum range | X-band better for narrow channels and anchorages |
Range and Bearing Measurement
Variable Range Marker (VRM)
The VRM is an adjustable range ring displayed on the radar screen. The navigator expands or contracts it until it touches the near edge of a target echo. The digital readout displays the range to that target. Range measurement by VRM is the most accurate measurement available on radar — significantly more accurate than bearing. Accuracy is typically within 1 percent of the selected range scale, or 30 meters, whichever is greater.
Electronic Bearing Line (EBL)
The EBL is a rotatable line extending from the center of the display (own ship) to the edge. Rotating it to bisect a target echo gives the bearing. In relative motion mode, the EBL gives the relative bearing from own ship to the target. In true motion mode or with heading-up stabilization, the EBL can be set to give true bearings. Bearing accuracy is limited by horizontal beam width — typical radar bearing accuracy is plus or minus 1 to 2 degrees.
Range Discrimination vs Bearing Discrimination
Range Discrimination
The minimum range separation between two targets on the same bearing that can be resolved as distinct echoes. Governed by pulse length: two targets separated by less than half the pulse length will merge into one echo. Improved by using short pulse length. Example: a 0.05 microsecond pulse gives range discrimination of about 7.5 meters (0.05 times 150).
Bearing Discrimination
The minimum angular separation between two targets at the same range that can be resolved as distinct echoes. Governed by horizontal beam width. Two targets within one beam width in bearing will merge. A 1-degree beam at 6 nautical miles means targets must be separated by at least 0.1 nautical mile (about 200 meters) to be resolved. Improved by narrower beam antennas (longer antennas).
Minimum and Maximum Detection Range
Minimum Range Factors
- 01Pulse length (primary factor): During transmission the receiver is blanked. Any echo arriving during this blanking period cannot be detected. Minimum range equals pulse length in microseconds times 150 meters.
- 02T-R switch recovery: The transmit-receive switch that protects the receiver during transmission requires a finite recovery time after the pulse ends before the receiver can operate.
- 03Vertical beam width and sea return: Wide vertical beam directs energy at close wave surfaces, creating sea clutter that masks nearby targets even when the receiver is active.
- 04Display ring: The blind zone at the center of the display obscures very close targets regardless of receiver capability.
Maximum Range Factors
- 01Radar horizon (primary factor): The earth's curvature limits range regardless of power. Maximum range equals own horizon plus target horizon: 1.22 times (sqrt antenna height plus sqrt target height) in nautical miles.
- 02Peak power output: Higher peak power extends range. Long pulse transmits more average power than short pulse at the same peak power.
- 03Target radar cross section: Large, metal, and vertical surfaces return more energy. A ship is detected at greater range than a small wooden boat of similar physical size.
- 04Atmospheric conditions: Standard atmosphere refracts radar waves slightly downward, extending range. Super refraction (ducting) can dramatically extend range. Sub-refraction reduces range below geometric horizon.
Blind Sectors, Shadow Sectors, and False Echoes
Blind Sectors
Areas where own vessel's structure completely blocks the radar beam. No targets are detectable in these arcs regardless of their size or proximity. Always documented in the radar installation records. Common causes: mast, funnel, king posts, deck cargo.
Shadow Sectors
Areas where the radar beam is partially obstructed, causing reduced sensitivity rather than complete blockage. Weak or distant targets may be invisible while large close targets are still detected. Shadow sectors extend beyond a blind sector on either side.
Coast Shadowing
A promontory, island, or high coastline can shadow targets behind it from external radars. A vessel passing close behind a headland may be invisible to other ships' radars while appearing clearly on its own radar. Also called terrain masking.
False Echoes: The Three Types Tested on the Exam
Multiple Echoes
The radar pulse bounces between own vessel and a strong nearby target (large ship, cliff, or bridge) and returns multiple times. Each return appears as a separate echo on the same bearing as the real target, at multiples of the true range (at the true range, twice the range, three times, and so on). They are equidistant from each other and from the true echo.
Identification:
Multiple echoes appear on the same bearing, equally spaced beyond the true target. The closest echo is the real one.
They disappear or move when own ship alters course slightly, breaking the reflection geometry.
Side-Lobe Echoes
The radar antenna radiates most of its energy in the main beam, but a small amount leaks into side lobes at angles away from the main beam. A very strong target illuminated by a side lobe returns a detectable echo. These appear as arc-shaped smears at the same range as the real target but spread over a range of bearings.
