Maritime and Marine Marine Navigation and Charting 1 — Questions and Answers
Question 1: What is the primary reference level (datum) used for depth soundings on US nautical charts?
- Mean High Water
- Mean Sea Level
- Mean Lower Low Water (MLLW) (Correct answer)
- Mean Low Water Springs
Correct answer: Mean Lower Low Water (MLLW)
US nautical charts use Mean Lower Low Water (MLLW) as the sounding datum, representing the average of the lower of the two daily low tides.
Question 2: On a US chart using the lateral buoyage system, what does a green buoy with an odd number indicate?
- Starboard side of the channel entering from seaward
- Port side of the channel entering from seaward (Correct answer)
- A midchannel safe water mark
- A special-purpose hazard marker
Correct answer: Port side of the channel entering from seaward
Green buoys with odd numbers mark the port (left) side of the channel when proceeding from seaward toward port, per the US lateral buoyage system.
Question 3: Which nautical chart scale would a mariner use for the most detailed view of a harbor or anchorage?
- Sailing chart (1:600,000 or smaller)
- General chart (1:150,000–1:600,000)
- Coastal chart (1:50,000–1:150,000)
- Harbor chart (1:50,000 or larger) (Correct answer)
Correct answer: Harbor chart (1:50,000 or larger)
Harbor charts have the largest scale (1:50,000 or larger), providing the greatest detail needed to navigate harbors, anchorages, and inland waterways safely.
Question 4: What is magnetic variation as shown on a nautical chart used to calculate?
- Compass deviation caused by onboard ferrous metal
- The difference between true north and magnetic north at that location (Correct answer)
- The effect of current on the vessel's course
- The rate of change of the compass bearing over time
Correct answer: The difference between true north and magnetic north at that location
Magnetic variation is the angle between true north and magnetic north at a given location, used to convert true bearings to magnetic bearings and vice versa.
Question 5: On a nautical chart, what does an anchor symbol enclosed in a circle indicate?
- A prohibited anchorage area
- A recommended anchorage area (Correct answer)
- A mandatory anchoring zone requiring a permit
- A commercial vessel-only anchorage
Correct answer: A recommended anchorage area
An anchor symbol enclosed in a circle marks a recommended anchorage area where vessels may safely anchor with adequate depth and holding ground.
Question 6: What is a navigational 'range' used for?
- Measuring the maximum radar detection distance
- Aligning two fixed marks to guide a vessel along a safe track (Correct answer)
- Indicating the effective broadcast distance of a radio beacon
- Describing the tidal range between high and low water
Correct answer: Aligning two fixed marks to guide a vessel along a safe track
A navigational range consists of two fixed objects — such as range lights or markers — that, when kept in line, indicate a safe track through a channel.
Question 7: What is the purpose of a 'Notice to Mariners' published by the National Geospatial-Intelligence Agency (NGA) and USCG?
- To announce new vessel registration requirements
- To issue corrections and updates to nautical charts and publications (Correct answer)
- To broadcast weather forecasts for coastal waters
- To list commercial shipping traffic schedules
Correct answer: To issue corrections and updates to nautical charts and publications
Notices to Mariners are published to inform mariners of important matters affecting navigation, including chart corrections, changes to aids to navigation, and updated regulations.
Maritime and Marine Marine Navigation and Charting 1
What is the primary reference level (datum) used for depth soundings on US nautical charts?