Lesson V: How a Sailboat Works Hull Speed and Buoyancy Super Sails! Lesson V: How a Sailboat Works Hull Speed and Buoyancy Preserving America’s Sailing Legacy * Engaging Sailing’s Next Generation

Introduction A sailboat’s hull is important for many reasons: Stability Safety Comfort at Sea Load Carrying Capacity Speed

Displacement vs. Planing Hull Speed Displacement Sailboats As they move through the water, they are constantly displacing a new patch of water This generates waves behind the boat Hull designed to cut through the water Planing Sailboats Able to sail on top of the water They can go very fast with minimal drag, but require a great deal of power to get “on plane” Displacement vs. Planing

Only for Displacement Hulls! Hull Speed How do you determine a boat’s maximum speed? As a displacement boat’s hull pushes through the water, she makes waves until she’s sitting between those waves This maximum speed is called “hull speed” The length of the wave is based on the boat’s LWL Hull Speed = LWL = the length of the waterline in feet Hull Speed = speed of the sailboat in knots Only for Displacement Hulls! Why??

J/122 LWL = 34.6 ft 7.9 knots Bermuda 40 LWL = 29.8 ft 7.3 knots Hull Speed What is the hull speed of a J/122? What about a Bermuda 40? J/122 LWL = 34.6 ft 7.9 knots Bermuda 40 LWL = 29.8 ft 7.3 knots

Laser LWL = 12.5 ft 4.7 knots Hull Speed What is the hull speed of a Laser? But Lasers have been recorded at speeds of as much as 16 knots! How is this possible?? When a sailboat planes, it is able to sail much faster than her hull speed Laser LWL = 12.5 ft 4.7 knots

Buoyancy How a Sailboat Floats When a 2,000 ton sailboat is launched into the water, what is keeping it from sinking? A boat will float so long as its total volume weighs less than the density of the water it displaces Review: How much water does a 2,000 ton boat displace? Buoyancy https://vimeo.com/28468671 – video on buoyancy

Weight Buoyancy Buoyancy Archimedes Principle The upward buoyant force [on a sailboat] is equal to the weight of the fluid that body displaces A sailboat will float so long as the gravitational weight of the boat is less than the upward buoyancy force Boats are designed to displace enough water to float Weight Buoyancy

So how is the weight of a massive tanker not enough to make it sink? Buoyancy A large boat floats because…even though it weighs a lot, it displaces a greater amount of water that weighs even more Wide hull Not solid (full of air) So how is the weight of a massive tanker not enough to make it sink?