The American Practical Navigator/Acronyms

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The American Practical Navigator
by the United States government

Bowditch, Preface, TOC, 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, 20, 21, 22, 23, 24, 25, 26, 27, 28, 29, 30, 31, 32, 33, 34, 35, 36, 37, Glossary, Acronyms



A amplitude; augmentation; away (altitude intercept); Arctic/Antarctic (air mass)
a semimajor axis
a altitude intercept (Ho~Hc); altitude factor (change of altitude in 1 minute of time from meridian transit); assumed
ABAND abandoned
AC alternating current; altocumulus
ACC Antarctic Circumpolar Current
add'l additional
ADF automatic direction finder
ADIZ air defense identification zone
AEB acquisition exclusion boundary
AERO aeronautical
AF audio frequency
AFC automatic frequency control
AGC automatic gain control
AISM Association Internationale de Signalisation Maritime (International Association of Lighthouse Authorities)
aL assumed latitude
Al., Alt, alternating (light)
A.L.R.S. Admiralty List of Radio Signals.
am amber
AM amplitude modulation
AM ante meridian (before noon)
Anch anchorage
antilog antilogarithm
AP assumed position
approx. approximate, approximately
ARPA automatic radar plotting aid
ASAM anti-ship action message
ASF Additional Secondary Phase Factor
AT atomic time
AU astronomical unit
AUSREP Australian Ships Reporting System
al assumed longitude


B atmospheric pressure correction (altitude); bearing, bearing angle
Bdy Mon boundary monument
BFO beat frequency oscillator
BIH Bureau Internationale de l’Heure
BIPM International Bureau of Weights and Measures
bk broken
bkw breakwater
bl blue
BM bench mark
Bn beacon
Bpgc bearing per gyrocompass
br breakers
Brg. bearing (as distinguished from bearing angle).
bu blue


C Celsius (centigrade)
C chronometer time
C compass (direction)
C correction
C course
C course angle
C can
C cylindrical
C cove
CALM catenary anchor leg mooring
CB compass bearing
CBDR constant bearing, decreasing range
CC compass course
CC chronometer correction
CCIR International Radio Consultative Committee
CCU Consultative Committee for Units of the International Committee of Weights and Measures (CIPM)
CCZ Coastal Confluence Zone
cd candela, candelas
CD chart datum
CD-ROM compact disk-read only memory
CG Coast Guard
CE chronometer error
CE compass error
CFR Code of Federal Regulations
cec centicycle
cel centilane
CEP circular probable error
CES coast earth station
CFR Code of Federal Regulations
CGPM General Conference of Weights and Measures
CH compass heading
CIPM International Committee of Weights and Measures
Cl clearance
cm centimeter(s)
CMG course made good
Cn course (as distinguished from course angle)
co coral
co- the complement of (90° minus)
COA course of advance
COE Committee on ECDIS (IHO)
COG course over ground
coL colatitude
colog cologarithm
corr. correction
cos cosine
cot cotangent
cov coversine
CPA closest point of approach
CPE circular probable error
Cpgc course per gyrocompass
cps cycles per second
Cpsc course per standard compass
Cp stg c course per steering compass
CPU central processing unit
crs course
CRT cathode-ray tube
csc cosecant
cup cupola
Cus Ho customs house
CW continuous wave
CZn compass azimuth


D deviation
D dip (of horizon)
D distance
D destroyed
d declination (astronomical)
d altitude difference
d declination change in 1 hour
dA difference of longitude (time units)
DC direct current
deg. degree(s)
Dec. declination
Dec. Inc. declination increment
Dep. departure
destr destroyed
Dev. deviation
DG degaussing
DGPS differential global positioning system
DHQ mean diurnal high water inequality
Dia diaphone
diff. difference
Dist. distance
D. Lat. difference of latitude
DLo difference of longitude (arc units)
DLQ mean diurnal low water inequality
dm decimeters
DMAHTC Defense Mapping Agency Hydrographic/Topographic Center
DNC digital navigation chart
dol dolphin
DR dead reckoning
DR dead reckoning position
DRE dead reckoning equipment
DRM direction of relative movement
DRT dead reckoning tracer
Ds dip short of horizon
DSC digital selective calling
DSD double second difference
DSVL doppler sonar velocity log
dur. duration
DW Deep Water Route
DZ danger zone


