What is definition of knockdown when sailing?

Answer 1

A broach -- when the boat is knocked on her beam's end. In non-nautical jargon, it's when the the boat heels near to 90 degrees and the mast is nearly parallel to the ocean surface.

While this is a very dramatic moment, as well as noisy, it's not usually dangerous as long as the boat is properly secured for weather like that, and doesn't take water. Racing sloops take knockdowns all the time, and without major -- or any -- consequences to the boat or crew.

The process is comparatively slow -- perhaps 5 seconds. Standing on the leeward rail, you shift position as the boat heels and, surprisingly, find yourself standing on the stanchions hip deep in water. And then the boat naturally heads into the wind and the weight of the keel rights the boat.

Typically, a knockdown is a sign you're carrying way too much sail.