We’re all afraid of the dark. We don’t have the eyes or the nose or the whiskers for it. People are hard-wired to see. After sunset, our ancestors hunkered down in caves or up in trees with good reason: The dark hides danger. A prudent mariner once told us, “It’s not dangerous to sail. It’s dangerous to have to sail.” That’s true, but it is possible, with some skill, to venture into the night or fog prudently and safely.
Night sailing has charms, and it can be thrilling and beautiful. It is, however, a skill you learn in daylight, gradually gaining confidence in your course plotting before you apply it to the mystery of a night on the water. Darkness introduces a new constellation of visual clues—lighted and reflective buoys and landmarks. It obliges you to tighten your navigation discipline, and redefines getting from point A to point B.
The most critical thing to explore in daylight is the effect of tidal current on your boat’s course. By understanding this, you can lay a compensated course to reach point B. It sounds difficult, but in practice it’s largely a matter of understanding tidal currents, applying corrections to compensate for them, and shaping a fail-safe course that acknowledges the limits of your vision.
Fog is different from night. A thick fog denies any visual clues, imprisons your boat in a mind-distorting cocoon, plays tricks with hearing, and amplifies some noises while muffling others. Fog is a trickster. It’s even more important that you repeatedly practice fog navigation and piloting in clear weather so you can trust your skill when “a thick o’ fog” blots out the world.
This discussion is only an introduction to the concept of operating a boat in low-visibility situations, and not a comprehensive treatment of it. Our aim here is to emphasize the importance of the basic skills involved, and encourage you to explore this topic more deeply. One especially good text for this is The Annapolis Book of Seamanship, by John Rousmaniere.
We’ll assume that your vessel is small and humble, and has no radar and no GPS or plotter. In fact, we’ll limit our electronic aids to a depthsounder, which we consider basic gear.
Basic Course Plotting
Basic low-visibility piloting requires knowledge of tidal currents. In New England waters, this information may be found in references such as the venerable Eldridge Tide and Pilot Book. It also may be found through direct observation—by, say, observing the speed and direction of the current as it flows past a buoy.
Course plotting requires some simple math to figure out how much a current will change—or set —your boat from its intended course. At the heart of the operation is the basic formula, Distance = Rate × Time. In order to travel 40 miles in 4 hours, we must travel at 10 knots. Distance (40) = Rate (10 knots) × Time (4 hours). Simple. We call it the “dirt” formula, as it’s typically shortened to D = rT.
Another basic concept to understand is compass error: Your boat’s compass is essential, but not wholly reliable. It’s thrown about in a seaway. The helmsperson’s attentiveness is variable. The compass itself is affected by magnetic anomalies. Learn just how far you can trust it on clear days so a dark night won’t terrorize you.
Most compasses have small errors that vary with the heading. Running compass courses between known marks at different points of the compass (“headings”), you can generate a “Napier diagram” or a “compass card” that allows you to adjust for this so-called “deviation.”
Plotting at Night
It seems to be another world of suppressed visual signals, confusingly spangled with insistent light beacons and mysterious moving “bogies.” Of course it’s not another world, but rather a reality in need of orientation and interpretation. Find your important marks and don’t be overwhelmed. Suss out the seascape behind the darkness.
Now for an exercise. Let’s assume we’re running at night. We’re at the red and white “ER” bell off of Bucks Harbor, Maine (A, on the drawing), and want to get to the lighted red and white “EG” bell that marks the entrance to Eggemoggin Reach (B). As designated on the paper chart with the letters Mo (A), the “EG” buoy blinks out a distinctive “A” in Morse code (dot dash, dot dash, dot dash…). The bearing from our position to our destination is 066° magnetic. The distance is 1.8 nautical miles. First we’ll calculate the amount of time it will take to reach “EG” at our current rate of speed. Then we consult the tidal current charts: How far and in what direction will the tidal current set us?
Let’s say the boat is moving at 5 knots. The basic formula, D = rT, is recast as:
T=D ÷ r
Plugging in the numbers, we get:
T = 1.8nm ÷ 5k = 0.36h (the formula needs a decimal fraction of an hour)
To figure the tide’s influence, you first figure out its speed and direction—either by observation, or by looking it up in a tide and current book. For our exercise, it’s 0.6 knot running SSW (tides, unlike winds, are named for the direction in which they flow, and not the direction from which they blow). As you run at 5 knots, the current will act on your boat over about 22 minutes, or 0.36 hour. What’s the offset distance?
D = rT, so D = 0.6 × 0.36, or 0.2
The offset is 0.2 nautical miles. So, set a new course from the red-and-white “EG” buoy to the point 0.2 nautical mile to the NNE of “EG” (C). And remember: This new course is only a compass heading. You’re not trying to arrive at this offset point. Rather, by holding this course, you’ll arrive at your intended destination, “ER,” by crabbing sideways with the current over those 2 miles (D).
Reading the tidal currents isn’t exact. If there’s a chance that an error or an unusually strong current could set your boat into dangerous water, calculate a “safety angle” that prevents you from wandering into trouble. Entering Bucks Harbor (E) requires other considerations (see below “The Depth Sounder as Navigation Device”).
Plotting in Fog
Running in fog is bewildering but not impossible—if you’ve learned from brighter days. All the piloting skills of night running apply here, but you won’t have visual clues. You’ll rely on your confidence with the current tables, “steering small” (keeping a tight course), and keeping your ears and nose on high alert. Your nose? Yes: Rookeries, tidal flats, and fish-processing factories have distinct smells that reach you when you’re directly downwind of them. And speaking of rookeries: Birds travel out to fish and return directly to their own rookeries. If a tern has a fish in its beak, and if you know where the rookery is, note the bird’s heading.
