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Operating in Reduced Visibility


Fog is the primary cause of reduced visibility, but haze, heavy rain and snow all present problems for mariners. Boating in these conditions presents two hazards, navigational errors and collisions. Preventing both of these begins with reducing your speed. The old saying, “Be able to stop in half the distance of visibility” doesn’t appear in the Navigation Rules, but it is very good advice; remember slower is better!

Reduced Visibility Operation Tips
  • A sailboat with an auxiliary engine, if under sail in fog, should have her engine available for immediate use, but you’ll be better able to listen for fog signals and other helpful sounds if you leave the engine off until it’s needed.
  • Fog signals must be sounded, at minimum, to the time interval(s) specified by the United States Coast Guard Navigation Rules.
  • Vary your interval so that there is no possibility of your signals being in step with another vessel’s, thereby preventing you from hearing them.
  • Listening for another vessel’s fog signals is just as important as sounding your own. If you have crew aboard, post a lookout well forward and consider having another person aft if possible.
  • The lookout should listen as well as look. Listen for other vessels, the sound of aids to navigation, breaking surf, and other helpful sounds.
  • Lookouts are especially important if your helm station is inside. Switch bow and stern lookouts occasionally to provide some variety and increase alertness.
  • If your engines are noisy, periodically shift into idle, or even shut them down for a few minutes to listen for faint fog signals.
  • The transmission of sound in foggy conditions is tricky, if you hear something, don’t jump to a quick conclusion about its direction and distance, listen some more.
  • If several craft are traveling together, it is advisable that they stay close in a column formation in which closely following vessels aren’t directly behind the leader so they can easily steer clear if the lead vessel stops suddenly.
  • If the fog is so thick that it is hazardous for them to be within sight of each other, each vessel should tow a floating object such as an empty fuel container or a cushion well astern on a line of approximately 150 feet. Then, each vessel can keep its “station” in column by keeping that object in sight, rather than the craft ahead.
  • Operating in Reduced Visibility Signaling Requirements
    Vessel Required Sound Signal
    Power-driven vessl making way One prolonged blast every two minutes
    Power-driven vessel not making way (stopped) Two prolonged blast every two minutes with a one second interval between them
    Sailing Vessel or Vessel not under command or Vessel restricted in ability to maneuver or Vessel constrained by draft or Vessel engaged in fishing or Vessel towing or pushing another vessel One prolonged blast followed by two short blasts every two minutes


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    Operating in Reduced Visibility