CHAPTER 18

Introduction to Pilotage

At sea there are neither roads nor signposts, but there is

an
number of ways of getting from one place to another, and the choice must be
almost unl1mted
made after careful study of the charts, taking into account such factors as the
draught of the ship, rocks, shoals, weather and other shipping. Having selected
the intended track and marked it in pencil, it is then most important to ensure
that the ship stays on it, otherwise she may so easily and quickly run into danger.
Navigation is the art of taking a ship safely from one place to another. It the
of of land she can find her position by of
ship is out sight sextant observation
the Sun, Moon and stars; or by radio navigational aids such as Consol, Loran,
ecca and Direction Finding when within the coverage of these systems. If
the ship is within sight of land she can establish her position by taking bearings
ot recognised
can check her
features on the land or seamarks; or she may fix by radar; and she
position by soundings.
Pilotage is that part of navigation which concerns the safe conduct of a ship
in the vicinity of coasts, in narrow waters, and in the vicinity of dangers such
as rocks and shoals. Broadly speaking, navigation in pilotage waters may be
considered as coming under two headings:
Coastal navigation,, which concerns that part of a sea passage in which the
navigator has the land on one side of his course and the open sea on the
other;
Channel navigation, which is required when ship has to be navigated in
a
narrow channels with dangers on both sides, and in rivers or harbours and
their approaches, as usually occurs at the start and finish of a sea
voyage.
This chapter is intended to introduce the seaman to the of
to describe the simple and more usual methods
art
pilotage, and
by which aship's position,
course and speed are estimated and checked when she is in
pilotage waters.

CHARTwORK
Preparing a chart for passage
Whether a ship is making a voyage of many hundreds of
miles or a small
craft is crossing a few miles of coastal waters, the
on a chart. Let us consider the
track planned must be pencilled
problem of taking a small vessel from Portland
to Plymouth. The general small-scale chart of the area is
extracted fron the
folio, and the planned track is marked in pencil. This track
consists of a number
of straight
lines
joning selected points ot the
making quite certain that
route,
they lead clear of any dangers. The
courses are then written against these
straight lines, both the true courses and the magnetic courses. The distances
from the destination can
then be marked at intervals along the route so that the
progress of the ship can be checked from time to time.

514
 CHARTwORK
515

E c a l e charts for the passage are now extracted from the folo and

p r c a in a similar way. It is these charts that must be used, because th

largest-scaled chart always has more detail on it.
Describing and plotting a position at sea
h e n it is necessary to describe a position at sea to establish a new danger
It
tne rendezvous between ships, or for a ship to report her ownand
be done
position,
distance
Can by giving the latitude and the longitude, or the bearing
rom a prominent landmark.

Plotting latitude and longitude. Place one edge of the parallel ruler along,a
parallel ot latitude and move the ruler until one edge passes through the latutuae

30E

S1 S6 N.
4t

FiG. 18-1. Plotting a position by latitude and longitude

of the place as indicated at the side of the chart. With the dividers, meas
the distance at the top or bottom of the chart from the nearest meridian to the
required longitude, and lay this oft from the same meridian along the parallel

of latitude shown by the ruler (fig. I8-1). If more convenient, the ruler can
be placed to the longitude and the latutude then be set off with the dividers.

Alternatively, the latitude and the longitude may be drawn in by pencil,

using the parallel ruler only.
Plotting bearing and distance. A position may be described by its bearing
and distance from a known position Such as a landmark or lighthouse; for
lies in a direction 136
example, '135 Eddystone 5 means that the position
from the Eddystone lighthouse and 5 miles distant from it. All such bearing
ngs
 IN'TROD1CTION TOPILOTAE

EDDYSTONE
LT. GP. .
" 17M.

135 EDDYSTONE 5

FIG. 18-2. Plotting a position by bearing and distance

are true bearings and the distances are in nautical miles.

Most charts have printed on them one or more compass roses from which a
line of bearing can be drawn with the aid of a parallel ruler. Each rose has an
inner and an outer circle of graduations; the graduations on the outer circle
show true directions, and those on the inner circle show magnetic directions
for the year in which the chart was published, the variation and its annual
change being indicated on this circle.
The distance scale is the scale of latitude at the side of the chart, one minute
of latitude being equal to one nautical mile. It is important to remember that
this scale on a chart alters with the latitude, and that the distance should
therefore be measured off that portion of the latitude scale which is abreast the
which is to be recorded.
position
To record the position quoted above, first measure five miles from the
latitude scale with a pair of dividers, then place the parallel ruler over the
nearest compass rose on a bearing ot 135; now move the ruler until one edge
passes through the Eddystone lighthouse, and lay off the distance with the
dividers in the direction of 135° from the lighthouse (fig. 18-2).

Transferring position from one chart to another

When planning a passage Irom one place to another and when on passage it
is frequently necessary to transter a point on the planned track, or the s h i n '

t r o m o n e chart to another.
position,
The scale of one chart may be different from that of another, and a position
 CHARTWORK

0260
0210
02T0

SHIP STEERING 270 SHIP STEERING 20

TRACK RUNS OFF
TRACK TRANSFERRED TO
SECOND CHART (SMALL SCALE) FIRST CHART (LARGE SCALE)

chart to another
FIG. 183. Transterring a
position from one

should therefore be laid off by its bearing and distance from some object
common to both eharts and checked by its latitude and longitude.

