Captain's License / Chart Plotting Techniques
Chart Plotting Techniques for the USCG Captain's License Exam
Chart plotting is one of the most heavily tested subjects on the USCG OUPV (6-pack) and Master license exams. This guide covers everything from reading a nautical chart's title block to plotting a three-bearing fix, correcting for current, applying TVMDC, and identifying every symbol the exam tests. Master these techniques and you will eliminate one of the top failure categories on the exam.
What the Exam Expects
The USCG chart plotting section uses NOAA Training Chart 1210TR. You work with physical tools on a paper chart. The exam tests TVMDC conversions, dead reckoning plots, fixes by cross bearings, running fixes, current and leeway corrections, danger bearings, chart symbol identification, and speed-time-distance calculations. Bring your own parallel rules, dividers, and pencils. Practice on the actual 1210TR chart before exam day.
1. Nautical Chart Components
Every NOAA nautical chart is a standardized document. Understanding its parts is the first step to using it quickly and correctly under exam pressure.
Title Block
The title block is located in the most open ocean area on the chart. It contains the chart's name, number, scale, edition date, the unit of measurement for soundings (feet, fathoms, or meters), and the horizontal datum (usually NAD83 or WGS84). Always read the title block before using a chart. The exam may ask which unit soundings are in or what the chart datum is.
Scale
Scale is expressed as a ratio such as 1:80,000, meaning one inch on the chart equals 80,000 inches on the water. Large-scale charts (1:10,000 or 1:20,000) show more detail and less area. Small-scale charts (1:500,000) show large areas with less detail. Harbor charts are large scale. Sailing charts are small scale. Distance is measured using the latitude scale on the side margins of the chart: one minute of latitude equals one nautical mile.
Soundings and Datum
Soundings are the numbers printed throughout the water areas of the chart. Each number represents the depth at that location referenced to the chart datum. On US charts the datum is Mean Lower Low Water (MLLW), the average of the lower low water of each tidal day over a 19-year National Tidal Datum Epoch. Charted depth is essentially the minimum expected depth under average conditions. To find actual depth at any moment, add the height of tide (from tide tables) to the charted depth.
Depth Contour Lines
Depth contours are lines connecting points of equal depth, similar to elevation contour lines on a topographic map. Common contours are 6, 12, 18, 30, and 60 feet. The area inside the 6-foot contour is often tinted blue or shown with a screened pattern to warn of shoal water. Closely spaced contours indicate a steep drop-off. Widely spaced contours indicate a gentle slope. Navigators use contours to plan safe routes and avoid grounding.
Compass Rose
The compass rose is printed one or more times on each chart. It consists of two concentric rings. The outer ring is aligned with true north and shows true bearings 000 to 359 degrees. The inner ring is offset clockwise or counterclockwise from true north by the magnetic variation for that area. The variation value and annual rate of change are printed in the center of the rose. Parallel rules are used to transfer bearings between the chart and the compass rose.
2. Chart Types and the Numbering System
NOAA classifies charts by scale and purpose. Understanding the system helps you pick the right chart for any situation and answer exam questions about chart selection.
| Chart Type | Scale Range | Best Used For |
|---|---|---|
| Harbor | 1:50,000 or larger | Entering ports, harbors, anchorages |
| Coastal | 1:50,000 to 1:150,000 | Coastwise navigation, inshore passages |
| General | 1:150,000 to 1:600,000 | Offshore passages, approach planning |
| Sailing | Smaller than 1:600,000 | Ocean passages, route overview |
| 1210TR (Training) | 1:80,000 | USCG exam — Block Island Sound area |
The Chart Numbering System
NOAA chart numbers indicate geographic region and scale. The number of digits and the first digits encode where the chart is located. Within the US, charts are organized by coast (Atlantic, Gulf, Pacific) and region. The 1210TR training chart is derived from Chart 13205, which covers Block Island Sound and Approaches in Rhode Island. This is the standard exam chart and you will use it for every chart-related question on the USCG exam.
Exam Note
The title block of 1210TR lists soundings in feet. Always confirm the unit before solving any depth problem. Mixing feet and fathoms is a common and fatal error.
3. The Compass Rose: True, Variation, Magnetic
Understanding the compass rose and the relationship between true north and magnetic north is fundamental to every bearing and course problem on the exam.
