Search Section

Covered in this section

•Introduction (found on this page)

•Search Patterns (see Search Patterns)

•Multi-vessel searches in SearchWell (see Multi-vessel searches)

This section of the system calculates the various search patterns and allows us to output the results as a GPX file to send to the vessel.

Terms we need to understand

•Leg length - All the search patterns, with the exception of the Expanding Parallel Line, use the leg length – this is the distance of the first leg of a search pattern (from the start to the turning point 01)

•Arc Angle - The following search patterns require an Arc Angle - 

oExpanding Parallel Line

oExpanding ZigZag

The Arc Angle is measured at LKP and will define how the pattern expands.  Each leg will remain the track spacing apart, but the length of the leg will increase as the vessel moves further away from the start position.  

•Sweep width - is the distance on either side of the vessel where the crew would be able to see the casualty

•Track spacing - this is the distance between the legs of a search pattern.  This must be less than, or equal to, the Sweep width.  At this point I want to mention (to be discussed later) that in the Pendulum search pattern, the relationship between the leg length and the sweep width directly affects whether or not the search pattern moves fast along the drift line as required for a fast moving casualty, or slowly along the drift line but allows for much more divergence as required for a slow moving casualty.

Leg length or Arc Angle and Track Spacing

oLeg length or arc angle - all the search patterns with the exception of the Expanding Parallel Line and Expanding ZigZag need a leg length.  The leg length can be given as a distance in nautical miles

oTrack spacing - this is required by all search patterns except the Sector Search and the Goal Keeper patterns

What information do we need to know and where does this come from?

We collect the required information and use this to calculate all the patterns, so let us look at the information that is needed and where it comes from.

To calculate any pattern we need to know  the information about the casualty

•the DATUM position 

•the drift bearing

and then the Coxswain needs to tell us the information about the vessel

•the length of each leg

•the track spacing based on the conditions in the area and the casualty type

•the speed that it would be reasonable to average during the search

So, lets go through each of these items.

Datum

We have three options in selecting the coordinates of the Datum position –

owe can use the DATUM that was the result of a test drift calculation

owe can use the DATUM that was the result of a wind, current and leeway table calculation

owe can enter our own DATUM, and this can be done in any of the three coordinate formats 

To tell the system where the information comes from, we just click on the small white radio button above the displayed information.

NB to note that the system displays the date and time when the calculation was performed – this allows the user to confirm that it IS the calculation that has recently been performed.

Distance away from DATUM

Then, some searches are not started at the DATUM position, so, below the displayed coordinates is the opportunity to start the search a distance away from DATUM …. Either up-drift or down-drift (a negative number will result in the pattern starting the given distance away from the DATUM but between the LKP and DATUM ie up-drift)

•A : The Parallel Line Pattern often starts at the edge of the search area nearest the LKP - it would have a negative distance from Datum

•B : The Goal Keeper Pattern will most often be at the edge of the search area furthest away from the LKP - it would have a positive distance from Datum

Drift Bearing

Drift bearing is one of the results of the DATUM calculation, and so we can use -

othe result of the test drift calculation

othe result of the wind, current and leeway calculation

othe user can enter their own drift bearing

The search pattern will be created using this bearing.  In the case of a Sector Search, the Expanding Box Search and the Pendulum Search patterns, the first leg will be along this drift bearing.  In the case of parallel line and Goal Keeper Searches, the first leg of the search will always start on the port side of the drift path on a bearing of 90 degrees to the drift bearing.

Speed

The Coxswain is asked what speed he thinks he would be able to average during the search.  This will be based upon the prevailing conditions and also the casualty type that they are looking for.

We use this information in two ways –

oIf the Coxswain provides us with a distance for the leg length, we use the speed to calculate how long each leg and ultimately the search will take to perform

oIf the Coxswain provides us with a time he wants to take for the leg length, we use the speed to calculate the leg length

Search Pattern form Header

•A : the search pattern header contains the information used by all the patterns.  When you first enter the Search Pattern section the only part of the form that is displayed is the header part.  When you click on the Calculate button, all the search patterns that can be calculated will be calculated and the output section will be displayed

•B : the output contains the list of available patterns (which depends upon what information has been entered) and then the details of each pattern.  The patterns that are not available will be greyed out.

Any time information is changed in the header part of the form the output section will be hidden and you will have to click on the CALCULATION button to force a re-calculation of all the patterns.

Search Pattern requirements

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