Steering by wind and swells

FINDING POSITION VERSUS KEEPING TRACK OF POSITION

In emergency navigation, you must distinguish between finding your position from an unknown spot versus keeping track of your position as you move away from a known spot. Keeping track of position using boat speed and course sailed is called dead reckoning (DR). In emergency situations, you must rely heavily on DR, since it is not easy to find your position accurately from the sun and stars without proper instruments.

The concern with the distinction between finding your position and keeping track of it rests entirely with the question of accuracy. With modern electronic aids like GPS, a navigator can simply read latitude and longitude from a dial to an accuracy of 100 feet or so.

But no matter how well protected, electronic instruments remain ultimately vulnerable to the rigors of the sea and the idiosyncrasies of all electronics. I have witnessed two GPS failures so far. They were handheld units on land. On

one, the battery would no longer accept a charge, and the other stopped acquiring signals. And this does not count cases where a vessel loses all sources of power. I am sure my experiences are not unique among those who frequently use GPS. Failures remain rare compared to total time in use, but our subject at hand is what to do in rare circumstances.

STEERING BY WIND AND SWELLS

Steering by wind and swells means holding a steady course using wind and swell directions as references. Without a compass, the actual bearing of the course you hold must be found from the sun or stars. Once on course, you look for a temporary reference mark on the horizon near dead ahead. Then holding course by it, you note the relative bearing of the wind and swells. From here on, the general procedure for steering without a compass is not much different

from normal sailboat steering.

The first, most immediate goal is to keep the bow pointed toward your temporary reference mark dead ahead. At night this temporary reference is likely to be a star. During the day, it can be a cloud formation on the horizon or even a slight change in the shading of the sky color.

Each time the bow swings off your mark, you bring it back. Then each time you bring the bow back (or every other time or so), check that the wind direction is right when the bow is on the mark. Eventually, the wind angle won’t be right when the bow is aligned. If the wind is off, check the waves and swells. If they still agree with the wind, it is time to adjust your heading and

find a new temporary mark. Generally, you check the wind first when sailing to windward, and you check the seas first when sailing downwind. In normal sailing, it might only be at this point that you first look at the compass.

In adjusting your heading relative to the temporary mark, you might go, for example, from keeping it right on the bow to keeping it halfway back the length of the bow pulpit, and so on.

Or you might pick a new mark altogether. Do whatever it takes to get the wind angle right again, then pick a new mark. In this adjustment, you are assuming that the temporary mark moved, not the wind and swells. But since you won’t have a compass to confirm that assumption, you won’t be able to make many adjustments like this one before you must go back to the sun or stars to see if the wind or swells have changed.

Telltales

To watch the wind direction, it is extremely helpful to rig telltales, pieces of string or strips of light cloth tied high in the rigging, out of the way of other structures on the boat (see Figure 1-1). Strips of plastic bag or cassette tape also make good telltales, especially in the rain. Telltales show the wind direction instantaneously. It is always better to use a telltale than to guess the wind direction by feeling it. Telltales are common on sailboats, less so on powerboats. But on any boat, if

you get stuck without a compass and must watch the wind direction carefully, the first thing you should do is rig a telltale. It is an instrument you can rely on. A prominent telltale on the bow of a powerboat can prove extremely valuable in some cases, even with all your navigation gear working properly, and can be even more valuable on a kayak.

Figure 1-1 Using telltales to read apparent wind direction. Here telltales are flying

from the luff of the headsail, leech of the main, windward shrouds, backstay, and

running backstay. Long telltales streaming overhead from the backstays are oft en

useful when sailing downwind.

Дата добавления: 2015-11-16