True North
True north points toward the geographic North Pole. The outer ring of the compass rose and all meridians (vertical lines) on the chart are aligned with true north. When plotting a course or bearing on the chart using the outer ring, you are working with true directions. Charts are drawn with true north at the top.
Magnetic North and Variation
Magnetic north is where a freely suspended compass needle points. It is not the same as true north and the difference, called magnetic variation (or declination), changes by location and slowly over time. On the US East Coast, variation is currently about 13 to 15 degrees westerly in southern New England, meaning magnetic north is 13 to 15 degrees west of true north. On the West Coast, variation is easterly. The compass rose prints the current variation and annual change rate (for example: Var 14 degrees 30 minutes W, Annual Decrease 3 minutes).
Reading the Inner and Outer Rings
The outer ring gives true bearings. The inner ring gives magnetic bearings already adjusted for variation. If you measure a course on the chart and read it from the outer ring, you have a true course. If you read it from the inner ring, you have a magnetic course. The difference between them is the variation. Always note which ring you are reading when setting up a TVMDC problem.
4. TVMDC: The Correction Formula
TVMDC is the most tested topic in chart plotting. The formula converts between true bearings (used on charts) and compass bearings (read from the ship's compass). Getting this wrong cascades errors through every subsequent calculation.
The Five Terms
Correcting (C to T)
Start at Compass, work left toward True.
C + D(E) = M + V(E) = T
Add easterly errors. Subtract westerly errors. Mnemonic: CAE — Correcting, Add East.
Uncorrecting (T to C)
Start at True, work right toward Compass.
T - V(E) = M - D(E) = C
Subtract easterly errors. Add westerly errors. Mnemonic: UWAS — Uncorrecting, West Add, Subtract East.
Worked Example
You plot a course on the chart and measure a true course of 085 degrees T. The chart shows variation of 14 degrees W. The deviation card for the heading 085 degrees M shows deviation 3 degrees E. What compass course do you steer?
Steer 096 degrees by compass to make good a true course of 085 degrees.
Why This Gets People
The most common exam mistake is reversing the direction of correction. Always write out all five values in the TVMDC column before doing arithmetic. Write E or W next to every variation and deviation value. Then apply the rule mechanically. Never try to "feel" which direction to go.
5. Plotting Tools
The USCG exam is a practical skills test. You must be fluent with physical plotting tools. Bring tools you have actually practiced with — this is not the time to try something new.
Parallel Rules
Parallel rules are the traditional tool for transferring bearings. Place one edge through the center of the compass rose and the desired bearing graduation. Then "walk" the rules (alternating which rule you hold fixed) across the chart to your position, keeping them parallel throughout. Draw your course line or bearing line along the edge of the rule. Practice until the walking motion is muscle memory — slipping is a common source of error.
Course Plotter (Weems and Plath Style)
A course plotter is a transparent rectangular tool with degree markings printed on it. Align one of the printed meridian lines with a vertical chart meridian (longitude line), then read the bearing directly from the degree scale at the edge of the course line. Many mariners prefer this tool because it does not require walking across the chart and avoids the slipping problem of parallel rules. Either tool is accepted on the exam.
Dividers
Dividers are used to measure distances on the chart by spanning a measured length between two points and then comparing that span against the latitude scale on the side margin of the chart. One minute of latitude equals exactly one nautical mile. Always use the latitude scale nearest to your plotting area (latitude values vary slightly across a chart). Open the dividers to the distance between two points, then transfer them to the latitude scale to read nautical miles.
Protractor
A protractor can be used to measure or lay off angles directly. When used with a straightedge, it can substitute for parallel rules in some applications. Circular protractors placed over the chart at your position allow direct bearing measurement without needing to transfer from a compass rose. The Douglas protractor is a popular variant used by many USCG exam candidates.
Pencils and Eraser
Use sharp pencils with a fine point for precise lines. A 0.5mm mechanical pencil is ideal. Bring several sharpened pencils because breaks are common. A good eraser is essential for correcting construction lines without damaging the chart. FriXion erasable pens work well on laminated chart reproductions but not on standard paper charts.