To lay of and take off courses and bearings from a chart

When the planned tracks have been pencilled on a chart, the true and magnetic
courses must be written alongside them. The methods used for converting
and
compass courses to true courses or gyro-compass courses to true courses,
of
vice-versa, apply cqually to bearings taken by compass to fix the position
the ship, as described later.
for any gyro error
Gyro-compass courses and bearings must be corrected
before they are laid off on a chart, and Similarly, true courses and bearings taken
off a chart must be corrected tor any gyro error betore they are applied to the

gyro-compass (see Vol. 1, Chapter 15).

Courses and bearings by magnetic compass, belore being laid off on the chart,
should be converted to true courses and bearings by applying the deviation
obtained from the deviation card (see Vol. 1, Chapter I5) and the variation,
the latter being corrected for the change of variation indicated on the chart.
Similarly, a true course or bearing taken ot a chart must be corrected for the
variation and change of variation, and for the deviation, before it is applied to

a magnetic compass (see Vol. I, Chapter 15)Ihese conversions from true to

compass, and vice versa, may be made by combining the three corrections and
applying them as a single, combined or total compass error. But it must be
remembered that the total compass error wil change with an alteration of
course by the amount of change in the deviation. The following example shows
how this combined error is calculated:
Variation is 15° 30'W (196t), imcreastng about 7 annually. True course from
chart is 158. What is the compass error in 1965?

By comparison between the true and magnetic roses the compass course will
be about 170° C, on which course the deviation trom the deviation table is
stated to be 4° E.
 518
TNTRODUcTION Tro piLOTAGE

Variation for 1961 15

Change of variation
Variation for 1965 16 W
Deviation for 170C E

Compass error 12°W

While the
ship is on a course
170° C all rted
o
true
bearings, and vice versa, compass bearings can
D *
by applying
error this conpass
whenever the ship alters course a new total compass error mustorbei calCuiatcd
and applied.
The
following examples show how a
compass error is
appliea
he bearing of a
lighthouse is 247° C by magnetic compass. What is
oEaring y the
compass error for the course which the
the true
on
ship is steering 1s
17
Brg. of Lt. Ho. = 247° C
Comp. err. =17 E (compass least-add)
True brg
204
The true course taken
the off a chart is 133°. What is the
compass couTse if
compass error is 13 W?

True co.
133
Comp. err. =
13° W
(( compass best-add)
Comp. co0. I46° CC

To find the error of a

gyro-compass or the deviation of a
compassB magnetic
Never miss an
opportunity of checking the error or dev1ation of a
by transits, particularly small crart were unknown compass errors
in compass
been introduced since the last table of deviations may have
was made.
If an observer sees two
objects in line he must be situated somewhere
line which joins them. The objects on the
objects are marked the
are then said to be 'in transit'. If
both
on
chart a
bearing can then be roundposition
line can be drawn through
the true them, and
bcaring is now taken of the objects irom
the
nearest compass rose. If a
in transit and compared with the compass
bearing calculated from the true bearing, the deviation magnetie
of the compass
particular direction of the ships head can easily be found. for that
a gyro-compass the error can be 1ound by In a ship fitted
with
with the true bearing on the compass comparing the gyro-compass bearing
the true bearing the gyro-compasS error
rose. thne compass reading is more
ishigh; if it is less the error is than
low'
 CHARTVORK 519

COMPASS BEARING OF TRANSIT 048

THEREFORE DEVIATION IS 3°W

FIG. 18-4. Checking deviation of magnetic compass by a transit

EXAMPLE I (fig. 18-4)

From chart, beacons in line bear
o35° (True)
Variation (corrected for year) 10 W
Therefore beacons in line bear
045 M (Magnetic)
From shp 048 C(by mag. compaSS)
Deviation w

ExAMPLE 2
From chart, beacons in line bear
o35° (True)
From ship " "
3 2 (Dy 8yro-compass)
Gyro error 3 (low)

Recording a ship's position on a chart

A
fix is the ship's position found from reliable observations of
terrestrial
objects, obtained either visually or by a radio navigational aid, and is shown on
the chart by a circle with the tume ot observation
agaunst it, thus: O 1100.
An observed position is the
tions of heavenly bodies, as
ship's position found from reliable sextant observa-
explaineda in the Admiralty Manual of Navigation,
Vol. II, and is shown on the chart
by circle with the time and the letters Obs.
against it, thus: O Obs. o530. When it is not possible
to obtain the
position by observations or by
ship's actual
from the last observed position
fixing,
or fix.
a theoretical position can be worked
up
A dead reckoning (D.R.) position is the ship's
on from the last hx, or observed position obtained by
plotting
position, the speed made good through the
water along the compass
course steered, and is shown on the chart thus:
o630 0730
 520 INTRODUCTION TO PILOTAGE

n cstimated position (E.P.) is the most accurate that the navigator can obtain
Calculation and estimation only. It is obtained from the D.R. position
ustcd tor the estimated effects of 'wind across', currents and tidal streams,
and is shown on thc chart thus:
A o8oo.

Plotting the ship's track

aving established the intended track of the ship on the chart,
Cannot
the navigator
assume that, because his compass is correct, his ship will necessarily
stay on that track and make good the expected speed over the ground.

