How does a sailboat sail into the wind ?

How does a sailboat sail into the wind ?
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Novice are the sailors who say that a hefty experience is required in order to sail safe and faster. But what they don’t know is experience doesn’t make a sailor perfect but the way he applies his skills does. For example, sailors and even captains think that a boat sails at a faster rate if the wind is flowing directly behind it. But this is just a myth. To sail at a faster rate, it’s not the speed of the wind that matters but the angle of sails that does. Want to know more? Read on.

How does a sailboat sail into the wind ?

You already know how a boat floats on water but do you know how does a boat sail?

The sails traps the energy from the wind and send it down to the hull of the boat. The hull uses this energy to displace the water, which moves the boat forward. The maximum speed a boat can attain is known as the hull speed. Though the concept sounds simple, this is not all. There are three main forces that acts on a sailboat. They are:

Driving force - This force is the result of the wind flowing across the sail. In order to utilize this force in the best possible way, the angle of the sail should be kept as small as possible.

Sideway Force & Heeling Force - Both these forces acts against the driving force. The best way to avoid them is to maximize the driving force, which will automatically reduce the sideway and heeling force. This can be done by first setting the sails free in the wind until they flap and then pulling them at the point when they just stop flapping. Doing this, creates the perfect drive.

These forces are generated because the wind pressing against the sails is not just diverted to the forward direction but also in various other directions. One such force that is generated due to this reason is the heeling force. This force directly acts upon the hull to make the boat heel. It is the boat’s keel design and the load of the boat that prevents the boat from capsizing.

Making the boat sail faster

Just applying a few basic principles of science can make the sailing faster, smoother and easier. The best way to make the boat sail faster is not by allowing the wind to sail exactly behind the boat. Doing this won’t make the boat sail faster but on the contrary will increase the forces acting against the driving force, which will result in fluctuation of the driving force.

When the wind is allowed to come on the sails from the side and the sails are turned at an angle of 45 degree, the driving force remains constant. This would make the boat sail at double the rate of its original speed. The highest speed thus attained is known as the hull speed.

But the forces are not the only thing that decides the speed of a boat. The boat as it moves in the water, creates a pattern of waves that gradually gets longer in length. Longer a wave along side a boat , faster will be the speed of the boat.

Parts of a Sailboat

Can a boat sail at the same rate as that of wind?

A boat can sail equal to the speed of the wind and sometimes even faster. It is believed that such boats create a wind of their own. But this is just the partial truth. If we dissect the physics behind it, then it is just the matter of resultant forces and relative velocities.

Suppose that the wind is acting from behind the boat. The speed of the wind flowing over the boat will be addition of the speed of the boat and the relative speed of the wind. As the boat approaches the wind speed, the relative velocity reduces to zero, which results in a negligible force acting on the sail.Thus the boat won’t be able to sail faster than the wind.

But if the wind is acting at an angle on the sails, all the vector velocities that are generated will be added. This means that, if the speed of the boat increases, the relative speed of th wind will increase and this will result in the increase of force on the sail. This not only results in a speed equal to the wind but sometimes even higher than it.

Physics of Sailing


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Boat Ed