Radar navigation and ship collision avoidance

An Automatic Radar Plotting Aid (ARPA) in excel version - Marine freeware software

The officer on watch must be able to maneuver the ship in any conditions: adverse weather and sea conditions, high-density traffic areas. He must be able to navigate "blind" too.

This software allows students, Cadets, Officers and Captains to verify the correct execution of drawings and calculations on the maneuvering board to have all the movement data of the ships in the area. The file allows them to simulate all evasive maneuvers and within few seconds to choose the most suitable maneuver.

The software concurrently supplies all information of 5 targets for anti-collision decision making. Of course the most important data is the CPA (closest point of approach).

The officer will obtain the following data for each vessels :

  • CPA - closest point of approach
  • TCPA - Time to CPA
  • RML - Relative Motion Line
  • SRM - Speed of relative motion
  • Direction - True course of the vessel
  • Speed - Speed of the vessel

“ Radar sheet “

After having collected the data of the target/vessel in two different times at least 6 minutes apart  :

  • Time 1 : bearing 1 & range 1
  • Time 2 : bearing 2 & range 2

the user will need to enter in cells with a green background :

true course and speed of own ship:

Radar own ship

for each target:  time, bearing and range

Radar data target

Time (separator symbol between hours and minutes): be careful to enter two dots 16:15 or dot (16.15) using the editing keys according to the operating system (OS) and not the dot in the numeric keypad !

a partial look at the Radar Screen:


CPA (closest point of approach), TCPA (Time to CPA), RML (Relative Motion Line), Relative Speed, Direction (True course of the vessel) and Speed of the vessel are immediately displayed !

Radar processed data1


" EvasiveAction sheet "

It allows to perform trial maneuvers, including speed changes, course changes, and combined course/speed changes.

In this sheet the officer can simulate the "anti-collision" maneuver by entering hour / minute of the maneuver, new true course and new speed of own ship:

Radar evasive action

Default Action Time : it is the time of the last radar observation incremented by one minute (the user can still modify it).

On the right side of the sheet : the Maneuvering Board after the " Evasive Action " :

Radar maneuvering board

All new data of vessels will be displayed:

Radar processed data
  • The length of the vectors indicating the true course of the targets is not proportional to their speed.
  • The distance scale is fixed at 1: 1
  • Speed scale: the default setting is to 2: 1 on either the "Radar" sheet or the "EvasiveAction" sheet (user can set it to 1: 1).

For further notice see Notes sheet in the file.


EPA (Electronic Plotting Aid) or ATA (Automatic Tracking Aid) or ARPA (Automatic Radar Plotting Aid) ?

General Rules : Equipments

All passenger ships and ships between 300 and 500 gt (gross tonnage) : 1 radar (X-Band) at least with an Electronic Plotting Aid (EPA) allowing electronic plotting of at least 10 targets (without an automatic tracking )

Ships over 500gt: the ATA equipment operates with an automatic tracking

Ships over 3000gt: 2 Radars fitted with an ATA. The ATAs must be independent of each other. Radars 2 operating in S-Band

Ships over 10.000gt : 2 radars - Radar 1 equipped with ARPA ( manual and automatic acquisition, at least 20 targets, automatic tracking and target information for for anti-collision decision making displayed. Radar 2 equipped with ATA or ARPA.

 An outstanding synergy between a skilled programmer (of Dutch origin living in Indonesia) and a professional navigator (Italian) have led to the publication of this program in excel. About two months of work by Mr. Schaap for analysis, development and testing with daily contacts between Indonesia and Italy led to numerous "alpha versions" after the release of the "final version". Jelle Schaap has been able to grasp and interpret the needs of those who go by sea: to him the merit of the realization of this project.