Jan AdkinsElectronic devices do something we can’t: count small. Circuits create frequencies and count pulses to allow division of the unforgiving minute into smaller and smaller increments. Our GPS positions depend on comparing nanosecond pulses from multiple satellites measuring distances as a function of the speed of light between us and geosynchronous orbit. On a coarser scale and an older electronic device, the transducers of familiar depth sounders send out a distinct frequency sonar pulse that bounces back from the bottom, is received by the transducer, and registers on a depth scale. Even old depth sounders with a light on a spinning arm can register the difference between a soft, hard, or broken rock bottom.
We’re all grateful for electronics, though few of us know just how those clever electrons slither through circuits. Faith in technology runs deep, and most of us are satisfied with the results. That’s well and good, but there are arguments for old-school simplicity. Indeed, WoodenBoat is a seed bank of what worked and what still works.
As a system increases in complexity, the likelihood of failure increases proportionally. Throughout your contemporary boat’s complexity lurks the likelihood of a rogue electron, a power surge, a loose bolt, or a misplaced cotter pin. Batteries die. Oars could break but it’s rare. Having fallback skills from another age could extract a happy outcome from a grim situation.
Two bits of crucial seafaring data are insistent throughout any voyage: how far is the bottom from your keel, and how fast are you traveling?
HOW DEEP?
Water is a great deceiver. Its restless surface seldom reveals what’s beneath the glitter and foam. Even a pond skiff has draft. How deep do the rocks and mud lie? Your chart is an approximation, the day-by-day hydrography is inevitably shaped by current, silting, go-fast wakes, and storm surge.
The word sounding, in the sense of determining depth, isn’t about noise but an active verb from its ancient root in Old English: sund, “sea.” The process is as simple and as reliable as hauling a bucket. In the age before electronics, a leadsman was belted into the weather rigging chains (anchors for the shrouds, extending outboard of the hull); he held a lead weight and about 25 fathoms of line. Even a modest brig could draw 12′, so the leadsman did more than drop a line. He spun a heavy lead plummet (of 5−10 lbs) on several feet of line in a vertical whirl and hurled it forward, out beyond the cutwater. The lead plunged, followed by successive coils of its line held in the leadsman’s off-hand. The line’s depth marks paid out through the leadsman’s fingers—a series of tactile icons made of knotted twine, leather, cloth, rawhide braid, and others so they could be “read” in the dark. When the lead struck the bottom, the depth was called out to the skipper with fractional modifiers, as in “By the mark, nine!” Close to nine fathoms!
A sounding lead and line is a comforting thing to have aboard. A small boat lead of about 3 lbs with 10 to 20 yards of hard-laid line will be sufficient. You will add your own marks, probably in feet (to avoid confusion with most modern charts, which are also in feet), numbers on vinyl tape or even burned into leather sewn through the line. Traditional leads have a cupped bottom that can be armed with tallow or some sticky goo that will pick up bits of the bottom, providing an often-useful anchoring indication. Some paper charts have abbreviations for the bottom conditions, such as sand, mud, pebbles, shells, and others. If you have a crew and are scouting a tight anchorage, you can send your dinghy ahead with a lead to feel out the channel and gauge the anchor scope.
When approaching an unknown shore, an Age of Sail captain might call for the deep-sea lead, with a much longer line in two or three coils held by successive leadsmen in the fore, main, and mizzen chains.
Jan AdkinsFATHOM is an anthropomorphic measure, the distance between a sailor’s outstretched hands, from an Old English word for “embrace.” We take it to be 6′. Depth on old charts and on some contemporary deep-sea charts is measured in fathoms. A cable length was a common sailing term for 100 fathoms, or 600′, about 0.1 nautical mile (6,076.12′).
It’s an ancient thing.
We can’t believe the pharaoh’s boatmen didn’t have their own sounding leads, but this funerary painting of way-back Egyptian river sailors proves they used sounding poles along the Nile banks and through the shallow Nile Delta.
A marked sounding pole is familiar to the thin-water sailors of the Florida Keys, the Intracoastal Waterway, the Gulf of Mexico, and the Caribbean Islands. A pole is direct, quick, and cheap—a 10′ to 12′ pole of sealed spruce, pine, bamboo, ¾″ PVC pipe (with capped ends, to float), or a straightish sapling reworked and sealed, painted with alternating foot bands, perhaps varying the color at 5′ and 10′ marks (scuff PVC with a 3M pad before painting). Even in a small sailboat, a long pole can be handy secured with two twine-seized rings to a backstay or shroud cable. A skiff or motor vessel will have some vertical or topside home for this basic tool.
