Early on a Saturday morning, Polly Conway picks up coffee and drives to Crown Beach in Alameda. She sets up a tent in the sand and waits under gloomy skies until the rest of the group shows up, and the monthly meeting of the East Bay Dipping Society is underway. Dipping is as simple as getting in the water for a few minutes, sometimes with chatting involved, and always followed by coffee and snacks. Conway started open water swimming during…