Hi Roadrunner and Matt Miller.
The Tandem is my first purchase of a Hobie product. Please help me understand how the Tandem's Twist & Stow mechanism is designed to work.
I'm obviously no expert on such matters, but here's my understanding.
Due to Hobie's unique 45 degree mounting system that allows the rudder to flip up on the deck, the rudder always behaves itself on left turns and always wants to pop out on right turns. The tongue and groove arrangement on the left side is designed to "catch" the rudder on right turns so it doesn't escape the pocket that it sits in, in the down position.
The "down" line is the latest in a series of implementations to get the rudder to positively engage in its down position pocket and keep it there at all times so that the tongue and groove system will be in a position to take over and positively engage it when necessary. It is not strong enough to hold the rudder in the down position at higher rudder pressures without help.
When everything works well, the down line "bumps or snaps the rudder around the left corner of the pocket (it sits a little offset here) where the tongue and groove are. So ideally, with any backward pressure (overcoming the down line), the rudder groove will slide back and engage the tongue for a positive lock up.
The TI rudder is much heavier than the other Hobie rudders. In order to lift it onto the deck easily, Hobie has made the TI up /down system a double purchase system. As a secondary effect, this also effectively gives twice the leverage when the line is pulled taut and lock. I suspect this has something to do with why your line broke. It could be the line was frayed as well; normally the Spectra line is pretty strong stuff.
The rudder doesn't need to fit tight in the pocket. On the contrary, it needs to slip in and out without binding. It does need to be able to seat in the pocket all the way though.
As Anakritis convincingly pointed out, some of the rudder housings are misaligned so the rudders can't fully seat in the down position. He has worked out a couple of ways to overcome this, pending his sea trials. I think he also did a nice job of explaining why the alignment criteria are more critical on the new system due to the relocation of the various elements.
Loosening the drum bolt is not normally done (except for friction reduction for the up/down pivot action), as it invites excessive rudder play. But as TIDALWAVE demonstrated, in this case excess rudder play is necessary in some cases to coax the rudder into the pocket so the tongue and groove can be engaged. I see this as a temporary solution only until a proper fix is available.
When these parts are molded, they are susceptible to warpage if they cool unevenly. IMO, it's easy to spot a warped rudder, but hard to see a warped housing. It almost has to be installed and operated. It sounds like Hobie has developed new inspection procedures that should identify faulty alignments before they leave the factory, and is also looking at a variety of options to correct the problem.
That's my take on the issue anyway. As stringy says, they'll get it worked out. It may take a little time though -- I'm sure they don't want to rush into a "false fix".