6. Dead Reckoning
Dead reckoning (DR) is the process of advancing a known position forward in time using course and speed. It is the backbone of all coastal navigation and drives most of the calculation questions on the exam.
The DR Plot: Step by Step
- 01.Start from a confirmed fix — a position you know is accurate (marked with a circle and time).
- 02.Convert your compass course to true using TVMDC. This gives you the direction to draw on the chart.
- 03.Use parallel rules to align with the compass rose at the true course value. Walk the rules to the fix position and draw the course line.
- 04.Calculate distance traveled using 60 D ST: Distance = Speed x Time (min) divided by 60.
- 05.Use dividers to mark the distance along the course line from the fix. Mark the DR position with a half-circle (semicircle) open toward the course line and write the time alongside.
- 06.Label the course line: above the line write C (space) the true course (for example, C 085T). Below the line write S (space) the speed (for example, S 8.5).
The 60 D ST Formula
This formula is your primary calculation tool. Memorize all three forms:
Time is always in minutes in this formula. Convert hours to minutes by multiplying by 60 before plugging in.
Worked DR Example
At 0800 you get a fix at a known position. You steer a compass course of 155 degrees C. Variation is 14 degrees W. Deviation on this heading is 2 degrees W. Your speed is 10 knots. Where are you at 0930?
7. Fixes by Cross Bearings
A fix is a position determined by two or more lines of position that intersect. Cross bearings are the most common method of obtaining a fix during coastal navigation. The exam will ask you to plot bearings, identify the fix position, and find coordinates.
Two-Bearing Fix
Take simultaneous compass bearings to two charted objects (lighthouses, towers, tanks, points of land). Convert each bearing from compass to true using TVMDC. Using parallel rules, draw each bearing line from the charted object back toward the vessel (reciprocal direction). The intersection of the two lines is the fix. Mark it with a small circle and the time. A two-bearing fix has uncertainty: if either bearing is slightly off, the fix moves.
Three-Bearing Fix and the Cocked Hat
A three-bearing fix is more reliable. Take bearings to three charted objects and plot all three lines of position. In theory they meet at a point. In practice, due to small errors in observation or plotting, they form a small triangle called the cocked hat. The navigator should assume the vessel is at the vertex of the cocked hat closest to the nearest danger. The smaller the cocked hat, the more confidence you can place in the fix. Place the fix symbol in the center of the cocked hat if no dangers are nearby.
Plotting the Bearing Line Correctly
A bearing from the ship to an object is drawn on the chart from the object toward the ship, not from the ship toward the object. This is the line of position (LOP). The vessel is somewhere along that line. When you convert the bearing using TVMDC and draw it through the charted object, you are drawing the LOP correctly. Label each LOP with the time and the object name. Label each bearing line above the line.
Bearing Angle Quality
For the most accurate fix, bearings to the two objects should be as close to 90 degrees apart as possible. Bearings less than 30 degrees apart produce a very elongated and unreliable intersection. Angles between 60 and 120 degrees apart give the best fix quality. On a three-bearing fix, aim for objects spaced about 120 degrees apart.
8. Running Fix and Advancing an LOP
When only one charted object is visible, you cannot get a two-bearing fix simultaneously. The running fix lets you use two bearings to the same object taken at different times.
Running Fix: Step by Step
- 01.Take a bearing to the charted object and record the time (call it Time 1). Plot the first LOP through the object.
- 02.Continue on your course and speed. After sufficient time has passed, take a second bearing to the same object (Time 2). Plot the second LOP through the object.
- 03.Calculate the distance traveled between Time 1 and Time 2 using 60 D ST.
- 04.Advance (transfer) the first LOP by the distance and direction of the course made good between Time 1 and Time 2. Draw a new line parallel to the first LOP, moved in the direction of travel by the calculated distance.
- 05.Where the advanced first LOP intersects the second LOP is the running fix. Mark it with a circle and label it with the time of the second bearing (R Fix 1030).
Accuracy Limitations
A running fix assumes the vessel maintained a constant course and speed between the two observations. Any current, leeway, or course change between the two bearings introduces error. The running fix is useful but less reliable than a simultaneous two-object fix. Label the advanced LOP with the original time and the notation "adv" or the time it was advanced to.
