Sailings

Question 1

Define Parallel Sailings

Answer 1

Used to find the distance steamed along a parallel of latitude between two meridians of longitude.
The distance East or West is called a DEPARTURE and expressed in Nm

Question 2

Define Plane sailing and its limitations

Answer 2

Plane sailing is used to find course and distance on a Rhumb Line. You solve the relationship between D.Lat, Departure, Distance and Course.

Limitations:
In accurate over distances above 600 Nm because it uses mean Lat.
Inaccurate at high latitudes because it does not account for the shape of the Earth

Question 3

Define Mercator Sailings and the limitations

Answer 3

Used to determine a Rhumb line course and distance between two positions.
It uses D.Long and Meridional Parts (minutes of Longitude). Therefore, can be used at high llatitudes and at any distance.
Limitations:
When calculating the distance at courses close to 90* or 270*. Small differences in course can create large differences in distance. So, when near these courses you should calculate to 6dp.

Question 4

What are the two types of charts and there advantages?

Answer 4

Mercator Chart and Gnomonic Chart
Mercator Chart:
Lines of Latitude and meridians of longitude are parallel
Rhumb line is straight
Course lines cross Meridians at the same angle therefore can measure bearings, courses and distance
land appears the correct shape
Gnomonic:
Meridians are curve and lines of latitude are curved
Great circle routes are straight and Rhumb lines are curved

Question 5

What are advantages and disadvantages to using a Great Circle over a Rhumb Line?

Answer 5

A great circle is a shorter distance then the a Rhumb Line therefore saving fuel and time.
A Great Circle may take you into higher latitudes therefore encounter bad weather with increased risk to damage to vessel and cargo and a slower steaming speed.

Question 6

When the Hemispheres are different how do you work out D.lat and D.Long

Answer 6

Add the positions together and name as B

Question 7

When the Hemispheres are the same how do you work out D.lat and D.Long

Answer 7

Subtract the smaller number from the larger one. Name with direction of travel

Question 8

What do you do if D.Long is over 180*

Answer 8

You minus 360* and change the sign

Question 9

To what dp should be distances and courses be>

Answer 9

1 dp

Question 10

In Mercator Sailings what is significant at courses near of 90* and 270*

Answer 10

Small change in course could lead to a big difference in distance. So, when near these courses you should calculate to 6dp

Question 11

What correction do you need to apply for each quadrant (NE, SE, SW and NW)

Answer 11

NE = 0
SE = 180-
SW = 180+
NW = 360-

Question 12

How do you name Initial Course and Final Course in Great Circle Sailings?

Answer 12

Initial Course = Same as elevated pole + same as direction of travel
Final Course = Opposite to elevated pole + same as direction of travel

Question 13

Which side should you draw the elevated pole in the sketch?

Answer 13

It does no matter which side you draw the elevated pole as long as you apply the 90* correction correctly.

Question 14

How do you calculate PA,PB, and P?

Answer 14

PA = 90* +/- AlLat (It can be + or - depending on the position of the pole in relation to ALat)
PB= 90* +/- BlLat (It can be + or - depending on the position of the pole in relation to BLat)
P = This is the D.long