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Plotting a course
Using GPS on board

Radio Navigation & GPS Systems



In the 21st century, when you cruise you need to take the best of both worlds - the modern and the ancient - which is to say that you must be able to find and position your boat with map, compass and pencil; however, you need to be quite familiar with the electronic gadgets and other newly designed stuffed (whose purpose is to make life easier anyway).
The oldest, most expensive and least effective navigation tool is the radio direction finder - RDF. It is far from accurate and its price is as much as the loran systems, which are more precise and present information in a form, which you might better use. The most important radio navigation systems for the non-professionals today are Loran-C and the GPS (Global Positioning System). Loran's systems are shore-based radio wave transmissions, whereas GPS receives signals from satellites in the earth's orbit. GPS revolutionized Loran the way Loran revolutionized RDF. GPS is by far the most accurate, least expensive, least susceptible to atmospheric and other inference.
Both Loran and GPS have the same functions - the main is to provide the information as to where the boat is (POS - position). They also give the SOG (speed over ground), COG (course over ground), range (distance) to destination (RNG), bearing of the destination (BRG), estimated time of arrival (ETA), Time Required to Get to the destination TTG), velocity (VMG), XTG (cross-track error), and of course, date and time. The newest GPS-s also include man-overboard function (also called save-position), anchor watch-out alarms, various waypoints. Most of the GPS-s also have a so-called NMEA ports, in the back of the instrument, for communication with other electronic devices such as depth-sounders, autopilots, laptops, and other equipment.
The effective use of the position (POS) is closely linked to the scale or precision of the chart in use. Reliable accuracy with most units that are so far available is about 100 m. So this should not be a problem in open sea or approaching the shore, but when you are very close to the port, or to the shore, you are to yourself - namely, you have to be on the alert, and to estimate very well and precisely the situation so that you enter the harbour and go lie alongside safely and clearly.
It is interesting to see how the circle of GPS error decreases with the increase of scale.
For a chart of 1:5000 scale the error circle is with 2 cm diameter, for 1:80 000, the diameter of this circle is about 1 - 2 mm. The Speed over the ground (SOG) measurement you need just for comparison with the data you get from the speedometer or log - so that you understand the tidal and stream currents.
GPS can have priceless role in planning a course, because you can input waypoints of the trip, or destination and the tool will calculate the course, distance, and approximate time to each point of the voyage. Because these gadgets have big memory, they can store really a lot of information about the currents, the reefs, also compass deviation/variation. It is needless to say that (provided you know how to use it properly!) GPS is faster and safer way to calculate than by hand. You can choose for the course output between great circle and rhumb line. The TTG and ETA functions help the planning of the course, which is essential.

Radar
It is an old-but-gold instrument: it can be of much aid for navigation in fog, for piloting; it can give you both distance and bearing to objects. If you can do the two jobs parallel - following on the screen of the radar and keeping the track on the chart, that would be the best.
Using radar to measure distance is simpler and faster way to take bearings.

Electronic Chart Displays
As in every, every field of life, the computer is fast taking over navigation. Electronic chart displays are the next step in the revolution, that is to say digitalized charts. These computer programmes which you buy, (and which are rather expensive, it may by added!), for certain water territory. They contain charts, currents, lighthouses, reefs, even buoys. everything you would need for a cruise. You can zoom in and out. If the laptop is connected to a GPS or Loran, it will show the boat's position all the time updated.

Warning: If you have a laptop with the necessary navigation programmes and a good GPS, do not consider yourself fit for difficult cruises. The devices do not guarantee you safe travel. They are of help, but they are breakable. Do not put your and your companions' lives at risk because you over-trust the electronic devices.