A very large, silent craft floating above the ocean water in the early morning hours for 5 to 10 minutes.

One morning while getting ready for school in Fajardo, Puerto Rico, around 7 a.m. on a totally clear day back in 1980 or 1981 I went out on our balcony with my little sister to get our school uniforms out of the dryer which was on the balcony.  
I looked at the horizon and saw a ship or saucer level with the ocean and thought it was a new cruise ship or even possibly a military vehicle because of how big it was, this craft was very big.  The object proceeded to move upward and at that point I knew it wasn't a cruise ship because I could see the ocean and the sky seperated underneath the ship.  
The craft then proceeded to move upward  and move slowly in a triangular shape in the same area.  It was more diamond shaped and had an off white or cream color with 2 rows of green lights. 
At that point I turned to my mothers room which I could see into from the balcony and told my mom to wake up and come look at this thing floating above the water.  By the time my mom got up and looked it was gone. 
If I had to make a comparison as far as size I'd say as big as a cruiseship.  I went to school and told my classmates about what I saw and they all laughed at me so I stopped talking about it.
Witness indicates that the date of the sighting is approximate.  PD