cross bearings and fix Practice Questions

1. When taking cross bearings to determine a vessel's position, what is the minimum number of objects required to obtain a reliable fix?

• A.Two objects, with bearings taken simultaneously✓
• B.One object, with two bearings taken 30 minutes apart
• C.Three objects, with bearings taken sequentially
• D.Two objects, with bearings taken 6 minutes apart

Why: A cross bearing fix requires simultaneous bearings to at least two charted objects; simultaneous observation eliminates the error introduced by vessel movement between observations. Two LOPs intersecting at a good angle (60°–120°) provide an adequate fix.

2. Two cross bearings are plotted from identifiable objects ashore. The resulting LOPs form a very small angle of intersection (approximately 10°). What is the primary concern with this fix?

• A.Small errors in bearing measurement are greatly magnified, making the fix unreliable✓
• B.The fix is highly accurate because the LOPs reinforce each other
• C.The fix is valid only if both objects are on the same side of the vessel
• D.The fix cannot be plotted if the angle of cut is less than 45°

Why: When two LOPs intersect at a small (acute) angle, small errors in either bearing produce a large shift in the plotted position; a good angle of cut is generally 60° to 120° for reliable cross bearing fixes.

3. When plotting a line of position (LOP) from a visual bearing of a charted object, the LOP is drawn:

• A.From the charted object in the reciprocal (180°) direction of the bearing✓
• B.From the vessel's estimated position toward the object
• C.Parallel to the course line at the object's location
• D.From the object in the same direction as the bearing taken

Why: A visual bearing is measured FROM the vessel TO the object; to plot the LOP, you draw a line FROM the charted object back toward the vessel using the reciprocal bearing, because the vessel lies somewhere along that line.

4. A vessel takes simultaneous bearings on three objects: lighthouse A bears 010°T, tower B bears 090°T, and chimney C bears 170°T. The three plotted LOPs form a cocked hat. Where is the vessel's most probable position?

• A.At the center of the triangle formed by the three LOPs✓
• B.At the intersection of LOPs A and B only, ignoring C
• C.At the corner of the triangle closest to the nearest danger
• D.At a point outside the triangle nearest to the vessel's DR position

Why: When three LOPs form a cocked hat (small triangle), the navigator's best position is the center of that triangle; if any hazard lies within or near the triangle, the corner of the triangle closest to the hazard should be used as the most conservative position.

5. A danger bearing is a type of LOP used to keep a vessel clear of a hazard. A danger bearing is plotted so that the vessel should remain:

• A.On the safe side of the bearing line, as determined by the direction of the hazard✓
• B.Always between the bearing line and the nearest landmark
• C.Exactly on the bearing line to maintain maximum clearance
• D.At least 2 nautical miles from the bearing line at all times

Why: A danger bearing is a line drawn past a hazard from a charted object at the minimum safe angle; by keeping the observed bearing of that object on the correct (safe) side of the danger bearing, the vessel is clear of the hazard.