Using information from an OBSERVER

It is very important that we get the following information from an observer

•What the casualty is and, as far as is possible, the condition of the casualty

•Position of the observer - Where they are observing from as accurately as is possible

•Time - What time they saw the casualty

•Bearing to casualty - A bearing from where they are to where the casualty is - we must know what device is used to measure this bearing so that we know whether it is a Magnetic or a True bearing

•Distance to casualty - If there is only one observer, we need to know how far the casualty is from the observer.  With this, we must be careful to find out what units the caller is estimating the distance in as we might need to convert the distance to nautical miles

One Observer

If there is one observer the LKP form will look like -

•A : This allows the user to tell SearchWell how many points will be used

•B : This indicates whether the bearings are True or Magnetic .... if there are more than one points and there are different bearing types (True and Magnetic) then the bearings must 
        be converted to either True or Magnetic before entering the value.

•C : If the point is found in the Points Table, it is quicker to use a filter to select out just those points that have the filter value in their name.  When using this, type the word you require and then PRESS ENTER

•D : This has the list of Points from the Points table. If a filter has been used, it will show the filtered points.  

  When you click on a point here, the coordinates of the point will be displayed in the Coordinates box.

•E : This is where the user can type coordinates if the position is not taken from the Points table, or, if it is taken from the Points table the coordinates of the point will display here

•F : The bearing in degrees from the observer to the casualty.  The bearing must be the same as that specified in "B" .... if True is selected, the given bearing must be True

•G : This only displays if One point is selected in "A" .... if more than one point is going to be given the distance box is hidden. The input must be distance from the observer to the casualty in nautical miles

•H : Click on this CALCULATE button to perform the calculation once all the input information has been given

•I : The calculated LKP coordinates are displayed here in the three major coordinate formats 

•J : This block gives information about the Caller 

oHeight above sea level if it is known

oApproximate distance to the horizon (if the height above sea level is known)

oDistance to the casualty

oThe True bearing from the observer to the casualty (particularly important when a magnetic bearing was input)

oThen the command for Google Maps that can be copied and sent to land based crew via WhatsApp/Telegram so that they can navigate to where the caller is

•K : GPX button which, when clicked, will create a waypoint of the LKP position that can be sent to the rescue vessel so that they can easily navigate to the LKP

The calculation

SearchWell uses the coordinates of the position of the caller with the distance and the bearing and calculates the estimated LKP coordinates.

Obviously, this is not very accurate, but it will give a "better than nothing" idea of where the casualty was at the time the observer saw it.

Two observers

The form for two observers is as follows - 

When the Two points button is selected, space for two inputs is displayed and the input for distance is removed

The LKP is taken as the point at which the two lines cross.

Three Observers

The form looks as follows - 

You can see that there is input space for three different callers, and the display shows information about all three callers.

What I illustrate here is that when a Magnetic bearing is input, the Magnetic Variation for the default station is displayed and can be changed, and the True Bearing to the Casualty is shown in the output box for each Caller.

The calculation

This time the three lines intersect each other forming a triangle called a "cocked hat". The coordinates in the centre of the triangle are taken as the LKP coordinates

This will tend to be the most accurate calculated LKP.

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