9. Range and Bearing to a Waypoint
Plotting range (distance) and bearing to a waypoint or destination is a fundamental skill used constantly in coastal voyage planning.
Finding the True Bearing to a Waypoint
Draw a straight line from your current position to the waypoint. Use parallel rules or a course plotter to transfer this line to the compass rose. Read the bearing from the outer ring (true). This is the true course to steer (before applying variation and deviation to convert to compass). Label the line with the true course above and speed below.
Measuring the Distance to the Waypoint
Open the dividers between your position and the waypoint. Transfer the dividers to the latitude scale on the side of the chart. Each minute of latitude equals one nautical mile. Count the minutes (and tenths of a minute if needed). This gives you the distance in nautical miles. For long legs, step the dividers in convenient increments (10nm steps) and count laps, then measure the remainder.
Converting to Compass Course for the Helm
Once you have the true course, apply TVMDC in the uncorrecting direction (T to C) to find the compass course to give the helmsman. Always confirm which variation applies by reading the compass rose nearest to your track. If the track crosses regions of significantly different variation, split the leg at the midpoint and apply the local variation for each half.
10. Danger Bearing
A danger bearing is one of the most useful practical navigation techniques and is tested on the exam. It allows a vessel to transit past a hazard safely without constantly re-plotting its position.
How to Establish a Danger Bearing
- 01.Identify a charted hazard (shoal, reef, rock) and a visible charted object (lighthouse, tower) near it.
- 02.On the chart, draw a line from the charted object through the edge of the danger (the closest safe point).
- 03.Measure the true bearing of this line from the charted object. Convert to magnetic or compass as appropriate for your compass.
- 04.As you approach the danger, monitor the compass bearing to the charted object. If the bearing is NLT (not less than) the danger bearing, you are in safe water. If it decreases below the danger bearing, you are standing into danger and must alter course.
NMT and NLT Danger Bearings
The direction of the safe side depends on the geometry. When passing a hazard to the south of a lighthouse, the danger bearing is labeled NLT (not less than) a certain bearing — meaning the bearing to the lighthouse must stay equal to or greater than that value for the vessel to remain in safe water. When the hazard geometry is reversed, the notation is NMT (not more than). The exam will give you a scenario and ask you to identify the safe condition.
11. Current and Leeway Corrections in Course Plotting
Water current and wind-driven leeway both push the vessel off the intended track. Correcting for them is essential for accurate coastal navigation and is tested heavily on the exam.
Set and Drift
Current is described by two values. Set is the direction the current flows toward (not from). Drift is the speed of the current in knots. A current with a set of 090 and a drift of 1.5 knots is flowing due east at 1.5 knots. If your vessel does not correct for it, you will be pushed east of your intended track. The difference between your intended track and your actual track (course made good) reveals the set and drift that acted on you.
The Current Triangle: Planning Ahead
To find the course to steer that compensates for current, use a vector triangle on the chart:
- 01.Draw the intended track line from departure point to destination.
- 02.From the departure point, draw the current vector: direction = set, length = drift (scaled to the same time unit as vessel speed).
- 03.From the tip of the current vector, open dividers to the vessel's speed through water (in the same time units).
- 04.Strike an arc with the dividers. Where it intersects the intended track line is the third point of the triangle.
- 05.The course from the tip of the current vector to the intersection point is the course to steer (before TVMDC). The length of the intended track segment from the departure point to the intersection is the speed made good.
Leeway
Leeway is wind-driven sideways drift. A vessel heading 090 degrees with 5 degrees of leeway to leeward is making good 095 degrees (wind from the north pushing the vessel south). Apply leeway to the course before applying current correction. For powerboats with low freeboard, leeway is typically small and often ignored. For sailboats and high-sided vessels, leeway can be significant and must be included in any accurate course calculation.
Determining Set and Drift After the Fact
Compare your DR position (where you should be) to your actual fix position (where you are). Draw a line from the DR position to the fix. The direction that line points is the set. The length of that line (converted to knots using the elapsed time) is the drift. This technique allows you to determine what current has been acting on you and correct future course calculations accordingly.
12. Chart Symbols: Buoys, Lights, Hazards, and Restricted Areas
NOAA Publication Chart No. 1 is the comprehensive reference for all US chart symbols. The exam will test recognition of the most common symbols. Learn these cold.