Identification:
Arc or curved streaks at the correct range of a strong nearby target but on different bearings. Most common with large close targets such as oil tankers.
Reduce gain slightly. The main lobe echo is brighter and crisper; side-lobe echoes fade first.
Indirect (Ghost) Echoes
The radar pulse reflects off own vessel's superstructure before reaching a target, or off a large structure ashore before reaching a target. The reflected energy illuminates a target that the main beam cannot see directly, and the echo returns via the same indirect path. The displayed range corresponds to the longer indirect path, placing the echo in the wrong position.
Identification:
Echoes of a nearby target appearing at wrong bearings, sometimes moving erratically. Seen near large reflecting structures.
These change position when own ship maneuvers, distinguishing them from real targets.
Radar Plotting: Relative Motion and True Motion
Relative Motion Display
In relative motion mode (the default on most vessel radars), own ship is fixed at the center of the display. All other objects appear to move relative to own ship. A stationary buoy moves astern at own ship's speed and on a bearing reciprocal to own course. This makes stationary and moving targets look similar at first glance — a plotting interval is required to distinguish them.
Most USCG exam radar plotting questions use relative motion because manual maneuvering board plots (the OAW triangle) assume a relative motion display. The line of relative motion (LRM) is the path traced by a target on the relative motion display over time.
True Motion Display
In true motion mode, own ship moves across the display according to its actual course and speed (input from the ship's gyrocompass and speed log). Stationary objects (buoys, land, anchored vessels) remain fixed on the display while moving vessels trace their actual tracks. This makes it immediately obvious which echoes are stationary and which are underway.
Drawbacks: own ship must be periodically reset before reaching the edge of the display. Speed and course input errors cause incorrect display of own motion. Gyrocompass and speed log accuracy are critical. True motion is favored for collision avoidance watchkeeping on larger vessels.
The OAW Triangle (Manual Radar Plotting)
The OAW triangle is the graphical method for determining a target's true course and speed from observations on a relative motion display. It forms the basis of all manual radar plotting and USCG exam radar plot questions.
Drawn from the origin for the plotting interval, in own ship's true course direction, with length proportional to own ship's speed. Represents what own ship did during the interval.
The line from the first plot position to the second plot position of the target on the relative motion display, measured over the plotting interval. This is what was directly observed on the radar.
The target's true course and speed vector, obtained by closing the triangle: drawn from the tip of O to the tip of A. Its direction is the target's true course; its length (to scale) gives true speed.
Plotting Procedure Step by Step
- 1.Observe and record the target's bearing and range at time T1. Plot this position on maneuvering board paper relative to own ship at the center.
- 2.Observe and record the target at time T2 (typically 6 minutes later for easy speed calculations). Plot this second position.
- 3.Draw the relative motion line (RM) from T1 to T2 and extend it forward. Where this extended line passes closest to the center of the plot is the CPA position. The distance from center to that position is the CPA distance.
- 4.To find TCPA: measure the distance from T2 to the CPA position on the RM line. Divide by the relative speed (RM line length per interval) to get time remaining.
- 5.Construct the OAW triangle: from T1 draw own ship's vector O. Connect to close the triangle with W — this is the target's true motion vector giving true course and speed.
CPA and TCPA Calculation
Closest Point of Approach (CPA)
CPA is the minimum distance between own vessel and a target vessel if both maintain their current courses and speeds. On a relative motion display, CPA is found by extending the line of relative motion (LRM) forward and measuring the perpendicular distance from own ship (center of display) to that extended line.
If the LRM extended passes through the center of the display, CPA is zero — a collision course. If the LRM extended passes ahead of center, the target will cross ahead. If it passes astern, the target will cross astern.
Key Rule
If bearing does not change and range decreases, CPA is zero — risk of collision exists. (COLREGS Rule 7)
Time to Closest Point of Approach (TCPA)
TCPA is the time remaining until CPA is reached. On a maneuvering board plot, TCPA equals the distance from the current target position to the CPA position on the LRM, divided by the relative speed.
Relative speed is the rate at which the target moves along the LRM. It can be calculated from the length of the relative motion vector per unit time during the plotting interval.
ARPA Display
ARPA computes CPA and TCPA automatically and displays numeric values for each tracked target. Alarm thresholds can be set for minimum CPA and maximum TCPA.
