A lighthouse that floats, it serves the same function such as:
The Overfalls main aid to navigation was a 375 mm dual electric lantern located 57 feet above the water line. Rated at 15,000 candle power, (approximately 1,000 watts), it flashed every 3 seconds from dusk until dawn. On a clear night it could be seen for 12 miles. The ship also had a dual diaphone fog horn with a range of 5 miles that sounded every 30 seconds in foggy weather.
A radio beacon with a range of 25 miles transmitted the call letters of the ship (NMJF) in Morse code. In foggy weather it was synchronized with the horn and broadcast every 30 seconds.