kriste almighty, jeffies, the very first sentence clearly states "raw water
cooling". That ain't exhaust, dude.

btw, jeffies, it is forbidden practise to install the exhaust water injection
point below the waterline, unless there is absolutely no way that can be done
(unusual, even in cases of the engine mounted in the salon).

now, jeffies, go back to watching TV.

who the hell was the stupid cluck who said a wet exhaust needs an
antisiphon
valve?

Maybe it was the ABYC (American Boat and Yacht Council) in its "Standards and
Recommended Practices for Small Craft":

"The waterlift system shall be designed to prevent siphoning through the raw
water pump when the engine is stopped. If this is accomplished through the
use
of a siphon break device, it shall be installed at the top of a loop which
shall
rise high enough to assure that the high point where the siphon break device
is
installed will always be above the water level surrounding the boat.
Depending
on the design of the boat, the condition of its loading, and the sea
conditions
encountered, this loop may be 30 to 45 cm (12 to 18 inches) above the
waterline
at repose. The loop shall be between the water pump outlet and the point of
injection of cooling water into the exhaust system."

Or maybe it was Calder:
"On any engine that is below the waterline, both the water injection line and
the exhaust pipe create the potential for water to siphon back into the
exhaust,
fill it and flow into the engine via open exhaust valves. The injection line
must have an effective siphon break."

who the hell were the stupid clucks who agreed with him/her?

Pretty much everyone, except you. Have you been right about anything in the
last few years?

You can backpedal and nitpick that the water injection line is not part of
the
direct path of the exhaust gases, but its pretty clear that everyone
considers
it part of the exhaust system.