Marie Flashcards
(25 cards)
What is bearing in navigation?
The horizontal direction of one terrestrial point from another, expressed in degrees.
What are the three different types of bearing?
- True bearing
- Compass bearing
- Relative bearing
Define true bearing.
The direction of an object or point in relation to true north, measured in degrees from 0° to 360°.
Define compass bearing.
The direction of an object or point taken with the compass, measured with respect to magnetic north.
What is relative bearing?
The direction of an object in relation to the current heading of a vessel, measured from 0° to 360°.
How is relative bearing measured?
From 0° to 360°, with 0° being dead ahead.
What is the function of an azimuth circle?
A device for measuring azimuths, consisting of a graduated ring equipped with a sighting vane.
What is a telescopic alidade?
A bearing circle with a telescope attached to the metal ring.
What is a pelorus?
A device for measuring in degrees the relative bearings of observed objects.
What is the formula to calculate gyro error?
Gyro Error = Gyro Heading - True Heading (based on quay line)
What is the acceptable limit for determining gyro error?
+/- 0.1 degree.
What steps are involved in determining gyro error?
- Observe the quay line
- Read the gyro heading
- Estimate true heading
- Calculate the gyro error
- Interpret the error
When is a gyro compass considered fast?
When the gyro error is positive.
When is a gyro compass considered slow?
When the gyro error is negative.
What is cross bearing?
The bearing of two or more objects used as intersecting lines of position for fixing the position of a craft.
How do you convert from compass to relative bearing?
Relative Bearing = True Bearing - Ship Heading.
If a vessel is heading 120° and a cruise ship bearing is 070°, what is the relative bearing?
310°.
If a vessel is heading 120° and a sailing vessel bearing is 240°, what is the relative bearing?
120°.
What is the true bearing of a ship sighted at a relative bearing of 090° while the ship is headed south?
270°.
What is the significance of variation in marine navigation?
It is the difference between true north and magnetic north.
What must be ensured when observing the quay line for gyro error determination?
The ship must be fully stationary to avoid drift.
What is the true heading if the quay line is aligned to 166° T and the gyro heading shows 165.3°?
Gyro error = -0.7°.
What is the true heading if the quay line is aligned to 221° T and the gyro heading shows 221.4°?
Gyro error = +0.4°.
What is the true heading if the quay line is aligned to 359° T and the gyro heading shows 000.8°?
Gyro error = -358.2°.
