Sailboat Topping Lift. Typically this control is. Thing by atlas.
This line would run from near the free end of. In this episode of ask precision sails darryl answers the question should i add a topping lift to my boat. As the mainsheet and optionally a boom vang pulls down on the boom along with gravity the sail is pulled taut.
Not a bad idea since it will likely be contacting the sailcloth even when let out.
Therefore the topping lift safely keeps the boom out of the cockpit even if the boat is off the wind. A topping lift is a line that helps hold up the boom anytime the sail isnt all the way up. Slack the topping lift a few inches after hoisting sail. It is particularly useful on fractional rigged boats with aft swept spreaders.