7/28/2017
Lesson 8: Dead Reckoning
Lesson 7: Dead Reckoning
• AGENDA:
– Definition of Dead Reckoning
– Six Rules of Dead Reckoning
– Define/Apply the 3 min & 6 min Rules
• Applicable reading: Hobbs pg. 134-138.
Dead Reckoning
DR is the process of determining a ship’s
approximate position by applying, from a known
position, a vector or a series of consecutive vectors
representing the true courses steered and the
distance run as determined by the ship’s speed and
time, without considering the effects of wind and
current.
Dead Reckoning
• DR is derived from DEDUCED, or DED, reckoning
which was the process by which a vessel’s position was
computed trigonometrically in relation to a known
point of departure.
• This is performed as often as required by the 6 rules of
DR
• Uses:
– Determine present position
– Project future positions relative to hazards
– Measure the effects of current (winds, seas)
– Alter course to account the effects of current
Plot a new Course Line with Every Fix
or Running Fix
Plot a DR Position
Every Hour on the Hour
Plot a DR Position at
Every Course Change
Plot a DR Position at
Every Speed Change
S-10
S-15
S-5
Plot a DR Position for
Every Line of Position (LOP)
Tank
Plot a DR Position for
Every Fix or Running Fix
Speed-Time-Distance Calculations
• STD calculations can be made 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 / 10
where: D = distance traveled (nm)
S = speed in knots
HOMEWORK
REVIEW
• What is Dead Reckoning?
• What are the 6 Rules of DR?