In this article, we will be using a few new terms which are specific to sailing and tacking, and we want to discuss those before we discuss anything else. We always talk about where the wind is coming from when sailing, so when the wind is coming from the port side and pushes the sails out to the right then we say: we are on a Port Tack.
When the wind hits our sails from the Starboard side and it pushes the sails out to the left then we say: We are on a Starboard Tack. To Initiate a successful tack one should know the phrases used by sailors. They use a set of phrases which have a particular meaning when tacking. Most of you are already familiar with these terms, for those of us who are not familiar, here they are:.
When the crew gets this signal they prepare the sheets to pull on when the time comes. Helm to lee: In short, this means I am turning the boat. This phrase basically means: Pull on the lines. At this point the boat has shifted 90 degrees to the other side so, it is time for the helmsman and the crew to move to the other side of the vessel.
If a tack is not performed properly as described above, sailboats will most likely encounter stalling. A key component of a successful tack is no doubt trimming of the sails. Most of us spend a lot of efforts into pulling in the lines on the new side of the sail that we almost forget that it is very crucial to get this step right. As you are sailing into the wind close-hauled , one of the most important maneuver to cruise efficiently and at the same time to keep your momentum and speed high would be proper trimming.
It is crucial to trim the jib before the mainsail. Note that nowhere in this argument did we need to say that the wind was faster than the boat. Now this force is mainly sideways on the boat, and it gets more and more sideways as you get closer to the wind. However, part of the force is forward: the direction we want to go.
Why doesn't the boat drift sideways? Well it does a little, but when it does, the keel , a large nearly flat area under the boat, has to push a lot of water sideways. The water resists this, and exerts the sideways force F k on the keel. This cancels the sideways component of F w. A little digression: the sideways components of wind and water on the boat make the boat heel tilt away from the wind, as is shown in the diagram below.
These two horizontal components have equal size but opposite direction: as forces they cancel, but they make a torque tending to rotate the boat clockwise. This is cancelled by another pair of forces. The buoyancy and the weight are also equal and opposite, and they make a torque in the opposite direction.
As the boat heels to starboard, the lead on the bottom of the keel, which has a substantial fraction of the weight, moves to port and exerts an anticlockwise torque.
These two torques cancel. So now back to our question:. Lots of boats can — especially the eighteen footer skiffs on Sydney Harbour.
Ask a sailor how, and he'll say "These boats are so fast that they make their own wind", which is actually true. Ask a physicist, and she'll say that it's just a question of vectors and relative velocities. Downwind diagram at left is easy. If the wind is 10 kt, and the boat makes 6 kt in the same direction, then the crew feels a wind of 4 kt coming over the stern of the boat.
The true wind v w equals the speed of the boat v b plus the relative wind v r. So you can't go faster than the wind. When the wind is at an angle, we have to add the arrows representing these velocities vector addition. Credit: Public domain The sun is out, the wind is blowing, and I've been busy taking some sailing lessons. Turns out there's an interesting bit of physics that allows sailboats to not only travel downwind, being pushed by the wind, but also to travel upwind , or nearly so.
An 18th-century square-rigged ship sailing downwind. Credit: Public domain But first let's 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. When they needed additional speed or wanted to travel upwind, they rowed.
The large square-rigged boats popular in the 18th and 19th centuries the classic pirate ship, for instance were also most effective on a downwind sail. Modern sailboats can sail in any direction that is greater than about 45 degrees with respect to the wind. They can't sail exactly upwind but with a clever boat design, a well-positioned sail, and the patience to zig-zag back and forth, sailors can travel anywhere.
To explore this, let's draw a diagram that labels all the forces on the sailboat. If you haven't seen a force diagram before, not to worry—it's just a few arrows and triangles. By adding the forces together we will get the total force on the boat and thus the direction in which it will move. Here's a basic sailboat.
The two parts we will focus on are the sail above the boat and the keel below the boat. The keel keeps the boat from tipping over and, as we shall see, plays a crucial role in moving the boat forward. A basic sailboat. Diagram credit: Tamela Maciel Now let's say we're trying to sail upwind with the wind coming from the left or "port" over the front of the boat. This sketch shows the sailboat as if we were looking down on the boat as it moves towards the top of the sketch.
Looking down on a sailboat, showing the equal and opposite forces on the wind and sail. Credit: Tamela Maciel The wind fills the sail into the shape of a wing, but because the sail is held fast at both ends, the wind can't push it out of the way. Instead the wind must change direction to flow parallel to the sail. The taut sail has created a force on the wind that causes it to change direction and Newton's third law tells us that there is an equal and opposite force on the sail by the wind, as shown by the red arrows in the diagram above.
If this was the only force acting on the boat, then we would be in trouble: the boat would move forward but also to the right. But sailboats have a secret weapon hidden below decks: the keel. Windward sailing also does not work if a boat is pointed directly opposite the wind direction, according to The Physics of Sailing.
Wind has to be moving against the boat at an angle of at least 40 degrees for most vessels. Angling too sharply into the wind causes the forces on the boat to become unbalanced, and moves the boat sideways in the water.
A sailor intending to travel windward toward a point exactly in line with the direction of the wind will have to zig zag back and forth to reach its target.
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