The vessel was operated in a westerly direction and towing a two person inflatable tube behind the vessel. The vessel was operating approximately 11-20 MPH. West of red nun #4, the tow line of the inflatable became slack. Once the tow line became taught it caused the attitude of the vessel to slow down and pull backward into the following sea (with 1 foot chop). The operator made a turn to port which caused the port rear quarter of the vessel to fill with water (vessel had low freeboard). Once the stern of the vessel was swamped, the vessel capsized.  At this point both occupant were thrown from the vessel.  Vessel occupants were not wearing life jackets
Greenwich                     