I am a tugboat captain we were proceeding south 30 miles off jacksonville florida it was 21:47. (9:47 pm) when my engineer asked me what was a light was which was approaching from our port stern at about the same heading as us 174â°magnetic when we first noticed it it was about 250 to 300 yards away not moving much faster than us which was 9.3 tks i should point out it was submerged but glowing a greenish yellow light at first i said it was the moon's reflection but the engineer pointed out that the moon's reflection was a little off our starboard bow we continued too observe this light as it slowly approached as it got directly abeam of our vessel i noticed that my radars started spoking and showing a screen like we were in a heavy rain storm but the sky was clear and no wind too speak of as this light continued too pass us it was only about 100 to 125 feet off our port side at this point we could make out a round structure between 30 to 40 ft. round and maybe 40 to 50 ft under water it continued to move south for about 3 to 5 min. then turned west and cross our bow at a range of approximately a 100 yards as it got about 30â° to 40â° off our starboard bow it came up and out of the water and became airborne it accelerated to a very high speed and was out of sight in a matter of seconds.