A safety tether is a strong strap that connects between the sailor’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, a stanchion base, 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 like that shown here.
A standard tether, as shown in this photo, is 6 feet long and has a shackle at each end. Typically the breaking strength of a commercial tether is over 5000 lbs. Different kinds of shackles are used, as described in the next pages.