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fog
Reprinted with permission of BoatUS.com

In 1916, Carl Sandburg wrote a wonderful short poem about fog, describing it as coming "on little cat feet" and "looking over the city and the harbour on silent haunches." But, when you're out on the water and are suddenly confronted by thick fog, there's nothing benign about it.

Of course, modern boat owners have access to a wide range of sophisticated "weapons" that can be used to great advantage in a duel with a fog bank. Due in great part to the digital age, radar has become both compact and affordable. As a result, it's found on more and more recreational boats 26' and up - a once unthinkable development. And, in the hands of an experienced, educated operator, radar is very effective in thick fog, where it can alert you to the presence of other vessels, locate navigational aids like buoys, and lead you through harbour entrances.

Radar is not, however, a panacea in conditions of low visibility at sea. Consider, for example, that in the notorious, fatal collision between the liners Andrea Doria and Stockholm off Nantucket, Massachusetts, in 1956: both vessels were equipped with operating radar and both crews were observing each other on the screen for some time prior to the accident. However, no one aboard either ship had much experience with the then-new equipment, and only the Third Officer aboard the Stockholm was manually plotting the relative positions of the two liners as they approached each other. Only he realized that the ships were heading on a direct collision course, not on parallel courses as suggested by both radar screens.

The point is that radar is only as good as its operator; that the accuracy of the image on the screen can be affected by distortion, clutter, and multiple echoes; and that the position of targets must be manually recorded over time to determine their true location and progress relative to your boat. (The latter, incidentally, was considered so important in the wake of the Andrea Doria disaster that it is now a matter of law; it's part of Rule 7 of the Coast Guard navigation rules.) Plotting radar positions isn't difficult. As Seaworthy suggested in an article several years ago, small-boat operators can use homemade plotting sheets, noting times and targets on a graphic representation of the radar screen. On today's sets, which don't require a hood during the day, you can use a grease pencil or erasable felt-tip marker, and do your plotting right on the screen. (Note that at least two observations are necessary to estimate course and speed. Three or more are required to identify changes in relative position.)

Don't make the mistake of thinking that only larger vessels get into trouble by relying too heavily on radar in the fog. Consider the Member and his wife who were coping with a thick fog by following a commercial fishing vessel down a river in Maine, past its mouth, to a navigational buoy about a mile offshore. They then headed their cruiser toward another marker but never found it. Setting a course from his estimated position, the boat owner adjusted the radar to show his destination, directly ahead, and an island he needed to avoid, to port. Proceeding in very limited visibility at approximately five knots, the vessel shortly went hard aground on an underwater ledge. Trapped by a dropping tide, the cruiser had to be abandoned; it later went ashore and broke up - a total loss (Claim #902517).

There are several lessons here, one of them being that using radar to locate navigational aids in the fog takes practice. Then, too, the radar may not be aligned to the boat's heading, which means the target on the screen will be skewed. There's only one way to solve both problems: on a clear, calm day, put someone else at the helm, concentrate solely on the radar screen, and try navigating from buoy to buoy using just the bearings and distances your set is providing. This helps you "see" what your radar is seeing as well as alerts you to any problems with the set's calibration. If you suspect the radar is misaligned, consult your manual and adjust the pot that aligns the radar to the boat's heading. (A recurring problem with calibration indicates the battery on the radar's memory processor board is weak and needs to be replaced.)

"GPS and loran are best used in conjunction with other equipment - including your depth sounder, your radar, and yes, your lowly compass, charts, and parallel rules."
 


Predicting Fog

On any body of water-ocean, bay, river, or lake-there is always a possibility that a cloud of fog could suddenly surround the boat and reduce visibility to zilch. In some parts of the country, San Francisco and Nantucket come to mind, you can practically set your watch when the fog rolls in. But on most bodies of water, predicting when the clammy gray stuff might appear isn't so easy.

To most boaters, fog is fog, but to weather forecasters there are different type of fog: radiation fog, which forms at night over land and smaller bodies of water; steam fog, which is caused by cold air over warm water; and advection fog, which is caused by warm air over cold water. For boaters, the marine fog that hides buoys, rocks and other boats is typical advection fog.

