I'll never forget the first time I saw a barge being towed at sea on a really, really long tow cable. From a distance the two vessels seemed a quarter mile apart, and I was tempted to sail my course and pass between them. But something didn't feel quite right, so I checked with the binocs and sure enough, there was a taut steel cable between them maybe 10 feet above the surface. I was practically shaking as I changed course, remembering how in my coastal village some years ago, a fishing boat at night got snagged by a towline like that and was rolled over, trapping and killing the fishermen. Imagine if you were out there at night yourself in your boat and saw two lighted boats in the distance: could you tell by the configuration of lights what they were? Someone at my local yacht club tangled with a fishing boat offshore one night, the unseen outrigger of which dismasted the sailboat. There are a whole bunch of ways to get into trouble at night if you don't correctly interpret the lights of other vessels. If you don't already have on board a resource for quickly looking up light configurations, this app may be what you need.