Sea anchor
Modern commercial sea anchors are usually made of cloth, shaped like a parachute or cone, and rigged so that the wider end leads and the narrower end trails. When deployed, this type of sea anchor floats just under the surface, and the water moving past the sea anchor keeps it filled. Some varieties are cylindrical, with an adjustable opening in the rear that allows the amount of braking to be adjusted when deployed.
History of the anchor
Killicks are primitive anchors formed by lashing tree branches to a stone for weight. Greeks were using mushroom anchors by 400 B.C. fashioned from a flattened stone with a hole drilled through the center and a triangular eyebolt at the crown for "tripping" the anchor out of its bed.