Dave Feit, Chief of Marine Forecast Branch at the Marine Prediction Centre, says there are several problems with predicting fog over the water. First, it is difficult to measure fog density. Unlike, airports, which have the means to measure fog, there is no way to measure fog on the water. Photos taken from satellites simply make fog look like a cloud, which it is. On the high seas (Feit's specialty), forecasting, or at least reporting, fog is relatively easy since the fog is more likely to cover a wider area and ships will relay messages about its appearance or disappearance. There is less uniformity, however, where land and water meet, which makes the weather forecaster's job much more difficult. An inlet may be socked in by fog, while a few miles away the sun is shining. The reason? More variables. Maybe it's the difference in tide, a hot thermal wind blowing off a steamy corn field, or a localized flow of water.

Feit, who keeps a boat on the Chesapeake Bay and has been caught in fog a time or two himself, says it could be quite awhile before numerical models are available that can accurately predict localized marine fog. Unfortunately, in many coastal areas, that's the only type of fog there is.

 

 

A Deep Subject

The more obvious lesson is that radar, regardless of its quality, will not identify underwater hazards like rock ledges or sandbars. If you find yourself in a thick fog and decide to proceed (at slow speed, of course!), you'd better have a good depth sounder and know how to use it. Here, too, the instrument itself won't keep you out of trouble. You'll have to track numerical depth readings - not just mentally, but on paper - if you want to be warned of water that's growing progressively shallower, perhaps because you're approaching a reef or shoreline.

Here's where an LCD recorder designed for fishermen really shines: instead of simply telling you in feet or fathoms how deep the water is, it provides a complete picture of the bottom and will inform you at a glance that you're approaching the shallows. The better ones will also let you know whether the bottom is hard or soft, which can be useful in avoiding hazards, anchoring, and double-checking your position on nautical charts (which normally identify bottom composition). Thanks again to the digital age, many of these recorders are only marginally more expensive than numerical-readout depth sounders. So, even if you never intend to do any fishing, they're a much better choice, especially for navigating in the fog.

Similarly, in the hands of an experienced operator, GPS and loran units can eliminate much (but not all!) of the guesswork and anxiety that go hand-in-hand with getting caught in fog. As position locators, both systems can be used, with or without radar, for navigating buoy to buoy in the thick stuff. The accuracy of GPS, in particular, is improving all the time as the government relaxes security-related signal degradation and upgrades (or adds) satellites. Simultaneously, the price of this equipment is coming down, and even more expensive, more accurate differential GPS systems with interchangeable digital-chart cartridges are reasonably affordable.

However, as with radar, these units are subject to malfunctions, to outright failure, and to distortion caused by a wide range of factors, from electrical interference to atmospheric conditions. And, like radar, they won't do everything: they won't tell you about underwater hazards and they won't alert you to the presence of other vessels in the area. GPS and loran are best used in conjunction with other equipment- including your depth sounder, your radar, and, yes, your lowly compass, charts, and parallel rules.

As we recommended earlier in the case of the radar, you would be well advised to practice your position- locating system on a clear, calm day, recording its quirks for later use in the fog. That's when a distance of 50 yards can mean the difference between safe passage and destruction for your boat. Determining your equipment's repeatable accuracy is the key here because that is its greatest strength. Use a good day to visit key navigational markers and enter a series of waypoints that will get you home or to a safe harbour. Then, on the next trip out-again, under close to ideal conditions-check the accuracy of your system by navigating to those same buoys using the electronics alone. Such "homework" will pay off in spades when the chips (and a curtain of fog) are down.

And by all means use your radar, depth sounder, and GPS (or loran) together, both in practice and when you're stuck in the pea soup. Find out to what degree one piece of equipment confirms the position, speed, and/or heading indicated by the other, and put that knowledge to work for you when visibility is limited or nonexistent.

The Old Fashioned Way

But what if, like a lot of boats, yours isn't outfitted with a full complement of electronics? When the fog descends, your options are more limited and the chances of your getting into trouble much greater.

Consider the case of the BOAT/U.S. Member who was enjoying an afternoon of sun and light winds as he cruised along the coast of Southern California in his 27' powerboat. His fun was interrupted by a darkening in the north, where a long gray line of advancing fog was beginning to block out the sun. The boat was fully engulfed "in a matter of a few minutes." The owner decided to inch his way toward his home harbour "at a very slow rate while keeping sight of land."

