Tack (square sail)

Rather than being a simple "bag of wind" held from behind, the sail must be pulled into a (fairly poor) approximation of an aerofoil, like a modern triangular sail, by hauling the windward leech as far forward and as tight as possible.

The sheet is in totally the wrong position to do this and so at this point the tack is brought into play.

It is a second line attached to the clew along with the sheet, but the inboard end may be taken to a suitable point well forward of the sail and pulled taut to tighten the leech into some kind of leading edge.

A common arrangement, however, is to have a separate shorter tackle which can be hooked on to apply greater force over the last few feet of movement.

The tackle which is just visible stowed behind the mooring bollard can be hooked into the strop or loop (labelled) on the tack in order to tighten the leach further if it should be required.