Radar & ARPA Trainer
Two modes. Mode A: solve the plotting triangle on a live radar display — T₁ and T₂ echoes are plotted for you, then WO, OA, and AB are drawn to reveal CPA, TCPA, and true motion. Mode B: parallel indexing — see how clearing distance is derived from the PI line.
What you're practising
Reading the plotting triangle (WO, OA, AB) to extract CPA and TCPA from relative echoes, and setting a parallel index line at the correct clearing distance.
Pass criterion
Label all three vectors, state CPA and TCPA from the ARPA readout, and explain what happens if the target echo crosses your PI line.
Plotting — what the examiners test
- • WO = own ship's track over the interval, laid off from T₁ — not from own ship
- • OA = relative motion from T₁ to T₂ — what you see on the radar screen
- • AB = target's true motion — the hidden vector the triangle reveals
- • CPA = perpendicular distance from own ship (origin) to the RML
- • TCPA = time from now until CPA, along the RML at relative speed
- • Risk of collision exists when bearing does not appreciably change — confirm with CPA
Module 09 — Study Notes
Full written notes covering radar principles, S-band vs X-band, modes, limitations, sources of error, ARPA, relative and true motion, and parallel indexing.
Open Module 09 notes →