Sailing boats get their power from the wind flowing across the curved surfaces of the sails. This is similar to how to wing on the airplane’s wings produces lift to keep the plane in the air. The sail uses the Bernoulli’s principle which means that airflow over sails creates lift. Sail works at it’s best at one small angle to the wind, so in order to be profficient at sailing you must know where the wind is coming from, and how to use some basic techniques. You should also probably learn how to stop the boat.
One does not simply sail directly into the wind. Instead of sailing directly into the wind, you point the boat towards the wind at an angle, and then “zig-zag” in direction you want to go. In other words, in order to get to a destination that is directly upwind of where you are, you have to go back and forth across the wind. You move by zig-zag, or turning repeatedly, to reach the destination (see “tacking” picture).
You make a little progress towards the wind each time, but travel some distance going back and forth. So, when the wind comes at sails from either left or right you should adjust the sails so that the wind flows out towards the back of the boat. This is called “tacking” and this pushes the boat forward. When tacking, your aim is to turn the bow through the wind and steer the boat onto the new course with a minimum loss of speed.
The boat doesn’t always move forward, but often times it goes a bit sideways, because of the total force produced by the sail that has a sideways element to it. The only time a sailboat move only forward is when the boat is on a run, meaning when the wind is directly behind you.
Sail Shape and No-Sail Zone
The curved shape of a sail determines the amount the wind must bend around it and the force it produces. The shape can be adjusted and they are usually used like this – sails are adjusted to be flat in very light winds – when the wind lacks the energy to bend around a full sail, full sail in light to moderate winds and flat again in strong winds when the boat is overpowered.
When two sails are used, it is potentially a more efficient when sailing into the wind, because it doesn’t have a mast in front of it to disturb the airflow. The air flowing through the slot between the sails, a jib slot, is compressed and will accelerate. This further decreases the pressure on the leeward side of the mainsail and so increases drive.
When you point your sails at an angle towards the wind, you are going along the path of least resistance. It’s interesting to note that when the wind comes at you and hits the sail, the shape of the boat and the wind upon the sail makes it so that overall, moving forward is still the path of least resistance. That’s why you can’t go directly into the wind, because in this case, going backwards would be the path of least resistance.
There is an area of about 45° on either side of the wind direction, into which it is impossible to point the boat and keep sailing. This area is known as the no-sail zone. When the boat is close-hauled (see picture “Points of Sail”), you are sailing along the no-sail zone. Once you point the boat closer to the wind, the sails will shake and the boat will slow down and stop.
To keep moving it’s necessary to sail a series of zigzags, first on one tack, then on the other (port and starboard tack), making progress to windward (side of the boat toward the wind) with each tack. For the reference, leeward is the side away from the wind.
Whenever sailing, there are a few things you need to pay attention to, always: that the sails are trimmed, the centerboard position (in the case of dinghy), the boat balance and heeling force, the boat trim in a fore and aft direction and the course where you’re going – always keep your eye on it.
The Importance of Keel When Sailing Into The Wind
First thing to know is that boats have a keel. If you’re a beginner, the keel is that flat thing that sticks down into the water vertically, so that the boat will only go in two basic directions – forward and backward – but not slide side to side. It is also called a centerboard, or daggerboard, and it is used to resist the sideways force. In dinghies the keel area can vary by simply raising the centerboard, but on a keelboat it is at fixed amount.
Even though the keel resists sideways force, the force isn’t completely eliminated, and on upwind courses, a sailing boat always slightly slips sideways. Furthermore, because of the keel, it has the effect of trying to heel the boat. Heeling is when boat is leaning to one side. The keel resists the sideways force but acts underwater, so the sideways resistance by the keel increases the heeling effect. This is counterbalanced by the crew’s weight – they move the other side – or by the weight of the keel in the keelboat.
How Do You Move While Sailing Into The Wind?
Let’s assume the wind is blowing South at 13 knots (15 mph, 14 km/h). Now let’s see how we actually move and sail into the wind while answering a few main questions.
If the wind is blowing South, then how fast can you sail North?
The fastest speed your boat can sail North, which is directly downwind, in this example, is the current wind speed, 13 knots. When you’re traveling downwind then the wind feels very calm on the deck of the boat since the boat is going in the wind direction and at the same speed. You can’t go faster than the wind, because you will ran out of wind.
