Speaking of Cam Cleats, out trimaran had a pair of Clam Cleats for the centerboard and another pair for the rudder blade (one to hold the foil up when desired and one to keep it down at high speed when sailing). The hold-down cleats both had and interesting mod that's worth remembering.
Clam Cleats are a rectangular block and have V-shaped teeth, lined up in a row to form sort of a long, toothy valley or trench. As you pull harder on the line, it sinks down, deeper into the trench and this increases the grip on the line. Obviously, if you cleat a centerboard or rudder blade, accidentally hit something, and pulling on the line just makes it grip harder, you might do some serious damage to the blade, rudder housing or hull. This is the danger of having cleated downhauls on rudders and centerboards, yet a rudder that tends to ride up at high speed is extremely annoying.
What they had done was to use the plastic Clam Cleats (some are plastic, some aluminum) and take a drill bit just slightly bigger in diameter than the hold-down line. Then they drilled a fore and aft, horizontal channel all the way through the cleat at the very bottom of the trench (the point at the bottom of the V-shaped teeth). In normal use the cleats work like any other Clam Cleat, with the V-shaped teeth gripping the line. If you hit something hard enough though, instead of locking everything up, the line gets pulled deeper into the cleat until it finally pops into the drilled channel - and at that point it can run free and release the blade to kick up.
It works quite well if you have your diameters all figured out. One of the more curious items I've ever hit while boating was a submerged brick chimney in the middle of a man-made lake. We were sailing the trimaran at about twelve knots and really nailed it squarely with the 4' long centerboard. The 7/16" line pulled through the big Clam and an impact that could have seriously damaged the boat just resulted in a small ding in the leading edge of the board.