A flat board or fin that can be lowered through the bottom of a sailing boat to help it move straight and prevent sideways slipping.
From 'centre' (middle point) + 'board' (plank). Developed in 18th-century nautical engineering as an alternative to traditional keels, allowing boats to navigate shallow waters while maintaining directional control.
This invention revolutionized sailing by letting boats sail in rivers and harbors where regular keels wouldn't fit—it's like giving a boat an adjustable spine that only shows up when needed!
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