- Judging Speed, Time, Distance and Angles at Sea

Echo sounders, GPS, RDF etc., all have their place for those who like 'em. I hesitate to criticise those who incorporate modern technology into their dinghy sailing. If I were foolish enough to do so I would undoubtedly be asked when I was going to throw away my compass, but today's innovations are often tomorrow's bygones. Those purists who shun engines and consider sail and oar the only way to go are also vulnerable, unless they eschew waterproof charts, quartz watches, marine glues, polyester sails etc., or even metal fastenings.

Nevertheless I do have reservations where gadgets requiring batteries are concerned. This has nothing to do with the fallibility of these items, merely my own absentmindedness. Before I saw the light and became a dinghy cruiser I had an expensive dial reading echo sounder on my cruiser, which used internal mercury batteries. When leaving the boat at the end of a trip I would often leave the thing turned on. Fortunately my lead line was always there for back up, but the price of the batteries was depressing! For those simple minded souls like myself I offer a few aids to navigation and pilotage which cost nothing and require only elementary arithmetic from the sailor.

SPEED

One knot = one nautical mile per hour = 2000 yards per hour. How nice to be able to ignore those foreign expressions! If we reduce the above figures we find that one knot = 1.66 feet per second (approximately). Fortunately we don't need to measure our speed constantly nor accurately, but if we know what our dinghy is capable of under different conditions we are able to make an educated guess when required; when looking for buoys in fog, for example.

First establish a convenient multiple of 1.66 feet against the side of the boat. Eight times = 13.5 feet is a convenient distance for the average dinghy. Owners of dimensionally challenged dinghies can chose a lesser multiple - 6x = 10 ft, for example. Now we have to find a simple method of measuring time without having to look at our watch. If we say to ourselves, or aloud for that matter - one hundred, two hundred, three hundred, four hundred etc. we will find that each phrase takes about one second to complete. Test yourself against a clock or watch when at home and modify the speed at which you speak until you find the system coincides with your timepiece. Then practise it until you are reasonably consistent. Other phrases would do just as well, but swear words are generally too short for the purpose.

Now when sailing you have only to drop a small screwed up piece of paper at say, 13.5 feet forward of the transom. Start counting immediately as you scuttle aft, and stop counting when the paper reaches the transom. If the paper takes 8 seconds for its passage you are travelling at 1 knot. If it takes 1 second, then you should not have the time to be playing with bits of paper as you are travelling at 8 knots! Anyway the method is to divide the multiple by the number of seconds and the result equals the speed in knots. If you are a 6 times = 10 foot person then if the bit of paper takes 3 seconds for the passage, you are doing 2 knots; 4 seconds = 1.5 knots. If you don't have any paper then you can always spit; a morsel of phlegm will usually last just long enough. Using the 'one hundred, two hundred' method can be useful for timing navigational lights like lighthouses and buoys. In fact I find that this is my main use for the technique.

DISTANCE

Distances over water frequently seem greater than they really are. The following ideas should produce figures which, although approximate, can be accurate enough for dinghy purposes. The light can affect an estimate. A bright clear day seems to make objects appear nearer than they actually are. A dull or misty day has the opposite effect.

Starting with the horizon. To a person with a height of eye of eight feet from the water the horizon will be about 3.25 miles away if the weather is clear. In a dinghy you will probably have to stand on the foredeck to attain this, so a height of 5 to 6 feet will normally be more practical giving a distance of 2.5 miles. You have to make sure the object is actually on the horizon. You should just see the bow wave of a power vessel for example, or the base of a lighthouse just touching the horizon if these objects are 2.5 miles away. Any ship of which the hull or part of the hull is below the horizon will be farther away. Incidentally, if you can see the base of an object when standing on the foredeck, but not when standing on the floorboards, then you know it is at a distance of somewhere between the two.

Now for buoys; a large navigational buoy becomes visible at about two miles away, but neither shape nor colour can be distinguished. At one mile its shape, colour and markings should become apparent; so will the markings on a light-vessel, or its modern equivalent. At a distance of 1.5 miles the smaller navigational buoys can be made out in smooth water, their shape at about 1 to 1.25 miles.

A man moving on a ship or on shore will show up separated from his background as a black mark at 1 mile but his limbs and features are indistinguishable. Between 600 and 800 yards a moving man resolves himself into a featureless vertical mark. At 400 to 500 yards the movement of a walking man's legs are noticeable and the rower's arms in a dinghy can be seen working; or his desperate attempts to start an outboard. At 200 to 300 yards a man's face without features, can be made out. The swirl of the tidal stream around a buoy can be seen also at this distance if the water us reasonably smooth.

ANGLES

It is also possible to measure angles without any instruments. If you hold out your hand at arm's length and spread your hand out wide, the horizontal width between thumb tip and little finger covers about 20°. If the fist is tight closed at arm's length the angle covered is some 10°. Extend the thumb and the angle from the thumb tip is about 15°. The nail joint is about 2°. Although these angles will vary between individuals, it is possible to confirm your own statistics with a compass. Once ascertained, only old age will alter these physical values!

All these angles can be useful in pilotage, particularly in brisk conditions when the spray is constantly in your face and all you may be able to manage is a quick extension of your arm and a suitable expletive.