Boating – Page 3 – Pirateering

The resistance of water combined with wind forces dictates which direction the sailing boat will sail. The correct angle of attack will propel a boat forward, even though the overall sail-force for your sailboat is sideways as the boat is sailing in a breeze. The boat can move forward then from that angle because the boat's centreline, or keel, does for the water what the sail does for the wind. Boats sail into the wind by positioning themselves at an angle that allows their motion to have a component that goes against the wind and a component perpendicular to the wind. The boat travels forward in the perpendicular direction, and the angle allows it to go against the wind while doing so. Although a boat cannot sail straight into the wind, it can move in every other direction around the wind. Although sailing directly into the wind is of course not possible, the craft can maneuver around the wind and sail in angled directions. To go in the direction of the wind, one would have to sail as close as possible to the wind, this is known as beating, and a boat is said to be in a tight lean. Squeeze your mainsail tightly and sail as close to the wind as you can without losing speed on your boat (close-hauling). Tips for Sailing Against the Wind Do not stop turning windward, you will soon see that forward sails are full to the other side of the yacht. Once you turn your sailing vessel to its opposite tack, steer the vessel enough to make the sails fill with the wind. Carefully keep your eyes on the boom, and when a sailboat comes into the wind, settle into the side facing away from the sails, you will be momentarily level on the water. If the keel points diagonally toward the wind and wind-force points at the keel, then the boat will sail diagonally in the wind. On a sailing ship, the wind, which is blowing against the ship at an angle, will inflate the sail, which forms a foil-like shape, creating pressure differences that propel the sail in the opposite direction of the wind. Unless the wind is blowing straight out astern (over the rear of the boat), sails push the boat forward due to lifting created by the wind passing through them, rather than the wind pushing against them. Sails are there because you can adjust the sails to allow the wind flowing across them to produce lift, similar to the wings on an aircraft, which is what pushes the boat forward. Wind-filled sails produce a shaped like an airplane wing; wind flowing over the back of the sail moves more quickly than the air moving across the front (flat) side of the sail. How Sailboats Are Steered Windward To steer, a sailboat is turned to face into the wind, and because the wind is filling the sail, it is creating a shape called an airfoil -- meaning that it is like a wing, too. If the sailing vessel attempts to sail straight at the wind, the wind moves directly over the sail and it loses the wind pockets that gave it the airfoil shape, and the sail flaps instead, just like a flag. Even though you cannot sail the boat straight into the wind, sailors refer to it as tacking or bending toward the wind. Once you have crossed that imaginary line and are steering the boat toward the direction of the wind, your sails will begin to waver, losing shape, and your boat will be slower. As you turn back, steering away from the wind, you will loosen your sails, sailing to a tighter bow, then to a beam bow (where the wind is blown across the sides, or beams, of your boat), then a wider bow. Your boat is not going to sail a straight line out in front, it is going to get pulled around by the wind, wherever it is going to be blowing. You do not want to be hesitant, because, in the turns, your boat goes through a "no-go" area, the dead-end corner, where it will not be propelled by the wind. If your tail is out of the V too much, you are still moving, but not sailing into the wind as far as your boat allows. How Propulsive Force Is Kept Constant When you let the wind blow on your sails sideways, and you are turning the sails 45 degrees, your propulsive force remains constant. When wind speeds are lower, the sails are slightly let out so that there is a greater amount of lift, hence more driving force. As the boat approaches wind speed, relative speed decreases to zero, which results in negligible forces acting on the sail. Therefore, the boat will not be able to sail faster than the wind. If a boat sails perfectly perpendicular to the real wind, such that the sail is level with the wind, and is being propelled by it, the boat can go only as fast as the wind -- not faster. When sailing downwind, the speed of wind at the sail is greater than the true wind speed, and that relative wind produces more power at the sail, which can propel sailboats faster than the actual wind speed. There is, of course, a limit on how fast a sailing vessel can sail ahead. When sailing upwind, the wind must move smoothly from the front of the sails back. When you combine a small correction to forward forces and water resistance against air, then the boat can be driven to the windward side, as you have found a way of sailing the least-resistance route to the wind. As you steer into the wind, moving from beam to near reach to near-haul, you need to trim your sails progressively so that they do not flap. Make sure the sails are trimmed correctly, not too much to steer over to the opposite side of the wind because a small boat with a tightly-trimmed mainsail could tip and be swept ashore.