The meaning of circulation
Circulation is one of the most misunderstood terms in sailing. Yet, circulation is essential to understand lift and why sails, wingsails, keels, rudde…
Navalapp
The Reynolds number
The Reynolds number is the ratio of inertia forces to viscous forces involved in the flow. Reynolds understood that while inertia forces were dominant…
Understanding the boundary layer
In 1904, Ludwig Prandtl introduced an approach to understanding and analyzing flows around bodies that produced a massive breakthrough: the boundary l…
Bernoulli’s principle
The physical significance of Bernoulli's equation is what is known as Bernoulli's principle. It states that when the velocity of a fluid increases, th…
Flows in sailing
Sailing boats interact with flows of two very different fluids: air and water. Moreover, sailing boats are able to make their way through the water su…
International Measurement System: Sails
The International Measurement System (IMS) is a set of rules that define what and how is measured on a boat. It is used by the Offshore Racing Congres…
Challenges in sailboat design
Using wind power and sails as the primary means of propulsion brings additional dimensions to the design of a sailboat compared to ship or powerboat d…
Sea state and wave forecasting
The performance of a sailing boat is affected by the presence of surface waves. To understand how the waves influence the boat's performance, we need …
Wind-generated sea waves
Wind-generated waves occur when the wind blows over the surface of the sea. They are divided into gravity waves (wind sea, and swell) and capillary wa…
Hull appendages, planforms, and wing sections: what are they?
Fin keels and rudders have become the standard configuration nowadays for racing and cruising yachts and everything in between, be it inshore or offsh…
Wind triangle
The wind experienced by a fixed observer (true wind) is not the same wind an observer on a moving yacht will feel (apparent wind). The wind triangle h…
Points of sail
The points of sail refer to the course a boat is sailing in relation to the wind. They are defined in reference to the wind angle, which is the angle …
What the hydrodynamic resistance is and why it matters
The motion of a sailing yacht through water requires energy to overcome resistance. It is essential to know the mechanisms behind the generation of th…
The air-water interface
Water and air are two different fluids that enter into contact at the ocean's surface at what is called the air-water interface. This interface plays …
Surface waves
Surface waves are created by disturbance forces applied to a specific area. It can be either the wind, a surface vessel moving through the water, an e…
What is the Froude number?
The Froude number is a dimensionless number used to quantify the influence of gravity on the motion of a fluid. It is the ratio of the inertia forces …
The evolution of hull and keel forms – Part 2
British "plank-on-edge" suffered from poor form stability. Yet, the deep down located ballast offered a considerable amount of weight stability and po…
The evolution of hull and keel forms – Part 1
Until the 19th century, the art of yacht design had been mainly influenced by tradition, economic and commercial motivations, understanding of materia…
The lines drawing: what it is and how to read it
The lines drawing is the conventional graphical representation of the hull. In the lines drawing, the hull's shape is represented by three different v…
Introducing the hull
The hull provides a volume to house accommodation, machinery, supplies, and cargo. It has to be seaworthy enough for the routes the yacht will sail an…