The ocean has many moods. On some days, it is beautifully calm and shipping operations can continue without interruption. On other days, the ocean can be wild, with enormous swells that have a negative effect on shipping operations and can even be extremely dangerous to ships. Similarly, windy conditions can be problematic to shipping, as can fog, while the dangers of icebergs – repeated often in the context of the Titanic tragedy – are well-known.
Good visibility at sea is important to safe navigation, although modern radar and electronic chart display systems help to make navigation safe, even in very dense fog.
Fog off the southern African coast is formed in two different ways :
Advection Fog forms mainly along the west coast when warm, moist air – originating from sub-tropical areas – moves over a cold current and comes in contact with cold air above that current. The temperature of the warmer air drops, and condensation occurs. (See the Diagrams A and B below.)
Other areas where this type of fog occurs include off the west coast of Australia, Chile and North Africa.
Fog formed from mixing of air masses with different temperatures. Off the southern Cape coast, the warm Agulhas Current meets branch currents from the colder Benguela Current. This brings warm, moist air above the Agulhas Current in contact with colder air above the colder current. The warm air cools and condensation occurs. (See the Diagrams C and D below.)
Other areas where this type of fog occurs include the Japanese coast, the eastern coast of Canada, and the coast of north-western Europe.
The effects of fog on shipping :
- Poor visibility will slow down harbour operations – ships’ movements will be slower, while some cargowork will also proceed more slowly. This is particularly true in container operations where the container gantry operators need to see the cell guides into which they need to load containers, or the twistlocks onto which they need to place containers.
- Despite modern electronic devices that assist navigation, ships at sea usually reduce speed in fog. This will delay a ship’s arrival at port, or cause the ship to have to increase speed when in clear weather to make up time. This results in higher fuel consumption and higher fuel costs.
- Skippers of small fishing vessels or leisure vessels that might not have sophisticated navigation aids and can become disorientated when in fog.
Strong wind will have significant effects on shipping.
- High-sided ships (e.g. large passenger ships, containerships, large bulkers in ballast, large tankers in ballast and oil rigs) present a large area to the wind. If a strong wind is blowing, it will be difficult to manouevre such a ship in a harbour. Therefore, strong wind will delay the berthing and sailing of these ships.
- Container operations are very difficult in strong wind as containers begin to swing while they are being discharged or loaded. Apart from the danger this poses to stevedores and the possible damage to other containers and even to the ship herself, this makes the work of the container gantry operators very difficult as they try to fit the swinging container into the cell guides on the ship or onto the twistlocks.
- In strong winds, ships may move a metre or two along the quay, also making container operations very difficult.
- Strong winds can cause ships to break mooring lines in harbour, posing a danger to the ship, and other ships in the harbour.
- A strong headwind can cause a ship to use more fuel to maintain her speed. A sternwind will assist the ship on her voyage.
Rough sea (caused by strong wind, aggravated sometimes by a sudden change in the depth of water or shape of the coastline) will have several negative effects on shipping.
- Rough seas can damage a ship and/or her cargo. Cargo can shift if the ship is rolling heavily, and this can cause the ship to list dangerously. The loss of the containership El Faro off the Florida coast in October 2015 was attributed to her being overwhelmed by heavy seas that had been caused by a hurricane in the area.
- Heavy swell off a harbour can make it very difficult for pilots to board or to disembark from ships. This can lead to the temporary closure of a harbour, leading to delays to shipping.
- Harbour installations can be damaged by heavy seas.
- Ships can be driven ashore by a combination of strong wind and a heavy swell. When the bulk carrier Ikan Tanda (above) broke down off the Cape Peninsula coast in 2001, 17-metres swells drove her ashore at Scarborough near Cape Town.
Although icebergs have a sinister reputation following the loss of the Titanic in 1912, they pose limited danger to ships now as they are tracked using satellite images and ships in the area receive regular updates on the position and course of icebergs.
However, with an increasing number of cruise ships and research ships going into polar regions, more diligent tracking of icebergs and floating ice sheets is necessary.
Freezing of water in harbours and waterways presents a problem for shipping, and some harbours in northern Russia (e.g. Archangelsk) and in Canada are closed for several months each year. Part of the St Lawrence Seaway and the entire Great Lakes in Canada are also closed during the severe winter months. (Harbours on similar latitudes in Western Europe remain open because of the presence of relatively warmer water, brought in by the North Atlantic Drift that has its origin near Florida in the United States.
The north-west passage (from the eastern coast of Canada to the Bering Sea) is open to shipping for several more weeks now as it appears that some of the northern polar ice sheets disappear for longer. A similar situation exists in the north-east passage (from north-western Russia to the Russian east coast).
Although the Antarctic region is not a general shipping area, specially-equipped polar research and supply vessels do go there in the summer months carrying supplies for several research bases in Antarctica and also carrying scientific teams to undertake research in meteorology, geology, animal life and forms of geophysics. Some cruise ships also venture into the Antarctic waters but are required to be ice-strengthened.