CH Navigation & Nautical Chart Production 2 — Questions and Answers
Question 1: In chart production, the process of converting raw survey soundings to chart datum depth values requires:
- Applying a magnetic declination correction
- Subtracting the water level (tide) at the time of measurement from the measured depth (Correct answer)
- Adding the vessel draft to each sounding
- Converting from NAD 27 to NAD 83 coordinates
Correct answer: Subtracting the water level (tide) at the time of measurement from the measured depth
Tide-corrected soundings are obtained by subtracting the observed water level above chart datum at the time of sounding from the measured depth below the water surface.
Question 2: What NOAA publication defines the specifications and standards for nautical chart compilation and hydrographic surveys?
- IHO S-44 Standards for Hydrographic Surveys
- NOAA Hydrographic Surveys Specifications and Deliverables (HSSD) (Correct answer)
- FGDC Geospatial Data Standards Volume 3
- USACE EM 1110-2-1003 Engineering Manual
Correct answer: NOAA Hydrographic Surveys Specifications and Deliverables (HSSD)
NOAA's Hydrographic Surveys Specifications and Deliverables (HSSD) document defines all technical requirements for surveys that will be used in nautical chart production.
Question 3: Electronic Navigational Charts (ENCs) used in ECDIS systems conform to which international standard?
- IHO S-57 / S-100 (Correct answer)
- ISO 19115 Metadata Standard
- OGC WMS 1.3.0
- FGDC Content Standard for Digital Geospatial Metadata
Correct answer: IHO S-57 / S-100
ENCs are encoded in IHO S-57 format (with S-100 as the next-generation framework), which defines the data model, feature catalog, and exchange format for official electronic charts.
Question 4: A 'scale of 1:80,000' on a nautical chart means that one unit on the chart represents:
- 80,000 nautical miles in reality
- 80,000 units of the same measurement in reality (Correct answer)
- One nautical mile per 80,000 cm on the chart
- 80 kilometers per chart centimeter
Correct answer: 80,000 units of the same measurement in reality
A representative fraction of 1:80,000 means one unit measured on the chart (e.g., 1 cm) corresponds to 80,000 of the same units in the real world (80,000 cm = 800 m).
Question 5: On a nautical chart, what does a magenta circle with a flashing light characteristic 'Fl(2) 10s 15m 12M' describe?
- A buoy flashing twice every 10 seconds, 15 meters above water, visible 12 nautical miles
- A lighthouse with 2-second flashes, 10-meter height, 15-mile range
- A light structure with group flashes of 2, 10-second period, 15 meters elevation, 12 nautical mile nominal range (Correct answer)
- A radio beacon transmitting on 10 kHz at 15-meter height
Correct answer: A light structure with group flashes of 2, 10-second period, 15 meters elevation, 12 nautical mile nominal range
The notation means: group flashing with 2 flashes per period, period of 10 seconds, light elevation 15 meters above MHWS, nominal range 12 nautical miles.
Question 6: Which chart datum is used for the height of land features and bridge clearances shown on NOAA nautical charts?
- MLLW
- Mean High Water (MHW)
- NAVD 88
- Mean Higher High Water (MHHW) (Correct answer)
Correct answer: Mean Higher High Water (MHHW)
NOAA references overhead clearances and land elevations to MHHW because it represents approximately the highest regular tidal water surface, giving conservative (safe) clearance values.
CH Navigation & Nautical Chart Production 2
In chart production, the process of converting raw survey soundings to chart datum depth values requires: