Sea anchor

A sea anchor (also known as a parachute anchor, drift anchor, drift sock, para-anchor or boat brake) is a device that is streamed from a boat in heavy weather. Its purpose is to stabilize the vessel and to limit progress through the water. Rather than tethering the boat to the seabed with a conventional anchor, a sea anchor provides hydrodynamic drag, thereby acting as a brake. Normally attached to a vessel's bows, a sea anchor can prevent the vessel from turning broadside to the waves and being overwhelmed by them.

Early sea anchors were crude devices, but today most take the form of a drogue parachute.^{[clarification needed]} Larger sea anchors are so efficient that they need a tripping line to collapse the parachute for retrieval. Being made of fabric, a sea parachute may be bagged and easily stowed when not in use.

A similar device to the sea anchor is the much smaller drogue, which is streamed from a vessel's stern in strong winds so as to slow the boat to prevent pitchpoling or broaching in an overtaking sea. The fundamental difference between the sea anchor and the drogue is that the drogue will slow the boat while keeping the heading steady, and is intended to be launched from the stern. The parachute anchor is designed to be launched from the bow and effectively stop the boat's progress relative to the current in an open sea.

Anything that can act as a source of sufficient stable drag in the water can act as a sea anchor; a common improvised drag device is a long line (a docking warp or anchor rope) payed out into the water; while this does not provide much drag, it can act as a drogue and aid in running downwind. Adding items to increase drag can convert this to a sea anchor. A (floating) bucket tied to the end of the line works as a basic sea anchor. In The Sea-Wolf, author and sailor Jack London described using various broken spars and sails, tied to a line, as an improvised sea anchor. A sail, weighed down with an anchor chain or other heavy object, will also work as an improvised sea anchor.

Early sea anchors were often improvised from spare parts aboard ship. An 1877 book used by the United States Naval Academy describes methods of making sea anchors. These took the form of a wooden or metal framework forming a simple kite-like shape of sail canvas, backed with a net or closely spaced ropes to provide strength. A small anchor attached to one corner kept the sea anchor from twisting. If the framework was wooden, the wood's buoyancy kept the sea anchor just under the surface, while an iron framework used a buoy to keep it at the proper depth.

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.

The size of the sea anchor determines how much water it can displace, and how much braking it can provide. It is also possible to use more than one sea anchor to increase the braking.

The 'series drogue' is a drogue (not a sea anchor) that allows the operator to increase or decrease the resistance by laying out more or less of a line with many small drag devices spread out along a line - this also serves to ease retrieval under heavy conditions.