At sea, it's all about visibility - in the truest sense of the word. However, reduced visibility does not mean fog. Meteorology only speaks of this when visibility is less than one kilometre. If it is one kilometre to two nautical miles, it is only referred to as "poor visibility". From two to five nautical miles, the meteorological term is "moderate visibility", above that it is simply "good visibility".
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If you can only see a grey soup beyond the pier heads in the morning, it is difficult to estimate how great the visibility really is. The range rings or the VRM on the radar can be used to measure the distance to a target that is still just visible. It is not uncommon to realise with astonishment that the visibility is not so bad, but that only the usual references are missing.
Radiation nebulae and advection nebulae
If you are woken up by sound signals after a clear, cold night and see thick fog from the saloon, it is probably radiation fog, which should clear up later. As visibility is often minimal with radiation fog, it is worth waiting for the sun's warming rays.
If, on the other hand, there is advection fog, visibility is rarely very poor - and so experienced skippers with radar and appropriate knowledge can venture out of the harbour very carefully. Not too much advection fog can be a good exercise in radar navigation. In real fog (with visibility below 1,000 metres), navigation should be left to the absolute professionals with very good radar equipment. It is better to stay in the harbour.
In fog: adapt your driving style
But what to do if fog appears en route? With advection fog, the crew can be surprised by even a slight change in wind direction with moderate or poor visibility if the conditions are right. This is often announced as a "fog risk" in the weather forecasts.
If visibility suddenly deteriorates, the driving style must be adjusted. The speed is reduced according to the circumstances so that any danger appearing in front of the bow can be avoided in good time. If you don't have a permanently installed radar reflector, you need to make it clear now at the latest - the right way round. And by radar reflector, we do not mean the thin tubes that do not have BSH approval and only give a false sense of security.
Safety measures in fog
Navigation lights should be switched on and, especially near the harbour, vessel traffic should be monitored on the harbour's working channel via VHF and channel 16 via Dual Watch. If possible, switch on the radar before the fog appears, even if the wall still seems far away. Firstly, radar antennas with magnetrons need a warm-up time, and secondly, you can never know exactly what is hidden in the fog - even if your own ship is still in the sunshine.
For safety reasons, the entire crew is also provided with life jackets and called on deck so that nobody can be surprised by a collision below. A life raft with an automatic hydrostatic release would be deployed quickly in the event of a collision. But it won't come to that if appropriate precautions are taken.
Emit sound signals
The entire crew is now mobilised: A lookout must be constantly on the lookout in all directions and also listen for ship noises or sound signals. If it makes sense under the circumstances, the lookout could also stand at the bow, where the ship's own engine noise is at a minimum. The navigator with the most experience constantly monitors the traffic situation, but should be replaced after 30 to 45 minutes if possible.
If you do not have an automatic foghorn installed, you have to emit the signal manually every two minutes: a long tone lasting four to six seconds. Some VHF devices that are connected to a fog horn can transmit the signals automatically as a tone. However, the BSH-approved fog horns with an automatic system are even better, as they are many times louder. Incidentally, it is extremely difficult to judge the direction of origin of a sound in fog.
The great importance of radar
Radar is the most important piece of equipment here. But it is even more important to be able to interpret a radar image. Appropriate training courses are offered for this, for example at Regina Sailing.
If fog occurs, the location, time and log data should be entered on the chart immediately. Electronics can fail - and this would be the worst possible time in fog! When navigating with a plotter and GPS, bear in mind that other skippers may choose the same waypoints, especially at prominent points. So a little deviation makes sense here. It is obvious that the positions of buoys are not suitable for this due to the risk of collision.
Avoiding large-scale shipping
The most important thing is to avoid large ships. The space just outside the buoy line or fairway is ideal here, deep enough for a yacht but already too shallow for freighters and tankers.
When passing islands, you should be aware that visibility is often significantly better on the leeward side than on the windward side, where the fog builds up. Together with radar and plotter, the use of an echo sounder is also very useful, as the depth contours provide a good navigational aid, also for checking the plotter with another system.
Find the harbour safely
If you are looking for a harbour entrance or the entrance to a small bay, you can first head clearly to one side or the other of the entrance until a certain depth of water is reached. Then sail along this depth contour, ideally so that the land is just in sight, but still with a sufficient safety distance. When the opening or harbour entrance is visible, the incoming and outgoing ships can be seen better in the side profile than with the narrow silhouette from the front or aft.
If, instead, you use GPS to steer directly towards the harbour entrance via the fairway, you are certainly not the only one following the direct route. The risk of running into heavy traffic without visibility is significantly greater.
If you don't want to venture into a bay or harbour in poor visibility, you can also anchor in shallow water outside the buoy line and wait and see. When at anchor, it is a good idea to watch the passing traffic on the radar. Very few pleasure craft anchors will ring for five seconds every minute, as the Collision Prevention Rules (KVR) provide.
However, if another vessel is approaching, the person at anchor can sound the short-long-short sound signal or, of course, reach for the radio and transmit a warning with their own position on channel 16. The AIS should always remain switched on when anchored in fog.
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Leon Schulz
Freier Mitarbeiter