HOW FAST?
Jan AdkinsRefresher/reminder: a mile is an anthropomorphic (human-based) measure. The word comes from Latin mille, “thousand.” An average man’s step is about 31½″. A stride is two steps (the distance between two left footfalls). Take a thousand of these strides for yourself or for a Roman legionnaire and the distance will be damned close to 5,280′, a statute mile. Rate of speed=miles/hour. A nautical mile is a globe-based angular measurement that has nothing to do with pedestrians; it is one minute (¹⁄₆₀ of a degree) of latitude. A nautical mile is a globally consistent measure of distance on the geometric matrix of the earth, which is why both ships and aircraft measure progress in nautical miles and speed in knots, or nautical miles/hour. The term knot (1 nautical mile per hour) comes from the old method of measuring speed in the water using a chip log.
Speed is another kettle of fish. Once again, water is a deceiver. Your vessel moves on the surface of a moving medium. “Guesstimating” your rate in knots, even for experienced salts, is chancy. Without an accurate rate of speed, you can’t navigate—can’t project your passage along safe legs and across currents that will change with time and tide.
The low-tech versions of hull-speed divination aren’t well-known and are usually eclipsed by the ubiquitous smart-phone, which puts digested GPS data directly in the skipper’s hands. This is hard data, and it seems authoritative. It isn’t. Recognize that the position and rate given are not through the water but over the ground, reflecting your boat speed with, against, or across current, and this data will change as the tidal currents accelerate, retard, and shift in bearing by the hour. You can’t assume speed and bearing at 1050h will be consistent at 1325h. GPS data is accurate at the moment it’s given, but shifting water will shift your projection. You still need tide tables and current charts to interpret how the currents will shift your boat’s speed and bearing. Plotting a passage’s course still demands geometric offsets and a bit of basic arithmetic, even some Kentucky windage.
The chip log (above) is a minor low-tech masterpiece, a device used for at least 500 years. The chip is a quarter-round wooden flat weighted with lead inserts near the bottom arc. It is connected by a three-part bridle; two legs attach firmly to the endpoints of the arc; the third to a peg seated in a hole at the point opposite the arc. Three sailors normally work the chip log. The chip is dropped over the taffrail and the reel held aloft by Sailor A to turn freely. Between reel and bridle is a length of line long enough to float the chip aft beyond the turbulent wake. The chip is a flat drogue that holds its place in the water at right angles to the log line. As the wake-line pays out, the first knot passes through Sailor B’s fingers and he calls “Turn!”; the instant he does so, Sailor C upends a (usually) 28-second sandglass held directly to his eye, carefully monitoring the time so that when the last grain falls Sailor C calls, “Nip!”. In that span of time, Sailor B has counted the number of knots passing through his fingers, spaced (usually) at 47′3″, and calls out the speed to the ship’s master or navigator: “Five knots and one fathom!” The fathom is translated to a fraction of the distance between knots. Sailor B gives the log line a sharp tug, which pulls out the bridle plug at the point of the chip so it lies flat in the water and can be reeled in easily. How accurate is the speed reading? The chip log is certainly affected by sea conditions and the state of the line, but within limits it is a remarkably reliable tool, though more suited to a big crew and long passages.
Jan AdkinsThe Dutchman’s log is a 14th-century knotmeter.
The Dutchman’s log is a 14th-century knotmeter you, too, may use when your batteries die. It’s based on your boat’s length. Sailor A in the cockpit starts a stopwatch as Sailor B drops a cork into the water at your boat’s bow. When the cork passes the taffrail, the stopwatch measures the time in seconds. After that, it’s algebra: D=rT (Distance equals rate multiplied by Time). Figure several cork passes and work out the numbers (the length of your boat in decimal fractions of nautical miles, and time in seconds as fractions of an hour). It’s a simple graph; from which any stopwatch time will provide your speed in knots.
Jan AdkinsThe elegantly mechanical patent log or taffrail log was a complex instrument of the 19th century.
The elegantly mechanical patent log or taffrail log was a complex instrument of the 19th century, using a bronze spinner trailed aft on a specially laid log line that resisted twist, so the spin of the bronze vanes was transmitted to a geared mechanical counter. This gauge, mounted on the taffrail, noted speed and distance traveled. This was essentially a passage-making tool, not practical inshore and certainly not in busy waters. A robust patent log is intricately clever and as beautiful as many of the tools of its age. It had an obvious disadvantage: sharks often tracked the thrum of the spinning vanes, saw the flashes of bronze, and ate them. 