The first thing to be said on this subject is that you should never be considering setting off on a journey in fog. Fog is rightly feared by professional mariners and has been for centuries. The first time you are caught out in it, especially in a confined area or where you know there is other shipping, the stress levels can build very quickly.
All of this said, if on passage, you may well find yourself overtaken by fog and a few simple precautions will help to protect you, your boat and your crew from danger.
First of all, if you see fog coming it is sensible to make a note of your exact position in the logbook and plot it on a chart. This not only gives you a starting point for navigation purposes but it also fulfills your obligations under the laws of the sea. You are maintaining a good and effective log and illustrating that you are doing all the right things too.
Next, you should make sure you have your navigation lights on. You should also brief your crew on your standing orders with relation to fog procedures and make sure that someone is briefed on how to make the appropriate sound signal for your vessel. Remember, this may alter dependent on whether you are underway and sailing or motoring.
If you are not all wearing lifejackets, make sure that changes. Everyone should be wearing lifejackets and have harness lines attached. You should also consider having one or two white flares easily accessible should you need them to mark your position to other shipping. If you have a portable high illumination lamp then get that ready also.
If you are in busy waters, have your liferaft prepared and easily accessible in the event that it needs to be deployed immediately. You should consider having all crew on deck and if you have the crew have just one crew maintaining a radio watch.
If you have RADAR and/or a chart plotter then this will be a great help. If you have echomax on board, make sure it is switched on. Needless to say, if your chart plotter is also linked to an AIS transponder then your radio operator should be glued to it, making sure that you are clear of all hazards and approaching vessels.
Last of all, make sure that you maintain detailed and regular log entries and plot fixes on your paper charts. If you are in an area with a lot of shipping then have a plan for keeping safely out of the shipping channels. This might mean following a depth contour and ‘buoy-hopping’ along a shallow water contour where big shipping cannot physically go. That way, if you lose your GPS or chartplotter, you can still safely pilot your way home using your depth sounder and a sharp look out.