Plotting the ship's track on the chart is complicated by the ettccts ot current
Odal Stream and wind, so her course and speed through the water (which
are obtained trom the
compass and the or other method ot speed log
w by no means be the same as her course and speed over the ground (which recording)
ne plotted track is required to show). To plot the ship's track on the chart it
Is
necessary to know the course and speed made good over the ground.
The
ship's track should therefore be
.
plotted in two steps as follows:
Starting from the last krown
position, plot the course steered through the
water and the distance steamed along that course in the intervening time,
thus
arriving at a dead reckoning position.
2. Plot in the correct direction from
the dead reckoning position the combined
effect of the current or
tidal stream and wind for the period
Sidered. The being con-
position now arrived at is the estimated
position.
The effects of current or tidal stream and wind must be considered before
proceeding with the actual
plotting on the chart. Currents must not be
with tidal streams. Infornation confused
on currents is obtained trom the
Admiralty charts, from special ordinary
the Admiralty Current Charts, and trom
Sailing Directions. Intormation on tidal streams 1s to be
found on
Admiralty charts and in special tidal atlases. The
always note down and remember the times of navigator should
stantly revise his assessment of the set and high and low water, and
con
ot rate the streams
time and place, remembering that the slower the according to the
will be the allowance speed of his ship the
great»*
necessary to make good his desired course.
The effect of wind can be estimated
vessel's behaviour. It is only necessary to only bytheexperience of the particular
moved to one side or the other of her judge amount the ship has been
course, because the effect of the
the speed of the ship is allowed for in the wind on
as shown by the
speed made good the through water
with her freeboard and
log.Leeway, which depends on the
draught of a
ship compared
on the extent to which her
resistance to the wind, is
often cancelled out
superstructures offer
windward': particularly is by her tendency to "bore to
this so with
ing sea: but
a
light, shallow draught vessel in quarter-
a
experienced helmsman will ensure that the
an
is that ordered, by taking care whenever the average course steered
course to
shiP is forced to windward of her
swing her back an
cquivalent amount to leeward of it.
The following example, illustrated
effects of current
in
fig. 18-5, is given to show how the
or tidal stream and wind are allowed for when the track is
plotted.
Suppose that at
ogoo the ship is known to be in latitude 57 45 N,
longitude
 CHARTWORK
521
TIDAL STREAM 000

26 260-2'5

cOURSE STEERED
000
SHIP'S TRACK
290-10

57 45'N
09001 40"W.
FiG. 18-5. Plotting the ship's track

a course
290 and making good a speed of 10 knots through
140 W,
the water. Steering
From the tidal stream atlas (or from information given on the chart
at rate of
it is found that at og0o the tidal stream should
be setting 260 a

N.E., force 8.
25 knots. Thè wind is A
the course steered and the speed through the water. The starting point
Plotting
fix or an observed the parallel
position. Place ruler on the nearest
may be a
the centre of the rose and through
that so its edge passes through
compass rose of graduations, and for
steered) on the outer circle
290 (the course being 110", the reciprocal of
that it also passes through
increased accuracy make sure
direction so as to pass through
the course. With the parallel uler transter this
line of length to show the whole run;
sutfhicient
the starting point A, and draw a the distance steamed through
this will be the course. The
ship's
will log give
example the speed is 1o knots, so
the between 0g00 and 100o. In this
water
to the latitude of A,
measure off 10 miles
from the scale of latitude corresponding B which is
thus obtainingthe point the
and layit off from A along the course,
at I000, and therefore marked thus: +1ooo.
dead reckoning position

NOTES
course must be corrected for
(i) If a magnetic compass
is
used the compass
before.
and laid off as
variation and deviation

(ii) If the dead reckoning position has been obtained trom a log reading, the
effects on the ship's speed
of a
head or following
a sea ur
wind will have been
trom the revolution
taken into account. If the
position nas been estimated
for together with the state of the ship's
table these etfects must be allowed
bottom.
on, from the
dead reckon1ng poStfi0n, the efect of any current, tidal
Plotting
stream or wind (other than that already allowed Jor 1n 1he speed made good through
strearn, which is setting
the water). It is now necessary to consider the tidal1s N.E. force 8. It is estimated
260° at 25 knots, and
the
eftect of the wind, which the
that the etfect of the wind will set ship in a 220° direction
from experience
at I'5 knots.
B line BC, 260, 2'5 miles, to represent
From the 1000 D.R. position lay oft a it with three arrows.
will be set by the tidal stream, and mark
the amouut the ship
 522 TNTRODUCTION TO PILOTAGE

T lay oft a line CD, 220 , 1'5 miles, to represent the drift of the ship
due to the wind.
We now have a scale diagram showing what happens during
The
one hour S run.
point D is the estimated position at 1o00, and is theretore
1000.The dotted line AD is the track which it is estimated markea the shiptnus
will
make good over thc
ground. Until a definite fix or reliable observed
obtained, this estimated position should not be position is
checks, such as
crased, even though subscquent
soundings, or a
single position line may cast doubt upon its
accuracy.

Shaping a
course, allowing for a tidal stream
Of more
w1ll keep a
importance to the
navigator is the problem of shaping a course that
ship on
planned track, allowing for a tidal stream.
a

EXAMPLE
Wnat course must a
ship steer when steaming at 12 knots to
090 i it is estimated that the tidal stream is make good a course
setting o40 at 3 knotsS?

