Last Known Position (LKP)

This section of the system is only used if we need to calculate the coordinates of the LKP.  If we already know this information we can go straight to the Datum calculation section.

What is the Last Known Position?

The Last Known Position (LKP) of the casualty, or Point Last Seen (PLS) or Drift Start Position (DSP), is a fundamental item of information in the estimating of where a casualty might be found.  

The accuracy of the LKP directly affects the probability of finding the casualty.  

There are various sources of this information

•The casualty himself in the form of coordinates from a navigation device, bearings from where he is to identifiable points, verbal descriptions.

•From an observer or  in the form of descriptions, or, if we are lucky, bearings from where they are to the casualty they are observing

What information do we need to know?

We need to know –

•The COORDINATES of the location the casualty was known to be at most recently

•The TIME the casualty as at this location - when there ismore than one observer it is important that the bearing from each observer is taken at the same (or very similar) time otherwise they cannot be used together in the calculations as the casualty will have moved during the time between the different bearings being taken.

Where could the information come from?

The information can either come from 

•A third party observer (or caller) on land or at sea

In this case, we can calculate the LKP using input from 1, 2 or 3 observers.  Obviously, the more observers, the more accurate the calculated LKP will be.

We need to know the following information from the observer

•Where the observer is.  This can come from

oThe position is stored in the Points reference table

oAsking for a WhatsApp location pin

oAsking them to describe where they are and finding the coordinates in Google Earth

•If there is only one observer we need and estimate of the distance from the observer to the casualty. 

As it is quite hard to estimate distance on the sea, the positions in the local points information have the height above sea level, and therefore the distance to the horizon.  This helps as we can ask the observer to tell us how far away in relation to the horizon eg. If the observer is standing at a place that is 45m above sea level, the horizon is about 13 nautical miles – so if the says that the casualty is about halfway to the horizon, we can estimate that the casualty is between 6 to 7 nautical miles away.

•The direction or bearing from the observer to the casualty and we must establish if this bearing is a True bearing or a Magnetic bearing.

•What the casualty is and, where possible, the condition of the casualty, with a description that can be used to identify the casualty when the crew reach the area eg color of kite or sail, color and size of vessel etc

•The time that the observer saw the casualty

•The casualty themselves

In order to be able to calculate the position of the casualty, he needs to give us a bearing from himself to a recognised point eg a lighthouse, a tower etc

Again, we can calculate the casualty's position from 1, 2 or 3 bearings, but we are likely to get a more accurate result if he can give us 3 points.

If the casualty can only give information to 1 point, we also need him to estimate the distance from where he is to the point.

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