A sailboat cannot proceed directly into the wind, but must instead use a sailing technique known as "tacking" to zigzag across a headwind. The main elements that have allowed sailboats to get closer to the capacity to sail upwind are the form of the sail and the hull of the boat. A sloop has one large surface area wing that can be held out to leeward by one person, while a schooner has two smaller surfaces that can be held out to leeward by two people. As with any form of propulsion, there is some effort required to drive a sailboat upwind. As you bring the boom round to hold the lee side of the sail out to leeward, you give way to someone else who is doing the same thing on the other side of the boat. This goes on until everyone has had a turn at holding the lee side of the sail out to leeward, after which time the boat can begin to point upwind again. The amount of effort required to drive a boat upwind varies depending on how far upwind you want to go. At first this is very easy, because all you are doing is swinging the lee side of the sail out to leeward, which requires only minimal effort since you are not pushing against anything.