Radar Plotting Calculator
Calculate distance between two targets or determine a single target's track and speed.
1. Distance Between Two Targets
Target A
Target B
Two-Target Plot
2. Single Target Track & Speed
Observation 1
Observation 2
Time Interval
Single Target Track Plot
**Formula Used:** The calculation is based on the Law of Cosines for distance between two points, and vector analysis for determining course and speed. The SVG plot is a visual representation and may not be perfectly to scale for all inputs.
About Radar Plotting Calculator
The Foundation of Collision Avoidance
While modern ARPA (Automatic Radar Plotting Aid) systems automate target tracking, understanding the mathematical principles behind radar plotting is essential for every Deck Officer. This calculator provides a digital version of the traditional "Maneuvering Board" (Mobard), allowing for rapid verification of target movements and spatial relationships between vessels.
1. Distance Between Targets
This finds the "true distance" between two observed objects (e.g., two ships or a ship and a buoy) using their relative position to your own ship.
Law of Cosines:
d² = r₁² + r₂² - 2r₁r₂ cos(Δθ)
2. Target Track & Speed
By observing a target at two different times (T1 and T2), you can determine its relative or true vector.
Vector Integration:
Speed = (√Δx² + Δy²) / ΔTime
Navigational Best Practices
- Bearings: Use "True Bearings" (gyro-stabilized) whenever possible for more accurate plotting results.
- Intervals: For target tracking, standard maritime practice uses a 6-minute interval, as it simplifies speed calculations (Distance in NM × 10 = Speed in Knots).
- Verification: This tool outputs North-up vector data. Always cross-check results with your AIS and ARPA overlays to identify potential system errors or "Target Swap."
Safe Navigation (COLREGs)
Under Rule 7 of the COLREGs (Risk of Collision), every vessel must use all available means to determine if a risk of collision exists. Regular radar plotting is a mandatory requirement for maintaining a proper lookout and making informed decisions to avoid close-quarters situations.