Tapping out SOS with a wrench makes sense. SOS has an unmistakable sound to it that is instantly recognizable to even the most novice Morse operator (even when I've practiced it, it has chilling effect on me).

Even though each tap (each clunk of the wrench) has the same duration the altered mark/space ratio makes it unmistakable. (Try it by tapping a rule on the desk or clapping hands.)

If a skilled Morse operator were ever in that situation I'm pretty certain at least simple messages could be communicated that way—almost anyone will recognize SOS, skilled operators will be able to do better.