Underway When the Fog Drops

Have you ever been underway when the fog dropped down like a window shade? Sometimes it happens just that quickly! There are a few things to think about, the least of which is other vessels in your area. Of importance are the ones that don't slow down in the fog!

The Navigation Rules provide for "sound signals" in restricted visibility. Fog is only one type of restricted visibility. Other conditions such as rain, snow, hail, smog and smoke, require mariners to use sound signals. The type of signal device varies with the size of the vessel. For the purpose of this discussion, we will concentrate on pleasure craft and light commercial vessels.

To start with, there are several types of whistle signals. Each signal is made up of one or more blasts of the whistle. In restricted visibility (fog, etc.), the signals for vessels underway are combinations of what are called "short" and "prolonged" blasts of the whistle. By the way, the Nav Rules use the term "whistle" to describe the signaling device. Under the Rules, the "horn" on your boat is a "whistle."

A "short" blast of the whistle should be sounded for duration of about "one second." A prolonged blast of the whistle should be sounded for about a "four to six second" duration. The logic is that the length of those blasts is different enough not to be confused with each other.

A blast is only one component of a signal. Single blasts of the whistle are arranged in "groups" of one or more to make up a signal. That is, various combinations of "short" and "prolonged" blasts make up a variety of signals.

An assortment of sound signals authorized in restricted visibility is used to identify different types of vessels, as well as whether their maneuverability is limited in some way. For vessels underway, there are a number of signals provided in the Nav Rules. We will focus on the main three signals. They represent the lion's share of the vessels underway.

Power-driven vessels, operating in restricted visibility, while underway and making way (progressing through the water under power), are required to sound one prolonged blast of the whistle every two minutes. If you hear such a signal, the trick is to wait two minutes and listen for the signal again. Based on the strength and proximity of those signals, you can estimate the position and direction of that vessel.

Power-driven vessels that are not making way (stopped, adrift, etc.) are required to sound two prolonged blasts of the whistle every two minutes. Unlike the power-driven vessel "making way," the one "not making way" sounds both blasts in succession. You need not wait two minutes to assess their direction, since they are not moving. You can immediately estimate their position.

All other vessels on the water (sailing vessels, fishing vessels, vessels with maneuvering constraints, etc.) are required to sound one prolonged blast followed by two short blasts of the whistle every two minutes. The prudent mariner will steer clear of vessels making that sound signal.

It requires great care and concentration to assess the position and direction of vessels around you in restricted visibility. It is wise to post a "dedicated" lookout. Also, remember to reduce your speed in the fog!

Until next time, I wish you clear skies, fair winds, and calm seas!