With the bracket attached to the mast, it is time to begin mounting the rest of the hardware. The tack lines are pretty self explanatory: they will attach to the old tack hook, run up through the tack cringle, and then straight down to the bracket.
The clew is the trickier one to lead. The clew line runs from the boom, up through the clew cringle, back down to a turning block on the boom and forward to a cleat where it used to be secured. Since we are leading the lines back to the cockpit, we need to get the clew line to turn down to the bracket where it can be led aft.
Turning blocks are pulleys that will change the direction of the line. This seems simple enough, but their placement is the real secret to their success. In theory, you could mount the turning blocks on the boom or on the mast, as both are locations where the line can come forward to and then turn down.
While the actual block doesn't really care about where you mount it, the geometry of the lines does. Imagine you have your reef line block mounted on the port side of the mast. You reef your sails while on port tack and everything is set up perfectly. Then you change tacks to starboard tack and the boom swings to port. All of a sudden, your clew line is slack and the reefed sail begins to fill with air instead of spilling it effectively. What happened is as the boom moved over, the distance from the cheek block on the end of the boom to the cheek block on the mast shortened. As a result, the reef line became slack and the clew was allowed to raise up a bit.
If the reef was setup on port tack, switching to starboard tack would result in a clew line so dangerously tight that it could rip the cringle right out of the mainsail!
To avoid these mishaps, all you need to do is be mindful of the moving parts at play and setup a system that will be geometrically neutral throughout the entire range of motion. Keeping forward cheek block mounted on the boom means that as the boom swings from side to side, there is no change in distance between the forward and aft cheek blocks, thus no change in line length nor tension.
Mounting the turning block at the deck as close to center-line as possible and on a hinging structure also gives more flexibility in the final setup. This allows the boom to swing from one tack to another without causing any changes in the sail shape.
While this may seem like a very small point to dwell on, it will make all the world of difference when you find yourself in a storm and don't have to worry about lines changing tensions as you maneuver your yacht to safety.
