Map Reading & Navigation – Part 7

One of the main problems with navigating at night or in poor visibility is that errors can occur and this may result in the inability to locate a particular waypoint.  This can occur for a number of reason which we will discuss and look at ways to resolve those errors.

The most important thing to remember, is that no matter how good or experienced a navigator you are, errors will always creep in.  This is not down to poor navigation, this is a consequence human verses terrain!

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Errors

If we accept that an error of 10% can occur is distance measuring due to pacing difficulties i.e constantly changing terrain, prevailing weather, or any number of natural issues.  Add to this an error of approximately plus or minus 4 degrees in your heading accuracy, it is easy to see how problems in poor visibility can occur.

Put all of this together, and you come up with the fact that as distance increases from 1km to 2km then 3km, the errors will accumulate until at the 3km point, your Area Of Probability (AOP) is no longer a point on the map, but an area of approximately 1 hectare or 100m x 100m (larger than a football pitch).

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Further errors can occur if you are navigating to a grid reference point rather than a feature.  Remember that a 6 figure grid reference denotes a 100m x 100m box and a 8-figure grid reference a 10m x 10m box.

With all of these built-in errors it is easy to see why you can miss a waypoint in poor visibility.  Therefore, we need a system which will allow us to locate our waypoint once we are within the estimated Area Of Probability (AOP).  To facilitate this we use search patterns to methodically search an AOP and locate the waypoints.

Search Patterns

Sweep Search:

This is the ideal pattern if you have a largish party, and can be instigated as you approach the AOP.  This search is best started approximately 100 – 300 metres before the estimated position of the waypoint.  The distance is dependant on the length of the leg so the 10% error of a 1km leg is 100m and 300m for a 3km leg.

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Courtesy of Mountaincraft & leadership – Eric Langmuir

With the leader maintaining the position of the original track, each member of the party moves out to the left to form a line at 90 degrees to the track.  The spacing is dictated by the visibility and each person must maintain visible contact with the person each side of them.

The party moves forward scanning the ground either side of themselves but no further than the adjacent person.  Once you have passed a distance twice that of the starting distance (i.e. for 100m walk 200m).  The party stops and the leaders maintains their position.  The rest of the group spreads out in a similar manner on the other side and then reverse their walk.

Expanding Spiral Search:

This search pattern can be under taken by a single individual and starts from the point at which the pacing and compass bearing end (estimated waypoint position).  The search is carried out with the aid of a compass on the cardinal bearings.

spiral
Courtesy of Mountaincraft & Leadership – Eric Langmuir

The search starts by walking the distance of visibility on magnetic north.  Turn right 90 degrees and walk east for twice the distance of visibility.  A further turn right 90 onto south then walk 3 times the distance of visibility.  This is continued with 90 degree turns and adding an extra distance of visibility each time.

As you walk, you are looking side to side in a sweeping visual search out the limit of visibility.  With each leg the search area expands until the waypoint is located.

Emergencies & Calling for Help

Always keep in mind that a situation might arise where you are genuinely lost for whatever reason.  This could lead to the deterioration of the physical well-being of your party.  They may be getting tired and a lot of standing around, whilst you try to work out where you are, could lead to the onset of hypothermia.

You should also consider the possibility that you are tired and cold and that the reason you are unable to re-locate yourself is due to your own onset of hypothermia.  Either way you have to react quickly are resolve the situation.

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Find somewhere sheltered, if possible, and get hot food and drinks prepared and consumed.  Get anyone in wet clothing into something drier and do whatever you can to keep everyone warm.

Take this opportunity to try one more time to work out where you are.  Use every technique available to you to either relocate your self or come up with a plan of escape.  Once all of this has been exhausted, consider the possibility that you may now be in an emergency situation and it is time to call the Mountain Rescue Team (MRT).

Remember, the members of each MRT will know their area like the back of their hands.  So, a conversation with them over the mobile phone (signal permitting) may be all that is required for them to assess your current position and start to talk you to an identifiable location.

If you can make mobile phone contact, the MRT may have access to SARLOC which can use your phone signal to pin-point your position.  If they can get this information, they will then be able to talk you down to a safe location.  However, if there are any members in the team whose wellbeing is under threat then the MRT will need to come to you to facilitate a rescue.

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Signalling

If you are in an emergency situation, it is important that you alert anyone within earshot or sight of you.  Therefore it is important that you know the signalling procedures when using a whistle and a torch.  Parties already on the hill may be able to reach you quicker than the MRT and offer assistance or even a means to safety.

Whistle:

Call for help – 6 blasts in quick succession repeated every minute.

Response from rescuers – 3 blasts in quick succession every minute.

Torch:

Call for help – 6 flashes in quick succession repeated every minute.

Response from rescuers – 3 flashes in quick succession every minute.

Remember, if you hear the 3 blasts or see the 3 flashes in response to your call DO NOT STOP – keep repeating the call until the rescuers have made visual contact with you.

Always use the Mountain Rescue as a final option not the go-to first option.  Do not call them unless it is absolutely necessary.  However, do not delay calling them when you really are in trouble.

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In Map Reading & Navigation – Part 8, we will be looking at electronic gadgets related to navigation.  When and how to use them and the related issues to be aware of.

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