I’m not saying it can’t work, I’m just disagreeing that water can’t act as a good insulator.
Water is a good conductor and a bad insulator. The reason a swimming pool at 20 Celsius feels a hell of a lot colder than air at 20 Celsius is because the water conducts heat out of your body faster.
When you stand an FV in a trub of icy water, several things are going on. The water and ice conduct well so chill the FV quickly. The high thermal mass means they are slow to warm up to ambient temperature. But the lack of insulation means they will warm up to ambient over a day or two unless you keep changing the ice bottles. The reason this setup doesn’t work well is the lack of insulation.
Exactly why the tub of water is effective at sinking excess heat from the fermenter. Look, not trying to be argumentative - if there’s one theme on this forum, it’s that there are multiple ways to make good beer. While more labor intensive than the zip up jacket, I’m just saying that this is a viable option for somebody on a budget (like I was when I started).
I would say try both, then see what you think. Maybe next time your fridge is full and you want to chill an FV.
I’ve crash cooled to 39F in a sleeping bag in order to fine with polyclar. It didn’t get quite cold enough to remove chill haze though. For that a fridge is better.
May do that. My fermentation fridge gets crowded for space sometimes, with beers in the pipeline.