As a pilot, knowing where you are, where you are going and when you will arrive is expected at all times. Navigation, map reading, understanding the compass, the GPS, radio navigation aids, etc. are all considered normal requirements. Pilots are expected to use mathematics and geography in the same manner as their maritime parallels, just a lot faster. A cargo ship or cruise liner travelling at 25 knots is considered fast. An airliner travelling at 300 knots is considered slow! Supersonic aircraft can travel at speeds over 1,000 knots – which would make the travel time from Accra to Takoradi just 6 minutes!. Imagine getting lost at 1,000 knots!
Ah, I hear a question. ‘What is a knot?’ This is a good question. The knot is a measurement of speed. It is not an internationally accepted unit under the ‘SI’ International System of units, yet it is a standard measurement of speed for wind, maritime vessels and aircraft. One knot is the same as 1.852 kilometres per hour or 1.151 statute miles per hour. Its origins go back a long way, and involve a lump of wood and a ball of string – literally!
Let us go back in time. Are you ready? Warning: Some poetic licence is about to be used: Whooooosh. Pfffffzt. Kbang. Whoooooaaaa. (flash of light and some eerie music).
We are aboard a sea faring vessel in the eighteenth century, sailing on the open water. The wind is in our hair, and we cannot see land, the sky is without clouds, and we wonder to ourselves ‘how fast are we going?’. Well, we are in the 18th century, we only have a simple timing device made of glass and filled with sand, it is similar to an egg timer, called an hour glass or sand glass, but ours allows the sand to fall from one end to the other in thirty seconds – it is a thirty second timer.
So, we have a way to measure time, and we know that speed is the relationship of distance travelled over time. We now need to know how far we travel in one thirty second time slot, which we can measure with our thirty second sand glass.
We look around us, there is nothing but water, and we have no reference points. We ask the Captain (a pleasant fellow who seems totally unperturbed by our time travel arrival on his vessel) if he has a tape measure – he does not. But he can tell us that the vessel is 15.433 metres wide at the widest point. You jump for joy, because you just worked out in your head that 15.433m x 2 x 60 =1851.96 metres! Why is that so amazing? No, it is not because you worked it out in your head – it is because that is practically 1.852km (since there one thousand metres in a kilometre), and you know that 1.852km is significant (find out why later). In your excitement you ask the captain for long ball of string and a small wooden log. The Captain obliges, and watches as you carry out your tasks.
You tie one end of the string to the log, and then measure 15.433m and tie a knot in the string, you continue to tie knots in the string at a pitch of 15.433m until you have lots of knots in the line. You have worked out that at a speed of 1.852kph, the vessel would travel 15.433m every thirty seconds, hence 15.433m (the distance between the knots) x 2 (since there are two lots of 30 seconds in one minute) x 60 (because there are 60 minutes in an hour) =1851.96m or 1.852km (which is important for some reason we are yet to discover!), and now can test the theory.
You walk to the stern (back) of the boat and drop the log overboard into the water. You set your 30 second sand timer and let the string pass through your fingers – counting the knots that slip past you. At the end of the thirty seconds you have counted fifteen knots – and so you know that the boat is travelling at 15knots x 1.852 kilometres per hour, or just under 28 kilometres per hour.
The log overboard with a string with knots in was the way that speed was measured for hundreds of years, and it was reported using the speed ‘knots’.
However, the distance between the knots was never intended to be related to kilometres. Not at all. It was a specific distance in relation to a specific dimension of the planet Earth, measured from North Pole to South Pole (also known as a line of longitude). Since there are 180 degrees (from 90 degrees North to 90 degrees South) between the two points, and since each degree is made up of sixty minutes (thanks to Babylonian mathematicians), it was decided that the distance between the two poles would make the reference distance for all navigation, whereby ‘the distance scribed upon the surface of the planet of one minute of one degree of a line of longitude would be called one nautical mile’. Or in other words, that would be 10,800 nautical miles from pole to pole, or 21,600 nautical miles around the planet (that is 40,003.2 kilometres to travel around the world). The string was then calibrated (remember they did not have calculators or computers then) using reference marks that related to a speed of one half of one nautical mile per hour, if measured for thirty seconds. Thus one knot is equal to one nautical mile ( one second of one degree of travel on a line of longitude) per hour! Sailing vessels could purchase pre-manufactured kits called which had a simple piece of wood tied to a reel of knotted string, accompanied by a calibrated sandglass! Simple – and without a need to recharge it – which was good since they did not have electricity either! Considering that they had far less educational material and content then, than we do today, and had no electronic calculators or computers, they had to make it simple, reliable and repeatable.
Oh, I hear somebody saying ‘that was not simple!’ Yes, it was – it really was. Can you think of a simpler, more reliable manner through which to measure speed at sea without the modern gadgets we have today? The problem today is that we often fail to see the simple solution, because we are surrounded by a complicated world that prevents us from using our brains as much as they had to in the eighteenth century. They HAD to think, they HAD to innovate – they could not just sit back and take things for granted – far from it. They were brave, they took risks, they were ready to give up their lives based on their mistakes, and discover new wonders based on their successes. Fortunately, there were many successes.
We thank our captain, and slip back through the time vortex - Whhhhhooooooop Splooooosh - finding ourselves back reading Fresh Air Matters in the twenty first century. We trust you had a good trip!
We see far too may complicated systems being put into place, at great cost. Many of such systems are unreliable, based on overly convoluted approaches, lacking a good dose of common sense. If the challenge of measuring speed can be resolved with a bit of wood, a ball of string and an egg timer… then surely we can solve all the world’s problems without complication… if only we put our minds to it.
Capt. Yaw is Chief Flying Instructor and Chief Engineer at WAASPS, and lead Pilot with Medicine on the Move, Humanitarian Aviation Logistics (www.waasps.com www.medicineonthemove.org e-mail capt.yaw@gmail.com )
No comments:
Post a Comment