2 min read · Updated 27 June 2026
Jackstays and tethers are how sailors stay attached to the boat — and staying attached is what prevents the most dangerous emergency at sea: going overboard. In rough weather and at night, a crew member clips a tether from the harness in their lifejacket onto a jackstay running along the deck, and stays connected to the boat come what may. It is a central part of offshore safety equipment.
Jackstays — the anchor line
A jackstay (or jackline) is a strong line of webbing or wire rigged along the deck from bow to stern, usually on both sides. It gives a continuous anchor to clip onto, so a sailor can move fore and aft — going forward to work on the foredeck — without ever unclipping. Rigged before conditions get bad, jackstays turn the whole deck into a place you can move about while staying attached.
Tethers — the connection
A safety tether is a short, load-rated line connecting the harness to the boat — to a jackstay or a fixed strong point. Clipped on, it keeps you attached if you slip, are knocked down, or washed by a wave. Many tethers have two clips of different lengths, so you can clip the second on ahead before unclipping the first — staying attached the whole time you move between anchors.
The harness
The tether clips to a harness — a strong webbing harness worn on the upper body with a load-rated chest attachment. On modern boats the harness is built into the inflatable lifejacket, so putting on your lifejacket also puts on your harness. It spreads the shock load across the body and gives the secure anchor the tether needs.
Why it matters so much
Recovering a person from the water is difficult, slow and uncertain — especially in rough weather, at night, or short-handed — and cold water and separation from the boat are rapidly life-threatening. Staying attached prevents the emergency in the first place, which is far more reliable than recovering someone once they're in. As sailors put it: the best man-overboard drill is not falling in.
When to clip on
Clip on whenever there's a real risk of going overboard: rough weather, big seas, strong winds, at night, when short-handed, and whenever leaving the cockpit to work on deck. Many skippers require crew to clip on before coming on deck in such conditions, and always at night. Offshore, the discipline of clipping on is a core habit. For the vocabulary, see the sailing terms glossary.
Frequently asked questions
- What is a jackstay on a boat?
- A jackstay — also called a jackline — is a strong line of webbing or wire rigged along a boat's deck from bow to stern, that a crew member clips a safety tether onto. It provides a continuous anchor to stay attached to while moving fore and aft on deck, so you can go forward to work without unclipping. Jackstays are rigged on both sides of the deck for offshore and rough-weather sailing.
- What is a safety tether?
- A safety tether is a short, load-rated line that connects the harness built into a sailor's lifejacket to the boat — to a jackstay or a fixed strong point. Clipped on, it keeps the sailor attached to the boat if they slip, are knocked down or washed by a wave, preventing the most dangerous outcome at sea: going overboard. Many tethers have two clips of different lengths so you can stay attached while moving from one anchor to the next.
- Why is it so important not to fall overboard?
- Because recovering a person from the water is difficult, slow and uncertain — especially in rough weather, at night, or when short-handed — and cold water and separation from the boat are rapidly life-threatening. Staying attached to the boat with a harness and tether prevents the emergency in the first place, which is far more reliable than recovering someone once they are in the water. The saying is that the best man-overboard drill is not falling in.
- When should you clip on with a tether?
- Whenever there is a real risk of going overboard: in rough weather, big seas, strong winds, at night, when sailing short-handed, and when leaving the cockpit to work on deck. Many skippers have a rule that crew clip on before coming on deck in such conditions, and always at night. In calm daylight conditions inshore it may not be necessary, but offshore the discipline of clipping on is a core habit.
- What is a harness in sailing?
- A safety harness is a strong webbing harness worn on the upper body, with a load-rated attachment point at the chest, that a tether clips to. On modern boats the harness is usually built into the inflatable lifejacket, so putting on your lifejacket also puts on your harness. It spreads the shock load across the body and provides the secure anchor that keeps a tethered sailor attached to the boat.