TIDALSTREAMO 2'

cOURSE TO
STEER
(FROM A)

SHIP'S TRACK

FIG. 18-6. Shaping a course. allowing for a tidal stream

Lay off the course to be made good, o90 (4B in

the direction of the tidal stream, o40 (AC) fig. 18-6). From A lay oft
Along AC mark off AD
the distance the tidal stream equal to
scts in any convenient
interval of time
scale; in this example a one-hour interval has been on a
chosen
three miles. allowed, so that AD will be
With centre D and radius cqual to the
distance the
interval of one hour (12 miles), describe an arc to ship steans in the same
cut AB at E. Then
which will be the course to steer. join DE,
This course is actually steered from 4, and AE is
the distance made good
an o9o" dircction in one hour and is marked
with two
in
arrowheads.
Reaching a
position at a dclinite tinme,
allowing for a tidal streara
IExAMP1E
What course must a
shif steer,
and at enal
speed must she
steam,
a position A to an
anchorag" D n
T2 onrs,
to
proceed from
150 at 3 knots ? alowing Jora tidal stream
setting
 FSTAULISuING 523
TUE
SUr's ros1T1ON
TRACK TO RE MADE GOOD IN I} HOURS

090-15
INHOJPS
STEAMED

BE

REA
TO
DISTANCE

A N D

S T E E R

TO
COURSE

at dennte
Fic. course and speed to reach a position
a
i8-7. Estimating
time, allowing for a tidal stream

Join AB, as shown in fig. 18-7. This determines the course and distance tu
be made good in I hours, i.e. 090, 15 miles.
From A lay off the direction of the tidal stream, 150°, and the distance
sets in 1 hours, AC, which is 4 miles. Join CB. Then CB represents the
course to steer, o73°, and the distance the ship must steam in I hours, 134
miles. The speed of the ship should therefore be 8:9 knots.

ESTABLISHING THE SHIP'S POSITION

Position lines
A position line is any line drawn on a chart on which the ship's position is
known to lie. It may be straight or curved. It may be obtained from a sextant
observation of the Sun or Moon or from individual stars, or from a compass
bearing of a landmark or seamark, or from a line of soundings, or from the range
of a powerful light when first sighted in good visibility.
If two or more position lines lying in different directions are obtained
simultaneously, the position of the ship should be at the point of intersection
is called 'fix.
of the lines, and this position a

A position can be found by using two position ines obtained at ditereut

times by transferring the first position line the amount that the ship has steamed
in the interval of time, adjusted for tidal stream, current and wind: it is then
known as a 'running fix.
It is usual to mark a position line drawn on the chart from a bearing of a
terrestrial object with a single arrow at the outer end; it it 1s transferred it is
narked with a double arrow at both ends.
The navigator of a small craft, with the aid of charts, compass, watch, lead
line, tide tables and some means ol estimating speed, can obtain position
lines by:
(1) a transit
(ii) a conpass bearing
(11) a horizon range of a powertul shore liglht

(iv) soundings.
The navigator of a big ship, who has the additional ands of sextant, log, echo
sOunding, radar and radio navigational aids, can obtain position lines froma
524 INTRODUCTION TO PILOTAGE

much wider range of methods. More essential than elaborate apparatus,

nowever, are accuracy, alertness and a dislike of taking anything tor grantea
In this chapter only those methods which are available in small craft are

described.

*****

'
- ***

. * .. .

FIG. 18-8. A simple example of the use of transits

CHIMNE ROCKS
BEAC
-O
CHlMNEY
ROCKSBEACON
AND 290WRECK
LEADS
WRECK BETWEEN

MEANS "IN TRANSIT")

CHIMNEY 'ON WITH' BEACON

FIG. 18-y. Leading marks and leading line

 ESTABLIsHING THE SHIP's POSITION 525
Transits
The metlhod of
checking the accuracy of a compass by a tran51t s L
been deseribed.
positionor
Nowthelet us see how transits can be used to establish the ship's
prevent navigator from approaching a danger
The simplest method of establishing a position without the aid ot a compas
Or Chart 1s shown in fig. 18-8. A fisherman has to abandon an anchor or o
nshing gear at the position X. Before leaving this position he observes tnat
objects B and D are in line with objects A and C respectively; he can theretore
return later to the same spot to recover the gear by steering a course wnie
keeps D and C in line until he sees B come into line with .
Leading marks (fig. 18-9). Many harbour plans show two marks which, when
kept in transit, lead the ship in the best channel. Such marks are calledleading
marks' and are shown on a chart by a line drawn through them called a eading
is 'on the
neWhen the marks are in transit, i.e. when the chimney with
beacon, take a compass bearing and compare it with that given on the chart.

