Wow. A boom claw. I haven't seen one of those on a boat for some time. They were used on boats with roller reefing booms where the mainsail was furled around the boom to reef it. You have two block and tackle systems for each side (port and starboard). When on a starboard tack (wind over the starboard side of boat), then you cleat in the port tackle. The same applies on the opposite tack, except you cleat in the tackle on the starboard side. The side not used remains "lazy" until you tack. If it leads aft to the cockpit, then that is convenient. You mentioned tabernacle. Not sure where that applies, but then you didn't offer any more photos. If you never use the roller reefing boom feature and have gone to jiffy reefing, you can toss the boom claw and install a conventional single vang from mid boom to mast base and run the line aft for convenience. But, actually this double vang situation that you now have makes for a better preventer too, depending on where they attach to the deck.