Cooling off a kettle-style grill I'm trying to slow-cook using indirect heat on my kettle-style grill, and having some temperature issues.

Most of my experience with my grill follows one of two patterns:


First cook the food item (almost always meat) sous vide. Dump an inordinate amount of white-hot coals from the chimney into the kettle. Sear the meat for about 30 seconds for a quick crust without affecting the perfectly-done interior. Rest and serve
Sear first (following method above), then cook indoors.


But, as much as I like the consistent results I get from cooking sous vide without having to pay attention, I am trying to improve my BBQ game.

So, I tried using fewer coals, preheating them a bit less, and reducing the air flow. Even still, low and behold, I got a fairly hot fire going that I really didn't want this time. 

So, how do I cool it down? I'm trying to get from over 300 down to under 200. I think water will do the trick, but I worry it will put out the fire. I already have the airflow restricted--again, I'd be afraid of closing it off too much and killing the coals. What tricks are available to drop the temperature to a range I can start maintaining.
Simple answer:  fewer briquettes.  Space them out a bit.  You can make fine adjustments by raising the cooking surface or lowering the briquettes.  I know my kettle has a lower briquette grill, if you take out the main one.  I've also seen briquette grills with sunken channels to create small pockets of heat.  I also have a couple of trapezoidal briquette holders, which I can use to position briquettes and create warmer or cooler spots.

Charcoal briquettes are designed to be a consistent temperature.  Of course, poorer quality briquettes will be less consistent or burn for less time, but in general any single briquette will burn as long and as hot as any other.

Trying to douse or smother the briquettes may cause smoke or steam, but it's not going to have a good, consistent effect.

Interesting comparison info from Dutch Oven cooking:  with a standard 12" Dutch Oven, 12 briquettes in a ring under the oven and 12 spaced around the edge of the lid will give you approximately a 350 degree oven for about an hour.  Temperature is adjusted by adding or removing briquettes.  This means, in a grill, 24 briquettes could give you a grill temp near 350, if the food is about 2-3 inches away.  (The linked chart has a slightly different arrangement; 12/12 is what I learned as a simple rule of thumb, but everyone has different practices...  or may desire top browning or bottom boiling.)