Wednesday, August 29, 2012

Tools of the Trade: In A Fog

Fog can be one of the most deadly atmospheric developments that a ship can meet. This is particularly true along coastlines, which - it should come as no surprise - is where the condition tends to be found. Felix Riesenberg's late 19th century advise that speed in fog should be moderate still applies today. Even with GPS and other high-tech navigational tools, there is always the potential for things to go horribly wrong.

That is no doubt why our seafaring ancestors had fairly stringent rules for how to navigate in fog. As Peter H. Spectre notes in his A Mariner's Miscellany, one should always remember four simple things when caught in a fog on the water: keep your eyes open, keep your ears open, keep your dead-reckoning plot and keep your head.

The conditions that lead to fog are almost standard. Regardless of where one is on the globe, these weather signs will apply. The largest issue is the contact of warm with cold. Warm air flowing over a cold surface, such as water or land, will cause fog. This is particularly true if humidity is high. Likewise, cold air coming into contact with warm land or warm rain will usually lead to fog. How dense the fog is depends on the temperature differential for the most part and to some degree a lack of wind as well.

Sailors identified certain particularly difficult fog conditions by name. The condition known as foggy breath arises when one can see their breath in warm weather, as if the air were in fact cold. Seamen agree that when this situation, which is usually a result of high humidity, occurs, fog will accumulate soon.

Advection fog is the thick, pea-soup fog commonly found off shore. This is caused by warm, humid air blowing over cold water. Radiation fog, on the other hand, is the type that clings to the ground or the water. Familiar to anyone who has spent time in bogs, bayous or swamps, this fog is caused by land that has been warmed during the day cooling down and cooling the air just above it as well. The air farther up remains warm, causing the type of fog which has been both the friend and foe of inland smugglers but is not as troublesome for the seagoing freebooter.

Knowing the conditions that can cause fog, feeling them in the air before the actual situations arises, can go a long way to keeping a ship safe at sea. Even in the thickest of fogs. Fore warned, as they say, if fore armed.

Header: Homeward Bound After the Storm by Monica Vanzant. This lovely piece is available for purchase at Fine Art America


Timmy! said...

"Speed in fog should be moderate" applies on the road as well, Pauline... Particularly in an Alaskan ice fog.

Pauline said...

Good point, Timmy! Almost everything that applies to navigating a ship in fog applies to driving a car in similar conditions. Stay frosty out there, Brethren.