OK - the things you put the arrow on and were asking about are part of the a barberhauler system that works like a "twinger" for the jib sheeting system so you can outhaul the sheeting angle for better jib shape downwind.

You should run a line through this cleat, through the sheave in the beam, through the beam, out the sheave on the opposite end of the beam, and through the matching cleat there. On each end of this line should be a plastic ring, or block with becket. The two sheet lines from each side of the boat that go to the clew of the jib should go through the appropriate ring.

The way this works - say you rounded A mark (with the mark to port) and you are going to head down the course downwind on starboard. While you are still on the starboard (windward) side of the boat, you ease out the main traveler, ease off the jib halyard slightly, rotate the mast to 90 degrees, ease the jib sheet, and pull the starboard end of the barber hauler until the ring is bottomed out on the beam. As you jibe, you will first need to release the starboard end of the barberhauler, jibe, then set the barberhauler on the port side once you've gone across.

The beam in the center of the trampoline (aka 'knee-knocker') is there to prevent the front beam from rotating. Early 5.2 models did not have the bolt that goes from inside the ends of the front beam into a plate in the hull to prevent rotation. This bar was the solution. It takes some getting used to.