Lost Your GPS? Make a Sun Compass!
I am dyslexic so please bear with me. Revised 20200725
The Scenario
What
do you do if your GPS has for some reason failed! Battery is flat, whatever
‘it’s ‘kaputt’!
And unlike ‘Rambo’
you don’t have a magnetic compass built into your knife
to fall back on for rough navigation. I can show you a way out. With your
watch, a piece of paper and a stick. I can show you a simple way to make a
Sun-Compass that is good enough for Basic Navigation on land or sea. A
flat card Protractor that is easy to produce without the use of design
drawing equipment as if you were out lost in the bush!
What is a Sun Compass?
The
simplest way to image it is, you have a basic Sundial, with a 360-degree
protractor attached around its base. The ‘TRUE’ north or south position of the
protractor would be at the 12 o’clock position of the Sundial, (Depending on
whether you are north or south of the equator). If you go to say an old
botanical garden or outside a public museum, you would probably find an old
‘Victorian’ styled bronze Sundial with the points of the compass also marked
around the Sundial. That is not only a Sundial, but it is also a Compass,
in effect it is a Sun-Compass.
How Do You Orientate A Sundial?
I
was an officer in an Army Reserve Armoured Reconnaissance Regiment, (4/19
PWLH). Our regiment used the Sun-Compass as an integral part of armoured
vehicle navigation in desert training exercises. (Imagine standing in the turret,
of a ‘steel’ armoured vehicle with a magnetic compass, it was useless!) For
some time I was teaching each new intake of lads returning from recruit
training. Part of their training was navigation. When teaching the Sun-Compass
I gave this simple example.
“Imagine
you are a landscape gardener working for the City. While working in the Museum
gardens you accidentally back you vehicle into the Sundial!’ Oh NO! What do you
do?” The lads would come up with all sorts of answers. To which I said ‘No
that’s All Too Hard!’ You have a watch don’t you? Then mix up a batch of
cement, slap it on the top of the pedestal, put the Sundial back on top, and
gently turn the Sundial until the shadow is on the correct time. Done! But what
else have you done? The points of the compass, which are built into the
Sundial, you have also now aligned them to north, south etc. Effectively you
now have a Sun-Compass, so lets refer to it from now on as a Sun-Compass
Sun-Compass Navigation
The
next question I would ask the lads was how would you use the Sun-Compass to
navigate? Well imagine the manager of the Museum comes over to you, (and you
hope he doesn’t lean on the Sun-Compass), and he gives you a simple job! “We
want you to move the Sundial 50 metres exactly due west of its current
position, over there, beyond the tall grass”. You might think to yourself, ‘you
museum boffin’, I don’t have a compass so how do you expect me to travel
exactly due west? So I asked the lads, ‘how would you do it?’ The lads would
again come up with some weird ideas such as, ‘Wait till sunset then head
towards the sun?’ "Well you could, but there is no overtime pay! No it is
simple, just put the Sun-Compass into your wheelbarrow, with the west mark
pointing to the front of your wheelbarrow. Now turn the wheelbarrow until the
shadow of the Sun-Compass is at the correct time. You are now facing west! Now
with your tape measure pegged to the ground at the start point, and keeping the
shadow on the correct time, simply plough your way through the long grass with
the wheelbarrow until you measure out 50 metres on the tape measure!
Done!"
‘Basically
lads, that is the simplicity of the Sun-Compasses we have fitted to our
vehicles. [Refer to the photo below]. The crew commander turns the Sun-Compass
until the required bearing is in line with the direction of travel. Then he
tells the driver to turn the vehicle, “left or right stick;” until the shadow
is on the correct time, “Steady--That’s it--Pick something to go to--Driver
advance!” Then you would travel the distance required using the odometer. Much
like navigating a ship. They can also be used to find the bearing to a
‘target’. Simply turn the Sun-Compass until the shadow is on the correct time.
Now you have orientated the Sun-Compass to true north, and you can then see the
bearing from your location to any object! That is exactly the way they find a
bearing to a fire from a fire tower. For this simple reason a Sun-Compass would
be a handy tool on a fire-fighting vehicle!
Sun-Compass Basic Design
Principals
To
the right is a photo of the 4/19
PWLH Sun-Compass that my Regiment used. To my knowledge they were all home
made with considerable care. They consisted of the following: -
- Direction Arrow - bolted to the vehicle in the direction of travel.
- Bearing Plate - The larger of the two, marked in degrees or mils.
- Time Plate – The smaller of the two. Each hour marked in about 15-degree intervals.
- Gnome – Steel Centre Pin bolted to the vehicle, most had a locking wing nut.
- Bubble Level - for levelling the compass before setting a bearing.
