The Physics of Sailing

Personal Interest

I was so excited when I came up with the idea to do sailing for this project! I'm so happy because not only will I be using the information I learn to work on this assignment, but it will also help improve my technique out on the water.

Not a lot of people realize, but sailing is a very technical sport. I know an olympic sailor at my yacht club that is constantly adjusting the controls on his boat, hoping for optimal speed. I've also been taught countless times that the way I sit in my boat will make or break my results in a race. What you learn throughout this presentation will help you understand why little things like that make a big difference!

Me sailing on a reach (the fastest point of sail)

The first boats

Steering Oar/Rudder

The steering oar was a stepping stone on the path to developing the rudder. Vikings exclusively used these long oversized boards that were attached to the middle of the boat to steer. Later, the Chinese developed the stern-mounted rudder.

History

Mesopotamia is credited with the creation of the first sailboat after discs depicting drawings were found in modern day Kuwait.

They showed simple, square rigged ships that were sailed down the Nile powered by a single papyrus sail.

Keel

The keel was an invention created by Norse sailors to keep their boats steady.

Anderson, Bryon D. “The Physics of Sailing.” Physics Today, American Institute of PhysicsAIP, 1 Feb. 2008, physicstoday.scitation.org/doi/10.1063/1.2883908.

Bergman, Jamey. “10 Top Innovations in the History of Sailing.” YBW, 1 Feb. 2019, www.ybw.com/features/10-top-innovations-in-the-history-of-sailing-17358#:~:text=The%20first%20sailing%20boats%3A,sail%20attached%20to%20a%20mast.

Chris. “Bramp Asks: Why Do Some Sail Boats Have More than One Sail and How Can Some Boats Go Faster than the Wind?” Boat Safe, 2020, www.boatsafe.com/bramp-asks-sail-boats-faster-wind/#:~:text=This%20is%20because%20you%20can,wing%2C%20that%20propels%20the%20boat.&text=By%20moving%20very%20fast%20through,faster%20than%20the%20true%20wind.

Jansen, Arjen, et al. “The Aerodynamics of Sailing Apparel.” Procedia Engineering, Elsevier, 26 May 2012, www.sciencedirect.com/science/article/pii/S1877705812016232.

Maciel, Tamela. “The Physics of Sailing: How Does a Sailboat Move Upwind?” The Physics of Sailing: How Does a Sailboat Move Upwind?, 2015, physicsbuzz.physicscentral.com/2015/05/the-physics-of-sailing-how-does.html.

Unknown. “Physics Of Sailing.” Real World Physics Problems, 2020 www.real-world-physics-problems.com/physics-of-sailing.html.

Unknown. “How Hull Drag and Wavemaking Resistance Affect Speed through the Water.” Sailboat Cruising, 2020, www.sailboat-cruising.com/hull-drag.html.

Wolf, Joe. “The Physics of Sailing.” The Physics of Sailing, 2002, newt.phys.unsw.edu.au/~jw/sailing.html.

Work Cited

The fastest point of sail

Beam Reach

The fastest point of sail is called a beam reach, which is when the wind is at a 90 degree angle to the sail(s) and the boom is far out over the side. The forward component of the wind force vector is greater than when sailing upwind (when the boom is more towards the center of the boat).

Upwind

The position of the sail while on an upwind tack is a 45 degree angle from the wind. The faster that the boat goes, and the greater amount of relative wind, the more force there is on the sails. This combination leads to a greater force driving the boat forwards.

Upwind

Downwind Sailing

The wind is pushing the boat along, meaning the speed at which you go depends on how much sail area you can hoist. An example is the use of the spinnaker, or a giant thin sail that is hoisted at the very front of the boat while going downwind.

Downwind

Heading into the wind

Irons

"Irons" is the term sailors use for when the boat is directly pointed into the wind. It's a tactic that's usually used for slowing down or stopping, as the position brings the boat to a halt. The flow of wind across your sails and the flow of water across your keel is interrupted, therefore stopping your momentum. You're no longer going forward, resulting in the wind having the power to push you back.

The sails "luff" when you're in irons

Top and Bottom

"Lift" Forces

The sail and keel on a boat work together against wind and water pressure to produce horizontal "lift" forces.

Other forces that affect a sailboat include the force of the wind propelling it forward and the viscosity of the water slowing it down. Additionally, gravity pulls the boat down and buoyancy keeps it afloat.

Heeling on the downwind leg of a race

Battan

Having flow over your sails is key, which is done by changing the shape of your sails to give a pocket for the wind.

In light wind days, some sailors sit on one side of the boat (the leeward side) so that there is a heel. This technique is used to move the sail and make it easier for the wind to catch on it.

There are certain tools on a boat that change the shape of the sail, including the outhaul and the battans. The outhaul is a line that stretches across the boom, it's purpose being tightening or slackening the surface of the sail. On heavy wind days, you want it to be loose so there isn't too big of a pocket (a big pocket would allow for too much wind to catch the sails and the driver would loose control). Light wind days call for a big sail pocket for the opposite reason. Battans are long strips of material that are inserted into the sail to form a shape. Without these, the boat would be unable to tack or jibe.

The shape of the sail

Examples

Vectors

Vw = Vb + Vr

When the wind is at an angle, arrows are drawn to represent the velocities.

Equations

and Components

Vw refers to the true wind and it equals the speed of the boat Vb added to the relative wind Vr

You would think that his equation would tell us that a boat can't go faster than the wind because as the boat approaches the wind speed, the relative wind drops down to zero, meaning the force in the sail is gone. However, you can trim the sails so that the wind flows over them, creating a lift. "Much like an airplane wing, this propels the boat. As you can see, there is a positive force against the inside of the sail, and a negative force pulling the outside of the sail" (Riley, 2019, 1).

Visuals

Vw = Vb + Vr

This is an example of that equation being used

Water resistance

Water

When a boat moves through the water, it creates friction. Minimizing that friction allows it to go faster. This is why, in some cases, sailors heel over their boats to make them go faster. Less hull in the water equals the boat going faster.

Another interesting thing is, if you get a ding/nick in the boat of your boat, hard-core sailors would stay up all night repairing it because it the friction it created would cause the boat to go 1/3 of a knot slower.

Drag

Sailing Apparel

Hull Drag

Drag

Believe it or not, the clothes you wear on a boat can have an affect on the speed. A study has been conducted in order to create sailing gear that minimizes drag on a Olympic class dinghy. The trail has proved that 12% of the total aerodynamic and hydrodynamic drag on a boat is created by the sailor. The experiment put state of the art wetsuits and spray tops in a windtunnel at various angles and wind speeds .

Any moving boat will create "hull drag", or net force opposing forward movement due to the pressure and forces acting on the hull.