What make and model of boat are you looking at?
Worm gear steering is hard to beat from the standpoint of how tough it is as squarerigger points out. My boat has a 32 year old Edson
worm gear unit which still looks quite good. I also worked on a vessel with a 10" Lunenberg double worm gear unit that was great. I have seen one broken gear on a very large and very old unit but this certainly seems like a very isolated incident to me and I would not be concerned about reliability
provided that it is in good condition and properly sized.
The real downside to worm gear steering is that the friction in the system is almost always higher. This means that the helm
does not give you as good of a feel of what is going on. The advantage of this is that you usually don't have to work quite as hard when it is rough (kind of like applying a friction brake partially to help you hold the wheel). For blue water
I really like them but for racing
, I would want something else. Another small annoyance is that there is a little bit of slop in the gears but this is very little on well made units.
is independent of the worm gear, it is more related to the fact that you are looking at a schooner style wheel. It is possible to put an autopilot on this type of wheel although it sometimes involves replacing the wheel itself. You end up bracing the autopilot off of the wheelbox. If it is a larger vessel, you could also add an arm to the rudder
post for the autopilot and you would need to make sure that the worm gear is not in the way.
By the way, there are actually multiple kinds of worm gears available. Most units have a single
gear and will use either one or two wheel shaft bearings. The larger units found on fishing
schooners and cargo vessels often have two worm gears that are opposed and a hinge mechanism. These only use 1 bearing and the wheel shaft actually oscillates back and forth. If the hole for the shaft in the wheelbox is actually a slot, it is usually this type of unit.