Outboard motors are typically mounted on sailboats via separate bracket, not clamped on the transom as on most powerboats. Check the bracket carefully in any boat you are considering. It needs to be sturdy and mounted securely, and it should be rated for the outboard motor's weight. Newer four-strokes are heavier than older two-strokes, so if you (or the previous owner) replace the outboard, you need to make sure the bracket is still appropriate.
Many outboard brackets, like the one shown here, can be moved up and down to raise and lower the motor. This is a beneficial function because the mounting does not always provide enough room for all outboards to be tilted forward on their own mounts. Measure this carefully if you're buying a sailboat with an installed bracket but no motor until you buy your own.
A final word: some sailboat builders have resolved the debate between inboards and outboards by designing the cockpit and hull with a well in which an outboard is mounted. In this case the outboard functions like an inboard with many of the advantages of both. While this design is a compromise in some respects, it works well on many boats. The biggest disadvantage is usually that because the well has fixed dimensions, it is impossible to install a larger outboard. Since newer four-strokes are larger than two-strokes of similar horsepower, it can be impossible in some cases to upgrade from an older two-stroke outboard to a four-stroke with greater or even comparable horsepower.