CHUR

CHURCH OPEN OF STAB POINT

(AS SEEN FROM X)
STAB POINT

DANGER

FiG. 18-10. Cleaning marks and clearing line

 526 INTRODUCTION TO PILOTA GE

and 1t
Cnsures that the objects scen in transit are the correct bjects, als
s
hecks the error ot the conpass.
Cleuring marks. When a hidden danger lies in the approach to an anchorage
is drawn on the chart. "This line leads
will olten be found that "clearingbeline'
a

in Bafe water if she keeps

outside it, that
lear of the danger and ship must In
a
marks the
fig. 18-10 the clearing
are
the marks arc kept 'open'.
1S Whenand
chiurch Stab Point; the church must be kept 'open of Stab Point,

Lradng ine and clearing line. When there is only one conspicuous object,
ot bearing drawn on the chart fromn that may be uscd to lead between
object
ne
dangers or clear ot them. The ship must then steer a course so that the object

18-11 the leading linc leads the

remains on the correct bearing. In fig. 255
show the
ship sately between shoals, and the clearing lines of 245 and 265
limits of safety. The bearing of the lighthouse must not be less than 245 or
more than 265° when entering or leaving this bay.

SHOAL
* * *

255

265

LIGHTHOUSE
-
SHOALSHOAL

FIG. 18-I1. Leading line and clearing line

FIXING BY POSITION LINES

The estimated
position, as we have seen, is the
position found from the course
stecred and the estimated
the ship has been moved
speed through the water, corrected for any distan
by the tidal stream,
current, wind and sea.
pOsition 1s hable to
error, in which case all n
subsequent plotting ot the
always necessary for the navigator to fix the trac
will he attected. It is therefore
position as often as possible by observations which provide definite snip»
positio
 FIXING BY POSIT1ON 1.INES
527

should DE
line
Any tiwo such lines will give a fix, but a third position
nes.
taken as a check.
Betore fiNing the s h i p ' s position, identify all the objects you are going to usc

and make certain that they are marked on the chart. It is no use taking the
to select
ot one conispicuous and then having to look
object
about tne
Dearing ot the
objects
to De

cross-bearings first note the

n a m e s
others. Vhen
observed and taking
write them down. After this the bearings should be taken as

and the time should be noted immediately atter

taking the
quickIy as possible,
Ast bearing. "The most favourable circumstances are when the fhrst object
later
nearly
ahead and the third abeam; the bearing ot the
observed 1s nearly is the ship, and unless the bearings
are

rapidly, especially if it near

will change
taken almost simultaneously it will be impossible to get a satistactory' Cut
when using a magnetic compass remember that the deviation which must
s
direction ot the ship
be the bearings is the deviation for the
used to correct
head when the observations were taken.

Selecting objects for a fix

When a ship's position is fixed by three bearings
the objects selected should,
about 6o degrees; the positionn
possible, lie so that their bearings differ by
t it is only possible to fix by two bearings,
the
lines will then make a good cut. If
that their bearings intersect as nearly
as
possible
objects selected should lie so

e r r o r in taking the observations

as then the effect of any small
at
right-angles, is reduced to a minimum.
the
them off chart
and laying on
but a
the ship in preference to distant objects,
Always select objects near
liable to
line obtained from a bearing of a buoy,
or of any other object
position not be relied upon.
move from its charted position, should

Fixing by cross bearings

of two different objects are obtaincd simul-
When accurate lines of bearing
the ship must lie at the point where those
two lines intersect. Suppose
taneously and a
that at 1015, from an observer on board a
ship, a lighthouse bore 040
as shown in fig. 18-12.
the
If these two lines are drawn on
church bore 125
interscction should be the ship's position at 1015. As.
chart, the point of their
arise in taking the bearings, and there may also be
may
however, slight errOrs
of the objects, a third bearing, called a
slight in the charted position
errors
and the chart were accurate
check bearing, should be taken. It all these bearings
In
this should
bearing through the point of intersection of the other two.
pass
practice, however, owing to such errors it will be found that the three bearings,
when plotted, form a small triangle known as a cocked hat' (shown shaded),
in which the check bearing is that of the fagstaff bearing o75
If a cocked hat is reasonably small the position of the ship is usually taken
as lying at its centre. Ii the cocked hat is large, however, the bearings should
be taken and plotted again to ensure that the objects have been properly
dentihed and that there was no error in correcting them. Then, if a large
cocked hat still remains, the position of the shipP should be taken as lying at

the corner of the triangle which will place her nearest to danger, thus ensuring
that subscquent alterations ot course tor rounding marks, etc. Will have a

probable satety margin.

 INTRODUCTION TO PIL0TAGE

LIGHTHOUSE

FLAGSAF

O/S

015

125
CHURCHK
Fic. 18-12. Fixing by cross bearings

As the cocked hat may also be caused by unknown deviation or gyro error,
every opportunityshould be taken to check the deviation or error of the compas.
The opportunity for a check on at least one direction of the ship's head arises
whenever two charted objects are passed in transit.
Example of a bad fix by cross bearings. If the ship is on the circumference of
a circle passing through the three objects, the three lines of bearing will always
meet at a point, even
when there is an unknown compass error. Any unknowm
compass error may theretore pass undetected and an incorrect position be
recorded, as shown in fig. 18-13, where the compass error is 10° high.
Note that the conspicuous chimney should not have been used when there
was a beacon on a nearly similar bearing much closer to the
ship.

