Shackles are often under high load. If one shakes open, the result could be dangerous. Chris Beeson shows how to make sure it won’t
Three methods for seizing shackles
I used to be doubtful about the necessity of seizing shackles. Nip the pin up tight with a shackle key or pliers and how can it possibly come loose? My mind was changed in 2011, while checking the rig of the old Jeanneau we used in our Crash Test Boat series. This was the rather concerning sight we found at the masthead.
The spinnaker block shackle’s pin had shaken itself free. Had we hoisted and flown an offwind sail, it would have draped itself expensively over the bow, possibly tearing itself in the process, as soon as the halyard chafed through on its mast exit.
What if a shackle securing a cruising chute sheet turning block rattled itself loose? You would have all the load in the sheet firing a block across the cockpit with potentially lethal consequences.
The problem is that boats are subject to a lot of vibration. Wind through the rigging creates vibration, current across an anchor chain creates vibration, engines cause vibration, so does sailing into waves. Shackle pins will work themselves free and problems will result. To prevent them doing so, we seize them.
We use one of three methods of seizing, or securing, the pin to ensure that it simply can’t loosen. One is using threadlock, which glues the pin in place but not with ‘super-glue’ adhesion so it can still be undone with standard tools.
A second method is using electrical cable ties, though it is worth remembering that these are subject to UV degradation and probably won’t last more than a season if they’re always out in the sun. The third method, the gold standard method of seizing shackles, is to use Monel wire. That isn’t subject to UV degradation and has excellent corrosion resistance properties.
Seizing with glue
We used Loctite 243 Blue, but search online for ‘threadlock’ if you want to see a range of alternative products that will do the job just as well as this one
Apply the threadlock to the thread of the shackle pin. It’s not very viscous, so make sure you’ve got something down to protect the deck from any drips
Once you’ve got good coverage on the entire thread, screw the shackle pin into the shackle, again watching out for any drips
Use pliers or a shackle key to nip up the shackle as tight as you can. This will help the glue to adhere without any risk of movement
This is the finished result. It’s the quickest and neatest of the methods and there’s no external seizing to foul on anything. Very tidy
This is the only method of seizing available if you are using the flush-pin type of shackle that’s often found in ground tackle set-ups
Seizing with cable ties
Cable ties are cheap to buy online or from many hardware shops. Thread it through the pin’s hole, then through the shackle’s loop
Next push the tie through the ratchet lock and pull it up as tight as you can. This will prevent the shackle pin from unscrewing itself
To make the cable tie seizing as compact as possible, use pliers to pull the tie through the ratchet lock as tight as you can manage
Snip off the excess length of tie leaving only a very short stub, to reduce any risk of the tie fouling or chafing on anything. It looks much neater, too
The finished article. It’s the quickest, simplest method and a good short-term solution. ideal for shackles that need to be undone occasionally over the course of the season
Here we see a cable tie seize on a shackle used to connect anchor and chain. It’s exposed to the sun, so is likely to become brittle from UV degradation after a year or so
Seizing with Monel wire
To start, with the shackle pin nipped up tight, cut a piece of wire about 15cm (6in) long and hold 5cm (2in) of it under the side of the shackle
Poke the wire up through the hole in the shackle pin then down through the shackle itself and repeat so you have two loops of wire around the shackle and through the pin
Use pliers to tighten the wire as much as you can to snug down the seizing onto the shackle. This helps to prevent any movement in the wire
With the second loop of wire wrapped and tightened, use pliers to twist the two ends of the wire together, again keeping it tight
Once you have got five or six twists on the ends, snip off the excess wire, press the twist against the shackle body and you’re done
This is Monel wire seizing on a spinnaker halyard block shackle. It’s a strong and durable solution for shackles that you can’t inspect regularly