The jacket stays full so water flows into the muffler as soon as you turn it over. But it's probably louder than the waterlock mufflers (I'm guessing). It seems the will do more silencing. But it will be odd getting used to the gurgle and blow as opposed to the steady sound at idle.

I'll be sure I have enough clearance above the waterline, if not I'll add the vented loop. My cooling system has two raw water lines out of the exchanger. One goes into the muffler(via the jacket, now), the other goes directly overboard.

When you replaced your jacketed pipe exhaust (I don't know what it is called), had it failed? Did you replace it to make the exhaust quieter, and did it, in fact? Quieter would be nice but I fear most of my noise comes from an un-sound insulated engine box. Only noisy when you're below.