One of the biggest maritime vessels in the world on Wednesday transited through the Bosphorus in Istanbul after completing the first line of a new gas pipeline between Russia and Turkey beneath the Black Sea. The vessel Pioneering Spirit, the size of several football pitches, passed through the Bosphorus towards the Mediterranean after laying the first section of the hugely ambitious TurkStream project. TurkStream, a project championed by President Vladimir Putin and Turkish counterpart Recep Tayyip Erdogan, aims to pump Russian gas to Turkey and Europe while avoiding Ukraine. With the Bosphorus otherwise closed to shipping traffic while the massive vessel passed, the Pioneering Spirit calmly but slowly sailed towards the Sea of Marmara and Mediterranean in full view of city residents. Russian gas giant Gazprom said in a statement on Monday that the Pioneering Spirit had completed the laying of the first of two projected lines for TurkStream. It said the average rate of the deep-water pipelay by the vessel was 4.3km per day after work began only in May 2017. Each line will have the throughput capacity of 15.75 billion cubic meters of gas per year, according to Gazprom. The pumping of gas is expected to start at the end of 2019. The twin-hulled Pioneering Spirit, described by its owners Allseas as the world’s largest construction vessel, is 382 metres (1,253 feet) long and 124 metres (406 feet) wide. Its captain was quoted by Turkish media as saying at the weekend the vessel was the size of six Boeing 747s, and is able to lift 2.5 Eiffel Towers at once. Gazprom said Pioneering Spirit would return to continue the deep-water pipelay of line 2 in the third quarter of 2018. It is now heading to its home port of Rotterdam.