When my wife, Dori, and I decided to cruise south in the winter and north in the summer, we didn’t consider the increased number of days we would be boating in fog.
Our summer months are now spent aboard our trawler, Liberdade, in New England, so we have learned to live with, and possibly even enjoy, a cool, foggy morning. We also can acknowledge that knowing we would be boating more in fog wouldn’t have caused us to change our plans, because in many ways, it has made us better boaters.
Handling a boat in fog presents a distinct set of challenges, even for the most seasoned mariners. Regardless of how experienced you are, fog is the one element of weather that is too often underestimated. Fog is insidious in how it impairs your senses and perception. The most immediate impact of fog is the drastic reduction in visibility, which can range from a slight blur of the horizon to a complete whiteout. In such conditions, familiar landmarks disappear, and you can quickly lose your bearings. The dangers are not always apparent until it’s too late.
Before we get into the techniques for safely navigating in fog, let’s first understand the different types of fog you can encounter and how to estimate when that fog will dissipate. Knowing what type of fog is present will also help you determine whether it’s safe to head out into it.
Advection Fog
This happens when warm, moist air moves over colder water. The air cools down, and moisture condenses into fog. This is most common along coastlines, and the type we experience up in Maine during the summer. This fog can persist for hours or even days, especially if the conditions that created it remain stable. It tends to dissipate slowly unless there’s a change in wind direction or temperature.
Radiation Fog
When the water cools down during the night, cooling the air above it, you get radiation fog, which forms close to the water surface. This fog begins to dissipate after sunrise, as the sun warms the air and evaporates the moisture. It can disappear within a few hours after the sun rises, but if it is extremely dense, it may last longer into the morning. This is also a common type of fog in coastal areas.
Sea Smoke
Sea smoke, often called steam fog, forms when cold air moves over warmer water. Water vapor rises and condenses into fog, often giving it a smoky appearance. Sea smoke typically dissipates quickly once the temperature difference between the warm water and cold air decreases. Wind can also break it up fast. It typically only lasts for a short time—from a few minutes to a few hours—depending on how long the cold air remains over the warmer water.
Evaporation Fog
Similar to sea smoke, evaporation fog develops when water evaporates into cooler air, making it saturated and foggy. Like sea smoke, evaporation fog can dissipate quickly once the air temperature rises, or the wind picks up. It’s usually transient and can clear within an hour or two if conditions change.
The Effects
Regardless of the type of fog, its tendency to disorient you can affect you in several ways. The first is loss of visual reference points. The absence of land, buoys or boats around you creates a psychological vacuum. This can lead to confusion about your direction and location.
The normal operating sound of your boat underway, that we usually take for granted, also becomes deceiving. Sound travels differently in fog, often becoming distorted. This can make it difficult to gauge the distance of nearby vessels or other hazards such as shorelines.
Last, your spatial awareness is reduced. The inability to see the horizon or detect changes in wave patterns may cause you to misjudge distances or even the motion of the boat itself. These effects might seem trivial, but in practice, they can significantly impair decision-making and increase the risk of collisions or running aground.
Disorientation in fog is a risk that even experienced mariners often overlook. It is easy to assume that because you have navigated in a variety of conditions, fog will just be another challenge to overcome. However, fog impairs two key elements of boating; knowing where you are and where you are going.
Without visual cues, you can quickly lose track of your heading, speed and position. What starts as a minor course correction can easily turn into a series of small errors that compound over time. For instance, in a thick fogbank, you might unknowingly drift off course, thinking you are maintaining a straight line. This can result in close encounters with other vessels, obstacles or even land, despite your best efforts to avoid them. Fog drastically alters your depth perception and accuracy with sound.
In any situation with poor visibility, but especially in heavy fog, instruments become the primary tools for safe navigation. The benefit from radar, GPS, AIS and your compass cannot be overstated, but herein lies the problem. While you may know how to use your instruments, you probably don’t practice using them in real-world scenarios often enough. As a result, when fog sets in, you may struggle to transition from relying on visual cues to navigating solely by instruments.
Knowing how to interpret radar and to make timely decisions based on it requires practice. Radar might show the positions of other vessels, but understanding the movement and speed of those vessels requires familiarity and confidence in reading the radar correctly. Most modern radars have a feature called mini automatic radar plotting aids, which allows you to acquire a target manually. Then, the radar automatically tracks the target, giving you its direction, speed and other relevant information necessary to avoid it.
In addition to using your GPS for your location, put a route into it that has been predetermined to keep the boat in safe water and away from navigational aids and buoys. By locking your autopilot on the route in the GPS, you will be free to pay more attention to radar and surrounding traffic. Have AIS display other vessel traffic on your GPS and radar screens.
Practicing using your navigation tools in good conditions is critical to using them in poor visibility. Try the following exercises during clear conditions.
Simulate Low Visibility
Practice navigating as if you were in fog, even when the weather is clear. Covering the helm’s windows or limiting your field of view while navigating with only instruments will allow you to simulate the conditions of low visibility.
Familiarize Yourself with Radar
Learn how to adjust the radar’s sensitivity and range, and how to identify and track moving targets. Practice acquiring and clearing targets, recognizing patterns and learning how your radar system displays different objects such as buoys, shorelines or other vessels.
Verify and Cross-Check
Develop the habit of verifying your position using multiple instruments. In clear weather, practice cross-checking your GPS, compass and radar readings with visual landmarks. This builds the habit of relying on instruments in poor visibility and helps you to confirm their accuracy in the moment.
Navigate by Compass
Practicing dead reckoning using your compass and GPS during good weather is another valuable skill. By doing this, you can learn how to maintain a steady heading, even without visual feedback.
Maintain A Proper Watch
Instruments can fail, and human senses, though impaired in fog, are still critical for detecting hazards such as the sounds of other boats, breaking waves or nearby buoys.
The best way to avoid the dangers of fog is to delay travel until conditions improve. However, the risks of navigating in fog can be mitigated by training in good conditions, practicing the use of all of your navigational instruments, and building confidence in those tools. By sharpening these skills in clear weather, you will be better prepared for the challenges that arise when the fog rolls in.
