Radar simulator
Click anywhere on the scope to set the EBL (bearing) and VRM (range) markers. CPA + TCPA are computed continuously per target — red < 1nm, orange < 2nm, yellow safe.
Head-on encounter
Two power-driven vessels meeting on reciprocal courses. Rule 14: both vessels alter course to starboard so each passes on the other's port side.
- Own course
- 000° T
- Own speed
- 12 knots
- Targets
- 1
- Range
- 6 nm
How to use the simulator
- Play / Pause — advance simulated time. The clock in the bottom of the scope shows minutes since t=0.
- Speed multiplier — 1× is one real second per simulated second; 60× makes one minute of sim time pass in one real second.
- North-Up / Head-Up— toggle the scope orientation. Head-Up rotates the world so own ship's heading points up; bearings shown are relative.
- Click anywhere on the scope to drop the EBL + VRM at that point. Bearing and range appear below.
- Target colours: red = CPA < 1 nm (collision risk), orange = CPA < 2 nm, yellow = safe pass.
CPA + TCPA in 60 seconds
CPA (Closest Point of Approach) is the minimum distance the two vessels will pass each other if both maintain present course and speed. TCPA is the time until that minimum distance occurs.
A constant bearing with decreasing range means CPA = 0 — you are on a collision course (Rule 7). The simulator highlights this in red. The conventional safe-CPA threshold in coastal/open water is around 1 nm minimum; less is a collision avoidance action required scenario.
A negative TCPA means the closest point is in the past — the target is opening and not a concern from a collision standpoint.
Test yourself
Take the radar quiz for theory questions on radar use, range scales, true vs relative motion, and collision avoidance.