On a boat, everything comes loose eventually, if it is not loose already from the day the boat was delivered. Loose shackles can result in a lot of damage, so it is important to seize all shackles.
There are different ways to do this.
Up to now I have been using tie-wraps to seize my shackles, because it is quick and easy. Tie-wraps degrade in the UV within a year or may get broken by rubbing lines or by another force on the shackle somehow, as you can see in the pictures.
Loctite 243 (blue) is another option to seize shackles. Put some loctite on the thread and tighten the shackle with a pair of pliers or shackle key. Loctite 243 is a medium strength metal bonding sort of glue. With some force you can break the bond. Stronger locktite (red and green) require heat to break the bond. What I do not like about Loctite is, that you cannot visually inspect if the bonding has been done properly. You just have to assume…..
I think the best and most secure option is to use Monel wire to seize shackles. You can visually inspect each shackle. On a crossing I do an inspection round on the boat every morning. I inspect all shackles, lines for wear and loose bolts. Some people choose to use Loctite and seizing wire. Better safe than sorry….