Colin Jones explains how you can join in the fun.

A CHART plotter (CP) is a great tool for reducing the frequency of those anxious moments on the water, when you are not sure of your exact position and life becomes a bit hairy. On several occasions, my own unit has prevented me from running into trouble, or else got me out of trouble swiftly and without fuss. But it's the pleasure that you can get from using it right that really does it for me. The most common CP task is the insertion of Waypoints. You can, of course, laboriously key them in as figures and so build up a list but a better way is either to use the CP's info box that displays the lat/long of the cursor's position and then store this in the machine's memory or simply move the cursor to your desired point and ask the CP to 'Insert WP at cursor'.

The software will assign each WP a sequential number, which you need to record on a written list, with a short description. My own method is to create a file for each route or trip. This can be given a cryptic name like BXMPLE = Brixham to Poole and the points such names as EXFWY = Exe Fairway Buoy, or as a distance into your route - eg BXMPLE30, indicating 30 nautical miles along the way. On the return leg, these will act as a countdown of the mileage remaining to your home destination. During the first stage of planning a major expedition, the CP compares poorly with a paper passage chart, because you cannot get a helicopter view of the whole route at a scale of practical use. The danger is that one of your legs will pass over a shoal area, which does not show at the small scale on the small screen. You can then find yourself ploughing through a fish farm - not ideal. The solution is to use the cursor to draw in an approximate route and then zoom in to fine tune each WP by moving it a bit closer to a cardinal mark, or giving it a bit more clearance at a headland. If you require checks every five miles, some of them might be 4.7 or 5.2 on your first draft, so they can be made more exact by using the CP's A to B distance measuring function. At the same time, you can verify that none of your lines is going to run you into trouble or cross a prohibited area. All the major cartography suppliers now have a gizmo which allows you to use your CP cartridge on a standard computer, so you can do all your planning at home. You can then take the time to plan 'safe marks' for the entrance to any harbour that may be suitable as a bolt hole if the weather turns nasty or you run into problems.

A pleasurable problem on a good CP is its versatility. Deep inside the menu structure there is often a function to change the colour (sometimes also the format) of the route line. Over a season, the CP memory might have several embedded routes, so it is useful to have them in different tints. This also distinguishes them from the continuous (or 'pecked') track history line. This can be even more useful if you use the 'Reverse Route' facility to trace your return leg. The Track History (TH) is a marvellous CP feature, but you must set it up properly. It works by recording a position mark at time intervals decided by the user. On a passage of 200 miles or more in a slow cruising yacht, you might only need a mark every 15 minutes, over several days. If you have a fast RIB or you want a record of your laps for post-race analysis, have them at the highest setting, which should record a position every few seconds. You can also set it up to record according to distance rather than time - every 10, 20 or 100 metres, again in a choice of colours.

The TH is worth learning well, because it gives an instant picture of where you are in relation to your planned line. This recently got us out of trouble during a diving expedition to the Glenan Isles, which are heavily fished by French trawlers. In pretty dense fog, I had to turn so many times to give way to them, that I was totally disorientated. No matter, the CP had recorded and tracked every new direction, so I was able to plonk the cursor where I wished to rejoin my planned route and the display immediately gave me course and distance to get there. A much under-appreciated CP function is variously known as the Ship's Head Marker or, in some makes, the Time Line. It is usually a line of dashes, which flashes on and off and stretches from the boat's bow directly in the direction of travel. Its flashing can be irritating to the newcomer and I used to turn mine off but not now. There is often a big difference between where the 'ship's head' is pointing and her Course Over Ground, as wind, tide and waves radically split the two.

One year, in the exceptionally fast tides of The Morbihan, I was quite convinced that we were heading straight up the channel but the Time Line showed that we were, in fact, ferry gliding sideways towards some nasty looking rocks, only just awash. On the same trip, we needed to round an island and then head for a green buoy. As we made the run, we could see half a dozen green marks. No problem. We slowly altered course until the flashing line coincided with our route line between turn and buoy. At this point, a particular green marker was aligned with the boat's bow and that was the one we needed to go for. 'Declutter' is another under-used CP feature. In an area like The Morbihan or Poole Harbour, the chart will have much more information than is required for any particular outing. Unless you have a ten or 12-inch display, an important item might get lost in the mass of on-screen symbols. If you are following a channel, you can temporarily erase all spot depths above your minimum and do away with many place names and such data as undersea cables, pilot stations and buildings ashore. Some advanced plotters even let you shift the depth contours to a level of your choice, but this is often quite deeply buried within the menu structure.

Navigation is the science of knowing where you are now and exactly where you will be at any given future moment. The good navigator is a person who has a catalogue of ways of verifying the former and several ways of calculating the latter. Furthermore, he has these things at his fingertips, so he can immediately answer the driver's questions about them. In this sense, the CP is an excellent navigator. A properly set up menu can immediately draw a line from your position to the location of the cursor. When you are not in need of this data, placing the cursor near the current position 'blinker', means that the line is not intrusive. When you want to identify a mark diagonally ahead, you simply put the cursor on it to get an info box of data. If you reverse the process (ie - you can see a mark at 195 degrees from you) swing the cursor to that compass figure and your line will pass through the mark in question. This is just one more way of linking up your eyeball navigation with what is on the screen and both are essential elements of safe navigation, especially at speed. The good navigator also works in approximations. In his head, a course of 178 degrees does not exist. It is "about 180" and "about half a mile". He can now immediately tell the driver (or himself) where to point the boat's head and then use CP info to fine tune these instructions.