Another key part of a boat’s running rigging is the mainsheet. This line runs between the boom and a fixed point in the cockpit (as shown here) or cabin top. As the line is let out, the boom and mainsail can swing farther out from the boat’s centerline. As described in Part 3 of this course, moving the sails in or out, called trimming the sails, is necessary for sailing at different angles to the wind.
Even in a small sailboat the force of the wind in the mainsail can be considerable. The use of a block and tackle in the mainsheet provides a mechanical advantage so that the mainsail can be managed by one person, with one hand, while sailing.
On most larger sailboats, the mainsheet mounts from the boom to a traveler rather than to a fixed point. The traveler can move the attachment point side to side for better sail shape.
Finally, notice the cam cleat where the mainsheet exits the block and tackle. This cleat holds the mainsheet in place after being adjusted.