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1 The chart and the almanac
Given that there is enough water to float your boat, navigation divides into two main sections. The first is working out where you are. The second is deciding how to move from there to your destination.
In the simplest case of all, you can see your goal, there is no current and no obstacles stand in the way. All you have to do is look at where you want to go and steer straight to it. This will hold good in still water and clear visibility over any moderate distance, but if the haven of your choice is too far away to be discerned with any certainty, you’re going to need a chart to find it successfully. An almanac will also be essential in order to refine raw information delivered by the chart.
Charts
The chart is the core unit of navigation. It’s really only a very detailed map produced to the highest standards of accuracy which shows the coast, the foreshore, the water and the nature of the seabed. It also indicates rocks, shoals and a variety of objects that will help you work your way from one location to the next. Charts come in two essential variants: paper and electronic. Both have a number of sub-groups. All use similar sets of symbols, scales and general conventions.
Types of chart
Step into a good chandlery anywhere in the world and you’ll find three sorts of chart on sale.
National charting authorities publish paper charts for their own coastline, and often many others too. One of the most prolific is the British Admiralty. If you’re operating in home waters, these are the yardstick by which others are measured. They come in full-sized, commercial grade charts also called ‘Standard Charts’ from an official chart agency, but ‘Leisure Charts’ are also issued. These are full-sized charts sold folded down to around A4 size. Unlike Standard Charts, they may not be completely up to date when sold. Smaller charts are issued in ‘Leisure Folios’ of popular sea areas. These sit more comfortably on a small vessel’s chart table and some carry additional data on the reverse side. Occasionally British Admiralty charts carry blow-up plans of specific harbours.
Commercial companies also publish paper charts. For example, Imray cover the whole of the British Isles and much of Europe and the West Indies. Commercially produced charts rely on survey data that is owned by the official authority but they may deliver it in a form that carries certain advantages. While an Admiralty chart is the ‘Bible’, a commercial unit can offer extras such as numerous plans which may save you having to buy additional Admiralty charts to achieve the same coverage. Further useful data may also be found on the back of such charts.
Electronic charts for use in GPS chart plotters are really computer-screen representations of the paper equivalent, but two essentially different types are on offer.
Raster scan charts are literally high-definition scans of a given paper chart. With such a chart, you may be able to magnify it on the screen, but by doing so you will not reveal any additional information. If you need more detail, you must call up a chart with a different scale. Raster charts are most often found on PC chart programs. Their similarity to familiar paper charts makes them popular with many navigators. Vector charts are typically seen in a stand-alone chart plotter unit, although many PC plotter software plotter programs use them as well. They are built up electronically so they look quite different from the traditional paper equivalent. However, complete information for a given area can be accessed via a single chart chip or CD. This sounds like good value, and so it is, but there is no free lunch at sea, so while everything may be in there somewhere, it is often far from obvious at first sight. To use vector charts effectively, you need to familiarise yourself with their little ways. You can read more about this in Chapter 11.
