Light

9

99 9

99

999 9 95 5

5

5

11 1111

1111

1111

11

6pa

FL 6s 58ft 9M

Tank

Long Point

20

20 2

020

20

20 212

0

20

20

2121

21 2121 2123 23 23 23 23 23

1515 15 1517

1717 1719

19 19 19

C- 085 TS - 12

080008

100810

Fundamentals ofNaval Science

Dead Reckoning and Current

Sailing

Dead Reckoning• DR - Determining the position of a

vessel by adding to the last fix the ship’s true course and speed for a given time.

Dead Reckoning• Uses:

– Determine when change course/speed– To predict the time of sighting lights and other aids to navigation

– Project future positions relative to hazards– Measure the effects of current (winds, seas)– Alter course to account the effects of current

Plot a DR Position Every Hour on the Hour

09001000

1100

Plot a DR Position atEvery Course Change

20

24

29C-125

c-090

C-080

Plot a DR Position atEvery Speed Change

15 21 27

S-10 S-15 S-5

Plot a DR Position for Every Line of Position (LOP)

Tank

0826

0826c-1

95s-1

0

Plot a DR Position for Every Fix or Running Fix

46

0846

370937R-Fix

0846c-106s-10 52

58

A new course line shall be drawn from every fix with 2 DRs

at your fix interval

Typical DR plot

Speed-Time-Distance Calculations • using a nautical slide rule,

electronic calculator, set of pre-computed tables, or speed nomogram.

D = S x T where: D = distance traveled S = speed in knots

T = time in hours

Three Minute Rule In 3 minutes a vessel travels in yards a

distance 100 times its speed in knots. D = S x 100

where: D = distance traveled (yds) S = speed in knots

Six Minute Rule In 6 minutes a vessel travels in miles a distance equal to its speed in knots divided by 10.

D = S / 10where: D = distance traveled (nm)

S = speed in knots

Terms Used in Current Sailing Track (TR)

Speed of Advance (SOA) Course (C) Speed (S)

Terms Used in Current Sailing

Set (S) Drift (D)

Course Made Good (CMG)Speed Made Good (SMG)

Sensibility Check 1. Current pushing ahead, decrease speed.

2. Current pushing astern, increase speed.

3. Current pushing left, steer more to the right.

4. Current pushing right, steer more to the left.