I am wondering why people want to put a plastic bag over the lower unit
of an outboard motor for winterizing (with holes on the bottom of the
plastic bag for drainage). I come across this suggestions in this
newsgroup; but I don't understand the reasoning. I understand that
rain water or melted snow water may find its way into the lower unit.
But I think they will be naturally drained out from the lower unit,
right? Why do I need to cover the lower unit if the water will be gone
by itself anyway? The owner manual of my Mercury outboard motor
doesn't say anything about covering up the lower unit in freezing cold
winter either.

Any idea? Thanks.

Jay Chan