What is this item?

[Captain Scott]

What do you want it to be? https://www.allenandballard.com/do-you-see-what-i-see/

[Hoosierdoc]

Originally Posted by michaelratinter

Looks like a running backstay to me.

Mine is setup like that. A 36” wire leader to the tackle.

[jt11791]

That's a jib cunningham. The single block attaches at the stem, the end of the wire goes to the cringle on the sail, and the fiddle block is anchored somewhere convenient.

[sparrowhawk1]

It's a barber hauler with 4 to 1 purchase. The end of the cable is secured to the clue, the block is secured to where you want to bring the clue, the end of the block and tackle is secured at a distance that gives you full use of the cable.The shackles are not the best option but on a cruising catamaran you would probably only use this when you're not going to set it up and take it down very often.

[Suijin]

Here’s a wild guess. It’s for hoisting your dinghy side-saddle to your boat. Pulley goes on a halyard. Tackle shackle goes to base of mast. Wire is for security to keep would be thieves from cutting it down from in the water. If the boat came with a dinghy with 3 point wire lifting harness that would be a clue.

Not how I would rig it but who knows.

Does not look like any barber hauler config I’ve ever seen. Maybe a jib Cunningham. It’s way oversized either way for your boat.

[Mike Banks]

Looks like a "Handy Billy" made of two mandolin blocks. It probably served as a vang or could be used as the mainsail boom control.

[Rooster2b8]

Did you by any chance get the boom brake for it? I’m looking for one for my Endeavorcat 30.