Being out in any form of restricted visibility, due to heavy rain, snow, mist or fog, is a major concern to all boat users because three things immediately come into play.
First – as soon as you are navigating in or near an area where the visibility has dropped below 1,000m (further than you might think) there is a fundamental change in how the rules of the road apply. Rule 19 of the International Regulations for the Prevention of Collision at Sea (IRPCS) effectively means that in these circumstances all the usual rules regarding stand-on and give-way vessels change to everyone becoming give-way vessels. After all, if you can’t see them clearly, how can you tell their intentions?
Second – your speed must be adapted to suit the visibility, meaning you must be able to comfortably stop within the distance you can see. So in open sea with just under 1,000m visibility that might not require any change of speed but if the location, traffic density or depth complicates things then somewhere between 6 and 10 knots may be more suitable. Any slower than that and you may have difficulty holding a straight course.
Your next steps should be to confirm your position and note it on a chart or logbook, turn on your navigation lights, ensure your crew are wearing lifejackets, switch on your radar and AIS if fitted, and comply with the correct sound signals. Lastly, ask all aboard to keep a look out using all available means. Third – a change of mindset is required. Restricted visibility takes practice, both in terms of technique and having the confidence to know it works. If you have a full set of electronic navigation equipment, including AIS and radar, fog is perfectly manageable but only if you know how to use it. Practise this on a sunny day by pretending you can only see 100m and finding your way back home using just your electronics and charts.
Out at sea, restricted visibility for commercial craft means following all of the above, except they don’t generally slow much, so holding a steady heading makes it much easier for them to work out your intentions. In shallower waters and especially if your boat isn’t fitted with radar, a depth sounder is another very valuable means