INCORRECT
FIX LIGHTHOUSE

MNEY

BEACON

ACTUAL
POSIT
TION
CHURCH

FiG. 18-13. Example of a bad fix by cross

bearings
 29
TN
BY PO8ITION 1.INE

A running fix
one object c a n
be
scen, ana 30 d
frequently haPpens that only
It
monent. This one line
canb eDea rug *
at a given
position ine
can
be obtained, object, or a
bearing of the
same
a second
ater
to
oDtAin a18Ix when
taken.
another object,
ExAMPLE
The tidal stream is
estimated as setting 3
A ship is steertng o90 a t 8 knots. light
b o r e 3to
the same
lighthouse bore o34°. At 1630
3 knots. At 160othe ship at 1630.
a
at

Find the position of through the light, as In

ng
o34° directionin an
to pass
Draw a ine 4CE line at 1600.
18-14(i). This is the position

LIGHTHOUSE
LIGHTHOUSt
630
POSITION LINE
90 318
090 4
090 4
A.
135

1630

second stepP
fix: () hrst step; (11)
A running
F1G. 18-14.
in a direction
drawn each
AB, CD and EP,
are
then if the
that three lines, run i n half a n hour);
Now suppose (the
distance
u n a f f e c t e d by
miles in length that she is
and each 4 provided
o90 B at at 1630, will be at 16o0 she
she will be C or Ë
A at 160o she 1s at
ship is at
Similarly, if m u s t be
tidal stream.
at 1600, BDF
wind,
current or
ACE 1s the position line transferred,
Then, since been
at D
F at 1630. has
position lineline.
1 6 3 0 - t h a t is, the original This is parallel
or
line at
the position transterred position
at each end.
the
line is
known
by
as
two
arrowheads

and the new

is distinguished
the run, and
position line and or wind during
with the original stream, Current must be
is set by the tidal position line
the ship the transterred
But which
to draw off from any point
the point through 8 h o w n First lay in
therefore
as
in ng. I8-14(11). steamed by the ship
two steps, distance
arrived at by the course
and
to represent
position
line
at B, lay
off
BC
on the original
T h e n from the end
of
this line, set in the
interval

the interval (AB). estimated to have been

ship is transferred
direction and distance the
position Iine should now be the allow-
the end. If
tidal stream, current
or
wind. The arrowheads
at each
ship
with two. the
by and be
marked
accurately
estimated,

topass through C' stream,

etc. has been
1630. At 1630 the
tidal line at
ance
made for the transterred position
on this
at some point
must be
 530 INTRODUCTION TO PILOTAGE

he
e ight bore 3i8°, and this position linc should now be drawn. T polnt
C cuts this second positlon
where the transferred position line drawn through
line is the ship's position at 1630.
ust be
eniphasiscd that the accuracy of a running fix depends entirely
On the correct estimation of the ship's track between the two bearings.

Fixing by a bearing and sounding

On approaching the land in places where the depth changes fairly rapidly, a
of a charted landmark
pproximate position can be found by observing a bearing
and at the same time obtaining soundings (fig. 18-15).

***** ****

LIGHTHOUSE
***** ******
3

..

7
7 8
1045
12
14
12
11 12 14
13 350°M
5

15
13
SHIP'S TRACK

FiG. 18-I5. Fixing by bearing and sounding

Make allowance for the height of the tide betore comparing the
soundings
with the chart; select a bearing which crosses the fathom lines as nearly as
possible at right-angles; and bear in mind that the fix will not be reliable unless
the fathom lines are very clearly defined.

Approximate position by bearing and horizon range of a light

This method is most useful for finding the distance of a
it
powerful light when
appears above the horizon or dips below it. The point at which a light thus
appears or dips may be checked by the observer changing his
height of eye.
The height of a light given o the charts and in the Light Lists is the
of the centre of the lantern above the level ol mean
height
high water
springs. The
 PREPARATION FOR A PASSAGE 53

charted listed
Weather Is
or
geographical range at which a light may be
seen u ar

expressed in miles for an observer's height of eye ot I5 t .

sea
attd
when the level of the sea is that of
M.H.W.S., i.e. when the or
tic 5 height
above the level of the sea is about the least. The
earlier, and thus from a greater
light can De
se therefore
distance, if the tide is appreciably lower tna
M.H.W.S., or it the eye of the observer is more than ft above the
Geographical Range Table, which gives the ranges from which a light may be
15 sea.A
seen for various heights of the light and the observer, is included at the beginnng
of each volume of the Admiralty List of Lights.

10FT -SHIP TO

HIGH WATER SPRINGS

LEVEL OF MEAN
HORIZONN -HORIZON
TO LIGHT -
140 FT

FIG. 18-16. Approximate position by bearing and horizon range of a light

For example, the geographical range at which a powerful light, whose height
1S given on the chart as 140 ft, will appear above or dip below the horizon on

a clear night when an observer, whose height of eye is 4o ft, is 21.0 sca miles
from the light. Fig. 18-16 shows the relative positions of the ship and lighthouse
at this range.

PREPARATION FOR A PASAGE

Before making a passage, careful preparation is required. This includes:

(i) collecting all available information regarding the navigational aids and
dangers which may be encountered, and noting the times at which it is
expected that they will be encountered or passed;
(i) selecting a suitable track for the ship, and noting which part will be
covered in daylight and in which darkness;
(ii) checking the accuracy of the compass and log:
(iv) making sure that the charts are corrected from the Admiralty Notices to
Mariners.
The following publications contain all the information required:
The Mariner's Handbook contains information on Admiralty charts and
navigational publications, general navigation, general meteorology and ice.
The Admiralty Tide Tables, which are published annually, give the times and
heights of high and low water at the principal ports.
The Admiralty Sailing Directions, which are usually called "Plots', e.g. the
Channel Pilot' and the 'North Sea Pilot, give very detailed descriptions
of the coasts with their harbours,
ports,
and directions for passing coastal dangers and
navigational
aids, and dangers,
entering ports and harbours,
thus amplifying the information indicated the charts. The
by latest
Supplement to a "Pilot' must always be consulted.
 532
INTRODUCTION TO PILOTAGE
The Admiralty Lists of Lights give
gnt-vesscls and fog signals than
more
complete particulars ot
snore lights,
contain
temporary information
are given the
on charts; ana
tne
not
given on a chart.