You
can see a slot to the left that housed a bolt and wing nut to lock the two
plates together. This gave you the option to lock in a correction for ‘Day-light
Saving’, ‘Grid North’ or both. There are numerous designs you can Google. One
web site is, The
Sundial Goes To War, which shows the history of Sun-Compasses used by the
military. Another site is, A
Hila Science Video, which will give you a basic understanding of the
Sundial.
Making A ‘PAPER’ Sun-Compass
This
is a basic survival idea to keep in mind. With nothing more than your watch, a
piece of paper and a pencil, you can make a Sun-Compass. Remember I said, “for basic
navigation” only. You will also require some basic map skills to get
yourself out of trouble!
Lets
start with the basic design principles of how to make the time plate. What do
we know about the Earth’s rotation? It takes 24 hours to spin a full
360-degrees on its axes. So the Earth rotates 15-degrees each hour. (15 X 24 =
360). So you need to produce a circular piece of paper with 15-degree divisions
around the edge, WITHOUT a protractor etc!? How do you do that out in the BUSH?
First:
- Start with a square piece of paper; take note of where the centre of the
piece of paper is. And as you fold the paper, pay attention to detail and
accuracy. The greater the care the more accurate will be the end product.
1/
Fold it diagonally to produce a triangle [see diagram 1]. From now on all folds
will emanate from the centre of the paper.
2/ Fold that in half to produce a smaller triangle giving you a 90-degree angle at the centre of the paper, [see diagram 2].
2/ Fold that in half to produce a smaller triangle giving you a 90-degree angle at the centre of the paper, [see diagram 2].
3/ Fold it in half again and you have now produced a 45-degree angle at the centre of the paper, [see diagram 3].
NB:
You need to produce angles of 15-degrees. (15 X 3 = 45-degrees.)
4/
Now fold the paper in thirds as shown, [see diagram 4]. This will give you the
three 15-degree angles required.
5/
Now cut across the doted line as shown in the diagram. If you are out bush I
suggestion you use your hunting/bush knife. Place the paper on a firm dry hard
wood log; place your knife-edge on the doted line, then use a rock as a hammer
on the back edge of the knife. ‘CHONK!’, one clean cut.
7/
Mark each of the 15-degree points as per the diagram. I live in Melbourne ‘Oz’
so I have marked this card for the Southern Hemisphere, at local time, and NOT
daylight-save time. Remember at midday in the Southern Hemisphere the sun casts
a shadow to the South. So your hourly markings need to track around the
southern half of the card. But at midday in the Northern Hemisphere the sun
casts a shadow to the North. So your hourly markings for the Northern
Hemisphere need to track around the northern half of the card.
How
do you work out the markings?
Well:
- The daily ‘NEWS’ comes from the; ‘North, East West
and South’.
And
when the sun rises in the East at 6:00 am the shadow is cast to the West!
How Accurate Is Your ‘Paper’ Sun-Compass?
It
all depends on you latitude, (your distance from the equator). Check the two
web sites given above. The
Sundial Goes To War shows you some of the Sun-Compasses are mounted on an
angle, so that the Gnome would be parallel to the earth’s axis. Those types of
Sun-Compass were mostly designed for use in the North African desert near the
equator. As you know on the equator at noon the sun is directly above and will
cast little or no shadow on a flat surface. So you would have to be say, 3
degrees of latitude or more from the equator for your Sun-Compass to be of some
use. I agree that this Sun-Compass in the equator region would be of little
use. If you are on the equator you are either in the jungle or a desert. So: -
- Plotting the angle to tilt the Gnome becomes too difficult to achieve with the limited survival equipment.
- If you were in the jungle there would be limited sunlight to use your Sun-Compass!
- If you were in the desert you would be better off sheltering from the sun by day; and navigate by the stars at night.
The
other link, A Hila
Science Video shows you why a Sun-Compass is ‘Out Of Wack’ so to speak for
the first and last 3 hours of daylight. So in
short, if you Are Not near the equator, your ‘Sun-Compass’ at midday is
quite accurate. And for the 2 or 3 hours either side of noon, it is reasonable,
depending on you latitude.
Lets say it is 1800 hours, (6:00 PM), the sun is
setting in the west, and you apply this method shown in this diagram. Either
way if you are in the Northern Hemisphere or the Southern Hemisphere, you would
point the ‘hour hand’ or the 12 o’clock position of your watch to the sun, and
divide the angle. That comes out to be a line at 90-degrees crossing your watch
through the 3 and 9 o’clock positions. Now check your Sun-Compass card! That
would mean at 0600 and 1800 hours your Paper Sun-Compass is also reasonably
accurate.
