There was so much that could have gone wrong when the Leiv Eiriksson drilling rig had to be towed through the insidious Bosphorus Strait, the eye of the needle between Europe and Asia. However, the "floating crew" from KONGSBERG was fully prepared for all the risks involved.

  • Ove Ronny Haraldsen
    Group Communication Manager

Bosphorus is the name of the strait which connects the Black Sea to the Mediterranean. This channel between east and west was formed around 7,600 years ago, when the rising waters of the Mediterranean and the Marmara Sea forced their way through land to the Black Sea. It is commonly thought that the resulting vast flood provides the historical basis for the Great Flood in the Bible.

Whether the towing operation of the massive drilling rig through the Bosphorus Strait reached biblical dimensions is a personal judgement. What can be confirmed is that Leiv Eiriksson is the largest rig ever to be piloted through these historical waters, and that the sailing would not have been possible without the help of dynamic positioning from KONGSBERG.

The amount of traffic crossing the Bosphorus Strait is huge. Every year, 50,000 vessels pass through the strait which cuts the metropolis of Istanbul in two. From the harbours on the innermost shores of the Black Sea, crude oil and gas are shipped out to the world markets. It is very rare for the strait to be closed to all traffic, but this was the case when Leiv Eiriksson was due to sail through the Bosphorus.


“The current was most definitely our greatest challenge while planning the operation. The current does not follow the channel in a straight line but runs in a zigzag pattern. Our major concern was the side current which could push us towards the shallow waters. If we had run aground in the middle of the strait, it would have been front page news,” explains Stein Svendsen from the company leading the operation, Ocean Rig. At seven o’clock in the morning of 31 December, Stein Svendsen and the rest of the crew are on the bridge of the Leiv Eiriksson, gazing down the strait.

The air is still cool and hazy after a cold night. But as Leiv Eiriksson sets its course for the mouth of the strait, the sea and air turn red in the morning sunrise. The operation they are about to execute is quite colossal. There are so many uncertainties. The level of performance required is extremely high. Despite this, the crew are remarkably calm. They’ve been through it all before - in a simulator at Kongsberg.

“The drilling rig is equipped with the very best navigation equipment from Kongsberg Maritime. We used the simulator to drill the crew in all kinds of potential situations, such as loss of engine power. We were also able to carry out drills in precise communication procedures between the rig and tugboat,” explains Anders Hovde of Kongsberg Maritime. Vebjørn Gulbrandsen was one of the participants who completed the drills in the simulator at Kongsberg.

The skills learned there were extremely important for the actual execution. “Our simulator training allowed us to remain calm. We didn’t have to worry about what might happen. We were well prepared for all eventualities. We’d all completed drills in all the different tasks to complete, in case one of us became incapacitated. That gave us an extra feeling of security,” explains Vebjørn Gulbrandsen.

On the last day of 2009, something extremely unusual happens. For 99% of the time, the current in the Bosphorus Strait travels from the Black Sea into the Mediterranean. On 31 December however, the surface current is travelling in the opposite direction. This is good news. In order to enter the strait, the Leiv Eiriksson has to completely empty its ballast tanks, allowing it to creep over the shallow waters on the southern side of the strait.

Majestically, the Leiv Eiriksson slides with the current past the well-known landmark - the Sultan Ahmed mosque - which stands proudly on an elevation, overlooking the mouth of the Bosphorus Strait. Once the rig is into the strait itself, the ballast tanks are refilled with water. The rig has to pass two bridges and has to reduce its height, lying lower in the water. Filling ballast in the middle of the current is a critical phase of the operation.

The system for dynamic positioning is changed from manual to automatic control. It is paramount that the rig remains in the same position during the ballast procedure. “All four tugboats kept a taut line throughout the operation to help stabilise. In combination with the powerful current, this presented a real challenge for the positioning system,” explains Stein Svendsen from Ocean Rig. 20 cm under the maximum height With the ballast tanks full, the sailing continues into the strait. The route has been carefully planned in advance. Each metre has been programmed into the rig’s K-Bridge system.

This is a complete navigational system from Kongsberg Maritime, used on ships all over the world. “Once the ballast tanks were full, the rig had a draft of 30 metres. We had to follow an extremely narrow corridor to avoid submerged shipwrecks and shallow sandbanks. On our sailing through the Bosphorus Strait, we had 6 metres clearance up to the bridge and only a few metres clearance of the seabed. We were just 20 cm under the maximum height permitted by the Turkish authorities,” confirms Svein Svendsen.

Joining the crew on the sailing was the British production company, Original Productions, creators of the successful series The Deadliest Catch shown on Discovery Channel. The documentary they filmed on the sailing has already been broadcast by a number of international TV stations.

In Norway, the documentary will be broadcast on Viasat 4 as part of the Nordsjøliv series (North Sea Life). The film also shows how the crew trained in the simulator in Kongsberg. After 7 hours and 30 km in narrow waters, the Black Sea finally opens its arms to the crew onboard Leiv Eiriksson.


There is a definite feeling of relief onboard the rig. All they have to do now is set their heading for their destination – the fields where Ocean Rig plans to drill for oil and gas over the next three years. Svein Svendsen and the rest of the crew describe the sailing through the strait as a memory for life, an overwhelming feeling of having taken part in something really big, the safety of knowing that the rig is equipped with the most advanced navigation equipment in the world, the feeling of mastering the technology and succeeding as a team. They are already looking forward to the return trip.