joshuatree
Captain
See the four towers on the sides of the channel coming in? They are navigation lights - the ones on the port side going in are red and on the right side green. With respect to the two towers, get a straight edge and see that the line up with the middle of the channel. So for a ship coming in, if he can only seen one tower light, then he is coming down the middle of the channel. Note that they piled rocks in front of the channel lights - they don't want ships knocking them over.
Thanks for the clarification, now it totally makes sense, almost like runway lights to line up to for a ship entering the channel.