## Waypoints

The idea of the waypoint forms the heart of modern navigation. You may choose to use few or many, but the concept must be understood and accepted so that you can make an informed decision based on the way you think and the circumstances.

It is standard practice to enter a number of predetermined positions along a predicted route into your navigator's computer. The theoretical ideal for a passage of any substance, offshore or along the coast, is to proceed from one of these waypoints to the next. This can be done informally, plotting them as you go, or as a pre-planned 'route'. More information about waypoints and how they should be selected and used will be found in 'Passage Planning' (Chapter 22). Waypoints are helpful on a chart plotter, although you may opt to use fewer of them, but with a paper chart they really do ease your task.

G0T0

By activating the 'G0T0' function, the receiver will give a distance and bearing to the next waypoint at any time. Distance and bearing to a known position is, of course, another form of expressing the yacht's position (Fig 19.2). This can often be a more convenient way of plotting a fix on the chart than trying to wrestle with lat/long over the folds of the paper with a plotter that is too short and a longitude scale that numbers from right to left in west longitude. As an aside, the concept of defining a fix in terms of lat/long and range and bearing is useful when transferring a position from one chart to the next. It is all too easy to make an error over a question of scale, or by reading the longitude the wrong way. If you transfer the position by both means, they should marry up; if they don't, you've made a mistake.

Using G0T0 for comparing the bearing of the waypoint and the present track makes adjusting your course to take you to it a doddle; always given that the tidal stream or current is expected to remain reasonably steady.

### Ghost waypoints

Where a leg of your passage looks like passing across a large section of chart without the need tor a natural waypoint, it is worth creating a 'ghost waypoint' purely for plotting purposes. If you make this the middle of a compass rose, plotting to or from it will be a breeze. More and more charts are doing this for you by means of so-called 'Plotter Reference Points'. Enter the relevant ones as waypoints and they will be most useful.

### Plotting waypoints

Waypoints arc conventionally plotted as a small square around the pinpoint of the actual position. They are labelled with a name, a number or a letter.

### Cross-track error

Your GPS receiver is aware of the direct track from one waypoint to the next, or from a defined position to a pre-entered destination. It will always be delighted to advise you as to whether or not you are off-track, which side you are off, and by how far, which is sometimes valuable to know.

Many receivers will also offer you a course to steer in order to return to the line, but this must be treated with intelligent caution. If staying on track is crucial to your safety you should determine whether the recommended heading could lead into trouble from your present off-track position. There may, after all, be dangers in the way, and the GPS will not know about them.

Even if the path is clear, the computer is often so desperate to get you back onto the original track that it demands an alteration so radical as to be irrelevant, particularly in a sailing boat. More often, it is better just to steer 'up' or 'down' by 20 degrees or so until track is re-established. The cross-track information is sometimes sufficiently unimportant for you to ignore the old track and opt instead for a fresh departure to the waypoint from where you arc now. Pressing G0T0 will generally restart the process. Maybe you can even miss out that waypoint and proceed towards the following one. The processor won't consider any of these options, so don't let it patronise you.

Despite these cautions, cross-track error can be extremely helpful down the last mile or two onto a landfall in thick weather. Under ccrtain circumstances it can also guide you through a series of dangers close by on cither hand, but before you consider using it for this, refer to the caveats in Chapter 23.

Except for the fastest power craft, cross-track error should not be considered a substitute for pre-planned course shaping over extended periods, particularly where a turn of tide is involved. Employing it for this purpose will sec you steering into the stream regardless of the overall strategic situation. You may well therefore sail considerably further through the water than is necessary. If this sounds like theoretical hot air, take a look at Chapter 20 for the reason.

### Man overboard function

This is standard equipment in most GPS receivers. If you suffer a crew member over the side and hit the 'MOB' button immediately, the inbuilt course computer will give a range and bearing back to the geographic location where the casualty was lost. It does this by creating a waypoint marked as 'MOB', then activating the G0T0 software to keep you informed of what you need to know most of all -where the casualty lies in relation to you. This can be a lifesaver on a dark night, but you must be aware of its limitations. The position given is a position on the sea bed. The boat and the casualty are both subject to any current or stream that is running. Their position in relation to one another is governed by the yacht's movements alone, and both are drifting downstream at a constant relative rate. The geographical position given by the computer remains where it was, but any current will be carrying both the yacht and the subject away from it. A mere 2 knots of stream will shift the victim a cable (200 yards) downstream of the waypoint in three minutes. Nevertheless, it is generally well worth the 10 seconds it may take to hit that button, so long as you note the time. If you should lose touch with your casualty and are within range of Search and Rescue services (SAR), they will be able to calculate the lost person's set and drift with surprising accuracy, working from the time and the fixed MOB position. Activating the function without glancing at your watch will degrade this accuracy severely in areas of strong current, unless your computer will read out the time as well as the fix, which many do not.