Harden Up

To turn a sailing vessel closer towards the wind.

The instruction changes the vessel’s heading and usually requires the sails to be trimmed in as the apparent wind moves forward. It is broadly synonymous with luff up or head up in this context, although command usage can vary between crews.

The turn is limited by the vessel’s close-hauled angle; continuing beyond it can cause the sails to luff and the vessel to lose speed or enter irons. Helm and sail controls should be coordinated without placing crew in loaded sheets or the path of the boom.