How did water get into my engine?

[Ferrari]

Yes there is there’s an anti syphon valve which allows air into the system from above and lets the water drain out.
You should hear a gurgling sound when the engine stops…..thats the sound of the water draining from the exhaust.
In your system which is nice and quiet, raw water is mixed with exhaust gases at the Elbow.Water and gasses are separated in a chamber and the gasses leave the boat above the water level. The separated water leaves the boat via a through hull underneath the water level. Standard systems spit water out of the exhaust with the exhaust gasses.

[model 10]

Originally Posted by Water Dragon

I'm not really familiar with this kind of water-cooled exhaust, and I'm trying to understand how it's supposed to work.

Water cooled ex? Do you have a water lift muffler or a water cooled exhaust pipe? If it's a water cooled exhaust pipe/hose set-up, that is your problem. The metal inner flex pipe is rusted through. Horrible system.

[Water Dragon]

There is no anti-siphon valve. Just a big pipe and some hoses. Water and exhaust exit through a single hole above the waterline. I'll try to draw a diagram and/or post some pictures.

[model 10]

Yeah, that sounds like a water cooled exhaust pipe/hose. My boat had that set-up. It failed and water logged the the engine too.
I don't know if you can still buy a new hose/pipe assembly. I converted to a water lift muffler which is a project. You have to figure out things like water lift size, the injection elbow, vented loop, plumbing etc.