Possibly the winningest mainsail in the history of the Lightning Class, the M-5 main is designed based on a tuning system which enables your team to "change gears" based on wind conditions and your sailing style by adjusting mast blocks and lowers tuning. The M5 setup allows more use of the backstay to control mainsail shape and headstay sag. Your rig can be set at a "base" setting for all purpose racing while also allowing tuning changes (between races!) to optimize your setup for the conditions.