Question 1

Explain with the use of a diagram the Earth's Magnetic Lines.

Accepted Answer

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Question 2

Explain Magnetic Variation.

Accepted Answer

Magnetic Variation ; Angle East or West between True North and Magnetic North
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Question 3

Explain with the use of a compass rose Variation.

Accepted Answer

Variation
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Question 4

Explain with the use of a diagram the approximate area where a Magnetic Compass is unstable.

Accepted Answer

Unstable area
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Question 5

Explain why a Boat Compass does not point exactly towards Magnetic North.

Accepted Answer

The Boat Compass does not point exactly towards the Magnetic North, because it is affected by ferrous masses and electric currents in the vacinity of the compass.
Electric wires, portable radios, binoculars, tools and other fero-magnetic objects will affect the boat compass.
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Question 6

Explain Compass Deviation.

Accepted Answer

Compass Deviation; Angle East or West between Magnetic North and Boat Compass.

Question 7

Explain with use of a diagram Compass Deviation.

Accepted Answer

Compass Deviation
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Question 8

What causes Compass Deviation?

Accepted Answer

Causes of Compass Deviation
Local magnetic fields:
 • Magnetic masses (winches / magnets from loud speakers / nearby radios / tools, etc.)
 • Electric currents producing a magnetic filed (lights / remote controls, etc.)

Question 9

Explain Conversions between the Norths.

Accepted Answer

Conversions between the Norths
 • True to Magnetic / Magnetic to True
 • Magnetic to Compass / Compass to Magnetic
 • True to Compass / Compass to True
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Question 10

When taking 2 bearings what results give the best accuracy?

Accepted Answer

2 LOP at right angles to each other.  To obtain more accurate results 3 LOP should be taken if possible to eliminate any errors that may occur from taking 2 LOP.
 
2 bearing LOP errors;
- Error in identifying the landmark (wrong lighthouse)
- Error in the concersion from Magnetic to True
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Question 11

When taking LOP what consideration should be taken to obtain the most accurate results.

Accepted Answer

For best results 3 LOP should be taken at about 120 degrees.
 
Taking a 3 bearing LOP eliminates errors than can occur with a 2 bearing LOP.
2 bearing LOP errors;
- Error in identifying the landmark (wrong lighthouse)
- Error in the concersion from Magnetic to True
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Question 12

Explain how you would determine your distance from a landmark by doubling your bearing.

Accepted Answer

Determining the distance from a landmark
Using a hand bearing compass, a pelorus, or an Automatic Direction Finder (ADF)
Doubling the bearing, e.g. from 30° to 60°:
Distance from the landmark (BC) = distance travelled by the boat (AB)
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Question 13

Explain how you would determine your distance from a landmark by doubling your bearing.

Accepted Answer

Doubling the bearing. ie. from 45° to 90°:
Distance from the landmark (BC) = distance travelled by the boat (AB)
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Question 14

Determine the distance off a landmark using distance travelled.

Accepted Answer

Distance from the landmark ≈ 6 times the distance travelled (A-B) for a change of bearing of 10°.
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Question 15

Explain distance off by Vertical Sextant Angle.

Accepted Answer

Vertical Sextant angle.
d = h / tg α  Measure α with a vertical sextant;
- read “tg α” off a trigonometric table
- read h off the marine chart
- calculation = d
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Question 16

Explain how to calculate the position of your vessel by using a vertical sextant angle and a bearing.

Accepted Answer

The boat position can be determined from a distance to the landmark (circle of position, vertical sextant), and a bearing (hand bearing compass)
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Question 17

Explain how to determine your position using 3 landmarks with horizontal sextant angles.

Accepted Answer

The boat position can be established from two circles of position (horizontal sextant angles, using three landmarks.
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Question 18

Explain the GPS accuracy on electronic charts.

Accepted Answer

Under the best conditions the horizontal accuracy of the GPS system is approximately 3 to 8 metres 95% of the time
The use of the Wide Area Augmentation System (WAAS), which provides corrections through a geostationary satellite, is one way to increase accuracy. Differential GPS, sending local corrections via ground transmitters close to US and Canadian shorelines, is another way.
Vertical accuracy is considerably lower.

Question 19

Explain the Limiting Factors of using GPS.

