Slightly tangentially, there's a great short documentary on the building of Chevron's Ninian Central Platform at Loch Kishorn in 1978 [0]. At the time of construction it was the largest "man-made movable object". The base and supporting column for the drilling platform itself was constructed entirely out of concrete and floated to ~100 miles north east of the Shetlands.
Really is quite amazing that you can float a 600,000 tonne object several hundred miles out to sea.