Successful, sector-agnostic entrepreneur, Kevin Mulleady, understands the importance of hobbies for personal growth and decompression. As an outdoor sports enthusiast, he spends his downtime enjoying skydiving, racecar driving, and boxing. But Kevin Mulleady is no stranger to the sea. In fact – another passion of his includes the invigorating sport of sailing. “The sea can be quite captivating, beckoning one to explore uncharted waters,” says Kevin Mulleady. “And the freedom of commanding a watercraft as it seamlessly slices through the waters is quite gratifying.” Beyond the pure enjoyment of sailing, Kevin Mulleady offers a new perspective on this watersport, with respect to its correlation with the physical sciences.

Physics is an Integral Part of Sailing

According to Kevin Mulleady, sailing provides numerous examples of well-known theories in physics. These theories include Newton’s law, vectors, resistive force, kinetic energy, wing theory, and Archimedes’ principle. Generally, there are two primary components of a sailboat: the sail and keel, responsible for enabling the boat to move forward through the water effectively. Therefore, to master the art of sailing, one must pay attention to the interaction between the wind and sails and between the water and keel.

Moving the Sailboat Downwind vs. Upwind

Sailing offers the capacity not only to travel downwind but also upwind, within reason. Downwind, sailing parallel to the wind is relatively straightforward: the wind, being faster than the boat, simply blows into the sails and pushes against them. The sails decelerate the air, so the sailboat essentially uses the wind’s force from behind to propel it forward. However, sailing downwind is not desirable as one can only ever sail slower than the wind’s speed. Sailing directly upwind, exactly anti-parallel to the wind, is also unfavorable, as it is impossible to travel any distance. The sails will just “luff,” a term used by sailors to describe the flapping when sailing with the spinnaker in the “no-sail zone,” outside 45 degrees on either side of the wind. Kevin Mulleady advises that one can overcome this luffing of the sails by sailing between 40 to 45 degrees to the wind – by tacking alternate lines on either side of the wind direction.

Using Newton’s Laws and Resistive Force to Sail Effectively

When one sails close to the wind, the shape of the sales generate lift. In order to flow around the sails, the wind has to deviate in direction – initiating a change in velocity. The acceleration of the air and the force that the sails exert on the air is in the same direction, which can be depicted by Newton’s first and second laws, where force is equal to mass times acceleration (F = ma). The force that the wind exerts on the sails is in the opposite direction. One will notice that this force is primarily sideways on the boat, which becomes increasingly so as one gets closer to the wind. “But remember, part of this force is still forward,” explains Kevin Mulleady. “And thanks to the keel that pushes the water sideways, the water in return resists this and exerts the sideways force on the keel, canceling out the lateral component of the wind. Thus, the forward component accelerates the boat, with the most ideal performance being achieved approximately 45 degrees to the true wind.”

Resistive force is a type of resistance experienced by sailboats. As the hull moves through the water, it faces friction from the water. Although some surface frictions will become reduced through lubrication, this isn’t the case with sailboats. A smooth surface helps reduce any water turbulence but won’t affect the resistive force from the water. The only way to combat the resistive force is to reduce the wetted surface. 

Kinetic Energy Also Plays a Crucial Role in Moving the Sailboat Forward

As the wind moves around the sails, releasing kinetic energy, the pressure is greater above the sail than below. With the pressure higher on the upwind side and lower on the downwind side, the boat propels forward.

Sailors like Kevin Mulleady typically do not aim to move directly with the wind because, as discussed previously, they never reach speeds above maximum wind speeds. Instead of sailing straight downwind, the sailor moves perpendicular to increase wind force and decrease water resistance. Although it may seem like the wind should make the boat go completely sideways, the sailboat design actually prevents this from occurring. Even though the wind will push the ship, the keel below the deck counteracts it. The keel is forced to move a lot of the water aside and cancels out the wind’s side force. Keels only work if not pointed directly forward, relative to the direction of the wind.

Representation of Wing Theory in Sailing

Another type of scientific principle behind sailboat keels is wing theory. Over 100 years ago, wing theory helped engineers understand the possibility of flight. Today, the concepts still apply to both flying and sailing. Wing theory states the most effective plane wings are long and narrow. The vortices made at the tips of airplane wings will use up energy. A long and narrow style wing will maximize the ratios between lift and vortex changes. When this theory applies to sailboats, it means that the most effective keels are deep and narrow. This design also prevents sideslipping. “Here, we see that there’s less room for resistance with a reduced surface area, and the sailboat’s speed reaches maximum potential,” explains Kevin Mulleady

Relation of Archimedes’ Principle to Sailing

Another physics theory related to sailing is the Archimedes’ principle. The guidelines for the principle state that the amount of force exerted by an object in the water must be equal to the amount of water displaced by the object. This force is called the buoyant force, and it will push up against the object. If the downward force is less than the buoyant force, it keeps the boat afloat. 

 

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