ARPA Basics and MARPA vs ARPA
ARPA automates the radar plotting triangle electronically. Understanding what ARPA does, its limitations, and the MARPA distinction is essential for the USCG exam.
ARPA (Automatic Radar Plotting Aid)
- +Automatically acquires targets within a defined guard zone or on operator command
- +Tracks up to 20 or more targets simultaneously (varies by system)
- +Continuously computes and displays CPA, TCPA, true course, and true speed for each target
- +Provides trial maneuver function — allows navigator to simulate a course or speed change and see the predicted effect on all CPAs before committing
- +Alarms for CPA and TCPA thresholds, lost targets, and target acquisition
- +Required by SOLAS on vessels over 10,000 GT and on passenger ships over 500 GT
MARPA (Mini Automatic Radar Plotting Aid)
- +Requires manual target acquisition — operator marks each target individually
- +Tracks fewer targets than ARPA (typically 5 to 10)
- +Computes CPA, TCPA, true course, and true speed once sufficient tracking history exists (usually 2 to 3 minutes)
- +Requires accurate heading sensor (fluxgate or gyrocompass) and speed input
- +Found on chart plotters and smaller vessel radars — not a SOLAS requirement
- +Less accurate than full ARPA due to shorter antenna dimensions and less processing power
ARPA Limitations — Critically Important for Exam
- !ARPA requires a settling period (typically 1 to 3 minutes) after acquiring a target before CPA and TCPA data are reliable
- !Target swap — ARPA can inadvertently switch tracking from one target to an adjacent one in congested traffic, causing grossly incorrect data
- !ARPA does not relieve the officer of the watch of responsibility — it is a decision aid, not a decision maker
- !Vector mode selection (true vs relative) must be understood — a true vector shows the target's actual course and speed; a relative vector shows motion relative to own ship
COLREGS Rules 7 and 8: Radar and Collision Avoidance
Risk of Collision
Every vessel shall use all available means appropriate to the prevailing circumstances and conditions to determine if a risk of collision exists. If there is any doubt, risk shall be deemed to exist.
Specifically, radar equipment if fitted and operational shall be used including long-range scanning to obtain early warning of risk of collision and radar plotting or equivalent systematic observation of detected objects.
Risk of collision shall be deemed to exist if the compass bearing of an approaching vessel does not appreciably change. Even an appreciable bearing change does not necessarily mean no risk, especially when approaching a very large vessel or a tow, or when approaching at close range.
Key exam point:
Assumptions based solely on scanty information (including scanty radar information) are expressly prohibited by Rule 7.
Action to Avoid Collision
Any action to avoid collision shall be taken in ample time and shall be large enough to be readily apparent to the other vessel, either visually or by radar. A succession of small alterations of course and speed shall be avoided.
If there is sufficient sea room, alteration of course alone may be the most effective action to avoid a close-quarters situation. Action shall not result in another close-quarters situation.
Speed shall be reduced or the vessel stopped if necessary to allow adequate time for the situation to be assessed. In restricted visibility under Rule 19, forward of the beam risk of collision requires: do not alter course to port (for a vessel forward of the beam — not for a vessel being overtaken on the port side).
Key exam point:
Action must be bold and readily apparent — not a series of small incremental changes. Use VRM and EBL to confirm the action is working.
Restricted Visibility — Rule 19 Radar Requirements
- →Every vessel shall proceed at a safe speed adapted to the prevailing conditions, with engines ready for immediate maneuver
- →Any vessel detecting by radar alone another vessel shall determine if a close-quarters situation is developing
- →If developing, ample time action is required to avoid a close-quarters situation
- →Alterations of course to port for a vessel forward of the beam are specifically to be avoided (except when overtaking)
- →Alteration of course toward a vessel abeam or abaft the beam shall be avoided
- →Stop or reduce to minimum steerage way if necessary until the danger has passed
Parallel Indexing Technique
Parallel indexing is one of the most powerful and exam-tested radar piloting techniques. It allows the navigator to maintain a precise track through a channel or past a hazard using the radar display alone — no continuous plot calculations required.
Setup Procedure
- 1.On the chart, identify a radar-conspicuous reference object that will be visible on the radar as the vessel passes — a prominent headland, charted rock, entrance buoy, or lighthouse base. The object must be clearly identifiable on the radar display and must not be confused with other targets.
