My guess is that you have the original aluminum rudder castings? Those use a black plastic cam to rotate over a spring loaded plunger... to lock the rudders down. I'd further guess that the cams are in the locked position which prohibits the system from functioning. You need to "open" the cams first.
Take a look at the cams FAQ here:http://www.hobiecat.com/forums/viewtopic.php?f=18&t=467
...If the cam sticks in the down position there are several methods to get it to rotate release. From above and forward of the assembly, lift the upper arm and rotate it aft and out of the way. Loop a line around the cam yank the line to pop the cam open. You can also use the tiller arm to assist this technique by wrapping the line around the cam, then lowering the tiller arm and wrapping the line a few times around the tiller arm. Pull up on the tiller arm which (through the line) levers the cam open. There are several tools that can also be used. I use a large blade screwdriver that can be inserted into the side of the cam to leverage it open. There is also a tool (Hobie Part # 83103 / 2003 Catalog page forty eight) that has a small hook that can be used (by drilling a small hole in the cam to allow it to be inserted) for leverage. You can also use a small flat blade screw driver to work between the cam and plunger... force the plunger down to unlock the cam. I find that this works very well even if the cams are dry and un-lubricated.
If the cam is really stuck down, the only tool needed is a small blade screwdriver. You work the blade between the cam and plunger to force the plunger down and release the cam... More.