I have the Davis Tiller Tamer on my Capri 18 and it works well for lake sailing; I haven't had a chance to use it on salt water yet. There were plenty of crew on my last (first with this boat) trip last year who were eager to take the helm.
I now have a Forespar telescoping tiller extension and I believe they have a bulkhead mounted fitting that allows it to work as a tiller lock. Has anyone used one of those?
I hesitate to get one because it looks like I'd need to cut a 2"x3" hole in my cockpit coaming to mount the fitting. That's a much bigger commitment that just drilling holes for 2 #8 screws.
Capri 18 #299
Moment of Zen