A safety tether is a strong strap that connects between the sailorÃƒâ€ s safety harness and a strong point on deck, such as a leg of the compass binnacle, a U-bolt installed in the cockpit expressly for the tether or a jackline. The safety harness is worn around the chest and shoulders and has two D rings to which the tether connects. Most sailors now use inflatable PFDs with a built-in safety harness.
A standard tether is 6 feet long and has a shackle at each end. Typically the breaking strength of a commercial tether is over 5000 lbs. Tethers are also available with double connections for the boat. Most double tethers have a 6-foot length and a 3-foot length. When it is necessary to move about the deck in dangerous circumstances, you can clip onto a new position with one shackle without having first to release the other shackle. This way, there is no vulnerable moment when you are not clipped in at all.
Both single and double tethers, in addition, are available with elasticized straps. The advantage of an elastic strap is that the tether does not droop down where it may snag on equipment or get in the way.
Quick-release shackles are opened by pulling on a cord they cannot be snapped into place like a snap shackle. The quick-release shackle is attached to the wearers harness and is designed to open with a jerk on the release cord. A sailor who falls halfway off the boat, for example, may have to release the tether (once he or she is secure) in order to move into a safe position. These shackles are inexpensive but may be difficult to release under extreme pressure
"Safety" shackles are more secure than the standard snap shackle and can not open accidentally under any circumstance. Safety shackles typically require a two finger maneuver to first move an inner lever bar against an internal spring and holding it open before opening the shackle jaw with your thumb. When this thumb pressure is released, the shackle snaps closed with the action of both springs and is then very secure against any risk of accidentally opening. The disadvantages are that it costs more and may be slower and more difficult to use until you become familiar with it.
The most important thing about a safety harness and tether is to use it. Usually this means using it before you think it's necessary. Almost all sailors who have fallen off a boat thought they were safe at the moment they fell. They didn't expect the boat to suddenly lurch, they thought their nonslip shoes wouldn't slip on a wet deck, they thought they had a secure handhold on the rail as they walked forward, they never thought the boom would hit them in the head and knock them overboard.
Even a tether is no guarantee, however. It's still important to wear a PFDs preferably the inflatable offshore type with safety harness built in.