The navigation of a small dinghy or cruiser always presents something of a problem. The two main difficulties are lack of fixing aids and equipment, and lack of a proper chart table. When sailing single-handed there is the added problem of lack of time and the inability to leave the helm for more than a few minutes. In consequence, the navigation suffers and is frequently reduced to mere map reading. Over the years I have developed a system, which is simple, cheap, quick, reasonably accurate and actually works. The main principles are to do all the work before setting sail and from there on use a few simple rules of thumb and mental arithmetic.

Navigational equipment en route is limited to a steering compass, plywood board, chart, plastic sheeting and a couple of chinagraph pencils. The helmsman must also be able to estimate the speed of the boat through the water to half a knot - not difficult with practice. The easiest way to get practice is to take a crew out one day, estimate the speed, drop a match stick over the bow, time it for the length of the boat and see how the calculated speed compares (see fig. I for speed chart). Time for one Speed boat length 14’ boat

a.t t Speed 16’ boat Seconds Knots Knots 1 8.3 9.5 1.5 5.5 6.3 2 4.1 4.8 2.5 3.3 3.8 3 2.7 3.2 4 2.1 2.8 5 1.7 1.9 6 1.4 1.6 7 1.2 1.4 8 1.0 1.2 10 0.8 0.6

The first stage of planning is to prepare the chart. Draw in the required track lightly in pencil and mark each leg of the track with direction (magnetic) and distance. Select the most prominent points (buoys, lighthouses etc.) en route from which it is hoped to take bearings. From each of these points plot magnetic bearings at 10º intervals using a different coloured pencil for each point to cover the area in which you will be sailing. Annotate every third line with the first two figures of each bearing (i.e. 36, 03, 06, 09 etc.) Draw an arc, radius maximum visible range from each of the prominent points (see fig. II).

For points on land use the half tide height to calculate range and make a small allowance when under way. The lights of navigational buoys average 6-8ft. above sea level and from an eye level of 3 feet disappear at about four miles. They are particularly useful at night. Any prominent points likely to appear in transit should be noted and the line extended to cut track. Sector lights should also be noted. If you are crossing any airways or busy shipping lanes mark these as they can often give a position to within a couple of miles. To make things easy next notch one of the chinagraph pencils to the scale of the chart. So far all this preparation can be done before you leave home.

Take the chart and fold around the plywood board so that the full route is on the face side, cover with the transparent plastic sheet or envelope, pull tight and pin both chart and sheet at the back. All the information you are likely to require can now be written in chinagraph on the plastic.

Ht. of object Eye at 3 ft. Distance at which it dips

Ht. of object Eye at 3 ft. Distance at which it dips Feet N. Miles Feet N. Miles 0 2 189 15 6 4 218 16 12 5 250 17 21 6 283 18 31 7 318 19 43 8 356 20 53 9 395 21 75 10 437 22 93 11 481 23 114 12 527 24 137 13 575 25 162 14

Figure II Against each harbour or possible diversion port write the time of high water, if it is tidal and only open for a limited period then write the times between which it will be possible to enter underneath. Calculate the times of slack water at various points along the route. Write the time at this point and also draw an arrow (three barbs for convention) showing the direction it will run after slack water and the maximum rate at which it will run later. Unless the tide atlas shows very much to the contrary, we then assume that the tide will run at ¼ max. for the first hour, ½ max. for the second, max. for the 3rd. and 4th., ½ max. for the 5th. and ¼ for the 6th. - an approximation but since the tide atlas only gives an average figure, quite accurate enough.

That's all the pre trip planning. Now for fixing. To obtain a bearing from any of our selected points we momentarily turn the boat head on, stern on or beam on to the point and read the steering compass. A quick correction for deviation (if any) and we can add 0º, 90º, 180º, or 270º - as the case may be - and we have a bearing. Two bearings give a fix. A quick interpolation between the bearing lines on our chart and the fix is plotted - don't forget the time alongside. We notice that one of the selected points is starting to "dip" below the horizon. A quick bearing and a little while later it vanishes - quite suddenly. By standing we can still see it, but sitting it is gone. We are now on the limit of visibility arc and with the bearing this gives us a fix. What to do with the fix? After heading for the next turning point, or to avoid a danger, work out a rough E.T.A. or just leave it in case the visibility clamps and we can start our D.R. from it.

There is a very useful rule for working out alterations of heading without plotting known as the one in sixty rule. This boils down to the fact that 1º is equivalent to 1 unit abeam for every 60 units travelled. For example, if we are 1 mile starboard of track after sailing six miles then our track is l/6 x 60 = 10º to starboard of required track, to sail parallel to our desired track we must then sail 10º port of our previous course. If we have 12 miles to go to the turning point then we require a further alteration of 1/12 x 60 = 5º to port to make. For example, see fig. III. In this case we assume the tide remains constant but the rule can also be used to work out a heading to allow for a beam tide. Assuming a beam tide of one knot on our desired track and a boat speed of 3 knots the alteration of heading required into tide to make good our track is ⅓ x 60 = 20º. The rule falls down for large angles although in practice one can estimate to within 10º.

For long straight legs it often pays to maintain a constant heading rather than attempt to regain track as the tide effects will frequently cancel out. For example, if crossing the channel, once clear of the coast, the tidal stream runs six hours one way and just over six hours the other, consequently for a twelve hour period the effect of tide can be ignored and a constant heading held, only altering heading from a fix to allow for tide at the end of the period. The track during the period will be “S” shaped but although fixing is continued as available no alteration of heading is made except to avoid dangers. Pre-drawn bearings and transit lines are particularly useful for inshore pilotage. If approaching a harbour with many off lying dangers, not only should the transit lines be drawn but also the safe limit bearings in case one has to tack in.

This system may sound complicated but it's absurdly simple in practice. One of the easiest ways to practice the technique is a "dry swim". An ideal way of spending a cold wet evening in front of the fire. Take two copies of the same chart and a friend with some knowledge of navigation. One plots in the normal approved manner reckoning in the tides etc., the other navigates with a chinagraph by rule of thumb. The navigator calls the headings and the plotter maintains a plot and calls back the wind, boat speed, fixing information, etc. The plotter must be fair but can vary the tidal streams slightly from those in the tide atlas, feed in a little heading and speed estimation error and decrease the visibility to nil if required. Try one fix an hour (plot time), vary the wind a little - particularly to windward, and don't forget leeway (plotter gives heading when close hauled and navigator calls time to tack).

Have a go! After all, Columbus had to start somewhere - you won't be the first navigator to find land where it was hitherto never known to exist. Who says that continents don't drift?