It is also called vertical fairlead, sheave block, and often used with swivel fairlead to direct wire rope from the winch to the load. So normally you can find horizontal sheave or vertical sheave in the back of swivel fairlead. The sheave is always used together with wire rope, rather than mooring rope guided through mooring pipe/chock. That is why it appears on tug, towing ship, or work boat more frequently. We sometimes call it sheave block because it has similar structure with crane block. Within a sheave, the important parts are shaft and groove made of alloy steel.
