Plotting the course for a sailing boat
Piloting skills need to be required for anyone who wishes to be skipper of a yacht - for even short cruises. They include two basic things - steering of the vessel safely, and making calculations with the purpose to establish your correct position. There is no form of navigation, which requires more alertness, experience and correct decisions than piloting. They say you'd better not lose your point than have the best means to find it. If you keep track of the position constantly, you will be able to react quickly and adequately.
Refreshing the boat's position can be done by you, or electronically. If you choose to give your trust to the machine, makes sure that every system has a back-up. One of the most stupid things that can happen to you is to risk and lose your life because you over-trusted an electronic device.
Before you even try to locate your boat on a chart, you must have a real idea as to where you are on the water. If you have a reliable GPS, then this is no problem.
The easier aids to use for positioning are navigational tools placed in critical spots only for this purpose. You will remember that many of these aids to navigation like buoys are labeled with a number or letter. Lighthouses are also shown on the map together with marks as to where the light can be seen furthest from. From a small boat, the limit of a lighthouse to be seen is between 5 and 10 miles.
Landmarks that are easily recognizable from land are included in the chart.
- Put the chart on a flat surface, then place one of the features of the chart facing its location on the ground. Then see if the second feature also matches up. If it does, you are positive where you are.
- Verify your position using the relative location of the other objects. Check other prominent features and try to determine if they are forward, behind, in line or side by side in relation to the first feature.
- You can take advantage of the relative location of the objects. It is difficult to estimate the exact sizes or height. The landscape and seascape is prone to change, depending on the location of the viewer. So you have to account for that. The most useful skill a seaman can have in the field of navigation is to develop the ability to transfer what you see on the map to what you see in the environment and vice versa.
To locate a boat on the map is the most crucial thing when you navigate. An easy way to do this is to imagine the sea as a flat surface, a two-dimensional space. In such two-dimensional environment all objects are located using linear (polar) co-ordinates. Rectilinear that are drawn on paper with little rectangles. The reference point in this system is the cris-cross of the Greenwich meridian with the Equator. Polar coordinates are not so common ashore, but in a boat, they are very helpful, if not indispensable. After you have selected the reference points, then there are two measures you need for the location of the object - the distance and the bearing. You need to draw also a Line of Position (LOP). Establishing correct LOPs is the knack of piloting.
In certain cases the skipper can avoid using compass and rulers by taking manufactured or natural bearing markers. For example if two buoys form a straight line when viewed from the boat (actually the first will almost completely cover the further one), then the boat lies on the line of those two objects. The natural objects are no different - just take for example an edge of an island and a hill, or a lighthouse. The most challenging use of natural ranges takes place when you maneuvre through shallow water and you need to make numerous fast course changes. Here the value of your reference points increases. The navigator and the skipper exchange information and take decisions on the spot, they may not even resort to the chart. They follow their intuition and what they see from the surrounding scenery. That is where practice and experience count - the more you have them, the easier you roam between other vessels and natural objects. Hence the more pleasure you get from sailing.
Using LOP you can identify safe zones past dangerous places - just draw a line tangent to the danger, then with the ruler transfer it to the compass rose, where the bearing is read with no marking of the chart.
In some cases, knowing your yacht is somewhere on a line is not enough to ensure your safety. So you need to know the exact position and for that you take the bearing of another object (preferably from 60 do 90 degrees away from the first), and you draw a line. The point where the two lines intersect is where you are. But this, of course, is if we assume that the navigator made no errors. Unfortunately, there is one informal rule which is called "The First Rule of Navigation" and it postulates: "All Navigators Make Mistakes". You can check the factor of mistakes but drawing a third line from a third object - and where the three lines intersect you will have a triangle. If it is small, then it means your calculations were accurate enough; if it is large, than you've made some mistakes. The larger the triangle, the bigger the place where your boat might be.
Taking bearings is not the only way you can identify your position - another approach is to use distance measurements instead of bearings. Distance can be taken electronically or with an optical finder, or with a tool like the sextant.