Looking beyond the fog?

31 May 2024 The Navigator

Navigating in fog or other restricted visibility will never be pleasant, but familiarity with the vessel’s procedures, capabilities and equipment will help make the process as safe as possible. Captain Tuuli Messer-Bookman AFNI, an experienced mariner and a professor at the California Maritime Academy in the USA, offers some advice on how to operate when visibility is low

Navigating in or near restricted visibility can be stressful for even the most experienced bridge watch officers. Radar and other technologies greatly enhance safety, but not every vessel is radar conspicuous (for instance, fibreglass and wood don’t show up well) and many do not broadcast AIS. While technology is a valuable tool, it doesn’t replace traditional, diligent watch-keeping.

Colregs Rule 19 addresses vessels operating in or near restricted visibility but offers no guidance as to precautions a watch officer should take. The Master and the vessel’s SMS documents should provide instructions as to what 'in or near restricted visibility' means and what specific precautions should be taken and when.

Estimating visibility

An important question to ask is, ‘How do I know when visibility is restricted?' I recall night orders stating, “Call the Master if the visibility drops below three miles” and wondering how exactly was I to know what three-mile visibility looked like!

If there are radar contacts/land you can see, then the visibility is at least as far as those contacts. If there are contacts you cannot see, then you know the visibility is less than that distance.

Practising estimating distances in clear visibility will enhance your ability to judge visibility as it is deteriorating. Remember that distance to the visible horizon can be found using the formula: distance = 1.17 x √height from the ground to the eye (in feet).
So, if your height of eye from the ground is 75 feet, the distance to your visible horizon will be approximately 10 nm. Using the metric system, multiply your height in metres above the ground by 13, and take the square root of that. That gives you the distance in kilometres. To find the distance in nautical miles, multiply by 0.54.

Once you know the distance to the horizon, stand in one spot (I stood at the centreline repeater) and see where the horizon lines up with a fixed point on the vessel. This could be the step on a foremast, or perhaps the horizon lies three fingers above the bridge wing rail. If the horizon is 10 miles away and is visually even with the third step of the foremast ladder, you have just established a reference point for 10 miles. If an object or foggy horizon is below the third step, you know it is closer than 10 miles. With practice, standing in the same spot and using visible objects at known distances compared to shipboard landmarks, you will soon become proficient in estimating distances.


Taking precautions

If you are unsure if the visibility is restricted, or if you are 'near' enough to trigger Rule 19, you should assume Rule 19 applies and take precautions. If you are ever in doubt (about anything) it’s time to call the Master. 

Restricted visibility may trigger an increased watch condition, and the Master or other senior officer may come to the wheelhouse.

  • Notify the Master and engine room: If you think the visibility is decreasing, or if the vessel is near a fog bank, the Master and engine room must be notified. If the Master cannot be reached, start the fog signals and follow the protocols in the ship’s SMS document.
  • Start sounding fog signals and ensure navigational lights are on: In restricted visibility, only the fog signals set forth in Rule 35 can be sounded. Manoeuvring signals (including the danger/doubt signal) are only allowed when ‘in sight of’ another vessel.
  • Slow down: The Colregs require vessels to move at a ‘safe speed’ but offer little specific guidance on what this should be in practice. When in or near restricted visibility, slowing down the ship can be prudent and sometimes required. Some situations require stopping altogether. Slowing down is not always simple. Make sure you understand when and how to slow the ship.

Immediate manoeuvre

Rule 19 requires engines to be ready for ‘immediate manoeuvre’. This can mean different things for different vessels. Officers should understand how their vessel manoeuvres at various speeds and load conditions. The ship’s turning diagram will help you figure out at what speed the vessel’s headreach (the distance it takes to stop) is shorter than its advance (the forward distance a ship takes to turn 90°). Most ships going faster than slow ahead can turn 90° in a shorter distance than it takes to stop. Knowing what these distances are at various speeds will help you decide if you should turn or try to stop the ship if collision is imminent.
Slowing the vessel:

  • Allows more time to assess the situation and determine if risk of collision exists
  • Has little impact on turning diameters (for most large vessels)
  • Shortens a vessel’s headreach 
  • Lessens the energy of an impact should there be a collision 

Hearing a fog signal forward of the beam may require slowing to bare steerage way.

Additional lookouts

Sound can become omnidirectional and muffled in fog. When operating in or near restricted visibility, you should post additional lookouts outside and at the bow and the bridge wings. Turn off any music in the wheelhouse and do not use headphones.
Lookouts must use all their senses including hearing – and smell. A lookout may smell the exhaust of a nearby vessel before they actually see it. Leaving wheelhouse doors and windows cracked, and posting lookouts in quiet spots will increase the chances of hearing faint sounds. If you think something is amiss, call the Master.

All available means

If the vessel is equipped with multiple radars, infrared devices, sound reception devices or other technology designed to assist in avoiding collisions, these must be used. All radar contacts must be acquired to generate meaningful information. Longrange radar scanning to determine risk of collision is also required, as is scanning on a low range to detect less conspicuous contacts that may be lost in sea clutter.

If another vessel in the area can be identified easily, perhaps by AIS, call them and make early passing arrangements. In restricted visibility there is no ‘stand-on’ nor ‘give-way’ vessel. Remember: in restricted visibility, neither vessel has right of way and both vessels are expected to manoeuvre to avoid risk of collision.