When fog descends it can throw up many disorientating scenarios and turn a relaxing day on the water into a test of your seamanship.
With AIS, chart plotters and radar now readily available for even the smallest of craft, some of the pressure has been taken off. However occasionally on deliveries, especially with older boats, these systems may not be available or have failed, so a good knowledge of traditional techniques is essential.
So here are our top tips and guide to sailing in fog.
Types of Fog
Fog is defined when visibility is 1,000 metres or less. The two main types are ‘Radiation’ and ‘Advection’. The latter is the type that sailors are most likely to come across. This forms when moist air flows across the sea towards colder waters; the cooling effect creating Advection Fog which we refer to as ‘Sea Fog’. It can occur at any time of day and with quite strong winds. With winds, over about F 4-5, the result may be low cloud and poor visibility rather than fog.
Ideally you should not be under sail in fog and although as stated above fog can form in wind, in most cases when fog is present the wind will be very light. You may not be able to manoeuvre quickly under full sail, the sail can obstruct visibility and white sails do not show up well in fog. In this instance, consider just keeping a main sail up for stability and some drive if possible.
It is only possible to measure the visibility accurately when motoring or sailing in fog, when you have another object in sight, so always assume that it is less than you think.
As a rough guide you should reduce your speed so you are able to stop in half the distance of the visibility because a conflicting vessel will need a similar distance to stop. It can take time to ‘see’ another vessel as you may not be looking directly at it when it first appears.
There are few visual clues in thick fog, so monitor the radar and chart plotter/AIS if fitted. Radar is an important aid in fog but do not rely on it to pick up all vessels around you, particularly when the sea may be lively and wave clutter obstructs the display, obscuring small vessels. AIS is a useful feature in fog but remember not all private yachts have AIS and some are set to only receive. If you do not have a plotter then plot regular fixes on a chart. so if for some reason you lose GPS you can quickly estimate your position and watch for tidal drift, especially close to hazards.
The depth gauge is also important in fog, a rapidly rising seabed can be an early indication of an approaching hazard, and contour lines can be followed to harbour entrances.
The autopilot is another useful tool when sailing in fog as it avoids you having to concentrate on the steering and allows you to focus on the navigation. Always ensure that you know how to disengage it quickly should you need to take avoiding action fast.
Keeping a Lookout when sailing in fog
The more crew on deck the better (provided they are not overtired or cold). Post a crew member to keep a visual lookout, preferably stationed away from the noise of your engine as it will be easier to pick up any noises such as other vessels or waves on rocks or shores.
Make Yourself Visible
When sailing in fog turn your navigation lights on even in daylight and make sure your radar reflector is up and working. If you have a floodlight then have it ready on deck to get attention if required.
Make Yourself Heard
There are lots of different sounds for different craft and eventualities but the main ones we are interested in are:
- A power-driven vessel making way through the water: The signal here is one prolonged blast (4-6 seconds) at intervals of not more than 2 minutes.
- A vessel not under command, a vessel restricted in her ability to manoeuvre, a vessel constrained by her draught, a sailing vessel, a vessel engaged in fishing, a vessel engaged in towing or pushing another vessel: Signal at intervals of not more than 2 minutes three blasts in succession, namely one prolonged followed by two short blasts.
- At anchor in fog a vessel less than 100 metres must: Signal at intervals of not more than one minute, ring a bell rapidly for about five seconds or may sound three blasts in succession. These should be one short, one long and one short again in succession.
Do not “make things fit”
We have all been in this situation, cold, tired, may be finishing a long passage and heading for an unfamiliar harbour when fog descends, if you are using the Almanac and paper charts rather than electronic charts you will no doubt be using lights, landmarks and contour lines as your guide in. If at any point you doubt your course or position, the that transit you are relying on does not look quite right do not try to “make it right”.
This is a mistake even airline pilots have made in fog and turned on to the wrong runway, although they had doubts because they wanted to keep schedule they convinced themselves and “made it right” with disastrous consequences.
When in doubt stop, go out in to open water again if you have to, check everything one more time.
When sailing in fog, Rule 19 completely replaces all others and means that all the usual stuff about power giving way to sail, overtaking boats keeping clear, giving way to vessels approaching from your starboard side and such like does not apply.
In particular, it is important to appreciate that there is no such thing as a “stand-on” vessel in fog.
Rule 19 – Conduct of Vessels in Restricted Visibility:
(a) This Rule applies to vessels not in sight of one another when navigating in or near an area of restricted visibility.
(b) Every vessel shall proceed at a safe speed adapted to the prevailing circumstances and conditions of restricted visibility. A power-driven vessel shall have her engines ready for immediate manoeuvre.
(c) Every vessel shall have due regard to the prevailing circumstances and conditions of restricted visibility when complying with the Rules of Section I of this Part.
(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. If so, she shall take avoiding action in
For more details on collision regulations and Rule 19 visit the R.Y.A website