by L.A. Gill

Most standard text-books on pilotage and navigation describe how to take bearings, running fixes, doubling-the-angle-on-the-bow, etc., when dealing with the problem of avoiding wrecks, shoals and other hazards, and finding positions offshore. This usually involves the use of a hand-bearing compass, or a Pelorus, a patent log, and much (drawing?) and calculating on the chart.

When cruising you will probably hug the coast, sailing into the bays to enjoy the scenery, thus always having a pretty good idea of your whereabouts. If passage making, you will want to sail across the bays in an effort to reach your destination as soon as possible. The problem seems to boil down to avoiding hazards when cruising, and finding your position and landfall buoys when passage making.

There are methods of solving both these problems with a sextant, by measuring horizontal angles which the vessel makes with two or more landmarks ashore. Many years ago I read of a gadget which adequately replaces the sextant for this purpose, and is easily and cheaply made from a coathanger. It is with apologies to the author of this book, the title of which I cannot remember, that I pass on the method of making and using this instrument.

As will be seen by the illustration (figure A), the first job is to construct a part of a circle, the arc of which corresponds to the arc of the coathanger. With a nail, a length of twine, a pencil and a pair of compasses, plus a little trial and error, it is possible to draw a demi-circle and to graduate its arc into degrees. The position of the degrees is transferred onto the coathanger by drilling holes, not right through, just the size to take a matchstick. Additional marks every five and ten degrees will assist in its use.

Next, as in Figure B, fix a length of wood from the middle of the coathanger to a point which represents the axis of the arc; the trouser bar can be used to support this radial bar. If made detachable the completed instrument will be easier to stow.

To operate, hold the assembled instrument horizontally and place one eye on to the free end of the radial bar. Then selecting two landmarks, A and B, some distance apart, place a matchstick in that hole on the coathanger which is in line with each landmark. (Figure D). The angle between your eye and A and B will then be shown by the number of degrees between the matchsticks. Figure D shows three marks enclosing two angles.

Let us now suppose that upon examining the chart before setting sail you notice a hazard offshore which, being on your course, you will have to avoid. On the chart, select two landmarks, one on either side of the hazard, then draw in a line from each mark to meet at a point well seaward of the hazard. This present the danger inside the apex of a triangle; (figure C). The angle at the apex, known as the “danger angle”, is then measured with a protractor and noted — call it X°. Now setting X° on your instrument, you only have to make certain that the landmarks ashore remain inside the two matchsticks when viewed from the free end of the radial bar, and you are bound to pass to seawards of the hazard (figure E). This operation is easily carried out even when single handed.

It follows that if you can find three landmarks and set up three matchsticks enclosing two angles, a greater degree of accuracy is obtained, allowing a more exact location to be pinpointed (figure D) such as a landfall buoy or a position off a harbour entrance. But, unless you can find three it is possible to arrive at more than one position, all situated on a very small arc, as a little experimenting with pencil and paper will demonstrate. If, however, you sail on this arc, by keeping the marks in line with the matchsticks, either the buoy will sink you or you will sink the buoy.

Unfortunately, some charts do not seem to locate many landmarks. It is worthwhile bearing this in mind when purchasing one.

To find your position at sea from bearings of marks ashore, using the coathanger instrument, two methods will be described, Both require three landmarks, one method is a little more complicated and involves more chart work.

As the instrument deals only in whole degrees, a little error may be expected, but half a degree can easily be judged, and as it is often difficult to plot a fraction of a degree one a chart under sail in a small boat, this is of little consequence.

The first method is simply to take a bearing from a position line. The position line is found by waiting until two charted marks are in a line, then at the moment of transit to take a bearing from the third mark, To plot onto a chart, draw a V on to a piece of tracing paper, the enclosed angle being taken from your instrument. Then, placing one leg of the V over your marks in line on the chart, slide it about until the other leg cuts your bearing mark. Your vessel’s position can then be pricked through onto the chart, or you may prefer to lay it off directly onto the chart as in Figure F.

The second method is best explained with reference to figure G. Select three marks, take two bearings and write them down thus: Flagstaff - 40°- Steeple - 30° - Tree Clump. On your chart draw a line between inner and outer marks. These two lines form the bases of two triangles. To complete the left-hand triangle, find the complement (of 90°) of your first bearing: i.e. 90°- 40° = 50°. From each end of the base erect a line enclosing the complement angle, i.e. 50°. Complete the second triangle in the same way using its complement angle, i.e. 60° (90° - 30° = 60°). Around the apex of each triangle draw a circle which will pass through the ends of the base. Where the two arcs cross, mark your vessel’s position; there will be two possible positions, but the right one will be obvious. It will readily be noticed that if the inner mark is out of line with the outer mark, displaced towards the vessel, a more accurate fix will be obtained.

I, personally, have found the greatest use for this instrument in locating buoys and harbour entrances, as often from the low vantage point of a dinghy they are not easily found. What are easily picked out are marks on the high ground ashore, which is good if they are charted.

It is all good practice to use this instrument; one day it may suddenly become necessary to know exactly where you are.

And then! Where are you?