E east
e base of Naperian logarithms
e origin of own ship’s true vector
e eccentricity
EBL electronic bearing line
ECD envelope to cycle difference
ECD envelope to cycle discrepancy
EC electronic chart
ECDB electronic chart data base
ECDIS electronic chart display and information system
ED existence doubtful
EDD estimated date of departure
EEZ exclusive economic zone
EGC enhanced group calling
EHF extremely high frequency
E. Int. equal interval
E. Int. isophase
EM electromagnetic (underwater log)
em other ship’s true vector
ENC electronic navigation chart
ENCDB electronic navigation chart data base
EP estimated position
EPIRB Emergency Position Indicating Radiobeacon
EPROM erasable programmable read only memory
Eq.T equation of time
er own ship’s true vector
ET Ephemeris Time
ETA estimated time of arrival
ETD estimated time of departure
Exting extinguished


F Fahrenheit
F fast
F longitude factor
F phase correction (altitude)
F fixed (light)
f latitude factor
f flattening or ellipticity
F.Fl. fixed and flashing
Fl. flashing (light)
Fl. (2) group flashing (light)
Fl. (2+1) composite group flashing (light)
fm(s) fathom(s)
FM frequency modulation
Fog Det. fog detector
Fog Sig. fog signal
ft. foot, feet
FTC fast time constant


G Greenwich
G Greenwich meridian (upper branch)
G grid (direction)
G gravel
G green
g acceleration due to gravity
g Greenwich meridian (lower branch)
GAT Greenwich apparent time
GB grid bearing
GC grid course
GCLWD Gulf Coast Low Water Datum
GDOP geometric dilution of precision
GE gyro error
GH grid heading
GHA Greenwich hour angle
GMDSS Global Maritime Distress and Safety System
GMT Greenwich mean time
Gp. Fl. group flashing
GP geographical position
GPS Global Positioning System
Gr. Greenwich
GRI group repetition interval
GST Greenwich sidereal time
GV grid variation
GZn grid azimuth


h altitude (astronomical)
h height above sea level
h hours
ha apparent altitude
Hc computed altitude
Hdg. heading
HE heeling error
HE height of eye
HF high frequency
hf height above sea level in feet
HHW higher high water
HHWI higher high water interval
Hk hulk
HLW higher low water
HLWI higher low water interval
hm height above sea level in meters
Ho observed altitude
Hor horizontal
Hor Cl horizontal clearance
HP horizontal parallax
Hp precomputed altitude
Hpgc heading per gyrocompass
Hpsc heading per standard compass
Hp stg c heading per steering compass
hr rectified (apparent) altitude
hr. hour, hrs., hours
hs sextant altitude
HSD high speed data
ht tabulated altitude
HW high water
H.W.F.&C. high water full and change
HWI high water interval
HWI mean high water lunitidal interval
HWQ tropic high water inequality
Hz Hertz


I instrument correction
i inclination (of satellite orbit)
IALA International Association of Lighthouse Authorities
IAU International Astronomical Union
IC index correction
ICW Intracoastal Waterway
IGLD International Great Lakes Datum
IHB International Hydrographic Bureau
IHO International Hydrographic Organization
IMO International Maritime Organization
in. inch, inches
INM International Nautical Mile
INMARSAT International Maritime Satellite Organization
INS inertial navigation system
int. interval
Int. Qk. Interrupted quick flashing
ION Institute of Navigation
I.Q. interrupted quick flashing
IR interference rejection
IRP image-retaining panel
ISLW Indian spring low water
ISO International Order of Standardization
ISO isophase (light)
ITU International Telecommunications Union
IUGG International Union of Geodesy and Geophysics
I.U.Q. interrupted ultra quick flashing
I.V.Q. interrupted very quick flashing
IWW Intracoastal Waterway

J – K – L[edit]


