I had noticed the marks on the side of the Wightlink ferries at various times. I had thought it was just marks from the dockside when the ship rubbed up against it. However, when walking around Spice Island, I got a look across at the Gunwharf terminal and saw some odd panels alongside the dock. I zoomed in tight on these to see if I could read what was written on the side.

It turns out that these are a vacuum clamp arrangement which holds the ship when it is docked. I assume that this replaces the old process of looping ropes over posts on the docks. The location would explain the marks that I have seen on the ferries. I assume there is some degree of freedom in the connection arms to accommodate the motion of the ferry even while it is in harbour. Now I am going to have to try and see these in operation. Next time we take the ferry, I shall try and get a good look.