RADIO

NAVIGATIONAL AIDS

PUB. 117

2005

IMPORTANT

THIS PUBLICATION SHOULD

BE CORRECTED EACH WEEK

FROM THE

NOTICE TO MARINERS

Prepared and published by the

NATIONAL GEOSPATIAL-INTELLIGENCE AGENCY

Bethesda, Maryland

© COPYRIGHT 2005 BY THE UNITED STATES GOVERNMENT

NO COPYRIGHT CLAIMED UNDER TITLE 17 U.S.C.

For sale by the Superintendant of Documents, U.S. Government Printing Office

Internet: bookstore.gpo.gov Phone: toll free (866) 512-1800; DC area (202) 512-1800

Fax: (202) 512-2250 Mail Stop: SSOP, Washington, DC 20402-0001

*76420140

NSN 764201401

NGA REF. NO. RAPU
THE PRUDENT MARINER

a. Warning On Use Of Floating Aids To Navigation and on Aids to Navigation in General, to Fix a Naviga

Position.

The aids to navigation depicted on charts comprise a system consisting of fixed and floating aids with varying degr

reliability. Therefore, prudent mariners will not rely solely on any single aid to navigation, particularly a floating ai

aid to navigation also refers to any device or structure external to a craft, designed to assist in determination of po

This includes celestial, terrestrial, and electronic means, such as Global Positioning System (GPS) and Differentia

(DGPS). Here, too, the prudent mariner will not rely soley on any single aid to navigation.

The buoy symbol is used to indicate the approximate position of the buoy body and the sinker which secures the b

the seabed. The approximate position is used because of practical limitations in positioning and maintaining buoy

their sinkers in precise geographical locations. These limitations include, but are not limited to, inherent imprecisi

position fixing methods, prevailing atmospheric and sea conditions, the slope of and the material making up the seabe

fact that buoys are moored to sinkers by varying lengths of chain, and the fact that buoy and/or sinker positions a

under continuous surveillance but are normally checked only during periodic maintenance visits which often occur 

than a year apart. The position of the buoy body can be expected to shift inside and outside the charting symbol due 

forces of nature. The mariner is also cautioned that buoys are liable to be carried away, shifted, capsized, sunk, etc. L

buoys may be extinguished or sound signals may not function as the result of ice or other natural causes, collisions, or 

accidents. Many of these factors also apply to articulated lights.

For the foregoing reasons, a prudent mariner must not rely completely upon the position or operation of floating a

navigation, but will also utilize bearings from fixed objects and aids to navigation on shore. Further, a vessel attempt

pass close aboard always risks collision with a yawing buoy or with the obstruction the buoy marks.

b. Use of Foreign Charts.

1. In the interest of safe navigation, caution should be exercised in the use of foreign charts not maintained throug

Notice to Mariners.

2. Foreign produced charts are occasionally mentioned in NGA Sailing Directions when such charts may be of a 

scale than U.S. produced charts. Mariners are advised that if or when such foreign charts are used for navigation it i

responsibility to maintain those charts from the Notice to Mariners of the foreign country producing the charts.

3. The mariner is warned that the buoyage systems, shapes, colors, and light rhythms used by other countries often 

a different significance than the U.S. system.

4. Mariners are further warned about plotting positions, especially satellite-derived positions such as from GPS

foreign charts where the datum is unknown or the conversion from WGS-84 is unknown.

c. Chart Notes Regarding Different Datums.

Particular caution should be exercised during a passage when transferring the navigational plot to an adjacent char

a different geodetic datum or when transferring positions from one chart to another chart of the same area which is 

upon a different datum. The transfer of positions should be done by bearings and distances from common features.

Notes on charts should be read with care, as they give important information not graphically presented. No

connection with the chart title include the horizontal geodetic datum which serves as a reference for the values 

latitude and longitude of any point or object on the chart. The latitudes and longitudes of the same points or object

second chart of the same area which is based upon a different datum will differ from those of the first chart. The diffe

may be navigationally significant. Additionally, datum changes between chart editions could significantly affe

positions of navigational aids found in the List of Lights and other NGA publications.

Positions obtained from satellite navigation systems, such as from GPS, are normally referred to the World Ge

System 1984 (WGS-84) Datum. The differences between GPS satellite-derived positions and positions on some fo

charts cannot be determined: mariners are warned that these differences MAY BE SIGNIFICANT TO NAVIGATIO

are therefore advised to use alternative sources of positional information, particularly when closing the shore or navi

in the vicinity of dangers.

(NGA/M
117 RADIO NAVIGATIONAL AIDS 

Radio Navigational Aids

Pub. 117

2002 Edition

CD-ROM