J irradiation correction (altitude)
K Kelvin (temperature)
kHz kilohertz
km kilometer, kilometers
kn knot, knots
L latitude
L lower limb correction for moon
l difference of latitude
l logarithm, logarithmic
LAN local apparent noon
LANBY large automatic navigational buoy
LASH lighter aboard ship
LAT local apparent time
lat. latitude
LF low frequency
L.Fl. long flashing
LHA local hour angle
LHW ower high water
LHWI lower high water interval
LL lower limb
LLW lower low water
LLWD lower low water datum
LLWI lower low water interval
Lm middle latitude
Lm mean latitude
LMT local mean time
LNB large navigational buoy
LNG liquified natural gas
LPG liquified petroleum gas
Log logarithm, logarithmic
Loge natural logarithm (to the base e)
Log10 common logarithm (to the base 10)
LOP line of position
LST local sidereal time
Lt. light
Lt Ho light house
Lt V light vessel
LW low water
LWD low water datum
LWI low water interval
LWI mean low water lunitidal interval
LWQ tropic low water inequality


M celestial body
M meridian (upper branch)
M magnetic (direction)
M meridional parts
M nautical mile, miles
M other ship
m meridian (lower branch)
m meridional difference
m meter,(s)
m U.S. survey mile, miles
m end of other ship’s true vector
m minutes
mag. magnetic
mag. magnitude
MARAD United States Maritime Administration
MB magnetic bearing
mb millibar(s)
MC magnetic course
mc megacycle, megacycles
mc megacycles per second
MC&G mapping, charting and geodesy
MCPA minutes to closest point of approach
Mer. Pass. meridian passage
MF medium frequency
MGRS military grid reference system
MH magnetic heading
MHHW mean higher high water
MHHWL mean higher high water line
MHW mean high water
MHWI mean high water lunitidal interval
MHWL mean high water line
MHWN neap high water or high water neaps
MHWS mean high water springs
MHz megahertz
mi. mile, miles
mid middle
min. minute(s)
MLLW mean lower low water
MLLWL mean lower low water line
MLW mean low water
MLWI mean low water lunitidal interval
MLWL mean low water line
MLWN neap low water or low water neaps
MLWS mean low water springs
mm millimeters
Mn mean range of tide
mo month(s)
MODU mobile offshore drilling unit
Mon monument
Mo.(U) Morse Uniform (light)
mph miles per hour
MPP most probable position
MRI mean rise interval
MRM miles of relative movement
ms millisecond(s)
MSC Military Sealift Command
MSI maritime safety information
MSL mean sea level
MTI moving target indication
MTL mean tide level
MWL mean water level
MWLL mean water level line
MZn magnetic azimuth


N north
N nun
n natural (trigonometric function)
Na nadir
NAD North American Datum
NASA National Aeronautics and Space Administration
NAUTO nautophone
NAVSAT Navy Navigation Satellite System
NAVSSI navigation sensor system interface
NBDP narrow band direct printing
NBS National Bureau of Standards
NCS network coordination station
NESS National Earth Satellite Service
NGVD National Geodetic Vertical Datum
NLT not less than (used with danger bearing)
n. mi. nautical mile(s)
NM nautical mile, miles
NM notice to mariners
NMEA National Marine Electronics Association
NMT not more than (used with danger bearing)
NNSS Navy Navigation Satellite System
NOAA National Oceanic and Atmospheric Administration
NOS National Ocean Service
NRML new relative movement line
NtM notice to mariners
NWS National Weather Service


Obsc obscured
Obs Spot Observation spot
Obstr obstruction
Oc. occulting
Oc.(2) group occulting
Oc.(2+1) composite group occulting
Occas occasional
ODAS oceanographic data acquisition systems
Or orange
OTC officer in tactical command
OTSR Optimum Track Ship Routing


P atmospheric pressure
P parallax
P planet
P pole
P pillar
p departure
p polar distance
PA position approximate
PC personal correction
PC personal computer
PD position doubtful
PCA polar cap absorption
PCD polar cap disturbance
PCP potential point of collisio
pgc per gyrocompass
P in A parallax in altitude
PM pulse modulation
PM post meridian (after noon)
Pn north pole
Pn north celestial pole
PPC predicted propagation correction
PPDB point positioning data base
PPI plan position indicator
PRF >pulse repetition frequency
Priv private
Priv privately
PROHIB prohibited
PRR pulse repetition rate
Ps south pole
Ps south celestial pole
psc per standard compass
p stg c per steering compass
Pub. publication
PV prime vertical
Pyl pylon


