of turns on both the port and starboard rigging screws required to increase the tension by 5% (1 mm stretch).• Tune the mast straight again using the lower shrouds and the intermediate shrouds. • Tension the backstay hard, but not exceeding 20% of the breaking load of the wire. Make a mark on your backstay tensioner so that you will always know when this normal load has been achieved. Use the “folding rule method” to find the correct setting. This will reduce the tension of the cap shrouds.• Increase the cap shroud tension back to 20% of the breaking load of the wire.• Slacken the backstay completely. • Now check the cap shrouds tension. It should not exceed 25% of the breaking load of the wire. Tuning under sail
Stopper-knot (figure-of-eight). • At about a 20° angle of heel and maximum pre-tension (20%), on the backstay, the leeward cap shroud must not be slack. If it is, increase the pre-tension, but not to more than 25% of the breaking load of the wire (the same number of turns on the rigging screws as per your pre- vious note).• Tune the mast straight laterally using the lower shrouds and the intermediate shrouds. • Check the tune for different backstay tensions and different sail combinations (reef).• The backstay must not be allowed to completely slacken at any time. If the masthead is able to move forwards, the mast is in danger of buckling aft. If using a tackle, put a stopper-knot in the tail to limit the reduction in backstay tension. To ensure good fore-and-aft stability for this type of rig, it is very important that the leeward cap shroud is tight. This high level of pre-tension will generate plastic defor-mation on all grp hulls. As far as strength is concerned, the hull should be able to support these loads, but the deformation will make it necessary to check the tuning while sailing. This is particu- larly important when the yacht is new and at the start of every season.
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