Language: jargon: sailing
Tether: Naut.
n.- A short length of line used to raise the tack of a sail.
- A short length of line connecting a sailor's harness to the boat. Often clipped (with a carabiner-type connector) to jacklines to allow limited mobility.
- Any short line or cable used to limit a range of travel.
v.- To limit the range of movement. The crew tethered the dinghy to the boom.
At the end of my tether": reaching the end of one's endurance.
In order to improve the lead of sheets to a sail, or to position it optimally (for example, a very high-cut yankee topsail jib set flying from a topmast), or even simply to get the foot above the pulpit and lifelines a short length of line might be used between the sail's tack and the deck fitting. Often the line is made up with two shackles attached with spliced eyes.
Very similarly, sailors will use a tether to keep themselves aboard the boat. If they get thrown by a wave, or lose their balance while maneuvering, they can only fall as far as their tether and thus avoid falling overboard. Even if they do fall over, they won't be left behind but will be dragged along.
For sailors, being at the end of their tether is a place. And it usually means they're about to do something stupid, like unclip their tether so they can edge out on the bowsprit to deal with the furling line... Another old saying comes to mind: "One hand for the ship, and one hand for yourself".
Attaching a short tether to the harness and the vessel, the sailor can free two hands to work on the job at hand even in heavy weather. If the tether is sized to the height of their chest above the deck, they will be able to lean back against it giving them some leverage (this is far easier to do than to describe!) Many sailors work with two tethers, the second being even shorter than the one described above, to make any distance they might fall, and the jerk as they come up short, smaller.
References:- Edwards, Fred; Sailing as a Second Language; International Marine Publishing Company; © 1988 Highmark Publishing Ltd.; ISBN 0-87742-965-0
- Street, Donald; The Ocean Sailing Yacht; W.W. Norton & Company, Inc.; © 1973 Donald M. Street, jr.; ISBN 0-393-03168-3