The Ampelmann is a Delft invention (see www.ampelmann.nl). This is a platform with underneath it 6 cylinders based on a flight simulator. This unit can be mounted on a ship. The cylinders are controlled so that the platform can compensate movements of the ship due to swells and waves. A walkway will lead maintenance personel on a not moving platform. The platform is complex due to a lot of electronica needed to quay the 6 cilinders.
The other practical solution can be:
1: a ladder is attached to the windmill with a possibility to slide vertically. On the bottom of the ladder a buyancy is placed. As the waves passes the ladder it moves up and down the same way the ship does. When maintenance personel is standing on the ladder they move a handle so the ladder is connected tight to the support structure of the windmill. Now they can climb up to do their work. The upper part of the ladder is fixed tight to the support structure. Only the lower part of the ladder should be able to move up and down. When maintenance is done the people move towards the lower part of the ladder and wait till the next wave touches the bouancy. Then they will pull on the handle so the ladder will move with the waves again.
2: The ladder can also be made movable by hydraulics. Now a floatable construction at the bottom of the ladder is not necessary. This reduces wear. On the ladder we can place a proximity sensor. A sensor of the same kind could be mounted on the bow of the ship. With both signals you can control the vertical movement of the ladder with hydraulic power. By doing this the ladder will move up and down the way the ship moves up and down.
Both above presented solutions are much more easy to implement and also cheaper to install. The disadvantage is that every windturbine needs such a system. With the Ampelmann system only some ships should have this system.