I was on the wheel of a 38' cabin cruiser with two friends on a cruise down Boston Harbor at about 2100 hrs. The harbor reflected the light of the city's buildings and visibility was very clear. We were close to, but past, Logan airport. I happened to look up in the sky and was really surprised to see a large object I would estimate at approximately 60-80 feet in circumference with a band of large square light panels undulating around its perimeter. Their circulation was in a wave like motion. I watched it as I also scanned the water for any impediments in it. I tried to figure out what the object was. I determined it was unlikely to be advertising as there was no message. The colors in the squares were yellow, red, blue, green. I wondered whether it was something being held aloft by a helicopter as the object was not fast moving (about 20 miles per hour)but their was no noise associated with the object. I commented to my guests, "Look at that, I will bet that is in the paper tomorrow." They looked at the object without comment because they could not figure out what it was. I had recently soloed as a pilot. I had attended the 82nd Airborne Division Intelligence course. I spent 13 consecutive nights in combat watching the night sky in Korea. I had never seen anything the like of what I saw those many years later. I was well trained to report exactly what I had seen nothing more, nothing less.