CH Navigation & Nautical Chart Production

Question 1

What is the primary horizontal datum used for nautical charts produced by NOAA in the United States?

Accepted Answer

NAD 83 / WGS 84

Answer

NOAA nautical charts use NAD 83, which is nearly identical to WGS 84, as the horizontal reference datum for all positional information.

Question 2

On a nautical chart, a sounding value shown in italics typically indicates:

Accepted Answer

A depth that is less reliable or obtained from an older survey

Answer

Italic soundings on NOAA charts indicate depths that are of lesser reliability, often sourced from historical or unverified surveys.

Question 3

What does the chart symbol 'Wk' followed by a dashed outline indicate on a nautical chart?

Accepted Answer

A wreck whose position is approximate or unsurveyed

Answer

A dashed outline around a wreck symbol indicates the wreck's position is approximate and may not have been accurately surveyed.

Question 4

The Mercator projection used for most nautical charts preserves which property?

Accepted Answer

True compass bearings (rhumb lines appear as straight lines)

Answer

The Mercator projection is conformal, preserving local angles so that rhumb lines (constant compass-bearing courses) plot as straight lines, which is essential for navigation.

Question 5

Which vertical datum is used as the reference surface for depths (soundings) on NOAA nautical charts in US waters?

Accepted Answer

Mean Lower Low Water (MLLW)

Answer

NOAA uses MLLW as the chart sounding datum because it represents approximately the lowest water level, providing conservative (safe) depth values for mariners.

(CH) Certified Hydrographer Practice Test

(CH) Certified Hydrographer Practice Test

CH Navigation & Nautical Chart Production