An unusual sight

.... at dusk this evening gave me my blip. This is (we think) the support 'barge' for the wind farm off the coast. It is behind the 'barge' and is between 13 and 20km off the coast and comprises 116 turbines on a 70 square km site. Question is.... why was the 'barge' being towed along the coast?
A run in the sun, tescos and shortly tennis training completes my Wednesday.