Summary GenNav - scale Worksheet

Scale
Scale = Earth Distance
Chart length



Worked Example 1 Worked Example 4
Two positions 10nm apart are measured at 5cm on What is the chart spacing in cms between parallels of
the chart? 60N and 61N on a chart with a scale of 1:1,000,000?
What is the scale of the chart?
Earth distance = 60nm
Scale = Earth Distance
Chart length Chart Length = Earth Distance
Scale
D = 10 x 1852 x 100 So: 60 x 1852 x 100
5 1,000,000
= 370,400 = 11.1cm

Therefore the scale is 1:370,400 Worked Example 5
Which is the largest scale?
Worked Example 2
Chart length between 60°N 005°W and 60°N a. 1 inch = 11.2nm
005°54’W is 10cm. b. 1 inch = 11.2sm
What is the scale of the chart? c. 1 cm = 11.2nm

Earth Distance (Along 60°N) = Departure a. 1 inch = 11.2 x 6080(feet in 1nm) x 12 inches
Scale = 1:817,152
Departure = ch long’ x cos lat b. 1 inch = 11.2 x 5280 (feet in 1sm) x 12 inches
=54’ x cos 60 = 27nm Scale = 1:709,632
c. 1cm = 11.2 x 1.852 x 100,000cm
So, Scale = Earth Distance Scale is 1:2,074, 240
Chart length
REMEMBER - SMALLEST NUMBER = LARGEST
= 27 x 1852 x 100 SCALE
10
= 500,000
Therefore the scale is 1:500,000
Worked Example 6
Worked Example 3 Point X is at 6130N and Y is at 5830N. If the track
A chart has a scale of 1:1,000,000. If the chart length between X and Y is a constant 120°T and the scale is
between A and B measures 1.5”, what is the distance 1:1,000,000 at 60N, what is the chart length in cm
between A and B in nm? between X and Y?

Scale = Earth Distance Earth distance X to Y = 360nm
Chart length
Earth distance = 1,000,000 x 1.5” 360nm x 1852 x 10
72960” (6080ft x 12) 1,000,000
= 20.6nm
=66.7cm