The nacelle is the enclosure surrounding the working parts of a wind turbine. Nacelle design can differ from one manufacturer to the next. A notable feature now found on some off-shore wind turbines is a large sturdy helicopter-hoisting platform built on top of the nacelle, capable of supporting service personnel and their tools, winched down to the platform from a helicopter hovering above it. Wind turbine rotors are stopped, feathered and locked before personnel are dropped down to or picked up from the platforms.