Section D-5 Plotting and Labeling

1

Objectives

The student will:• Learn how to use the CPS plotter• Know how to label course lines, LOPs, DR positions,

Fixes• Know the required standards of accuracy for chartwork• Be able to plan a cruise

2

The New Mk II Plotter

• Used to measure TRUE directions on a chart

3

Plotting Shapes

North Arrow ALWAYS points North

(using Lat/Lo lines)

Clear tape allows navigator to mark and measure

distances

The New Mk II Plotter

4

Boat symbol indicates

direction of travel

Arrow points to Reciprocal reading

on Plotter Rose

Grid Lines

Arrow indicates direction of

Bearing

Reading the Scales

Longitude Chart Line

Points True North

Parallel to Longitude

Line

5

90° TRUE100°

Magnetic

Variation

10° West

Reading the Compass

Rose

090°270°

000°

180°

6

Finding the TRUE & Magnetic course between two points

7

C 300/ 320 M

A

B

300° True

NORTH

Variation20° West

320°Magnetic

S 10.0

Aid

We want to go 040° True from the aid

8

C 0

40/ 0

20 M

Turn the Plotter Rose

to the direction 040°Variation20° East020°

Magnetic

S 10.

0

130

True Bearing of 130°

/ 110 M

9

Aid

Turn the Plotter Roseto the bearing 130°

NORTH

Bearings go UNDER the line

Variation20° East

110° Magnetic

Drawing Parallel Lines

.

NORTH

Plotter Roseindicates a bearing of

340°

Required distance

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Parallel Lines

Bearing of 340° should

be maintained on plotter

Orig

inal L

ine

New

Lin

e

Standards of Accuracy

• For directions– to the nearest degree– in 3 digits (e.g. 075)

• For time– to the nearest minute– in 4 digits (e.g. 1345)

11

Standards of Accuracy continued

• For distances– to the nearest tenth of a nautical mile– 10.1 nm

• For positions expressed as latitude and longitude– to the nearest tenth of a minute L 43° 21.3’ N Lo 123° 10.5’ W

• For speed– to the nearest tenth of a knot – 5.2 kn

12

Planning a Cruise

• Establish a point of departure– determine an accurate fix– aid “close aboard” means boat is at the aid

• use dot (or circle) at base of charted aid• charted dock can be point of departure

• Establish a destination– a clearly identifiable location marked on the chart and

recognizable from boat– last part of any cruise is done through conning

• Plot on chart

13

Plotting and Labelling Chart

• Look for marked hazards– plot around them

• Track is the line showing the intended path of the boat.

• TRUE Course equals the Track unless compensating for wind or current– no wind or current in this course

14

Labelling Charts

• A FIX

• A DR position

• Course Line– course in TRUE & Magnetic – speed

• LOPs

15

XKnown position = FIX

C 045 / 055 M

S 6.0

Always draw lines from FIXes

The FIX

A FIX is plotted as a dot inside a small circle

16

The DR Position

• Plotted– at any convenient time interval– every hour on the hour– when change in course– when change in speed– when a bearing is taken

• Usually plotted only one hour ahead of the boat’s position

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0900

C 045 / 055 M

S 6.0

0800

The DR Position

Note how all symbols have a dot marking the EXACT position

0700

FIX

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LOPs

• Drawn TOWARD the object from seaward

• Time is placed on the ‘north’ side of the line (FIX does not require LOPs labeled with time).

• Direction of Bearing (in True) is placed on the ‘south’ side of the line followed by a slash and the Magnetic Bearing

19

Finding the Expected Duration

• Measure along the course line from the point of departure to the destination

• For Speed– powerboats, assume most economical cruising speed– sailboats, estimate from direction and force of wind

• 60D=St , solve for t

20

Finding the Compass Course to Steer

CDMVT

To steer0

in this course

T plus or minus

V

From

compass rose

From

Course Plot

21

Selecting Aids and Landmarks

• Study chart to find aids and landmarks you can use for either conning or plotting

• Identify possible LOPs– ranges, lights, steep cliffs, points of land in line, towers, steeples,

depths

22

Using LOPs

• LOPs drawn parallel with the track can give an indication of “cross-track error”– the boat’s distance to the left or right of the track

• On the water, a back bearing on the point of departure will give an early indication if the boat is on track– calculate reciprocal, (boat track = +/- 180)

– if back bearing equals reciprocal, boat on course

– if back bearing less than reciprocal, boat is off course to left (Left Less)

– if back bearing greater than reciprocal, boat is off course to right

23

Using LOPs continued

• An LOP that cuts the track can give an estimate of the distance travelled from the last known position (FIX)

• By taking time into account, determine– ETA – Speed Made Good

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0947

1000Measured distance

Using the measured distance (D),

And the time (t) it took to get to that bearing

you would find the Speed Made Good (SMG)

with 60D=St

Using your speed (s) and measured distance (D),

you would find the time (t) expected to get to that bearing from the FIX

with 60D=st

Add the time to the FIX time to get ETA

C 0

39 /

019

M

25

S 10.

0

C 054 / 034

MS 6.0

18

00

17

00

18

43

347 / 327 M

2000

1843

1852

091 / 071 M

1900

C 0

23 /

003

MS

6.0

2100

C 119 / 099 M

2034

S 6.0

You are the navigator on a boat coming into port at dusk on a wet and very windy night.

You draw a line from your last FIX on a course of 054°T to the buoy CS 47.

You plot DRs as every whole hour approaches.

At 1843, you spot a buoy ahead and think you are on track.

You take a bearing of 347° True on a TV tower

You take a bearing of 091° True on a chimney.

FIX

You realize the buoy straight ahead is CS 48 which marks an area of foul ground.

At 1852, you alter course to 023°, again heading for buoy CS 47.

You mark DRs for every whole hour.

At 2034, you pass close aboard CS 47 and change course to 119° to follow the range into the harbour.

26

Keeping a LOG

• To maintain a permanent record of the cruise

• Enter– times– courses steered– bearings– FIXes– ETAs– Latitude & Longitude

27

LOG

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