Use of a vest has nothing to do with proper coat, it has to do with keeping you dog comfortable in a harsh conditions, doesn't really have to do with water temp either. More like a wet dog is more comfortable sitting around in freezing temps. with wind-chill etc. for hours on end, with a vest keeping their body heat trapped to their body. A wet dog, even a dog with the best longest thickest coat whatever; will get cold if he has to sit unmoving for hours on end in freezing temps. Now if I had my dog out retrieving birds, and then moving around generating heat, she probably would die of heat stroke in a vest. But most duck dogs just sit after a cold weather retrieve, waiting for the next. They don't move around and generate heat, and they start to lose core temp. lose too much core temp. and you get hypothermia. It's not the coat, water or retrieving, it's the Sitting that will Kill Yah.