Q quick flashing
Q(3) group quick flashing (3 flashes)
Q(6)+L.Fl. group quick flashing (6 flashes) plus a long flash
Q Polaris correction
QQ' celestial equator


r end of own ship’s true vector
R Rankine (temperature)
R refraction
R own ship
R red
R rocky
R coast radio station
RA right ascension
RACON radar transponder beacon
rad radian(s)
RB relative bearing
R Bn radiobeacon
RCC Rescue Coordination Center
RDF radio direction finder
RDF RDF station
Rep. reported
rev. reversed
RF (rf) radio frequency
R Fix running fix
rk rock, rocky
RLG ring laser gyro
rm relative DRM-SRM vector
R Mast radio mast
RORO roll-on/roll-off
RML relative movement line
RMS root mean square
RSS root sum square
RTCM Radio Technical Commission for Maritime Services
RZn relative azimuth


s second(s)
S sea-air temperature difference correction
S slow
S south
S set
S speed
S sand
SALM single anchor leg mooring
SAM system area monitor
SAR search and rescue
SART search and rescue radar transponder
SBM single buoy mooring
SD semidiameter
SD sounding doubtful
sec secant
sec. second, seconds
semidur. semiduration
SENC system electronic navigation chart
SES ship earth station
SF Secondary Phase Factor
SH ship’s head (heading)
SHA sidereal hour angle
SHF super high frequency
SI International System of Units
SID sudden ionospheric disturbance
sin sine
SINS Ships Inertial Navigation System
SLD sea level datum
SMG speed made good
SNR signal-to-noise ratio
SOA speed of advance
SOG speed over ground
SOLAS Safety of Life at Sea Convention
SP spire
SP spherical
SPA sudden phase anomaly
SPM single point mooring
SRM speed of relative movement
SS signal station
U.S. Sur M U.S. Survey mile(s)
sub, subm submerged


T air temperature correction (altitude)
T table
T temperature
T time
T toward (altitude intercept)
T true (direction)
t dry-bulb temperature
t elapsed time
t meridian angle
t' wet-bulb temperature
tab. table
TAI International Atomic Time
tan tangent
TB true bearing
TB turning bearing
TB air temperature atmospheric pressure correction (altitude)
TC true course
TCA time of satellite closest approach
TCPA time to closest point of approach
TcHHW tropic higher high water
TcHHWI tropic higher high water interval
TcHLW tropic higher low water
TcLHW tropic lower high water
TcLLW tropic lower low water
TcLLWI tropic lower low water interval
TD time difference (Loran C)
Tel telephone
Tel telegraph
TG time difference of groundwaves from master and secondary (slave) stations (Loran)
TGS time difference of groundwave from master and skywave from secondary (slave) station (Loran)
TH true heading
TMG track made good
TOD time of day (clock)
Tk tank
TR track
Tr transit
Tr tower
Ts time difference of skywaves from master and secondary (slave) stations (Loran)
TSG time difference of skywave from master and groundwave from secondary (slave) station (Loran)
TSS traffic separation scheme
TZn true azimuth


U upper limb correction for moon
UHF ultra high frequency
UL upper limb
Uncov uncovers
UPS Universal Polar Stereographic
U.Q. ultra quick flashing
USGS United States Geodetic Survey
USWMS Uniform State Waterway Marking System
UT Universal Time
UT0 Universal Time 0
UTl Universal Time 1
UT2 Universal Time 2
UTC Coordinated Universal Time
UTM Universal Transverse Mercator


V variation
V vertex
v excess of GHA change from adopted value for 1 hour
var. variation
vel velocity
Ver vertical
VHF very high frequency
VHSD very high speed data
Vi violet
VLCC very large crude carrier
VLF very low frequency
vol volcano
vol volcanic
VPF XX vector product format
V.Q. very quick flashing
V.Q.(3) group very quick flashing
VRM variable range marker
VTS vessel traffic service


W west; white
WARC World Administrative Radio Council
WE watch error
WGS World Geodetic System
Wk wreck
WMO World Meteorological Organization
WWNWS World Wide Navigational Warning Service
WT watch time

X – Y – Z[edit]

X parallactic angle
XMTR transmitter
y. yellow
yd(s). yard(s)
yr(s). year(s)
z zenith distance
Z azimuth angle; zenith
ZD zone description
Z Diff. azimuth
Znpgc azimuth per gyrocompass