That proved to be a big mistake. The visibility was so poor that in order to keep track of the coastline, the helmsman had to stay close inshore. Over a period of minutes, he found the swells getting larger and larger. Suddenly, "one, about 10 feet tall hit us and pushed us into the reef, where we immediately lost power." Successive waves threw the helmsman's companion from side to side, injuring her. Fortunately, his call to the Coast Guard was quickly answered, and both people were soon removed to safety. The boat, however, wound up on the beach and split in two down the centreline. It was a total loss (Claim #978876A).

Let's look at what this unfortunate boat owner could have done differently when suddenly confronted by fog. First, his decision to continue ahead, staying close to the shoreline "in order not to become disoriented and lost" was clearly the wrong one. A strategy of proceeding at slow speed through thick fog toward a safe harbour sometimes works, but it's a disastrous choice unless you're in open water that you know is free of invisible hazards like boulders, ledges, and sandbars. Hugging the beach-where such hazards are common-is a recipe for disaster.

When you find yourself with virtually no visibility and don't feel confident of your ability to navigate through the thick stuff, there's only one appropriate strategy: stop. Here, again, you're faced with a choice. If you're in a high-traffic area, in shallow water close to shore, or in a shipping lane, then you should almost certainly proceed slowly out of harm's way, plotting and following a compass course that will take you directly to safer and, ideally, sheltered water. (In the cited case, of course, heading offshore to open water was the best choice available.) Resist the temptation to speed up, not only because speed makes collisions of any type more likely and more serious, but also because increasing engine rpm results in more noise and reduces your ability to hear other approaching boats, both big and small.

When you're well clear of other vessels, and potential hazards like surf and strong currents, it's time to turn the arsenal of weapons that have served fog-bound boat operators for hundreds of years: the anchor and the whistle or horn. Set the anchor, and pay out plenty of scope (a 3:1 ratio of line length to water depth may do the job, but 5:1 is better). Waiting out a thick fog "on the hook" isn't fun, but - if you've chosen a decent location and have done a good job of anchoring - it's very safe. By contrast, stumbling along through the pea soup, hoping that nobody will run into you, that you won't hit anything, and that your compass will lead you to the next buoy is nerve-wracking and risky. (This is also true for boats that are equipped with electronics. Stopping and waiting out the fog is often a better choice for them too.)

However, while at anchor, you should take a few precautions. The most important one is having some kind of warning device close at hand. First, if you hear another vessel approaching in the fog, you can alert the other helmsman to your presence and avoid a collision. Second, if nightfall is approaching, you may be able to attract the attention of a passing, radar equipped-vessel that can give you a lift or lead you and your boat to a safe harbour. Third, if you are unavoidably "stuck" in a high-traffic area, you can sound the device at regular intervals to warn off other vessels. In the smallest of boats, a whistle is adequate, but buy a good one. The Fox 40, widely used by dog trainers and law enforcement personnel, has an extraordinarily loud, piercing tone, it's made of non-corrosive plastic, and there's no internal "pea" to stick. The renowned Acme Thunderer is a popular alternative. Somewhat larger boats usually rely on a handheld horn fed by an attached canister of compressed gas. These are available in at least two sizes (standard and "mini"), and they are very loud.

However, if you're regularly sounding long blasts, you'll soon empty the canister; then, unless you've got extras, the horn will be useless. Always buy canisters (particularly for mini-horns) at least three at a time; they're cheap insurance. Another possibility is the newer Air Zound horn, which you can recharge yourself with an included hand pump. It costs about four times more than the typical, standard size gas horn, but you'll never run out of propellant.

Finally, use your ears: sounds are held closer to the water by fog and you can hear engines, buoys, etc., sooner than on clear days when the same sounds are projected upward. Sound can be deceiving in thick fog; it's often difficult to pinpoint the direction of the oncoming vessel. However, you'll never even come close if you yield to temptation and turn on your boat's stereo FM radio or tape player to help pass the time. Other background noise - like loud conversation - is also a problem. In the fog, you simply can't afford to give up one of your very best tools: your ears.