Pulled alongside my boat. I was afraid I was going to hit it. Stayed about 20 feet and hovered just off surface.

I was on watch while sailing our boat north for the summer, watching 2 lights off in distance. This thing appeared out of nowhere 10 to 20 feet off my starboard bow. I was afraid I was going to hit it. It was a cube shape. Bottom 3 or 4 inches was florescent blue, which did not reflect in the water, as a light might. Rest was too dark to see except white light on top. Approx. 3 feet square. It was not in the water. Did not bob with waves. Did not continue on like something I would have just passed. It made no sound. I looked at it for several seconds as it stayed right beside me. I then reached across the cockpit for binoculars. When I turned to it again, it had pulled off about 60 feet and kept on same trajectory as boat. Then, white light on top began to grow brighter and brighter. It created a white cone about 3 feet into the air above. It remained for about 10 seconds and slowly and smoothly made its way SE. Watched it go. Was soon out of sight. Was not scary or threatening. I am a retired NGO director and have lived on a boat for the past 20 years. I am 76, in good health and not bonkers. I do not drink or do drugs and was well rested.