Whether you need to create a temporary fender quickly, or you want to produce a fender that will last as long as nylon lasts, you can do so with a half-dozen feet of scrap rope taken from a discarded dock line. In a real pinch, you can even take one of your current dock lines and craft a quick rope fender to hold your boat away from a rough wharf that can, when the need is passed, be shaken out to become a dock line once more.
Cut a 72-inch length of 1-inch nylon rope and lay the rope flat on a table. Grasp the rope 60 inches from the right end with one hand, and 18 inches from the right end with the other hand. Bring your hands, and the rope, together to form a loop.
Pinch the sides of the loop in the rope together with one hand. Grasp the rope, insert its end through the loop and wrap the longest part of the rope around the left end of the loop, tightly. Continue tightly wrapping the loop so that you're wrapping toward the right end of the loop, until you are within 2 inches of the right end of the loop you've wrapped in rope.
Push the end of the rope through the opening on the right end of the loop. Grasp the top of the wraps with your right hand. Grasp the 1-foot-long left end of the rope that, until now, has been lying almost-forgotten, with your left hand, and pull the left end of the rope smartly, drawing the loop on the right closed.
Mount the fender to a fender board by inserting the 1-foot length of rope through the hole in the fender board, then secure the fender board to the side of your boat.
A very quick, very temporary rope fender can be created by poking a hole in the bottom of a garbage bag from the galley, shoving a few feet of line out of the bag through the hole, then balling up the end of the rope inside the bag. Close the end of the bag with a piece of twine to keep the rope inside, then tie off the end of the rope that's sticking out through the hole to one of your boat's cleats.