How to move east or west?
Now let’s see how fast can you go east or west when sailing into the wind. You may think you’d go slower than 13 knots but that’s knot true – you can go faster. This is because sailboats have a keel which allows the boat to slide forward on the water easily, while at the same time makes it difficult to push the boat sideways. So what happens is that the sail collects the wind and pushes you. As that wind spills out of your sails there is new wind coming from the South replacing it, so you keep getting more and more power. Since you’re not running “away” from the wind, you can never run out of wind, like when you go downwind.
What about South – Sailing Towards the Wind?
Now let’s see how fast can you go South. The wind is blowing from the South itself. The one thing you can’t do is go directly South, meaning you can’t just go directly at the wind. But, you can go at an angle. If you go at a small angle from the West towards the South you’d be going a lot towards West, but also slightly towards South – which is where you want to go.
Now if you narrow the angle a bit more towards South, you’d be going slightly slower, but much more towards South now, which is where you wanted to go. If you keep pointing towards South more and more you’d be going more and more South, losing speed and at one point you’d stop, and that’s if you kept your boat directly pointed South.
Somewhere between South and West you’d find your sweet spot, often about halfway between South and West, where you’ll still moving well and you’re getting equal amounts of West and South. At some point your sailboat may go too much towards West, so you’d turn your boat to South and East and do the same thing in a different direction, and continue on. So you’re going a little bit to southwest and a little bit to southeast, southwest and southeast, but keep moving South constantly. Until you reach your destination. This is why sailboats zig zag when traveling towards the wind.
Sailing Directly Into The Wind
If you point the boat “directly into the wind” then the wind doesn’t hit the sail at all, but goes around it on both sides and you don’t move at all, except backwards. This is called “in irons”, or into the wind (see picture). It’s very exciting to sail close to into the wind, because the boat is tipping quite a bit, and the wind “feels” stronger. This may not be the most efficient way, but it’s a lot of fun.
Downwind sailing, on the other hand, when the wind is coming from behind you, and maybe a little bit from the sides, is a different story, and you may even use different sails to sail downwind. It’s still similar in the sense of what’s actually going on, but the boat moves differently. It’s not uncommon to just put up and take down different sails depending on the direction you’re going.
Some Good Tips When Sailing Into The Wind
If there is no wind then you’re going nowhere. Only when there is some wind, your sailboat can move. The sail uses the Bernoulli’s principle which means that airflow over sails creates lift. In other words, as velocity increases pressure decreases, creating a lift that acts at right angles to the surface. When velocity on both sides of the sail and the difference in velocity between the sides of the sail both increase, so does lift.
To find the correct angle for the sail in the wind, let it out until it begins to flap like a flag, then pull it in until the shaking just stops. Repeat regularly to check the trim.
For those new to sailing, let’s learn what tiller and rudder is, so you know how to stop the boat. A tiller is that which is used to control rudder. A rudder is used to steer the boat. To stop the boat, you can use several methods. One of them is lying-to method. What you do is you turn your boat using the tiller until the wind is blowing from a point just forward of abeam. Let both sails out fully so that they flap. Then the boat will stop and drift until you pull in the sails.
How to Tell the Wind Direction
Someone once said that the “sails are a sailboat’s engine, and the wind is that engine’s fuel”. The main thing to know, is that when you sail, you don’t actually feel the true wind. What you feel is called the “apparent wind”. Knowing this will help you tremendously to find the direction of the wind and adjust the sails accordingly.
True wind is the wind we feel when stationary. When we sail we feel apparent wind, which is the combination of both true and apparent wind produced by moving through the air. The only time you feel true wind is when stationary.
To tell the true wind direction you can look at flags on the shore or on the moored boats, or by smoke on the chimneys. It’s also useful to use telltales, which are pieces of yarn or fabric attached to a sail, or any rigging on a sailboat.
Additionally, you are your own best indicator. Here’s how to tell the wind direction. Turn your head slowly from side to side, noting the turbulence and sound in your ears. Even the slightest draught creates turbulence. Keep turning until the sound is the same in both ears, and the turbulence is the same on both cheeks. This is the direction of the wind.