12 time, speed and distance
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Navigation
NAU 102
Lesson 12
Time, Speed, Distance
Calculation of Time, Speed and Distance
A daily task for a navigator.
Calculation requires accuracy and speed.
When will I get there?
How fast should I go?
Speed
Unit is the Knot (kt. or kn. or knt.)
From the knotted speed log.
Speed
Unit is the Knot (kt. or kn. or knt.)
1 knot = 1 nm/hour
Speed = Distance/Time
Calculation
Several Methods
Mental Calculation
“6 Minute Rule”
Logarithmic Scale
Nomogram
Mathematical Formula
Mental Calculation
Solve using simple ratios of time units.
e.g. ½, ⅓, ¼
Your speed is 20 kts. How far will you travel in 30 minutes?
You travel 6 nm in 20 minutes. What is your speed?
10 nm
18 kts
“6 Minute Rule”
6 minutes is 1/10th of an hour.
Every 6 minutes, you travel a distance equal to 1/10th of your speed.
Move the decimal point 1 place to the left or right.
“6 Minute Rule”
E.g. If your speed is 15 kts., how far will you travel in 6 minutes?
15.0
1.50 nm
“6 Minute Rule”
E.g. What is your speed if you travel 2.7 nm in travel in 6 minutes?
2.7
27 kts.
“6 Minute Rule”
You can use multiples of 6 minutes as well.
6 minutes = 0.1 hour
12 minutes = 0.2 hour
18 minutes = 0.3 hour
Etc.
“6 Minute Rule”
E.g. If your speed is 15 kts., how far will you travel in 18 minutes?
15.0
1.50 nm x 3 = 4.5 nm
Logarithmic Scale
On some charts and radar plotting sheets.
Nomogram
On some charts and maneuvering boards.
Nomogram
E.g. How far will you travel in 16 minutes at 13 kts?
Nomogram
E.g. How long will it take to travel in 2.5 nm at 16 kts?
Math Formula
Distance = Speed x Time
D = S x T
S = D/T
T = D/S
ETA
Estimated Time of Arrival
What time will I get there?
For short voyages:
Transit Time = Distance/Speed
Transit Time + Departure Time = ETA
ETA
Example
You depart Point A at 0800 and steam for 60 nm to Point B at 13 knots. What is
your ETA at Point B?
Transit Time = 60 nm/13 kts = 4.6154 hrs
= 4 hrs + 0.6154 hrs * 60 min/hr
= 4 hrs 37 min + 0800 = 1237
ETA
For longer voyages, we need to know about Time Zones.
Time Zones
Earth is divided into 24 time zones.
Time differs by an hour from neighboring zones.
Everyone in the zone keeps the same time.
Time Zones
Each time zone is 15° of longitude wide.
360° / 24 = 15°
Zones are numbered (“zone descriptions”)
0 through -12 in east longitude
0 through +12 in west longitude
Time Zones
Time Zones
First, calculate the central meridian of a zone
E.g. ZD +4
Zones extends 7.5° east & west of the center.
Zone Boundaries
15° x zone description
4 x 15° = 60° W
Time Zones
Time Zones
To find the zone of a particular location:
•Divide by 15
•Round to the nearest whole number
•Convert longitude to degrees & tenths
Time Zones
ZD = -9
141.5°/15 = 9.43
141° 30’ = 141.5°
E.g. What is the ZD of 141° 30’ E
(- E/+W)
ZD = -10142.66°/15 = 9.51
142° 40’ = 142.66°
E.g. What is the ZD of 142° 40’ E?
Introduction to Navigation
Questions?
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