While the saildrive gearing is symmetrical, the normal transmission has
three gearing options, none of which are symmetrical.

I remember an article (by Pascoe, I think) about a large power boat that
used reverse gear to have a counter-rotating prop. The shift linkage
was reversed, of course. The owner couldn't figure out why the
transmission needed service every 50 hours.

Interestin. G we learn something new everyday.
I do note the reduction difference is not all that great between ahead and
astern and would have to wonder how noticeable the difference would be, versus
putting the prop on backwards. I also have a problem seeing how someone could
put the prop on backwards, other than in a twin screw application.

Shen