ORD-10
Ordinary
Piloting
Instructors: George Crowl
Course Outline
a. Latitude / longitude. Plot positions.
 b. Degree system of direction, variation, deviation
 c. Measuring speed and distance
 d. 24 hour time system
 e. UTC / GMT / Zulu time and conversion
 f. DR table of headings / distances
 g. Use your Sea Scout Pocket Reference!

ORD-10a.
Demonstrate your understanding of latitude and
longitude.
 Using a Mercator chart, demonstrate that you can
locate your position from given coordinates and
determine the coordinates of at least five aids to
navigation.

Latitude / Longitude
Houston is about 30° north of the equator, and 90° west of
Greenwich. Numbers increase up and left in the US.
60 Minutes per Degree






60 minutes per degree
1 minute = 1 nautical mile
(measured north / south)
1 NM = 6080 ft
60 seconds = 1 minute
1 second = 101 feet
In Java, latitude increases
south and longitude
increases east. Why?
Plotting a Position




Determine the parallels on the chart that bracket the latitude.
Place the pivot point of the compass on the closest line.
Spread the compass until the lead rests on the given latitude.
Move to the approximate longitude and swing an arc.
Plotting a Position



The same process is repeated using the longitude scale and the given longitude.
The desired position is the intersection of these two arcs.
If plotted correctly, the intersection should occur at the crest of both arcs.
Minutes / Seconds
Minutes / Tenths, Hundredths




Measure in degrees, minutes, seconds (N29° 34’ 47”) OR
Measure in degrees, minutes, and tenths, hundredths, thousandths
(N29° 34.783’)
N 29° 34’ 47” = N 29° 34.783’
See the left and bottom edges of your chart, and the 1/10’ marks on
the middle.
EXERCISE – Plot the following coordinates:
 N41°41.4' W072°05.5'
 N41°40.2' W072°01.1'
 N41-39.6
W071-57.6
 N41-37.5
W071-59.6
 N41-39.0
W072-01.4
Plotted Points
Determine Coordinates of…

1. Channel Island Light Fl 8s 20ft 5M

2. Bowditch Bay Light G9 Fl G 4s

3. Oyster River Light G1 Fl G 2s

4. Bowditch Bay Buoy R N 14

5. Bowditch Bay Light R16 Fl R 4s
Coordinates are:
1.
 2.
 3.
 4.
 5.

Channel Is Light
BB G9 Fl G 4s
OR G1 Fl G 2s
BB R14 R N 14
BB R16 Fl R 4s
N41°41.7'
N41-37.5
N41-36.7
N41-39.8
N41-38.8
W071°53.7'
W071-55.0
W072-01.0
W072-04.5
W072-07.9
ORD-10b.
Explain the degree system of compass direction.
 Explain variation and deviation, and how they are
used to convert between true and compass
headings and bearings.

Degree System of Compass Direction
(Outer Ring)
360° in a circle, 0° and 360° at North (star)
 090° = East
 180° = South
 270° = West
 Any intermediate
direction measured
by numbered angle

North Magnetic Pole
Compass does
not point N
 Changes
everywhere
 Points 3° E
here, so (-)
subtract
from True

Variation (inner circle)
Compass variation – same for all compasses
 Plotted on chart
compass rose
 Listed on bottom
of chart also
 Look at your chart

Deviation
Deflection of a compass
needle caused by a
magnetic influence
Deviation
Different on EVERY boat
 Different on EVERY heading for every boat!
Defiant Compass Swing 4 NOV 06
Motor on, under way
 Also –E & +W
TRUE VAR MAG DEV COMP

007
035
092
120
154
182
213
243
274
305
332
007
-4
-4
-4
-4
-4
-4
-4
-4
-4
-4
-4
-4
003
031
088
116
150
178
209
239
270
301
328
003
-3
-1
+2
+4
0
+2
+1
+1
0
-1
+2
-3
000
030
060
090
120
150
180
210
240
270
300
330
360
Variation, Deviation & Compass
Correction

TC VAR MC DEV COMP

117 -3E

T

Add Whisky (+W)

V
114
+2W 116
Makes Dull Company -
Hand compasses = no deviation, because deviation
depends on where you are on the boat
Sample Deck Log
Compass Correction
East is Least (-) “-3E”
West is Best (+) “+15W”
Compass Correction
T True
V
Variation
 M Magnetic
D
Deviation
C
Compass


TV Makes Dull Company
ORD-10c.

