Hello Zlod basically theres a handle that slots into a shaped hole in the goosenevck turning this handle causes the boom to rotate.The sail wraps itself around decreasing its area. The usuall problem is that the sail becomes baggy and the boom tends to droop at the aft end. I overcame this by putting bits of soft pipe insulation into the sail as it rolled up which increased the diameter of the roll at the aft ewnd so the boom didnt droop. seems to have worked well on my boat.