A walk along the pier can make for a pleasant evening. Watching the ships is interesting even if you have no real connection to the sea. And sometimes, small details spark curiosity. For example, have you ever noticed that some smaller boats have clear spinning discs on their windscreens? What are those for?
Ship windows are usually quite large. They’re not only great for enjoying the view, but they’re also essential for safety, especially when navigating near the coast, around other vessels, or while docking in a harbor. Good visibility is a basic requirement for safe operation.
That’s exactly why those discs exist. They’re clear view screens – rotating glass panels that very effectively clear away water from rain or waves. Ships do have regular rubber windscreen wipers, but in heavy rain they’re sometimes too slow or simply not effective enough. The view through a clear view screen, however, stays remarkably good even in difficult conditions.
This is actually a fairly old invention. A clear view screen that sheds water by spinning was patented in 1917 by two Britons, Samuel Augustine de Normanville and Leslie Harcourt Kent. It was designed primarily for ships, but at the time they also imagined it being used on various optical devices, including telescopes. In the UK, these rotating glass discs are still sometimes called Kent screens.
A small electric motor sits at the center of the disc. Press a button and it begins to spin, using centrifugal force to fling water droplets away. Some versions are heated so they don’t fog up or freeze in winter. Tugboats often use them because they must operate close to other vessels even in very poor visibility. Ferries, floating cranes, dredgers, and other workboats use them as well. Other ship types can also have clear view screens, though you won’t see them on luxury yachts or cruise ships for aesthetic reasons. Large, slow-moving vessels don’t really need clear view screens as they rely on tugboats for slow-speed manoeuvres, and speedboats avoid them for aerodynamic, aesthetic, and visibility reasons—the frame and motor can actually obstruct the view a little bit.
Clear view screens are not limited only to ships. Rotating glass discs are sometimes installed on locomotives, railway maintenance vehicles, and even on the windows of port buildings or cranes. They’ve also become popular with operators of CNC and other metalworking machines, which tend to spray coolant all over the protective glass. At one point, manufacturers even tried to market clear view screens for cars, but the idea never caught on. Car windows are relatively small, and the spinning disc, its frame, motor, and wiring would block too much of the driver’s view.
