Nighthawk

Nighthawks were often made of sheet metal. They surrounded the jackstaff and were suspended on a halyard so they could be raised or lowered to suit each pilot's whimsy. According to Frederick Way, Jr. it was set at the pilots line of sight with the horizon or just above it. A light that showed above the nighthawk was on shore, a house, a government light, or whatever. If a light was seen below, it would be on a raft or rowboat.
I made a nighthawk for the Natchez but it was never installed. Too bad!

Michael, Alan's explanation is good, but allow me to take this possibly a step further: if you are looking out of a pilothouse, you can usually see the shore line, even on the darkest of nights. The nighthawk is put where each pilot wants it (raised or lowered vertically on the jackstaff). Thus, where the nighthawk, on the jackstaff, appears to intersect the bank or other obstruction in line with the pilot's vision, the pilot knows about how far he is from the object....sort of a range-finder. This tells the pilot he is, say, an "easy distance" from something, or he may use it to tell when he has to start making a turn to keep from hitting the bank. On unimproved and/or unmarked rivers, the best water is usually deep in the bight of a bend, and the nighthawk tells him basically that he is as deep in the bend as he can get without hitting the bank -- that is, NOW is the time to start your turn. If you are an artist, or have taken art lessons, you were taught basically the same thing by holding up your pencil or brush at arm's length to get your proper scale and measuring one or more pencil lengths, half a pencil length, etc.

Towboats use(d) the same thing in the form of a peep light, a dim blue light mounted somewhere on the jackstaff on the head of the tow. When that light appears to intersect the object ahead (in the pilot's line-of-sight), it tells him how far he is from that object. Peep lights are still used today for much the same purpose especially on narrow, shallow waterways and on the Intracoastal Canal. We now have very powerful searchlights that can also be used to look at the banks, but using the old method keeps one from having to use the light, or from having to use it so much. Radar has more or less rendered the use of the "nighthawk" concept on larger rivers obsolete.

Thanks, Alan and Bob. I appreciate your explanations. It's long been a mystery to me; now I understand.