I missed Jeff's comments, but PROPERLY designed I have few qualms about the structural integrity of spade rudders for coastal or even offshore sailing. But in recent years I've noticed an increase in reports of spade rudder failures from boats sailing off-shore. So due diligence is the key if you plan to go off-shore with one, to make sure it is a sound design.
The responsiveness of a well balanced spade rudder is a pleasure, especially for daysailing or racing, and docking under power (particularly in reverse). But on longer trips it can grow wearisome and can be more work for the crew or an autopilot/windvane. They do not generally want to steer straight of their own accord, necessitating a fair degree of attentiveness at the helm.
As an all round compromise, I prefer a skeg-hung rudder, with the prop in an aperture: For the protection it offers from collision with floating debris. For it's tracking ability. For it's resistance to snagging pot warps.
Pacifc Seacraft Crealock 31
Skeg hung rudders tend to track straight with very little helm input. On our boat, we can walk away from the helm without even tightening down the clutch and the boat will hold it's course long enough to mind a sheet or traveller, or duck below to grab gear. If we lightly tighten the helm clutch we can go forward to tend a sail. For longer periods, our autopilot (when the d*&@ thing works!) doesn't have to work very hard to keep the boat on course.
We pretty well sail through the Chesapeake crab pots without worry (we don't deliberately run them over, but don't get worried about doing so either). Having snagged pot warps on both spade rudders and bulb keels, it's not something I want to deal with when I have a boat load of kids aboard.
Sure there are downsides to the skeg-hung rudder. More wetted surface area (drag). They do not generally steer nimbly in reverse. They usually are not balanced like a spade rudder, so they do require more effort to turn (but with the mechanical advantage of a wheel it's less noticeable.) However, it is this lack of balance that makes them hold their course with little input, so it's a trade-off.
Also, it IS possible to design a balanced skeg-hung rudder, if that is an important priority in the design brief.