ON PASSA GE
Care and use of charts at sea
The surface of the chart
can best be
CIearer a soft pencil and a soft rubber
preserved (and plotting will
be much
and ink or indelible pencil be used for are
account should used; on no

plotting. The chart

pen
Tolded along its proper creases and should
be always
ng the iront ot the chart table to kept dry. In wet weather a towel
placed
lean on, and removal of your cap before
eaning over it, will save the chart from
ake damage.
IS less
care
likelv
of the
parallel ruler and of the points of dividers. A
to slide or roll about if
turned over
parallel ruler
on its back when not n use.

Coasting
LAghts. Never pass
light without checking its period and
a

Light-buoys. Do not rely characteristics.

light-buoys alone, because the light sometimes fails.
on
Buoys and seamarks.
visible
Do not fix
your position by buoys when other
are close to the
ship. Remember that the buoys objects
trequently changed as the shoal extends, and marking a shoal are
by local authorities before there is time for they may be moved
the charts. On the information to be occasionally
the other hand, after a notice embodied on
and embodied on a concerning the movement or buoys
has been
unforeseen
promulgated chart, there may have been some
delay in putting the notice into effect.
Bays. Remember that currents and tidal
and streams often follow the
consequently set into bays and
bights. coastline
Fixing the ship
1. Fix
frequently when
together with the reading ofpossible. Jot down the bearings and
the log, in
your notebook.
times of each fix,
be unnecessary, but Many fixes
suddenly reduce visibilityeventually
tog or rain squalls may may
warning, and the last fix obtained then becomes of
the without
Always select objects close to the ship
2.
greatest importance.
regular intervals and getpreterence
in
is
preferable to fix at to distant
constant So objects. It
a
track. check on the
3. Always use the
ship's
largest-scale chart.
4.Having fixed the ship's poSition on
it and project from it the the chart, always write the time
ship's future track. against
The position of the ship
should
intervals, by dead reckoning if no fixalways be marked on the chart
is
Write the course on the middle of the possible.
at
frequent
. Keep careful and
a line which represents it on the chart.
continuous
book, throughout the time the reckoning on the
chart, and in your note-
6. Do
ship is at sea.
not have two charts on the table at the
between the scales same time, because confusion
may arise.
 533
ON PABSAGE

nand
between ielands use objects which are all on one o
7. When passing ately
been separaa
all on the other whenever po8sible; the two islands may have

surveyed. land, consideraoi

8. When taking the bearing of the edge of a low point of is the charted
unless the high water mark (which
CTTOT
may be introduced is emphasised when there is a large tiaal

is clearly defined. The error

coastline)
range and the beach gradient is slight.
available for taking bearings are mountain sumnmts
9. When the only objects inaccurate and
shoula

or inconspicuous marks, your

fix may be very
or distant with caution, or even disregarded
if there is no
other reason

great
be treated
for mistrusting your estimated position.
is necessary when transferring
from one çhart to anotner,
10.
Great care Transfer your position by Dearng
because they may be drawn on different scales. and then cneck
c o m m o n to both charts,
and
ot a well-charted
distance point of your position
error by verifying that the latitude
and longitude
TOr
any major
are the same by each chart (fig. 18-3).
which to pass dangers. The general
distance at
13 rule in coasting to pa
Saje and identitying alt o
make certain of seeing
Close
enough to the shore to and beacons, and thus be able
prominent landmarks, such as lighthouses
obtain frequent hxes.
so that ir
the coast,
which will not converge with
A cOurse should be steered on
can continue
or mist obscure the landmarks the ship
should suddenly
fog It requires experience
to decide at
course without running into danger.
her clear of coastal dangers. Beware ot
what distance the ship's track should pass its
to the land to identity
the half-way position, which is not close enough
out to ensure being
well clear of all dangers.
features easily and yet not far enough
outside the 3-tathom
track of the ship should pass
As a rough guide, the planned line when the
ft or less; and outside the 5-fathom
line when the draught is 1o coast they
between 1o and 20 ft. When
there are dangers n e a r the
draught is least one mile by day and at least two miless
a clearance of at
should be given
be adjusted for the prevailing weather,
These distances will have
to
at night. the nature of the coast and the probable
tidal streams and
currents expected,
the ship's position, both by day and at night.
opportunities for fixing
course to conform with the rule of the
Sighting other ships. When altering
road, always:
alter the course in plenty of time;
) intention clear;
(i1) alter course sufficiently to make your
course until all risk of collision is
take care not to resume your original
(i)
past.
a similar course must be
that every vessel sighted steering
Do not assume
destination as you are, or that other vessels sighted are
bound for the same

skill than your own.

navigated with more

Fog and thick weather

When it is seen that the ship is about to enter fog, note the bearing and
course of any ships in sight; and, if possible, obtain
approximate entering and
a fix. Betore distaice a fog the following precautions should always be taken:
 534 INTRODUCTION To PILOTAGE

or
is held be 'such a
rate
Reduce to a moderate speed. Moderate speed to

speed as will enable a vessel, after discovering another vessel meeting ne

collision irom
StOp and reverse her engines in suflicient time to prevent any
taking place'. (See Annex to the Internatiornal Regulations-Chapter 20.)
2. Operate radar, if fitted.
3. Station lookouts both on the forecastle and aloft.
4 It in soundings, start sounding.
5. Have an anchor ready for letting go when in the vicinity of land.

