(Bearings in degrees, distances in nm, velocities in knots, time only in minutes)

Ship A:

deg

knots

nm

Course

Veloc.

CPA_0

------

Ship B:

min

deg

nm

Time 1

Bear.1

Dist.1

Time 2

Bear.2

Dist.2

Delay

------

Trial A

deg

kt

tKA:

tVA:

RESULT:

New Course Ship A: (velocity unchanged!)

Trial Course (=tKA, tVA) of Ship A gives:

RADAR - Description

Based on RADAR-observations this program calculates possible courses in order to avoid collisions.
(Klick COMPUTE to see a default-solution. All input-data can be changed).
You may either use "North-Up" (true orientation) or "Head-Up" (relative orientation) of radar-screen,
but do not mix these while entering courses and bearings.

Description
Ship A is assumed to be your ship. Enter course, velocity and desired distance CPA_0
(=ClosestPointofApproach) to ship B.
Enter time1 (minutes only, ignore the hours) for the first observation by radar, bearing1 in degrees 0...360,
and distance1 in nautical miles. The same again for observation at time2.
Allow for 1...6 minutes Delay after time2, until the manoeuvre is started. Then hit COMPUTE.
The results first show the existing situation by actual CPA. KB is the true course of ship B,
VB its (or:"her") true velocity. KBr is the course of B on the radar-screen, and VBr the relative velocity on radar screen.
The manoeuvre to change the course should start at time3,
when ship B is at bearing3 and distance3.
One possibility is, to stop ship A completely. The consequence for nCPA (=new CPA) is indicated.
Proceeding with constant(!) velocity VA, new possible (limiting) courses for ship A then are given.
The symbol [>] means, new radar-course nKBr compatible with CPA_0 is bending to the right relative to old KBr,
analogous [<] nKBr bending to the left, from manoeuvre-point on.
If velocity-change is acceptable, a possible course and velocity is given for both [>] and [<].
You may also enter a trial course tKA and trial velocity tVA for ship A.
The resulting minimal distance tCPA is shown in the last line.
Here, tΔ= ... indicates the course-change from KA to tKA, positive to starbord, negative to portside.
A symbol # in front warns if tCPA is too small. A symbol ? warns if violation of §19 of ColReg (see below). Note: Avoid a change of course to portside if ship B is forward of the beam of ship A.
Avoid a change of course towards ship B if it is abeam or abaft the beam.
(see:§19, International regulations for the prevention of collisions at sea). Explanation:
The new courses KA1, KA2 are obtained by finding an intersection of a circle (radius VA) around the end-point of the velocity-vector
VB of the true course KB, which intersects the new relative course-vector nKBr at two points, in direction KA1,KA2, or eventually at none.
New courses between these two limiting values are possible, but at reduced velocity
(explicit example given, but handle with care) !

Copyright
This program is free software: you can redistribute it and/or modify
it under the terms of the GNU General Public License as published by the Free Software
Foundation, either version 3 of the license or any later version.

This program is distributed in the hope that it will be useful, but WITHOUT ANY WARRANTY;
without even the implied warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.
See the GNU General Public License
(www.gnu.org/licenses/) for more details.
If errors are encountered, kindly send a note to info@ocean-navigation.de.
Author: Heiner Müller-Krumbhaar
- Last update 28.feb.2023.