"HK" wrote in message
. ..
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.

And they still are one of the most popular consumer boat configurations sold
today.