09
Apr
Sailing a boat is simple when youre navigating downwind with the wind at your back. Unless the wind is blowing from directly astern over the back of the boat the sails propel the boat forward because of lift created by wind blowing across them not by wind pushing against them.
Sails generally arent kept at exactly perpendicular to the wind direction.
How do sailboats go against the wind. To go against the wind a sailboat is propelled by the combined force of the wind on the sails and the keel against the water. With the keel restricting the lateral movement of the boat over the water and the force of the sail pointing slightly forward the resulting force is a small forward vector that propels the boat against the wind. On a sailboat wind blowing against the boat at an angle inflates the sail and it forms a similar foil shape creating a difference in pressure that pushes the sail perpendicular to the wind.
The sailboat extracts energy from the wind by slowing the winds speed relative to the water and then uses the energy to drag and accelerate the boat. To sail against the wind you have two alternativesmotoring or beating. The true wind equals the speed of the boat plus the relative wind.
As the boat speed approaches the wind speed the relative wind drops towards zero and so there is no force on the sail. So you cant go faster than the wind. When the wind is at an angle we have to add vectors representing these velocities.
Sailboats can go faster than the wind when the wind blows from either side of the boat. This is called a reach. Because the wind comes from the side as the boat goes faster the apparent wind that is the wind as seen from the boat doe not decrease and may actually increase.
By using a triangular sail design and centerboard overdeveloped keel it was possible to travel against the wind using a technique known as tacking. Tacking allows the boat to travel forward with a wind at right angles to the boat. But first lets start with the downwind case.
If the sailor wants to travel in the same direction as the wind then all he or she has to do is hold the sail perpendicular to the wind and let the boat be pushed from behind. This is the most basic point of sail and was often used by ancient Egyptian Greek and Roman sailors. Sailing a boat is simple when youre navigating downwind with the wind at your back.
You let out the mainsail perpendicular to the wind to capture the most energy. As the wind presses directly into the sails to make them puff out that natural force propels the boat forward. Plotting an upwind course against the wind is much harder.
Sailboats utilize both true wind and apparent wind. One force pushes the sailboat and the other force pulls or drags it forward. If a boat sails absolutely perpendicular to true wind so the sail is flat to the wind and being pushed from behind then the boat can only go as fast as the windno faster.
Lets bring this to our sailboat. Sailboats cant actually sail directly upwind. They have a region of angles with respect to the wind direction that is physically impossible to go into.
That range of angles is 45 from where the wind is coming from as shown below. The direction that is exactly 45 away from the wind is called close. Unless the wind is blowing from directly astern over the back of the boat the sails propel the boat forward because of lift created by wind blowing across them not by wind pushing against them.
As you steer more toward the wind direction you trim the sails in tighter to keep them full and keep generating lift. The only other force added by the hull and keel is of course the drag due to the water. This drag force then becomes the only force opposing motion in the direction of the sailboats movement.
While the drag force is less than the lift force the sailboat will accelerate forwards against the wind. Its easy to see how square riggers sailed before the wind but how did and do sailing ships sail into the wind. This video is about How do sailboats sail into the wind.
About Press Copyright Contact us Creators Advertise Developers Terms Privacy Policy Safety How YouTube works Test new. Below the level of the water on the boat the sailboats shape helps force the boat to go straight forward as opposed to in the direction of the wind. In addition you have the keel that is shaped like a wing and has a lot of weight to stop the yacht from.
Dinghy sailboats generally only utilize wind propulsion as well as sailboats whose owners prefer to go motorless. Sailboats have been around for thousands of years and only recently has it become standard for them to have engines. Small sailboats such as a Hobbie Cat or Sunfish do not have a motor.
They are generally propelled solely by the wind. True wind always pushes a boat. If a boat sails absolutely perpendicular to true wind so the sail is flat to the wind and being pushed from behind then the boat can only go as fast as the windno faster.
Thats not because theres no apparent wind. Its because the apparent wind cant help the boat when its hitting flat against a big sail. How do sailboats travel against winds.
Sailboats cant travel exactly opposite of the direction of the wind but they can do whats called tacking which takes a course like this. The reason this works is that sails work a lot like wings. Sails generally arent kept at exactly perpendicular to the wind direction.