Buoys
Red Nun Buoy — cone-shaped, shown as filled red triangle on chart. Keep to starboard returning from sea (Red Right Returning). Even-numbered.
Green Can Buoy — cylindrical, shown as filled green square on chart. Keep to port returning from sea. Odd-numbered.
Preferred Channel (Junction) Buoy — red and green banding. If top band is red, treat as red (keep to starboard in preferred channel). If top band is green, treat as green.
Safe Water Mark — red and white vertical stripes. Marks safe water all around (mid-channel, fairway). Can be approached from any direction.
Isolated Danger Mark — black and red horizontal bands. Marks a hazard with navigable water all around. Pass with caution on all sides.
Special Purpose Buoy — yellow. Marks special areas (anchorage, traffic separation, spoil areas). Not part of the lateral system.
Light Characteristics
Fl — Flashing. Light on for less time than off. Fl(4) means 4 flashes in a group.
Oc — Occulting. Light on for more time than off.
Iso — Isophase. Equal time on and off.
Q — Quick flashing. 60 flashes per minute.
Mo(A) — Morse code flashing. Mo(A) flashes Morse A (dot-dash). Common on safe water marks.
Example: Fl R 4s 15ft 5M — Flashing Red, period 4 seconds, height 15 feet above water, visible 5 nautical miles.
Hazard Symbols
Rock awash at chart datum — asterisk with plus sign inside a circle. Extreme hazard.
Submerged rock — plus sign inside a circle with sounding. Depth may vary with tide.
Wreck dangerous to surface navigation — stylized ship symbol with masts showing above water.
Submerged wreck — dashed outline of wreck symbol with depth sounding.
Obstruction — shown with depth sounding and appropriate symbol. Avoid by wide margin.
Shoaling area — blue tint or fine dot pattern inside depth contour lines.
Restricted Areas and Other Symbols
Prohibited Area — shown with magenta border and labeled. Entry prohibited without permission.
Restricted Area — shown with magenta dashed border. Entry restricted under certain conditions.
Anchorage Area — anchor symbol and labeled boundary. Vessels may anchor here.
Traffic Separation Scheme — arrows showing vessel traffic lanes. Crossing TSS lanes is regulated by COLREGS Rule 10.
Fog signal — horn or diaphone symbol at light or buoy. The type and character of sound signal are noted.
13. Common Exam Question Types
The USCG chart plotting exam is predictable. The same question types appear on every exam. Study these patterns and you will not be surprised by anything you see in the testing room.
TVMDC Conversion Questions
Given a true course and the variation and deviation, find the compass course. Or: given a compass bearing, find the true bearing. These appear on almost every exam. Always write all five TVMDC values in a column. Label E and W carefully. Apply CAE (Correcting Add East) or the reverse methodically. Never try to do this in your head.
Dead Reckoning Position Questions
Starting from a given fix at a given time, plot a dead reckoning position after a specified time at a given speed and course. Find the DR position's latitude and longitude or identify the nearest charted object to the DR position. These require both TVMDC conversion and 60 D ST calculation followed by plotting.
Fix by Two Bearings Questions
Given two compass bearings to two charted objects, plot the fix. Find the latitude and longitude of the fix, or identify what the fix is nearest to, or compute the course and distance to a destination from the fix. These require converting two bearings with TVMDC, plotting two LOPs, and identifying the intersection.
Running Fix Questions
Given two bearings to one object taken at different times, advance the first LOP and find the running fix. These require 60 D ST for distance, correct LOP advancement direction, and accurate parallel line drawing. Practice this technique multiple times before the exam.
Current Problem Questions
Given a DR position and an actual fix, find the set and drift that caused the discrepancy. Or: given set, drift, and vessel speed, find the course to steer to make a desired track. Vector triangle on the chart, reading the result with parallel rules and compass rose.
Speed-Time-Distance Questions
Given any two of speed, time, and distance, find the third using 60 D ST. ETA problems: given departure time, distance, and speed, find estimated time of arrival. Or find what speed is needed to arrive at a waypoint by a given time. These are pure arithmetic and should be the easiest points on the exam.
