Question 19 AXS01 - Auxiliary Sail Endorsement

The Correct Answer is A **Explanation for Option A (Resistance to lateral movement):** A deep keel projects significantly downward into the water. Its primary function is to provide lateral resistance (sideways resistance) to the force generated by the sails. When the sails are trimmed to move the boat forward, they also generate a substantial lateral force (leeway). The deep, flat, vertical surface of the keel resists this sideways movement, allowing the vessel to convert the force of the wind primarily into forward motion. **Why the other options are incorrect:** * **B) Height of the center of gravity above the hull resulting in a more stable vessel:** This is incorrect. Keels, especially deep bulb keels or fin keels, are designed to carry significant ballast (weight) very low down. This configuration *lowers* the vessel's center of gravity (CG) relative to the hull, which is the mechanism that increases stability and resistance to heeling (tipping). * **C) Length-depth ratio resulting in a faster hull design:** This is incorrect. The length-depth ratio is not a standard hydrodynamic term used in this context; typically, designers consider length-to-beam ratio or displacement-to-length ratio. More importantly, while a modern deep fin keel is often used on high-performance, faster designs, the keel itself primarily increases *wetted surface area* and *drag*. Its benefit (stopping leeway) outweighs the drag penalty, but it does not inherently create a faster *hull design* based on a length-depth ratio. * **D) Mast height to compensate for increased lateral resistance:** This is incorrect. The mast height is determined by the required sail area and design considerations (like stability), not the lateral resistance provided by the keel. While a deeper keel allows for a larger sail plan (and thus often a taller mast) because it provides the necessary stability and lateral resistance to handle the larger forces, the keel's depth does not directly *increase* the mast height; rather, it *enables* it.