Safe Speed (Rule 6) in Fog and at Night

Fog changes everything on a bridge. The horizon disappears. Lights you would have seen at six miles appear at half a mile, if at all. Sounds carry strangely. And a collision that would have been easy to avoid in daylight becomes a matter of a few minutes and a radar screen.

The rules for this situation are some of the oldest and clearest we have. They are also some of the most often ignored.

Rule 6: safe speed

Every vessel must proceed at a safe speed at all times, meaning a speed at which she can take proper and effective action to avoid a collision and stop within a distance appropriate to the conditions. The rule lists factors to weigh, including:

• Visibility
• Traffic density, including fishing vessels and others
• The vessel's maneuverability, especially stopping distance and turning ability
• Wind, sea, current, and nearby hazards
• Draft in relation to the depth of water
• The characteristics and limits of the radar, including small targets it may miss

There is no number. Safe speed depends on the vessel and the situation. A large tanker that needs more than a mile to stop is in a very different position from a small crew boat.

Rule 19: conduct in restricted visibility

Rule 19 applies to vessels not in sight of one another in or near an area of restricted visibility. It requires a safe speed adapted to the conditions, with engines ready for immediate maneuver. A vessel that detects another by radar alone must decide whether a close-quarters situation is developing, and if so take early action. The rule also limits which course changes are appropriate depending on where the other vessel is.

And there is one line every mariner learns early: a vessel that hears another's fog signal apparently forward of the beam, or cannot avoid a close-quarters situation with a vessel forward of the beam, must reduce speed to the minimum at which she can be kept on course, and if necessary take all way off, navigating with extreme caution until the danger is over.

Sound signals

In restricted visibility, vessels must sound fog signals. A power-driven vessel making way sounds one prolonged blast at intervals of not more than two minutes. Whether signals were sounded, and whether anyone was listening, are common questions after a fog collision.

What radar does not change

Radar is an enormous help, and the rules expect vessels to use it properly. But radar does not make fog into clear weather. Small craft, wooden boats, and targets in sea clutter can be missed. Radar plotting takes time and attention. Courts have long held that radar is an aid that brings duties of its own, not a license for full speed.

How safe speed is judged afterward

The analysis looks at what the vessel could actually do at the speed she was making. How far did she need to stop or turn? How far away could she reliably detect another vessel in those conditions? Did the bridge have time to assess and act? The ship's own maneuvering data, radar settings, and VDR recordings usually answer those questions.

Fog collisions often come down to the same decision: someone chose to keep the schedule instead of slowing down.

About the author

Captain Mitchell S. Stoller is a Master Mariner Unlimited, former Exxon tanker master, and former Los Angeles Harbor pilot. About Captain Stoller