Chart Plotting Practice Questions

1. On a Mercator chart, one nautical mile is measured using the:

• A.Latitude scale at the side of the chart, at the boat's approximate latitude✓
• B.Longitude scale at the top or bottom of the chart
• C.Bar scale only, regardless of latitude
• D.Distance between meridians at the equator

Why: One minute of latitude equals one nautical mile, so distance is read from the latitude scale on the sides. Because the Mercator latitude scale expands toward the poles, always measure at the mid-latitude of the leg, never on the longitude scale.

2. The 'bow and beam' bearing technique gives you, at the moment the object is abeam:

• A.Your speed over the ground
• B.Your compass deviation
• C.The set of the current
• D.The distance run between the bearings, which equals the distance off when abeam✓

Why: Taking a bearing 45° on the bow and again at 90° (abeam), the distance run between the two bearings equals the distance off the object when it is abeam. It is a special case of doubling the angle on the bow.

3. Which of the following factors most significantly affects the amount of leeway a vessel experiences?

• A.The depth of water under the keel
• B.Wind speed, vessel's freeboard, and the angle of the wind relative to the vessel✓
• C.The vessel's speed through the water only
• D.Tidal current direction

Why: Leeway is primarily determined by wind speed, the vessel's freeboard (amount of hull above water presenting wind resistance), and the relative angle of the wind. Higher freeboard and beam winds produce the greatest leeway.

4. A vessel steers 090°T at 8 knots STW into a head current setting 270°T at 3 knots. What is the SMG?

• A.11 knots
• B.8 knots
• C.5 knots✓
• D.3 knots

Why: A head current (set 270°T, opposing eastward heading 090°T) directly subtracts from the vessel's STW. SMG = 8 − 3 = 5 knots. The CMG remains 090°T since there is no lateral deflection.

5. When a navigator plots a fix from simultaneous cross bearings, the fix is marked on the chart with which symbol and label?

• A.A circle with a dot at its center and the time of the fix written alongside✓
• B.A small triangle with the word 'FIX' written inside
• C.A half-circle with the time written alongside
• D.An X with the letters 'EP' and the time written alongside

Why: Per Bowditch (American Practical Navigator) and NGA Chart No. 1 plotting conventions, a fix obtained from simultaneous observations such as cross bearings is plotted as a dot enclosed in a circle with the time written alongside. A semicircle (half-circle) around a dot marks a DR position, a square around a dot marks an estimated position (EP), and a running fix is a circle around a dot labeled 'R Fix' with the time.