Lesson IV: How a Sailboat Works: Hull Type Science of Sailing Lesson IV: How a Sailboat Works: Hull Type 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

Hulls Identification based on # of Hulls Which do you think are fastest? Why? Monohull Catamaran Trimaran

Keel Full Keel Pros – easily tracks through the water on a straight course Cons – slower to turn and increased drag due to surface area below the waterline Fin Keel Pros – faster than full-keel and easy to turn quickly Cons – smaller keel provides less resistance to forces that could cause a sailboat to go off course  more difficult to steer

Keel Bulb Keel Winged Keel Provides more ballast weight by concentrating weight at the bottom to improve stability Winged Keel Provides additional hydrodynamic stability and allows a shallow keel to perform more effectively

How much water does she displace? Hull Displacement Hull Displacement – the amount of water a sailboat “shoves to the side” when floating A J/122 sailboat weighs 14,900 lb How much water does she displace?

Displacement Hulls What is meant by heavy or light displacement hulls? Displacement / Length Ratio Use a boat’s length compared to her displacement to determine if a boat is heavy or light D/L Ratio = Displacement (lb) / 2240 [ (0.01 X Length (ft) ]3 Light 200 or less Medium 200 - 350 Heavy 350 or more

Displacement Hulls When calculating D/L Ratio, you must use the sailboat’s “Load Waterline Length” (LWL) This is the hull’s length where it comes out of the water at the bow and the stern LWL

Displacement – Length Ratio Let’s use the previous example of the J/122 J/122 Specifications LWL = 34.6 ft Displacement = 14,900 lb Displacement (lb) / 2240 [ (0.01 X Length (ft) ]3 14,900 lb / 2240 [ (0.01 X 34.6 ft]3 Is the J/122 Light, Medium, or Heavy? D/L Ratio = 161

Displacement – Length Ratio Racing sailboats will have a much lighter D/L Ratio

Ballast Ballast – weight in the keel and bottom of the boat that counter’s heeling Indicator of stability This tells us the boat’s purpose By comparing a boat’s ballast to her displacement, you can determine the best use for that boat Coastal – less than 35% Average – 35%-45% Offshore – greater than 45% Ballast Displacement

Ballast / Displacement Ratio Let’s use the previous example of the J/122 Ballast Displacement J/122 Specifications Ballast = 5,600 lb Displacement = 14,900 lb 5,600/14900 = 37.6% Coastal – less than 35% Average – 35%-45% Offshore – greater than 45%