Sometimes referred to as a “Drogue”, a Sea Anchor differed from a traditional Ships Anchor, in that it’s purpose was not to anchor a Ship at Sea, but serve to stabilize it from drift or to slow it down without compromising Sail Pattern or Wind coefficient. A Ships Anchor was quite heavy, and took time to be property set in a Sea Bed. Conversely, raising said Device also took time. The first example of a Sea Anchor may have developed with Dutch Traders in the 15th Century.
These devices were a series of wooden “plates” or Slabs, through which was drilled a common center opening. The components were fitted on a wooden pole (often 1-foot in diameter and 8 to 10-feet long). Often such Ships carries several such devices. In application, a Sea Anchor could be thrown overboard and allowed to float to a predetermined depth (often derived from previous measurements taken -known as “Soundings”). The Sea Anchors shape would gradually slow a Vessel without compromising Sail Deployment or weather (Wind).
In some cases, a Sea Anchor could be used to about right stop a Ship - temporarily, without the necessary time needed to withdraw it, compared to the Ships primary Anchor. With Ship evolution and The Age of Steam, the need for Sea Anchors diminished. Variants are still used with Racing Yachts. These are often designed a “Water Chutes” and work very much the same way an Aircraft Rear Chute is used to “slow” down a decelerating Aircraft on the ground.