jamesgangnc wrote:


The original design is because the early i/os really did use the lower half
of an outboard. Early big merc outboards actually have some parts that are
interchangeable with the early i/o legs. As to the reason, it let them
build a boat with some of the advantages of an outboards but without the
finicky, easily damaged, aluminum 2 stroke engines.

I/O's came about mainly because auto engine makers provided cheap
engines that could be mated, sort of, with a lower unit assembly that
delivered higher horsepower at a lower price than the outboards of the day.