Mast Tuning and Mast Bend

There have been a handful boats in the last few seasons who have reported developing slight but permanent fore/aft bends in the top tapered section of their mast. Any combination of excessive headstay length, loose lower shrouds, and overcranked backstay could lead to a scenario where the mast is being “overbent.” On many boats without runners you have the visual clue of seeing inversion wrinkles in the mainsail to indicate that too much backstay is on. However, many of the J/105 mainsails are designed fuller (to provide power when sailing in the class configuration in light), making it possible to exceed recommended mast bend without inverting the mainsail.

Hall Spars recommends no more than 9 inches of bend in the mast, as measured by taking the main halyard shackle to the gooseneck, and measuring the distance between the halyard and the aft side of the mast at its widest point (usually between the upper and lower spreaders). We recommend that, with the rig tuned for racing, you pump down the backstay until reaching the maximum recommended bend, then marking your backstay adjuster as a reference. As an additional precaution, you can install a spacer stop above the cylinder to ensure that no one overcranks the backstay. If you want to generate more headstay tension when the mast is at full bend, then release the backstay, take up more turns on the lower shrouds and/or the headstay, and then retrim the backstay.

Owners who sail in predominately light air areas should be most attentive; because for most of their sailing, the sailmakers recommend loose lower shrouds as being fastest; just don’t forget to tighten them up when it’s windy. If you want to set your rig up once and not fool with it, make sure the lower shrouds are tensioned to at least hand tight plus 2-4 turns.