Night Time Special Event – Rally Navigation
Over recent years the club has held a ‘Night Time Navigational Event’, an exercise in driving and route planning using the Ordnance Survey Landranger maps.
Whilst almost everyone can happily read a map when stationary, to navigate along strange roads whilst in motion can become quite confusing. The addition of darkness is yet another complication ! Whilst road navigation is perhaps not important for competitive events held by off-road clubs, even a gentle venture down a byeway requires accurate map reading – one wrong turn and you could be following a bridlepath, or in a farmyard with an angry landowner facing you !
Navigational events are fun, but involve going outside in the cold and wet ! A popular variant held by motor clubs is a ‘Table Top Navigational Rally’. In this you practice your navigational skills and compete in the dry and warmth, preferably next to your favourite pint. This article introduces some of the navigational techniques used during competitive road rallies, that can also be applied to Table Top rallies.
You need a map, pen, pencil and paper, ruler. Use a soft pencil so that any marks on the map can be rubbed out later, there is no need to use a highlighter etc.
When reading grid references a Romer makes things easier, but not essential. This is a small piece of plastic with map scales etc. printed round the edge. The most useful part of it is the top right corner, which has 1:50,000 scale map gradations (divisions of a grid square) marked along and down it, counting backwards from the corner. When you place the correct numbered marks on the grid lines of the map, the corner of the Romer shows the point the map reference refers to. Romers can generally be found in specialist outdoor shops.
In a Table Top rally, compass, GPS etc. will be of no use !!
The maps used for road rallying are the ubiquitous Ordnance Survey Landranger series at a scale of 1:50,000. Each map covers an area of 40×40 km (25×25 miles), the series covers the whole of mainland Britain and the major islands in just over 200 overlapping sheets.
What does the term 1:50,000 mean ?
It is the scale of the map, the Representative Fraction (RF) which is the standard method of expressing a scale on all maps using the metric system. So a scale of 1:50,000 means that on this series of maps one centimetre on the map represents 50,000 centimetres on the ground. Translated into distances most can visualise, 1 centimetre on the map = 500 metres (546.8 yards), 2cm equals a kilometre and 1.25 inches is approximately one mile.
A national grid map reference gives a precise location on the map in terms of the grid lines printed on the map in blue. A map reference is given as an even number of digits – the first half of it refers to the “Eastings” which run across the map, the second half to the “Northings” which run upwards. To remember how to read a grid reference think of crawling first and then standing up.
By convention, a map reference does not refer to a point, but a square area whose size depends on the accuracy to which the reference is quoted. On road rallies this only applies to four figure references, which refer to whole grid squares; six and eight figure ones can be considered as points.
Four Figure – these refer to an entire 1km grid square; the square is the one to the right of the vertical grid line and above the horizontal one, e.g. on map 152, 7241 is the grid square containing Briary Wood Farm.
Six Figure – these refer to a point to an accuracy of 100m (2mm on the map) e.g. Briary Wood Farm is at 725417. To plot this with a Romer, first find the grid square, then position the “5” mark on the top edge of the Romer on vertical grid line 72, and the “7” mark on the right edge of the Romer on horizontal grid line 41.
Eight Figure – these refer to a point to an accuracy of 10m (0.2mm on the map). Whilst a GPS might provide this detail, it is not possible for a human to read the maps to this accuracy. The extra digits (4th and 8th) are more commonly written as a fraction, typically ½ or ¼ . This would give an accuracy to the nearest 25m.
Letters and Prefixes – map references only refer to a point within a 100km by 100km area; on a rally this is not a problem, as each Landranger covers an area less than a sixth of this size. To give a map reference which is unique across the whole country, you need to specify the two letter code for the area. Sheet 152 is in area SP (look at the top right of the map, in large blue outline letters) so the example above would be SP725417.
A rally (real life or table top) proceeds between numbered stages, known as ‘Time Controls’ (TC). These are typically manned, at each time control the instructions for the next stage are released. In a 12-Car Rally organised under RACMSA rules the average time between any stage must be not more than 30 mph.
Between any two time controls there may be one or more ‘Passage Controls’ (PC), these are not manned but represent answers to questions – e.g. name of farm, spot height on map, number of intersections passed. Any question that can be answered by reading the map or being observant whilst driving.
Whilst some road rallies provide pre-marked maps identifying the route, in the typical 12-Car RACMSA Rally the route is indicated by a series of clues that may be found from reading the map. This provides an exercise for the navigator as well as the driver. In a Table Top Rally everyone plays the role of the navigator – may be the driver just gets the beer !
The only thing that can go wrong when following a route is that you can get lost ! In a road rally mileage covered is often recorded to reveal this. Additionally Passage Controls (PC’s) can be employed to test your powers of observation. For example, between two Time Controls (TC’s) you may be asked to record the names of farms passed, or spot heights or any other feature that you may drive past. Since racing on public roads is not allowed, it is not time that is necessarily important, rather points collected by spotting all the Passage Controls and completing stages within a specified mileage. In a Table Top Rally it is difficult to measure distance covered, so just Passage Controls, representing features on the map are used.
The following are examples of just some of the types of clues that are employed, these are the ones that will be used in our own Table Top Rally.
A simple route could just be a sequence of points defined by grid references that you must pass through. Grid references can also have the direction of approach and/or the direction of departure attached. The approach direction always comes before the reference and the departure direction comes after it.
NE345980 means approach 345980 from the North East.
765987W means depart 765987 to the West. N123456SW means approach 123456 from the North and depart to the South West.
A typical route defined by map references might therefore be:
TC1 664228SW, via W670222E, via NNE672½204½, via 679205E, TC2 W689½205
This is the opposite of the Pass Through clue; plot all the points, then draw in a route which doesn’t go through any of those marks. For example
AVOID: 459636 442649 431653 450664 438671 448678 459675 470677 464689 477695
The name of this type of navigation comes from the Tulip Rally, which first used it in the 1950s.
Tulip, or ball and arrow instructions, are simple diagrams of the route junctions with the ball indicating where you come from and the arrow indicating where you are going to. Normally they are given in order !
Tulips may be orientated as on the map, or turned around so that the ball is always at the bottom, or most of the balls and arrows may be left off deliberately. Sometimes they may be squared up.
Herringbones, or Straight Lines as they are sometimes called, are a very simple method of defining the route, once you understand how they work. Imagine the route drawn with a little bit of road leading away from each junction, then pulled tight like a piece of string. The route that you take is then a straight line, missing roads on the left and right accordingly. The way to convert the herringbone to a route on your map is to consider 3-way junctions as leave a road on the left or leave a road on the right.
If the junction on the map is shaped like this, going straight on from A to B you would leave a road on the right. However also turning from C to A or from B to C you would leave a road on the right. For each of these three cases the junction on the herringbone will look the same. Similarly, to leave a road on the left you could be going straight on from B to A, taking a right from A to C, or turning right at the T-junction from C to B.