A RNLI lifeboat crew from Rhyl was called in to help take the injured man from the Svanen heavy lifting vessel.
The crane is being used in the construction of the Rhyl Flats windfarm.
The worker suffered major bruising and cuts after falling 4m (13ft) on to the ship’s deck.
The RNLI said it was called to the incident in the early hours of Thursday morning, and the rescue involved difficult manoeuvres to avoid massive anchor lines keeping the Svanen in place.
Another boat, the MarineCo Hahti, helped by acting as a bridge between the crane and the lifeboat in what has been described as difficult conditions, with a choppy sea.
The injured man was transferred to an ambulance in Rhyl and taken to Glan Clwyd hospital.