All sailboats should carry a foghorn for making signals to warn other boats of your presence when sailing in fog. The US Coast Guard requires having and using this equipment in situations of reduced visibility.
When under sail, a sailboat should make the sound signal for a boat with limited maneuverability every 2 minutes. This signal is one long blast (4-6 seconds) followed by two short blasts (1 second each). When under power, a sailboat should use the powering signal of only the one long blast every 2 minutes.
Three basic choices for a fog horn include compressed-air horns, manual horns, and VHF radios with fog horn signals through a hailer. Each type has advantages and disadvantages.
Shown here is a typical compressed-gas foghorn.
Advantages of compressed-gas foghorns:
- Loud
- Inexpensive
- Refills available
Disadvantages of compressed-gas foghorns:
- May be rapidly depleted during extensive time in fog
- Multiple refills must be carried in foggy areas
- Expensive when used for extensive periods in fog
