Durban's Single Buoy Mooring

By Chris Hoare - May 2005

Did you know that about 80 percent of all crude oil imports to South Africa, come through Durban's single buoy mooring (SBM)? Last year that was 16,7 million tonnes.

Look at some of the numbers involved and be impressed: a typical VLCC (Very Large Crude Carrier) is worth about US$120 million, has a deadweight of 300,000 tonnes and carries two million barrels of crude oil worth US$100-110 million. It is 335 metres long (that's three rugby fields) and 58 metres wide. Its draft is 22 metres.

A typical tanker has five decks and a bridge deck above the main deck, and will have a top speed of 14-15 knots (about 25km/hr), driven by a 35 000 horse power engine that is two-storeys high; it burns heavy fuel; stopping distance is ten nautical miles (16 km). Most tankers come to Durban with Iranian and Saudi Arabian crude from the Arabian Gulf.

Last year 78 VLCCs called at the SBM which is anchored 2.6 km off Reunion [on the Bluff], and has a 1.6 km exclusion zone around it. The SBM is in 48 metres of water and is held in place by eight seven-ton anchors, each on the end of 330 metres of chain whose links are made from 90 mm diameter steel. The SBM is owned by a consortium of oil companies.

Picture by Chris Hoare, courtesy SAPREF

Smit Marine, a SAPREF contractor, operates the SBM. When a tanker arrives, five of their highly experienced men are taken on board by helicopter. One is the ship's pilot who oversees the docking process and monitors all the operations and the weather conditions during discharge. Another is the discharge advisor, and the other three are divers who couple the floating hoses to the ship's discharge manifold and monitor the mooring hawsers and hose connection throughout the discharge operation. They are all also on standby to respond to any emergencies. Discharge normally takes about 42 hours. Should weather conditions worsen, the pilot takes the vessel off the SBM until the weather abates.

Said SAPREF's marine manager George Franklin, a master mariner with 38 years marine experience, "We take the utmost care when discharging oil at the SBM. Almost all tankers calling at the SBM are modern double-hull vessels with separate ballast tanks, and every vessel must be positively vetted by Shell Marine's rigorous quality system before acceptance for any business. In SAPREF'S offices at Bayhead we are able to monitor conditions at the SBM including wind speed, pull on the mooring hawsers, swell height, etc. We are also one of only a few operations in the world having a full back-up team of divers on standby onshore, and we have procedures and systems in place to ensure the spill-free discharge of crude oil at the SBM within the hostile environment in which we operate."

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