• Tension the backstay 15% of its breaking load. • Give, if necessary, the mast a slight positive bend using the interplay between the aft and forward lower shrouds. The job of the forward lower shrouds is to prevent the spreaders moving aft if there is little load on the backstay. Tuning under sail • Sail the yacht with backstay (15%) and windward runner set to 15-30% of its breaking load. Check that the cap shrouds do not begin to slacken until about a 20° angle of heel. • While sailing, check that the stayed section of the mast is straight laterally. Adjust if necessary using the aft lower shrouds and intermediate shrouds. The unstayed bare upper section will bend to leeward under sail, and you cannot compensate for this.• Reef the sail and check for lateral straightness. If the deviation from the straight line is greater than 5 mm, the lower shrouds and/or intermediate shrouds must be adjusted. • While sailing, both with full and reefed main, check the longitudinal trim of the mast. The mast must have a slight positive bend at the spreader area. Sight up the aft side of the mast from deck level. Under no circumstances must the top of the mast be allowed to move forward. If it does, there is a risk of the mast buckling aft (inverting). The backstay and forward lower stays must always be sufficiently tensioned to counteract this. If using a tackle to tension the backstay, put a stopper-knot in the tail to limit the available tension reduction. The risk of buck- ling should be kept in mind when checkstays are used. • When you are satisfied with the tuning, lock the rigging screws.
20° Continued... Stopper-knot (figure-of-eight). 47