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.
Anvil
The great majority of modern anvils are made of cast or forged steel (the latter is stronger) that has been heat treated. Inexpensive anvils have been made of cast iron and low quality steel, but are considered unsuitable for serious use as they deform and lack rebound when struck.