You’ll plot your course in fog just as you did your night course, but you’ll typically go from one sound-making buoy to another. The sound differences aren’t as numerous as light signals, but there are variations: bells, gongs, whistles, and horns. Bells have a clear, distinct sound. Gongs are either one-, two-, or three-toned. Whistles and horns are not distinct; they’re more a faint sigh than a musical note.
Let’s now plot a course from Bucks Harbor, back out into Penobscot Bay, in fog. Setting off from the red-and-white “EG” buoy (A chart above) with a course to the “ER” buoy, you have only the distant toll of the next bell to confirm your navigation.
Either by using current tables or by observing the tide’s direction and speed on lobster-pot buoys, you estimate a current strength and direction of 0.8 knot, SSW (B). This current is giving you a push, adding about 0.6 knot to your speed of 5 knots. The current will displace your boat for about 19 minutes—about 0.32 hour. As we did with our nighttime exercise, plot the current’s offset and correct the course to compensate for it—about 0.29 nautical mile to starboard of the destination (C). This new course will be 251 magnetic—again, a heading to be consistently held, and not a bearing to a mark.
Just how foggy is it? You might see the red nun N 28, or the green can C 27 (D), after 6 or 7 minutes have passed, and you’ll pass N 32 in 14 or 15 minutes. Listen for the bell and watch your depthsounder with care, because the shallow rocks at C 31 will be on your port in about 11 minutes.
When you arrive at your waypoint (E), turn to your new course—which you should have worked out ahead of time. Dithering in the fog is dangerous.
Fog Signals
Running in the fog, your boat is obliged to blow a horn once every minute. If you’re anchored or aground near or in a channel, your responsibility is a bell ring every minute.
Lighthouses
Lighthouses, with their great height, power, and range, can transmit more data than a simple light. Some of them “blank out” (don’t shine) in certain sectors of their 360° sweep. Others may have a “red zone” (in which the light is seen as red) to define a dangerous area or shoals.
Vessel Lights
A trawler towing a net: The green-over-white light configuration on the mast indicates that trawling is in progress.
Night courses will put you in broad fairways and frequented passages where commercial traffic is common. As a recreational boater you have an obligation to give commercial traffic right-of-way. Swift ferries don’t deviate from their courses, even if they could. Fishing craft maneuver in unexpected sweeps. Tugs work all night. A nightmare scenario for any sailor is to run between a tug and its towed barge, which can be hissing along 500 yards aft: The towline will catch such an unfortunate boat, and the barge will fatally overrun it.
A pilot boat on duty: A white-over-red mast-light configuration indicates a pilot boat en-route to or from a ship.
Commercial vessels running at night show a distinct pattern of lights. This pattern will tell you what the vessel is and generally what course it’s taking. When you encounter moving lights, immediately consult your memory, or a light-reference card, and identify the situation. Is it headed toward you or away? Mark its bearing from your boat and continue to take bearings; if they are constant, you and the vessel in question are on a collision course. Adjust. The accompanying drawings show a few examples of the light configurations. There are many, and it’s a standard question on the Coast Guard captain’s license test.
Tug with a tow: The two white masthead lights indicate a tugboat; the yellow light over the sternlight indicates a barge under tow.
A Note on Night Vision
It might be tempting to use a searchlight at night, but remember: Bright lights kill night vision—your ability to see in low-light conditions. Use one eye, or ask a crew member to locate reflective numbers on the can and nun buoys that mark progress along your course. The compass illumination should be red and dim, as should any light used to consult charts or notes.
Electronics
GPS and radar are great, and we’re not advocating you toss them overboard. But reliable skills will remain with you when the power fails and the lights go out. For that reason, we suggest that you don’t ever abandon the paper chart—or the skill to use it. Use electronics to sharpen your traditional skills of piloting and navigation on sunny days. Even when you’re running a sure-as-hell digital course, mark your passage on a physical chart, take times, and make notes.
Running a GPS course is reassuring and precise, and falling GPS prices have put them within the reach of most boaters. The whirling basketry of navigational satellite orbits and the elegant electronic circuits that connect them to your boat and to your position anywhere on Earth is surely one of the marvels of our age. A GPS unit may give you a graphic image of your position on a chart, or it may give you coordinates that you can mark on your paper chart. It’s precise in a way that William Harrison, who built the first practical chronometer for the British Admiralty, could not have predicted.
It’s even possible to use your smartphone as a GPS and plotter. Like all handheld electronics, these are vulnerable to the corrosive ocean environment; a robust, clear, easily sealed waterproof pouch is essential. And like all handheld electronics, battery life is limited. Be aware of recharging schedules.
Radar senses land, other boats, and reflective buoys. It’s an abstract representation, so it demands that you learn to translate its view to your real-world needs. Once again, sunny-day familiarity makes a competent fog and night practitioner. Piloting is part of radar savvy. Familiarize yourself with your unit’s several scales, and recognize that radar doesn’t reflect the actual shore itself, but the first substantial vertical objects inland.
If you have crew, one reliable radar watchperson should be on duty through fog and night navigation. Radar watches can be tedious after a short time, so change off the watcher every bell—that is, every 30 minutes. The nautical watch system was developed to keep watchers sharp.
The Depthsounder as Navigation Device
If you’re new to the area, heading directly into Bucks Harbor on an inky night might not be the best idea. Try to enter a harbor by running along a gently shoaling shore, where the readings on your depthsounder can verify your location without peril of a grounding. The sounder is a critical tool for both night and fog navigation.