Knowing how to sail against the wind takes more practice and skill than any other sailing task. If you do it right, you can sail almost anywhere.
Since sailboats are powered only by the wind, it seems intuitive that they can easily sail downwind. However, when it comes time to turn around and head home, it can seem impossible to sail home with the wind blowing directly against the boat. But, this motion can be reversed because the sail of a moving sailboat is shaped like a cushion of air, much like the wing of an airplane.
In sailboats, the wind blowing against the boat at an angle blows up the sail. It forms a foil similar to that of the airplane. This creates a pressure difference that pushes the sail perpendicular to the wind direction.
Image credit: American Sailing Association
The force of the sail’s profile shape is balanced and combined with other forces, including the boat’s maintenance. The keel is the long, thin piece that protrudes from the bottom of the boat.
From the water, the boat is pushed forward by air resistance combined with wind pressure against the sail. It moves in the opposite direction to the wind, which in sailing terminology is called windward or upwind.
The keel is important because, without its balancing effect, boats would drift to leeward. Sailing windward also does not work when the boats are pointing directly against the wind. Instead, for many sailboats, the wind must move against the boat at an angle of about forty degrees.
If the sailboat leans too far into the wind, the forces on the boat become unbalanced. In this case, the boat moves sideways toward the water.
It is easy to sail against the wind if the sail of your sailboat is slightly tilted in a direction that is further forward than the sail force. The boat can move forward in this regard because the centerline or keel of the boat does to the water what the sail does to the wind.
The force of the sail is kept in balance by the force of the keel. This keeps the boat from moving in the direction of the sail’s force. A proper angle of attack keeps the boat moving forward, even if the full force of the sail is directed to one side when the boat is going against the wind.
When the sail is angled from the centerline of the hull, the force acts more forward than to the side. When the slight change of the force forward is combined with the resistance of the water to the air, the boat can pull to windward because it has found a way to run a course of least resistance to the wind.
When it comes to how to sailing upwind, you should know that a sailboat that sails too close to the wind or at too small an angle to the wind is called a pinch.
To reach their destination, sailors who want to sail upwind to a point that coincides with the exact wind direction must zigzag to reach their destination. This technique is the tack. Sailors can use the tack method to reach a point in either direction and sail at an angle closest to the wind direction.
In practice, sailing against the wind is usually done on a course and at an angle of about forty-five degrees to the headwind. To reach certain points, it is sometimes necessary to change the wind direction between starboard and port. The term for this is “tacking.”
Tacking is sailing a yacht or sailboat against the wind. This means it is always better to have a strong wind in the opposite direction than a weak wind at your back. No wind is the worst-case scenario. Think about vectors.
The wind creates forces on the hull of the boat due to the change in momentum caused by the sails. The force acts both in the direction you are moving and perpendicular to the motion. The keel absorbs the perpendicular force and tilts the boat. Motion is then generated by the remaining forward vector.
If your destination is upwind, how will you sail there? Because of the lift created by the wind blowing across rather than against them, the sails propel the boat forward. This happens when the wind is not blowing directly over the stern of the boat.
When you start steering downwind, trim the sails and keep them full so that lift is continuously generated. However, if you sail too close to the sail and wind, you will “windward”.
This means that the edge of the headsail will begin to swing in and out and the boat will slow down. If you keep turning into the wind, the whole sail will soon flap like a giant sheet you hung up to dry.
Turn further into the wind, however, and you’ll soon see the sail fill up on the other side of the boat. This is known as tacking, and the scientific reasons are explained below.
Today’s sailboats can sail up to an angle of about forty-five degrees into the wind. As an example, if the north wind is blowing into the sails, the boat can sail to the northeast on a port side. The boat can sail northwest, west, south, and east on the starboard side, which means the wind is coming from the right side of the boat.
Port tack means the wind comes from the left side of the port. The tack means the side of the boat from which the wind is blowing.
Even though you can’t literally sail your boat into the wind, sailors call this tacking or beating to windward. You will see that when you make the new tack, you are sailing in the direction that makes a right angle to the previous tack.
This happens with a wind direction of about forty-five degrees, but this time from the other side. By zigzagging and repeating the tack, the boat moves to leeward.
A sailboat sailing upwind will turn onto its point at each tack. This is the point at which the boat is neither starboard nor port and is sailing directly into the wind.
On the other hand, boats cannot sail directly into the wind. Therefore, if a boat is sailing into the wind, it is said to be on the beam when it loses steering. For this reason, a boat sails upwind with trimmed sails, which is also known as close-hauled.
What Are the Main Forces Sailing Against the Wind
Four different forces act on a sailboat when sailing against the wind:
- Viscosity of Water
The two forces that can propel or stop the boat are the viscosity of the water and the force of the wind driving the boat.
The viscosity of the water slows the boat down and helps it stay on course. The other two forces are buoyancy and gravity. Buoyancy pulls the boat up, and gravity pulls the boat down. These forces keep the boat afloat while it sails against the wind.
The combined effect of water and wind is a net force that pushes the boat diagonally against the wind. The water’s drag combined with the wind’s force determines the direction in which a sailboat sails. The pressure exerted on the sail by the wind has two components:
- Lift component: pushes the sail vertically into the wind.
- Drag component: pushes the sail in the direction of the wind.
The lift changes the direction of the wind force with respect to the direction in which the wind is blowing. The angle between the wind and the shape of the sail determines the direction of the wind force.
The forward movement of the boat and its lateral sliding are slowed down by the resistance of the water. In order for boats to sail diagonally to windward, the lean must be minimal compared to the forward motion. A keel significantly reduces lateral planing.
If a keel prevents leaning to some degree, sailboats can only move in the direction of the keel. This is also the direction of the sailboat’s centerline. As long as the wind force is diagonally forward toward the keel, the boat will move forward in the direction of the keel.
If the keel points diagonally into the wind and the wind force points diagonally forward, the boat must sail diagonally into the wind. On the other hand, the boat cannot sail diagonally into the wind if the leaning is too great.
Final Thoughts: How to Sail Against The Wind
There you have it! Like everything else on the water, sailing against the wind takes practice. If you can master this skill, you can sail almost anywhere in the world with a suitable sailboat.