To my knowledge there is only one boat that goes from just a short way from Hosteria Grey to Refugio Grey(and back). It leaves the Hosteria in the early morning every day in the high season and then departs Refugio Grey at around 10 a.m. getting passengers to the Hosteria at around 2 p.m.
It is a tour boat but the tour portion of the trip really starts after Refugio Grey when it goes alonside the glacier and they serve up some Pisco Sour along with some fresh picked Glacial Ice at around 10:30 a.m. which is a lot better than the poor excuse for the coffee that they serve. The boat also delivers supplies to the refugio and its campsite store. I'm not aware if they do any touring on the leg from the Hosteria to the Refugio.
Some passengers take the boat both ways as a tour. Others just take it from one place to the other. For the portion from the Refugio to the Hosteria, I booked my space at the Refugio. I had to wait one day for a space to be available. I know that doesn't completely answer your question.