At the crane • Follow the instructions for the appropriate fractional rig. Tuning under sail Tuning • Follow the instructions for the appropriate fractional rig. • For rigs with single (aft) lower shrouds, it is absolutely vital never to let the masthead move forward creating a negative bend of the mast. • Follow the instructions for the appropriate fractional rig. For rigs fitted with double lower shrouds, tuning will be carried out using the aft lower shrouds when the forestay has been tensioned to the maximum permitted load. The aft lower shrouds affect both the lower part of the longitudinal mast curve (limit bend) and in-line tuning (straighten mast). The forward lower shrouds are tensioned only enough to prevent the mast buckling aft (inverting). This is particularly important when sailing in rough seas. The backstay must always be tensioned to prevent this. Without forward lower shrouds or a baby stay, there is nothing but the backstay, and possibly swept spreaders, to prevent the mast inverting. A mast which inverts usually suffers serious damage, and in the worst case, the rig may be lost. If you are using a tackle to tension your backstay, put a stopper-knot in the tail to limit the reduction in backstay tension.
Stopper-knot (figure-of-eight). 49