One of the greatest dangers a sailing yacht can encounter is fog. If fog is forecast, then most skippers will sensibly delay their departure until they are sure the conditions are clear. However, if fog begins to form when you are at sea it is important to be prepared and know what precautions to take. This will help to make your vessel detectable or visible in fog and keep the crew safe.

Types of fog

There are two main types of fog, usually referred to as land fog and sea fog.

Land fog, technically referred to as radiation fog, forms at night in clear conditions when the land cools rapidly, causing water vapour in the air to condense into tiny water droplets. Land fog normally lifts or disappears after the sun has risen but sometimes persists through the morning. This type of fog can be found along rivers and estuaries and sometimes extends one or two miles out to sea but it will soon disperse if the sea temperature is higher than the land temperature.

Sea fog, technically referred to as advection fog, is formed at sea and is more of a threat to sailors as it can last longer than land fog, needing a dry wind to disperse it. Sea fog is formed when moisture laden warm air flows over cold water. The warm air is cooled by the cold water beneath which results in the water vapour in the air condensing into tiny droplets.

Other types of fog include frontal fog and sea smoke. Frontal fog develops when warm air at the front of a depression rises over colder air, while sea smoke forms in arctic regions when very cold air flows slowly over a a layer of warmer air above the sea.

Preparation

A good first step to take is to study the prevailing weather in your sailing area in order to know what the conditions are like through the year and when different types of fog are likely to develop. For example in many areas, advection fog is more likely in spring when sea temperatures are at their lowest but air temperatures are rising.

Radar reflectors

Most larger leisure vessels and all commercial vessels are fitted with radar. Radar works by the transmitting and receiving of high frequency radio waves. The radar first sends out the radio waves which then reflect off all kinds of objects to a greater or lesser extent. The reflected waves are picked up by the receiver.

A large, tall, metal ship makes an excellent reflector and will be easy for the receiver to pick up. A small wooden or plastic boat will be almost impossible to detect unless it has a mast with a purpose built radar reflector attached. Radar reflectors are not expensive but are very effective and all small vessels should carry one. The higher the reflector is mounted, the more efficient it will be.

All small vessels should carry a foghorn with spare cannisters.

Sailing into fog

If you are sailing a yacht into fog there are a number of actions you should take.

• Turn on the navigation lights.
• Get the crew on deck and ensure everyone is looking out and listening for other vessels.
• Put on lifejackets and clip on if the weather is rough.
• Fog usually only occurs in a light wind, so consider running the engine very slowly to be able to manoeuvre instantly if necessary.
• Partially furl in the genoa to help with forward visibility. Keep the mainsail hoisted as this will help make your vessel more visible to others.
• Unless permanently mounted, hoist your radar reflector high into the rigging.
• Make sure the liferaft is ready if needed.
• Make sure the foghorn is ready and working.
• Listen on VHF channel 16 or your local harbour channel if appropriate.
• Plot your position on the chart.
• Keep a regular check of your speed, course and position.
• If your vessel is fitted with radar, an experienced crew member should monitor it until the fog clears.
• Stop the engine at regular intervals to listen out for other vessels.

Collision avoidance

All skippers of small vessels should know the Collision Regulations which give instructions for vessels operating in restricted visibility including rain, snow and fog. Here is a reminder of which specific rules are appropriate for navigating in fog:

Rules 4-10

Section 1 of the Steering and Sailing Rules.

Rule 7b

Proper use shall be made of radar equipment if fitted and operational, including long range scanning to obtain early warning of collision and radar plotting or equivalent systematic observation of detected objects

Rules 11-18

Rules in this Section of the Steering and Sailing Rules apply to vessels in sight of one another.

Rule 19(a)

This Rule applies to vessels not in sight of one another when navigating in or near an area of restricted visibility.

Rule 19(b)

A power-driven vessel shall have her engines ready for immediate manoeuvre.

Rule 19(d)

A vessel which detects by radar alone the presence of another vessel shall determine if a close-quarters situation is developing and/or risk of collision exists.

Rule 19(e)

Except where it has been determined that a risk of collision does not exist, every vessel which hears apparently forward of her beam the fog signal of another vessel, or which cannot avoid a close-quarters situation with another vessel forward of her beam, shall reduce her speed to the minimum at which she can be kept on her course. She shall if necessary take all way off and in any event navigate with extreme caution until danger of collision is over.

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