Here's evidence of how rigging a preventer the wrong way can cost you a new boom

Here’s another photo from the finish of the ARC in Saint Lucia – one of several broken booms this year. This is an annual feature of the rally unfortunately, but there were a few more than normal this year. 

The shame is that almost all of them are avoidable. You need to rig a preventer and lead it the right way.

This 49ft French catamaran rigged a preventer downwind, but in the wrong position. If you enlarge the photo you can see exactly why this one broke during an accidental gybe.

The better way to run a preventer is to take it from the boom end to
a snatch block at the bow and back to a winch at the cockpit, where it
can quickly be released.

To make it easier to set up on each
gybe you can rig a permanent preventer line from the boom end to the
gooseneck that can be connected to the rest of the preventer line
running to the bow and back.  

David Durand, a crewmember on the catamaran told me they knew that they shouldn’t have led the preventer straight to the midships cleat at this acute angle but they lacked a spare winch or fixing point aft. Hmmm. You could lead a preventer right forward and make it off back at a quarter cleat if you had to, or maybe invest in a mobile clutch that you can move around as it’s needed.

They’re damned expensive, but not as much as a new boom… Here’s an option from Spinlock.

Here’s another break. The boom on this yacht folded neatly round the central mainsheet attachment during an accidental gybe. They weren’t using a preventer.

Boom break 2