DWO Chart Work and Pilotage 2 — Questions and Answers
Question 1: When taking a three-bearing fix, what does a 'cocked hat' indicate?
- The vessel is in dangerous shoal water
- The three lines of position do not converge at a single point due to accumulated errors (Correct answer)
- Excessive compass deviation is present
- The vessel's speed changed during the fix
Correct answer: The three lines of position do not converge at a single point due to accumulated errors
A cocked hat is the triangle formed when three bearing lines fail to meet at a single point, indicating errors in the observed bearings or timing.
Question 2: Using the mnemonic 'Can Dead Men Vote Twice,' what is the correct formula to convert compass bearing to true bearing?
- True = Compass + Deviation + Variation (Correct answer)
- True = Compass - Deviation - Variation
- True = Compass + Variation - Deviation
- True = Compass × (Deviation + Variation)
Correct answer: True = Compass + Deviation + Variation
The mnemonic 'Can Dead Men Vote Twice' gives: Compass + Deviation = Magnetic, Magnetic + Variation = True, so True = Compass + Deviation + Variation (applying correct signs).
Question 3: A vessel steers 090°T at 12 knots. A current sets 270°T at 3 knots. What is the vessel's speed over ground?
- 15 knots
- 9 knots (Correct answer)
- 12 knots
- 6 knots
Correct answer: 9 knots
A current setting 270°T directly opposes the vessel's 090°T course, reducing speed over ground to 9 knots without altering the course made good.
Question 4: What is the purpose of a running fix?
- To determine position using radar bearings only
- To find position using a single object's bearing taken at two different times (Correct answer)
- To verify a GPS fix against a visual bearing
- To calculate ETA at the next waypoint
Correct answer: To find position using a single object's bearing taken at two different times
A running fix uses two bearings on the same object taken at different times; the first line of position is advanced to the time of the second bearing to produce a fix.
Question 5: What is 'leeway' in coastal navigation?
- The angular difference between a vessel's heading and course made good caused by wind (Correct answer)
- The difference between magnetic and compass course
- The rate at which a vessel drifts with a tidal current
- The distance a vessel travels sideways during a turn
Correct answer: The angular difference between a vessel's heading and course made good caused by wind
Leeway is the angular difference between a vessel's steered heading and its actual course made good, caused by the sideways force of wind on the hull and superstructure.
Question 6: What is a 'danger bearing'?
- A compass bearing affected by a local magnetic anomaly
- A pre-plotted bearing limit that, if crossed, places the vessel in danger (Correct answer)
- The bearing of a hazard measured from the vessel's charted position
- A bearing taken on a light during restricted visibility
Correct answer: A pre-plotted bearing limit that, if crossed, places the vessel in danger
A danger bearing is a pre-calculated bearing line on a known object; if the vessel's bearing to that object passes beyond the danger bearing, the vessel is approaching a charted hazard.
Question 7: When must a vessel's estimated position (EP) be used instead of a fix?
- When two or more lines of position are available
- When only dead reckoning data is available and no external references can be obtained (Correct answer)
- When the GPS and radar agree on position
- When speed has been constant for over one hour
Correct answer: When only dead reckoning data is available and no external references can be obtained
An estimated position is used when no external lines of position are obtainable and the vessel's position must be inferred from dead reckoning alone.
DWO Chart Work and Pilotage 2
When taking a three-bearing fix, what does a 'cocked hat' indicate?