Chart Symbol Identification
The exam may show you a symbol from the chart and ask what it represents, or describe a feature and ask what symbol marks it. Common tested symbols include the safe water mark, isolated danger mark, various buoy types, rock awash, submerged wreck, and restricted area boundaries. Study Chart No. 1 directly — the authoritative NOAA publication is free as a PDF download.
How to Maximize Your Score
- • Always write TVMDC as a full column. Never skip steps.
- • Label every line you draw on the chart (course lines, LOPs, DR positions).
- • Use dividers for all distance measurements. Never estimate.
- • Double-check arithmetic before committing to a final answer.
- • Work the actual 1210TR chart at home before the exam date.
- • Practice under timed conditions. The exam time limit is real pressure.
14. Frequently Asked Questions
What does TVMDC stand for in nautical navigation?
TVMDC stands for True, Variation, Magnetic, Deviation, Compass. It is the sequence used to convert between true north bearings (used on charts) and compass bearings (read from the ship's compass). To go from Compass to True (correcting), you apply each correction in sequence from right to left, adding easterly values and subtracting westerly values. The mnemonic CAE — Correcting, Add East — helps remember the rule. To go from True to Compass (uncorrecting), reverse the process: subtract easterly values and add westerly values moving from True to Compass.
What is variation on a nautical chart?
Variation is the angular difference between true north (the geographic North Pole) and magnetic north (where compass needles point). It is caused by the Earth's magnetic field, which does not align perfectly with the rotational axis. Variation changes by location and changes slowly over years. On every NOAA chart, the variation value for that area is printed in the center of the compass rose along with an annual rate of change. On the US East Coast, variation is westerly (magnetic north is west of true north). On the West Coast, variation is easterly.
What is deviation and how is it different from variation?
Deviation is the error in a specific compass caused by the vessel's own magnetic fields from engines, electronics, metal structure, and cargo. Unlike variation, which is the same for all vessels in a given area, deviation is unique to each compass on each vessel and changes depending on the heading. Deviation is recorded on a deviation card specific to that compass. Deviation can be easterly or westerly and may be zero on some headings and several degrees on others. The total compass error is the sum of variation and deviation.
How do you plot a dead reckoning position?
Start from your last known position (a fix, marked with a circle). Convert your compass course to true using TVMDC. Draw the course line from the fix in the true direction using parallel rules aligned with the compass rose. Calculate the distance traveled using 60 D ST: Distance equals Speed times Time in minutes, divided by 60. Use dividers to mark that distance along the course line from the fix. Mark the DR position with a half-circle (open toward the course line) and write the time beside it. Label the line: true course above (C 085T) and speed below (S 8.5).
What is a fix in coastal navigation?
A fix is a confirmed position determined by two or more intersecting lines of position (LOPs). A two-object fix uses simultaneous bearings to two charted objects. A three-bearing fix uses three objects and is more reliable. When three LOPs do not meet at a perfect point but form a small triangle called a cocked hat, the navigator assumes the vessel is at the most dangerous vertex (closest to shoal water). A fix is marked on the chart with a small circle and the time.
What is a running fix and when do you use it?
A running fix is used when only one charted object is visible. Take a bearing to the object at Time 1, then continue on course and speed and take a second bearing at Time 2. Calculate the distance run between the two bearings. Advance (slide forward in the direction of travel by the distance traveled) the first LOP to Time 2. Where the advanced LOP intersects the second LOP is the running fix. It is less accurate than a simultaneous two-object fix because it assumes constant course and speed between observations.
What is a danger bearing and how do you use it?
A danger bearing is a compass bearing to a charted object that defines the boundary between safe water and a hazard. Draw a line on the chart from the charted object through the edge of the hazard. Measure the true bearing, convert to compass. As you transit past the area, continuously take bearings to the object. If the bearing remains NLT (not less than) the danger bearing, you are in safe water. If the bearing drops below, you are in danger. The notation NLT or NMT (not more than) depends on the geometry of the hazard relative to your track.
How do you correct for current when plotting a course?
Use a vector triangle on the chart. From the departure point, draw the intended track to the destination. From the departure point, draw the current vector (direction = set, length = drift speed for one hour). From the tip of the current vector, open dividers to the vessel speed through water and strike an arc that intersects the intended track. The line from the tip of the current vector to the intersection point is the course to steer. The length from the departure point to the intersection point (on the track line) is the speed made good. Convert the course to steer from true to compass using TVMDC.
