Kotug Rotortugs RT Ambition and RT Evolution were charged with a special task this morning as they towed new cruise ship Viking Star on her first call to the Port of London. RT Ambition and RT Evolution towed Viking Star through the Thames Tidal Barrier on the Upper River Thames and assisted her to swing and berth at Greenwich, towage operator Kotug said. At 228 meters long, Viking star is the largest vessel to call Central London, requiring moorings to be specially lengthened to accommodate the cruise ship, the Port of London Authority (PLA) said.