World sailing offers fairly explicit expectations regarding jack-stays. We also offer our own additional advice, including one that recommends jack-lines ideally be installed so that a sailor who is clipped in can’t go over the side (see “Jack-line installation advice) is not always possible, especially on monohulls. In most cases, the chest-high lifeline will keep above water the head of the person who is overboard. Other benefits of a high life line are:
Your tether won’t tangle your feet as you go forward, since it is attached above, not on deck
You have a line to grab if the boat suddenly lurches or falls off a wave
The clunking tether shackle along the deck won’t annoy crew members trying to sleep below or damage the boat.
It’s quick and easy to rig and remove.
The Aladdin cleat also makes an excellent place to secure flag halyards
There are also some other negatives.
If your upper shrouds are located quite a way inboard, you’ll likely have to go forward on the outside of the high lifeline, which can add risk in some scenarios.
When clipping in, your center of gravity is higher and you are less stable.
We use a trucker’s hitch to tension the lifeline where it attaches to the pushpit stanchions. Virtually all of the load on the lifelines is transferred to these pushpits. Past tests have shown that the railings on some boats are not as strong as they need to be to withstand the dynamic loads of a human bodies hurled against a lifeline (minimum 4,500 pounds), so you will want to make sure yours is up to the task.
We use a simple clamp-on Aladdin cleat (aka flag cleat) to guide the lifeline past the shrouds.
CS Johnson marine makes a stainless steel guide especially designed for attaching to a shroud