- 2.Determine the desired track and the intended closest point of approach to the reference object. Measure the perpendicular distance from the intended track to the reference object on the chart.
- 3.On the radar display, set the EBL or use the parallel index line feature to draw a line parallel to the intended track at the measured offset distance from the reference object. This is the index line.
- 4.Monitor the reference echo as the vessel proceeds. If the echo remains on the index line, the vessel is on the intended track. If the echo moves toward own ship's side of the line, the vessel is being set toward the hazard — alter course away. If the echo moves away from the index line, the vessel is being set away — alter toward.
When Parallel Indexing Excels
- +Restricted visibility — fog, rain, heavy precipitation
- +Confined channels with strong cross-current set
- +Night passages past rocky headlands with few lights
- +High-traffic areas where visual attention is limited
Limitations
- !Reference object must be radar conspicuous and clearly identified
- !Requires stabilized display (course-up or north-up with gyro input)
- !Not reliable with a compass-stabilized display that drifts
- !Does not account for leeway on sailing vessels
Sea Clutter, Rain Clutter, and Radar Controls
Gain
Controls the overall sensitivity of the radar receiver. High gain detects weak, distant targets but also amplifies background noise, creating a speckled appearance. Low gain misses weak targets. Correct setting: just enough gain that the display shows a light speckle of noise across the screen — this confirms sensitivity is maximized without excess noise. Reducing gain to clean up the display risks losing genuine targets.
Too low = missed targets. Too high = noise-filled display masking targets.
Sea Clutter (STC)
Sea clutter (Sensitivity Time Control) suppresses strong echoes from nearby wave surfaces that would otherwise mask close-range targets. STC is applied only at close range and automatically reduces sensitivity near the origin, then restores it at greater ranges. In rough weather, sea clutter can mask targets within a mile or two. Setting STC too high on a calm day degrades sensitivity for no benefit and may hide small targets.
Use STC when nearby wave returns are masking close targets in rough sea.
Rain Clutter (FTC)
Rain clutter (Fast Time Constant) circuit differentiates the received signal, emphasizing sharp-edged returns from solid targets while suppressing the gradual, diffuse returns from precipitation. Rain produces distributed clutter that can fill large areas of the display, hiding targets within it. FTC reduces this clutter. However, FTC can also reduce the amplitude of target returns — do not set FTC so high that genuine targets disappear.
Use FTC when precipitation is masking targets. Do not use routinely on clear days.
| Symptom on Display | Most Likely Control | Action |
|---|---|---|
| Close targets masked by wave returns | Sea Clutter (STC) | Increase STC slightly until clutter reduces; avoid over-suppression |
| Targets in rain or precipitation invisible | Rain Clutter (FTC) | Apply FTC to differentiate solid targets from diffuse precipitation |
| Display uniformly bright — washed out | Gain or Brilliance | Reduce gain until light speckle noise is just visible |
| Display too dim — missing weak targets | Gain | Increase gain until background noise is just visible |
| Image blurred or indistinct — poor resolution | Tuning | Adjust tuning control until image is sharpest |
| All targets weak despite correct gain | Tuning | Retune — receiver frequency has drifted from transmitter |
Radar and ARPA Exam Tips
Horizon Formula: 1.22 not 1.15
The radar horizon uses 1.22 times the square root of height in feet. The optical horizon and light dipping distance use 1.15. Confusing these two constants is the most common wrong-answer trap on radar range questions.
Short Pulse Improves Range Resolution
Shorter pulse length provides better range resolution and shorter minimum range, at the cost of less average transmitted power and shorter maximum detection range. Radars automatically switch to short pulse on close range scales.
Bearing Is Less Accurate Than Range
Always use ranges from two or more objects for the most accurate radar fix. A single range-and-bearing fix from one object is less accurate because bearing accuracy is limited by beam width (typically 1 to 2 degrees), while range accuracy is typically within 1 percent of range scale.
ARPA Needs Settling Time
ARPA data is unreliable immediately after target acquisition. Allow at least 1 to 3 minutes (check manufacturer specification) before trusting CPA and TCPA readouts. Acting on unverified ARPA data immediately after acquisition is an unsafe practice.
CPA Zero Means Collision Course
When the extended line of relative motion passes through the center of the display, CPA equals zero — a collision course if no action is taken. This is the fundamental collision avoidance indicator on radar.