6. Order silence on deck.

7 Close watertight doors in accordance with ship's standing orders
S. Start the prescribed fog signal and listen for fog signals of other ships.
9. Warn the engine room.
10. Memorize the characteristics of navigational fog signals to be expected.
11. If in doubt about the at once
any ship's position, alter
course to a sate
course, parallel to or away fromn the coast. If this is not possible, stop and anchor.

Fog signals from shipping. When hearing before the beam the fog signal ot a
vessel the position of which is not certain, if circumstances permit you should
the exact time at
stop enginesand then navigate with caution. Note in the log
which the engines are stopped.
Article 15 of the International Regulations for Preventing Collisions at Sea
states that 'Power-driven vessels shall sound at intervals of not more than two
minutes . their appropriate sound signals. Make your signals regularly,
clearly, and deliberately in accordance with this article. If possible, time them
so as not to coincide with the signals of another vessel, but having once started
a signal on no account break oft in the middle ot it in order to listen to the

other vessel's signal.

The sound signals prescribed in Article 15, which are intended to announce
the presence of a ship, must not be confused with those in Article 28, which
are made only to a ship in sight to tell her how you intend to direct your course
in compliance with the Steering and Sailing Rules.
Fog signals marking navigational dangers. Do not rely on hearing a fog signal
from a light-vessel, lighthouse or buoy, because the direction of sound is often
deflected by fog and there are often large areas into which the sound does not
penetrate. Bell buoys and whistle buoys are also unreliable in calm weather, as
their sound signals may be operated by the motion of the sea.

PILOTAGE IN NARROW WATERSS

When rounding points of land, spits, shoals, buoys and light-vessels, allow
plenty of room; cutting corners is dangerous. When passing a buoy it is easy to
see which way the tidal stream is setting by observing the 'wake' made by the
buoy. Similarly, the direction in which a light-vessel is heading will, unless she
is moored head and stern, indicate the direction of the tidal stream if the wind
is not strong enough to swing her across it.
When rounding buoys and light-vessels to windward and against the strean,
they should always be given a wide berth. A ship passing near any light-vessel
that has clear water on all sides of her should pass downstream of her, because
underestimation of the strength of the tidal streanm may result in collision.
 THE SHTr's LOG 535

o m p a r e the name, shape, colour and topmark of a buoy with that

Shown on the
chart, to avoid the possibility of mistaking one buoy 1or
anotc
Low-lying land
When the land is too indistinct to fix the ship's position by bearings
shore objects, fix by bearings of beacons and light-vessels, it avallaDic,
preterence to
bearings of
buoys
where the shore is distant and low-lying (as in the Thames Estuary, Tor
Cxample) buoys nay be the only guide. Before making a passage in sucn
IOcality, especially it the weather is
likely to be thick, lay down on
the cnart ai
urreauired courses and make due allowance for the tidal stream that should
running at the time when you should pass them. Note in advance cach
course and the distance to be run on it, also the time it will take to steam ito"
u o y to buoy o r from beacon to beacon. Then check the tirne and course a

It, arrival
ou proceed.
a
after passing one
buoy, the calculated time of your at
second
buoy elapses
but you have not sighted it, proceed with tne
utmos
aution and stand by to anchor.

Fog in a narrow channel

In tog it will be necessary to lay your ship's course close to the starboard-hand
buoys instead ot in mid-channel, and to reduce speed; consequently your
courses from buoy to buoy, adjusted for tidal stream, current cr wind, must be
Worked out afresh and entered in the notebook.
Always carefully check the type of each buoy sighted. When departing from
a buoy, work out acCurately the time at which the ship should pass and sight
the next buoy at her present course and speed. If at the end of that time the
next buoy is not in sight, stop the ship and, if possible, anchor, because when
the ship's course has been laid close to the buoys there is a very small margin
safety.
THE SHIP'S LOG

The log should be written up at the time when each incident recorded actually
occurs. Full instructions tor Writing up the log and various meteorological
tables are given inside the cover. The following notes amplity the instructions.
Distance run is an estimation ot the distance the ship has run through the
water in each hour or on each course, taking into account the revolutions,
the log reading, the state of the bottom and the effect of the wind.
Barometer readings. The reading of a mercurial barometer should be corrected
by the barometer correction slide before cntry in the log. An aneroid
baroneter should be adjusted to give the barometric pressure at sea level
and theretore no correction is needed lor the entry in the log.
nchor bearings should be the bearings of shore marks from the position of
the anchor. If, subsequently, anchor bearings are checked to ascertain
whether the ship is dragging, allowance must be made for the distance
between the anchor and the bridge.