Describe three kinds of devices used aboard ship for
measuring speed and/or distance traveled and, if
possible, demonstrate their use.
Speed Logs
Speed by RPM
 Dutchman’s log 5”/30’ = 3.56KT
 Ground Log
 Chip Log
 Patent Log
 Taffrail Log
 GPS

Chip Log
Patent / Taffrail Log
10c. Measure Speed and Distance
Distance is measured in
 Nautical miles
 = 6080 feet
 Speed is measured in
 Knots
 (Nautical miles per hour)

Measuring Distance
Always measure distance on the Latitude scale!
 OR – use the scale on the chart

Why We Use Vertical Scale
Measuring Course – Parallel Rules
Using parallel rules
•
A
SSPR
p. 22
B
Measuring Course – Plotter
Plotter – align using your dividers
 Grommet on longitude line

Deck Log Plan
Start your deck log with true course and distance.
Derive mag course and perhaps compass.
Speed Time Distance
S (speed)
60 (minutes)
=
D (distance)
T (time)
Estimate Speed, Calculate Time
6.0 = 9.3
60
X
60x9.3 = 558÷6.0 = 93 = 1+33
ORD-10e.

Explain the 24-hour time system and demonstrate
that you can convert between 12- and 24- hour time.
12- vs. 24-Hour Time












12-Hour
1:00 AM
2:00 AM
3:00 AM
4:00 AM
5:00 AM
6:00 AM
7:00 AM
8:00 AM
9:00 AM
10:00 AM
11:00 AM
Noon
24-Hour
0100
0200
0300
0400
0500
0600
0700
0800
0900
1000
1100
1200
12-Hour 24-Hour
1:00 PM 1300
2:00 PM 1400
3:00 PM 1500
4:00 PM 1600
5:00 PM 1700
6:00 PM 1800
7:00 PM 1900
8:00 PM 2000
9:00 PM 2100
10:00 PM 2200
11:00 PM 2300
Midnight 2400
24-Hour Clock Faces
ORD-10d.
Understand Universal Coordinated Time (Greenwich
Mean Time or Zulu Time) and zone time.
 Demonstrate your ability to convert from one to the
other for your local area.

Zone Time
UCT / GMT / Zulu
Zone
Standard DST
Zulu
 Eastern
1000
1100 1500
 Central
0900
1000 1500
 Mountain 0800
0900 1500
 Pacific
0700
0800
1500

ORD-10f.
Make a dead reckoning table of compass and
distances (minimum three legs) between two points,
plot these on a chart, and determine the final
position.
 Note: Ideally this requirement should be met while
under way. If this is not possible, it may be
simulated using charts.

Dead Reckoning

Record of ships progress based on
 Course
 Speed
 Time traveled
 Known starting point (fix)
 Checked every hour, minimum
 Checked at every course or speed change
Dead Reckoning Terms
DR
 EP
 Fix
 LOP
C
S

Dead Reckoning Position
Estimated Position
Established position by any means
Line of Position
Course
Speed
Dead Reckoning (DR)

Start from a fix

Label all lines on chart

Numbers are rounded off

Use Military time

Courses & bearings
are 3 digits (045, 218)

Label course with C &
bearing with B (C045, B126)
• Speed in Knots (1/10 K) placed under the
course line
• Distance to nearest 1/10 NM place after
speed
• DR is marked by a dot and semicircle

• Fix is marked by a dot and circle with the
time 
• Estimated position marked by a dot and
square [·] and time
Chart Labeling
DR
C083
S8.4 D3.6
.
.
Estimated
Position
FIX
.
DR Exercise
Navigator cruising in Bowditch Bay.
 Plan the cruise with given data.
 We will then give you the instrument readings to
make that cruise.

Deck Log RW OR to DR
Bowditch Bay RW OR to DR
DR to BB R6
BB R6 to RG D
BB R6 to RG D
RG D to RG CP
BB R6 to RG D
Summary
Make a plan
 Write it down (deck log, chart)
 Follow it if you can
 Navigation requires times. Write them down!
 DR ahead, it makes life easier
 The perfect is the enemy of the good. A decent new
heading on time is better than a perfect one late.

Fair Winds

And a following sea