What datum are soundings referenced to on NOAA charts?
Soundings on NOAA charts are referenced to Mean Lower Low Water (MLLW), defined as the average of the lower low water height of each tidal day over a 19-year period called the National Tidal Datum Epoch. MLLW represents approximately the minimum expected water depth. At low tide, actual depth is near the charted depth. At high tide, actual depth equals charted depth plus the height of tide from the tide tables. Land elevations are referenced to Mean High Water (MHW). The title block of each chart confirms the unit of soundings (feet, fathoms, or meters).
What chart is used on the USCG captain's license exam?
The USCG exam uses NOAA Training Chart 1210TR, a reproduction of Chart 13205 covering Block Island Sound and Approaches in Rhode Island. The 1210TR is sold commercially and is not the same as the actual navigational chart, but the exam questions are designed specifically for it. Buy a copy and practice on it before your exam. Learn the compass roses (there are two), the major landmarks, depth contours, and buoyage in the area. Familiarity with the chart alone saves significant time during the exam.
How do you read the compass rose on a NOAA chart?
The compass rose has two concentric rings. The outer ring shows true bearings 000 to 359 degrees, aligned with true north (the chart's meridians). The inner ring shows magnetic bearings, offset from the outer ring by the local magnetic variation. The variation value and annual rate of change are printed inside the rose (for example: Var 14 degrees 15 minutes W, Annual Decrease 3 minutes). To use the rose, place parallel rules from the center of the rose through the desired bearing graduation, then walk the rules to your chart position without changing their angle.
What plotting tools are allowed on the USCG chart plotting exam?
The exam is open book and you may bring your own plotting tools. Standard tools include parallel rules or a rolling plotter, dividers, a protractor or course plotter, pencils, an eraser, and a basic calculator. The Weems and Plath parallel rules are the traditional choice. Many candidates prefer the Weems and Plath course plotter or the Douglas protractor as an alternative. Bring the tools you have practiced with. Do not show up with an unfamiliar tool and try to learn it under pressure.
What is leeway and how does it affect course plotting?
Leeway is the sideways drift of a vessel to leeward caused by wind acting on the hull, deck, and superstructure. It is expressed in degrees. A vessel heading 090 degrees with 5 degrees of leeway to leeward (wind from the north) is actually tracking 095 degrees over the ground, absent current. Leeway is applied to the compass heading to find the course made good. For powerboats with low profiles, leeway is usually negligible. For sailboats and vessels with high freeboard, leeway can exceed 10 degrees and must be included in all course planning calculations.
How are buoys identified on NOAA nautical charts?
Buoys appear on NOAA charts with standardized symbols. Red buoys (nun buoys, cone-shaped) are shown with filled red triangles. Green buoys (can buoys, cylindrical) appear as filled green squares. Lighted buoys have a magenta teardrop or flare symbol added to indicate the light. The chart notes each buoy's number or name, light character (for example, Fl G 4s for flashing green 4 seconds), and sound signal if applicable. Preferred channel buoys show red-green banding. Safe water marks show red and white vertical stripes.
What is the 60 D ST formula and how is it applied?
The 60 D ST formula is: 60 times Distance equals Speed times Time. In practical form: Distance = Speed x Time (minutes) divided by 60. Speed = 60 x Distance divided by Time (minutes). Time = 60 x Distance divided by Speed. Time is always in minutes in this formula. To find how far a vessel traveling at 8 knots goes in 45 minutes: D = 8 x 45 / 60 = 6.0 nautical miles. To find ETA: compute time = 60 x D / S, then add the result in minutes to the departure time.
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Quick Reference: TVMDC Correction Table
| Direction | Easterly Error | Westerly Error | Mnemonic |
|---|---|---|---|
| Correcting (C to T) | Add | Subtract | CAE |
| Uncorrecting (T to C) | Subtract | Add | UWAS |
CAE
Correcting, Add East. Apply when going from Compass toward True.
60 D ST
D = S x T / 60. Time always in minutes. The only formula you need for DR.
1 min lat = 1 nm
Always measure distance on the latitude scale, never the longitude scale.