DWO Chart Work and Pilotage 1 — Questions and Answers
Question 1: What datum is used for soundings on US nautical charts?
- Mean High Water
- Mean Lower Low Water (MLLW) (Correct answer)
- Mean Sea Level
- Mean Low Water
Correct answer: Mean Lower Low Water (MLLW)
US nautical charts use Mean Lower Low Water (MLLW) as the chart datum for soundings, providing a conservative safety reference.
Question 2: What does blue tinting on a nautical chart typically indicate?
- Deep water exceeding 200 meters
- Restricted anchorage areas
- Shallow water less than the specified depth contour (Correct answer)
- Areas of strong tidal current
Correct answer: Shallow water less than the specified depth contour
Blue tinting marks shallow water areas on nautical charts, warning mariners of potentially hazardous depths.
Question 3: What does the abbreviation 'PA' printed next to a chart symbol mean?
- Protected Area
- Position Approximate (Correct answer)
- Port Authority
- Pilotage Area
Correct answer: Position Approximate
PA stands for Position Approximate, indicating the charted feature's location has not been precisely surveyed.
Question 4: On a nautical chart, a magenta circle with a dot in the center represents what type of navigational aid?
- A danger rock awash
- A light buoy
- A fixed light structure such as a lighthouse (Correct answer)
- A radiobeacon
Correct answer: A fixed light structure such as a lighthouse
A magenta circle with a central dot indicates a fixed light structure on a nautical chart, such as a lighthouse or light tower.
Question 5: Which statement correctly describes a large-scale nautical chart?
- It shows a large geographic area with minimal detail
- It shows a small geographic area with greater detail (Correct answer)
- It has a smaller representative fraction than a small-scale chart
- It is used primarily for ocean passage planning
Correct answer: It shows a small geographic area with greater detail
Large-scale charts (e.g., 1:10,000) depict a smaller geographic area with greater detail, making them ideal for harbor and coastal navigation.
Question 6: What does the abbreviation 'ED' following a sounding on a nautical chart indicate?
- Existence Doubtful (Correct answer)
- Extra Deep
- Electronically Determined
- Estimated Depth
Correct answer: Existence Doubtful
ED stands for Existence Doubtful, meaning the charted feature may not actually exist or its position cannot be verified.
Question 7: What is the purpose of a 'cautionary note' printed on a nautical chart?
- To indicate areas closed to commercial shipping
- To warn mariners of specific navigational hazards or restrictions (Correct answer)
- To mark areas requiring special entry permits
- To identify areas with unreliable tidal data
Correct answer: To warn mariners of specific navigational hazards or restrictions
Cautionary notes alert mariners to specific hazards, regulated areas, or conditions requiring special attention that cannot be shown by standard symbols alone.
DWO Chart Work and Pilotage 1
What datum is used for soundings on US nautical charts?