Now you know your Sun-Compass is accurate at 0600, and
from 1000 to 1400 and at 1800 hours. As I said above rough enough, “for basic
navigation”. This is the best you can do for navigation at sea. But if
on land you can make some fine corrections.
How To ADJUST Your Sun-Compass.
How many times have you
seen an example of how to find ‘North’, by standing a stick vertically in the
ground and using a hand full of pebbles to mark out the movement of the shadow? It
takes some 3 to 5 hours right! At the end of all that you know where north is,
but it is NOT portable. Well do the same with your Sun-Compass.
At 1200 hrs local time, peg out your Sun-Compass with
a straight stick set vertically in the centre for the Gnome. Rotate the card
until the shadow is on 1200 hrs. It is now aligned with True North! (That is
exactly the same as the story above, about fixing the Sundial in the museum
gardens.) Lock it into position! Then at each hour from 1200 to 1800 mark the
actual shadow position of the Gnome on your Sun-Compass card. [If you have
daylight after 1800 then mark those positions also]. Then pick up the card,
fold it through the North-South line, and pinprick each hour mark through to
the other half of the card. Flatten the card out again and mark all the
corrected hour marks on the card. Your Sun-Compass is now complete and correct
for any time of daylight hours, and it is ‘portable!’ But if you
make one in mid summer don’t put it away and expect to use it in mid winter. It
will not be accurate due to the change in the Summer
and Winter Solstice. Your Sun-Compass is only accurate for the week or two
that you made it.
Below are some photos of the fine-tuning I did with my
Sun-Compass on the 26-28 July 2018, [Mid Winter in Melbourne]. I set it up at
noon on the roof of my house, in a position to be well clear of trees at
sunset. Then as described above, I spent the next 48 hours checked and marked
each hourly shadow, [when there was a shadow].
Quite frankly if I was out bush for just a day walk
and I was ‘geographically embarrassed’ relying on this Sun-Compass I would be
stopping by about 1600 to set up a warm/dry shelter. Then spend the rest of what
daylight is left to plan my way out.
How To Navigate Using Your Sun-Compass
To Take A Bearing To An Object: -
Adopt the handhold position. [Simply make a fist and
grab the bottom of the Gnome stick and hold the stick vertically. Rest the
Sun-Compass card horizontally on the top of your fist.] Look across or through
the stick to the object in the distance. Still looking at the object turn the
card until the shadow is on the correct time. Look through the stick to the
bearing on the other side of the card. That is the bearing to the object.
Plotting On Your Map The Bearing To The Object: -
Place the bottom tip of the stick on the object on the
map. Drop the Sun card down the stick to rest on the map. Rotate the card until
the north of the card is aligned with True North of the map. [NB: Not
Grid North]. Now using the card as a protractor, mark the bearing with a dot.
Remove the card. Use the stick as a straight edge; draw a line from the dot
through the object creating a bearing and a back-bearing line to the object.
To Find Your Location On The Map: -
[This is called a resection]. Lets say you are now
‘geographically embarrassed’ because of your broken GPS. All you have is this
Paper Sun-Compass! You are not exactly sure of your location on the map? Pick a
prominent feature, like a mountain that you can identify on the map. Take a
bearing to the object, as described above. Plot the back-bearing from the
object on your map. Pick another object at say 120 degrees different to the
first object, do the same again. Where the two lines cross should be within a ‘bulls
rough’ of your location on the map. Do that again and you will most probable
get a triangle. You should be within the triangle on your map.
To Take A Bear On Which To Travel: -
Adopt the handhold position as above. Look through the
stick to the far edge of the card; rotate the card until your looking through
the stick to the bearing you wish to travel. Hold the card on that same
bearing; turn yourself until the shadow of the stick is on the correct time.
You are now facing the bearing you wish to ravel.
Aiming OFF
There are some clever ideas used in navigation
particularly by those in competitive orienteering. One is called ‘aiming off’.
Think of it this way. You are trying to navigate to a road junction, or a hut
on a road. You plot the bearing to the hut. You march off on that bearing. BUT
99% of the time you will just come to ‘a road’! Which way is the hut, left or
right? To solve this problem you purposely ‘aim off’ two or three degrees say
to the right of the bearing. So that when you come to ‘just a road’, the hut
must be to the left. Considering the ‘accuracy’ of your Sun-Compass it would be
advisable to use ‘aiming off’ when navigating.
Hoping you never need to use this idea! But if you
give it a test run I would be interested in you comments PLEASE!
Some Other Articles of Mine
The Charge At Beersheba 1917
Advance Australia Fair - Complete - Australian National Anthem
The ‘Futurist Interpretation’ Automobile
GBY [God Bless Ya]
Yours Adrian Deacon