The only singlehanded bosun's chair that allows you to work ABOVE the masthead without leaving the chair. The only bosun s chair that allows solo, unassisted ascents of the mast, the Mastclimber fits over any taut 3/8" to 5/8" rope halyard. Constructed from 1 1/2" ballistic nylon webbing with a fiberglass-reinforced seat,Mastclimber combines: Climb the mast quickly and safely using only leg muscles. With no need for static lines, the easy-to-use climber is operated by alternatively standing up on the leg straps, which allows you to slide up the one-way jammer of the bosun s chair. To descend the mast, the procedure is reversed. Recommended by Practical Sailor in June 2010. Maximum waist size 50". Check out our West Advisor video on Mastclimber See how a rigging professional uses the Mastclimber to safely and easily ascend the mast, as West Marine's Mark Chandler demonstrates this product in our West Advisor Video, Climbing Your Sailboat s Rig with the ATN Mastclimber.