Tiller tamer
From your post, I suspect that you are really looking for a way to keep the rudder from flapping back and forth while the tiller is rotated so that it points straight up. I installed a tiller tamer this season. It works great keeping the tiller centered while at the dock or at anchor. It also provides self-steering when the rig is balanced. The best $35 gadget I ever bought. However, one thing it does not do is keep the tiller under control while it is rotated so that it points straight up. I tried a few different ways of lashing the tiller to the stern pulpit to keep the rudder straight while the tiller pointed up, but nothing worked. There is simply too much leverage working against the tiller. It was never a big problem on my boat (Oday 23), so I didn't worry about it; I let the rudder move back and forth. Unless you suspect that the rudder movement is causing a problem, I would just rotate the tiller up and out of the way, and lash it to the stern pulpit.
