A new law took effect in California this month.

All gasoline powered marine inboards sold in the state must be fitted
with a catalytic converter. I guess if these prove effective, we'll
all be converted to catalysism sooner or later. :-)

The major concern in the past has been the enormous amount of heat
that a catalytic converter requires in order to work. From what I
understand, the converters are mounted immediately behind the exhaust
manifold, and the cooling water is introduced into the exhaust line
after the converter has done its job.

Even so, at least some of the systems include a system that restricts
engine rpm to 2500 if the catalytic converter overheats. One
manufacturer has been quoted as "this slower speed will give the
boater several minutes to shut down before the increased heat begins
to melt nearby rubber hoses and belts."

Lovely......