Rule 19: No Port Alteration for Forward Target
In restricted visibility, if a vessel detected by radar alone is forward of own beam and risk of collision exists, Rule 19 prohibits altering course to port (except when overtaking). This is one of the most-tested restricted visibility rules on the USCG exam.
Identify False Echoes by Maneuvering
All three types of false echoes (multiple, side-lobe, and indirect) will change position or disappear when own vessel alters course. Real targets maintain their actual positions relative to the chart. Maneuver to confirm whether a suspicious echo is real.
X-band for Navigation; S-band for Rain
The exam distinguishes X-band (9 GHz, 3 cm wavelength, higher resolution, standard for navigation) from S-band (3 GHz, 10 cm wavelength, better rain penetration, longer range detection). Know which band is preferred for each application.
Parallel Indexing Requires Stabilized Display
Parallel indexing only works correctly on a stabilized display (north-up or course-up with heading input). A head-up display rotates as the vessel turns, rendering the index line useless. Most exam questions about parallel indexing assume a stabilized display.
ARPA Does Not Replace the Watch
ARPA is a navigational aid. The COLREGS explicitly require radar plotting or equivalent systematic observation — ARPA satisfies this requirement, but the officer of the watch remains responsible for all collision avoidance decisions. ARPA alarms must be acknowledged and acted upon promptly.
Frequently Asked Exam Questions
What is the formula for minimum radar range?Show answer
Minimum range in meters equals pulse length in microseconds multiplied by 150. For example, a 0.1 microsecond pulse gives a minimum range of 15 meters. The formula comes from the fact that the radar is blanked during transmission — any echo returning during the pulse cannot be received. The pulse length controls how long that blanking period lasts, and at the speed of light, each microsecond corresponds to 150 meters of two-way travel.
What does a steady bearing and decreasing range indicate?Show answer
A steady compass bearing with decreasing range indicates a risk of collision under COLREGS Rule 7. This is the fundamental collision avoidance indicator. If the bearing does not change and the range is decreasing, both vessels are on converging courses and will reach the same point simultaneously if no action is taken. Even if the bearing changes slowly, Rule 7 warns that risk may still exist, especially with large vessels or tows.
What is the difference between relative and true ARPA vectors?Show answer
A relative vector on an ARPA display shows where the target will be relative to own ship after a set time interval. It indicates the target's motion relative to own ship — useful for immediately seeing which targets are converging. A true vector shows the target's actual predicted position after the time interval based on its true course and speed, just as it would appear on the chart. True vectors make it easy to see if a target is really a vessel underway or a stationary object, and to assess the actual navigational situation.
How does sea state affect radar performance?Show answer
In rough seas, wave faces facing the radar reflect energy back, creating sea return or sea clutter — a bloom of returns near the origin that masks close targets. Sea clutter intensity increases with wave height and decreases with distance from own ship. STC (sea clutter control) is used to suppress this. Additionally, vessel rolling in a seaway causes the radar beam to sweep above and below the horizon, causing target fading. A wider vertical beam reduces this fading but increases sea return.
What is a guard zone on an ARPA radar?Show answer
A guard zone is a user-defined area on the radar display, typically an annular ring or sector, within which the ARPA system will automatically acquire any new target that enters and sound an alarm. Guard zones allow the watch officer to be alerted to approaching traffic without continuously monitoring the display. Targets entering the guard zone are acquired and begin the tracking and CPA/TCPA calculation process immediately.
When is a vessel required to have ARPA?Show answer
Under SOLAS, ARPA is required on vessels of 10,000 GT and above, and on passenger ships of 500 GT and above. Vessels between 300 GT and 10,000 GT must have automatic tracking capability (ARPA or equivalent). Smaller vessels are not required to have ARPA by SOLAS, though MARPA-equipped plotters are widely used. For USCG exam purposes, know that ARPA requirements depend on vessel gross tonnage.
Continue Your Captain's License Prep
Radar and ARPA navigation connects closely with rules of the road, GPS and electronic navigation, and chart plotting. Work through all three to complete your exam readiness.
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Radar fixes, OAW triangle plotting, blind piloting, and controlling the radar — the foundational companion to this ARPA page.
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Practice with real USCG-style radar questions. NailTheTest practice exams include CPA/TCPA calculations, radar controls, band comparisons, false echo identification, and COLREGS restricted visibility scenarios.
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