Radar and ARPA Part 2 Flashcards
Parallel index lines - Explain how the OOW would regain track and then remain on track
- alter course (into the tide) until the vessel regains track with the PI off the headland.
- Adjust heading to make good the required ground track.
What should be checked when parallel indexing and position fixing?
- Heading marker alignment
- Gyro error and gyro input
- Alignment of radar with gyro input
- Positive identification of navigational objects of interest
What is a SART used for and what type of radar would you expect to see its transmissions?
- A Search and Rescue Transponder is type of distress signal.
- It can be seen on a 3cm (X-band) radar
Describe the use of a True Vector
- It indicates the direction a target is moving in.
- (heading on a sea stabilised radar)
Describe the use of a Relative Vector
It gives indication of risk of collision if in the direction of own ship
List the five factors to take into account when setting the CPA/TCPA alarm on the radar?
- The state of visibility
- Traffic density
- Manoeuvrability of the vessel
- Proximity of navigational hazards
- Master’s standing orders
How many targets can the OOW expect to be able to track at one time?
Between 20 and 40 depending on the size of vessel
List, in order, the six pieces of information ARPA is required to give about a target
- Present Range
- Present Bearing
- Predicted CPA
- Predicted TCPA
- Calculated True course
- Calculated True speed
After acquiring a target how long should the OOW wait before being given reliable information based
on steady state tracking?
3 minutes
Explain what can happen when two acquired targets are moving close to each other on the display and what action the OOW should take.
- As two targets get close to one another their tracking gates may overlap.
- The radar may get confused and stop tracking one target with the other one given its vector
- One vector should be deleted from this target
- The target should be re-acquired
How does a radar work?
- Transmits electro magnetic pulse at a known speed
- Meassures the time difference between the transmission being sent and the transmission being received
- ** Distance = S X T / 2 **
Minimum detection range
(Radar pulse length)
- A radar cannot detect anything within half a pulse length
- Due to the return not being received
Minimum detetction range
(Antenna height)
Affecting the area close to the vessel similar to a blind sector
Minimum detection range
(Vertical beam width)
Linked with antenna height and blind sectors
Maximum detection range
(Antenna height)
- The higher the better
- The radar horizon is further
