Need to get up your mast in a hurry, but don’t have a rock-climbing harness or bosun’s chair handy? Luckily, a Swiss Seat, a jury-rigged harness, is your solution. You’ll only need about 15–20 feet of stout rope (sail ties work in a pinch, but you’ll need to sister a couple together to achieve the proper length).
Start by folding the rope in half. Pass this bight in between your legs (from stern to bow), and hold the loop in situ by squeezing your thighs together. You’ll then lead the two ends around your waist, passing them through their respective sides of the loop. Next, pass the ends backwards, crossing the rope ends behind your back, below your navel, and again behind your back. Lead the ends forward and tie a figure-8 knot in one end, offset to one side (so the knot will be on your hip). Use the other strand to tie a figure-8-follow-through knot.
If you are using sail-tie material (webbing), or thinner-diameter static line (anything under 6mm), it is a good idea to tie a spare waist belt with another piece of rope/webbing, again tying it off with an offset figure-8-follow-through knot.
Take a halyard, tie a figure-8 knot roughly two or three feet above the shackle, and pass the bitter end through the waist belt, as well as through the leg loop. Tie a follow-through finish to the knot, and add a safety backup by clipping the shackle to the halyard above the knot. You’re now ready to go aloft.
The only drawbacks to the Swiss Seat are that it cuts off circulation if it’s used for more than a few minutes, and it takes longer to tie than it does to cinch up a bosun’s chair or climbing harness.