Accepted Answer

Limiting Factors of using GPS;
 
- Ionospheric and tropospheric interference
- Satellite positioning
- Calculating ability and accuracy of the GPS unit
- Multipath signals; Natural or artificial interference
- Horizontal chart datum and chart reliability
- Disappearance of details in vector charts at small scales
- Loss of signal due to accidental disconnection
- Loss of signal due to automatic cut-off at slow speed

Question 20

With the use of a diagram explain the cycle of tides.

Accepted Answer

Tide cycle.
 
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Question 21

Explain tides. Duration / Time Intervals / Range / Height.

Accepted Answer

Tides;
- Duration of Tide : time between Hi & Lo tides around measurement time.
- Time Intervals : time between measurement time and nearest Hi or Lo.
- Range of tide : height difference between Hi & Lo.
- Height Difference : height difference between height at measurement and nearest Hi or Lo.

Question 22

Explain how to determine the height of tides in feet without tide tables.

Accepted Answer

The rule of incremental 12ths;
– Particularly useful for tides in feet
 
– Assumes: Tide duration = 6 hours, 
                   Change in heights before or after a High or a Low =
•  1/12th of the total tide range during the first hour
•  2/12th during the second hour
•  3/12th during the third hour, and then the reverse:  3, 2, and 1 twelfths.
Height at any time = sum of the 12ths of the range accumulated since the High or the Low tide used as a reference.
Example:
1/12, 2/12, 3/12
- Falling tide
 
- Range = 11 feet (difference between the height of the High and the height of the following Low).
 
- Drop, four hours after the High?
 
- (1/12 + 2/12 + 3/12 + 3/12) x 11' = 9/12 x 11' = 99'/12 = 99 inches, or 8.25'

Question 23

Explain how to determine the height of tides in meters without tide tables.

Accepted Answer

The rule of 10ths and Quarters:   1/10, 1/4, 2/4, 3/4, 9/10
- Particularly useful for tides in meters
 
- Assumes: Tide duration = 6 hours,
Change in heights before or after a High or a Low =
•  1/10th of the total tide range after one hour
•  1/4 after two hours
•  2/4 after three hours
•  3/4 after four hours
•  9/10th after five hours
- Gives directly the height of the tide, without adding fractions.
- More precise, close to a High or a Low, than the method of the 12ths.
Example:
1/10, 1/4, 2/4, 3/4, 9/10
- Rising tide
- Range = 6 m
- Tide, four hours after the Low?
 
• 4 hours after the Low = 2 hours before the next High
• Tide height 4 hours after the low = 3/4 x (6m) = 4.5 m

Question 24

Explain a Vector.

Accepted Answer

A vector is a way to represent a phenomenon which can be defined by;
- A direction
- A magnitude (intensity)
Examples:
- A movement (direction, and distance travelled)
- A speed (direction, and magnitude)
- A force (direction, and magnitude)

Question 25

Explain how to determine Resulting Speed using vectors.

Accepted Answer

Resulting speed: Place the two speed vectors (“distance travelled” in one hour) at the end of each other.
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Question 26

Explain how to determine Resulting Distance Travelled using vectors.

Accepted Answer

Resulting distance travelled: Place the two vectors representing the “distance  travelled” during the time considered (e.g. 50 min or 1 h 40 min) at the end of each other.
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Question 27

Explain with the use of a diagram Set and Drift.

Accepted Answer

Measuring current Direction (“Set”) and Speed (“Drift”)​​​​​​​
 
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Question 28

With the use of a diagram explain how to compensate for a Known Current.

Accepted Answer

Compensating for known current;
The vector construction is for one hour. Given the  boat speed of 6 kn (arc of circle, 6 NM radius), the boat direction is chosen to offset the effect of the current (AC) and bring the boat back to the desired track (AB).
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Question 29

Explain with the use of a diagram how to compensate for leeway.

Accepted Answer

Leeway to port (wind on the starboard side)
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Question 30

Explain Nautical Miles

Accepted Answer

Distances are measured in Nautical Miles
- Abbreviation: “M” or, preferably, “NM”.
- Original Definition: 1’ (from the Center of the earth) at the surface of the earth.
- Only the Parallels of Latitude have a constant separation. Therefore, 1 NM = 1’ of Latitude
- Current definition: 1,852 m

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