Radar plotting

Question 1

Formula for Targets True Speed?

Answer 1

W - > A / Plotting Interval X 60

Question 1

How to get CPA?

Answer 1

Right angle from relative line of approach to centre (+)

Question 2

Formula for W -> O?

Answer 2

Speed / 60 X Plotting Interval

Question 3

Formula for TCPA? (In minutes)

Answer 3

A -> n / O -> A X Plotting Interval

Question 4

How to get Targets true course?

Answer 4

Ruler over W -> A and roll to middle (+)

Question 5

How to get Aspect of target?

Answer 5

Extend line from W -> A and draw line from own vessel (+) -> A, aspect is degree between those two lines

Question 6

What symbol do I put at CPA?

Answer 6

n

Question 7

What symbol for O -> A?

Answer 7

(>)

Question 8

What symbol for W -> O?

Answer 8

>

Question 9

What symbol for W -> A?

Answer 9

> >

Question 10

How do you find your speed reduction if you are given a CPA (on a VRM)?

Answer 10

1. Basic report
2. Arc out VRM from centre (+)
3. DRAW out R.L.A (relative line of approach) from edge of circle back trough A, to W - > O line to find O1
4. New speed = W -> O1 / PI x 60

Question 11

How do you find your new CPA and TCPA if you reduce your speed?

Answer 11

1. Basic report
2. Calculate W -> O1 and plot
3. Draw line from O1 -> A and extend
4. Calculate new CPA (n1)
5. Calculate new TCPA , A-n1 / O1 -> A x Plotting Interval

Question 12

How do you plot an Instant alteration of course? (course given)

Answer 12

1. Basic report
2. Arc out W->O to Port or Stbd
3. Draw new HDG from centre through W to arc, this is your new O1
4. Join O1 to A for a new R.L.A

Question 13

How do you plot a Course alteration for desired CPA?

Answer 13

1. Basic report
2. Arc out CPA circle (VRM) from centre
3. Draw R.L.A from edge of VRM back through A and extend
4. Arc out W->O to Port or Stbd
5. Mark out O1
6. Draw line W->O1
7. Roll W-O1 to centre, that is your HDG

Question 14

How do you plot delayed alteration of course?

Answer 14

1. Basic report
2. Find A1, O->A / PI x Delay
3. Arc out W->O to Port or Stbd
4. Take new HDG through W and find O1
5. Join O1-> A in base plot then transfer to A1
6. TCPA A1->n1 /O1->A x PI
7. Add to A1 time

Question 15

How do you plot desired CPA by delayed alteration of course?

Answer 15

1. Basic report
2. Arc out VRM
3. Find A1
4. Draw R.L.A from VRM edge to A1 then transfer to A and extend
5. Arc out W->O
6. Find O1
7. Join W->O1
8. Roll to centre, this the C/A

Question 16

How to find set, rate & drift on a radar plot?

Answer 16

1. Identify fixed object
2. Draw up a vector triangle with “another way” «_space;towards W from A
3. A-W is your tide
4. Roll to centre to get tidal set
5. Measure the length to get drift
6. Calculate speed, A->W / PI x 60

Question 17

How to do a basic radar plot?

Question 18

How do you plot TTR? (Time to resume)

Answer 18

1. Mark out CPA VRM
2. Transfer original O->A to edge of VRM
3. Where the two R.L.A meet is your TTR

Question 19

How do you plot delayed reduction of speed?

Answer 19

1. Basic report
2. Find A1
3. Find O1 on original W->O line
4. Draw new R.L.A through A->O1 then transfer through A1

Question 20

How do you plot desired CPA by delayed reduction of speed?

Answer 20

1. Basic report
2. Draw VRM
3. Find A1
4. Draw new R.L.A through edge of VRM to A1 then transfer through A to get O1 on W->O line
5. Calculate new speed