 To show how a ship is brought into a harbor at night, we will start by assuming that at 2010 the Savannah has fixed her position here at latitude 37 degrees 36 minutes north, Longitude 74 degrees 47 minutes west. Her course is 230 degrees true and she is making a speed of 20 knots. As the visibility of lights is computed for clear nights, we will also assume that the visibility is unlimited. Observe that the course has laid down heads directly for this temporary flashing buoy which has replaced the Chesapeake light ship. Continuing to study the chart, observe that these primary sea coast lights may be sighted. Hog Island light, 14 miles. Cape Charles light, 20 miles. Cape Henry light, 19 miles. These distances of visibility are for heights of eye of 15 feet. On the bridge of the Savannah, the height of eye is 55 feet. So the navigator must determine their visibility from that height. To do this, he must combine the visibility from the light and the visibility from the ship. The total is the maximum distance at which the observer can see the light from an elevation of 55 feet. From the light list, the navigator finds Hog Island light to be 180 feet high. Cape Charles is also 180 feet in height. The height of Cape Henry is listed as 157 feet. Referring to table 8, Bowditch, he finds the visibility for 180 feet in height to be 15.4 miles. And for 157 feet in height to be 14.4 miles. Also from this table, he finds the distance of visibility for 55 feet. The height of eye of the Savannah's bridge to be 8.5 miles. While the visibility for a light 180 feet high is 15.4 miles. Note that in the light list, the Hog Island light is only cataloged visible for 14 miles because its candle power is only 1000. Therefore it must be realized that irrespective of height of eye, the intensity of the light even on a normally clear night cannot be depended on to be seen more than 14 miles. Cape Charles light is extremely powerful, 740,000 candle power, and Cape Henry light fairly powerful, 160,000 candle power. The navigator draws in the circle of visibility for Cape Charles and Cape Henry that he has computed, as well as the 14 mile circle for Hog Island light. However, he also draws in a circle about Hog Island light with a radius of 23.9 miles, which would be the maximum visibility of the light from the bridge were it sufficiently powerful. Based on the above work, the navigator determines and advises the captain that Hog Island light probably will not be sighted, but might be any time after 21.30, bearing 283 degrees. That Cape Charles light will be sighted at 22.18, bearing 263 degrees, and that Cape Henry light will be sighted at 22.37, bearing 248 degrees. Concerning these lights and for inclusion by the captain in his night order book, the navigator gives the captain a memo like this. The navigator had been previously advised that the captain would write the night order book only to the time of sighting Cape Henry light. Otherwise, all boys and navigational lights which might be visible after identifying Cape Henry light would be listed in the foregoing memo. A stopwatch is used for timing the sequence of periods of illumination and darkness which make up the characteristics of a light. If they do not check with those expected, the prudent navigator slows, stops his engines, or anchors until the situation has cleared. The savanna proceeds down the coast. At 21.39, Hog Island light has not yet been sighted, so the navigator sends a lookout aloft to a height of 90 feet in an attempt to see Cape Charles light. At that height, the lookout can see Cape Charles light 26.3 miles away or 2.4 miles further away than if on the bridge. The navigator plots this new circle of visibility on the chart. At 21.47, the lookout reports the loom of a flashing light. It bears zero to two degrees relative. Adding a relative bearing to a true course gives a true bearing. Thus, the true bearing of the light seen is 2.52 degrees. The description of the flashes given over the telephone to the navigator, who times them with a stopwatch, definitely identifies the light as Cape Charles light. An estimated position cannot be determined in as much as the distance of a loom of light is most questionable. At 21.49, the officer of the deck, searching with his binoculars, sites a short flashing light bearing 308 degrees. The OOD has hog island light in mind. However, its period seems to be erratic and not three seconds on every 30 seconds. At 21.53, the light becomes steady, indicating the mast head light of some vessel which has just come over the horizon and into the visibility circle of the Savannah's bridge. At 21.54, the loom of Cape Charles light is seen by a lookout on the bridge of the Savannah, bearing 254. At 22.01, the aloft lookout reports seeing the light of Cape Charles. It bears zero to six degrees relative, or 256 degrees true. This permits the determination of an estimated position because the distance of the light when it is on the horizon can be accurately computed. At 22.07, the bridge lookout reports a short flashing light on the starboard beam. When timed, this proves to be hog island light, and at 22.10, it bears 312 degrees. At 22.10, Cape Charles light became visible on the bridge, bearing 259 degrees. Note that hog island light was sighted by a persevering lookout using binoculars, and at a distance of 17.8 miles, nearly four miles outside its expected radius of visibility. The ship's position now being definitely fixed. The captain decides to proceed on the same course until Cape Henry light is sighted. At 22.24, hog island light bears 328 degrees, and Cape Charles light 266 degrees. At 22.26, hog island light is no longer visible. The short-time hog island light was visible, allowed both obtaining a fix and determination of course and speed made good. These three facts are invaluable when approaching restricted waters. At 22.32, the aloft lookout sighted Cape Henry light, bearing 012 degrees relative, or 242 degrees true. At 22.39, Cape Henry light was sighted from the bridge, bearing 244 degrees, at which time Cape Charles light bore 276 degrees, and the fix is plotted. The navigator shifts to this larger scale entrance charts with soundings in feet. Course was changed to 227 degrees, and the ship proceeded by taking cross bearings of Cape Charles light, Cape Henry light, and boys when they were in sight. As the ship proceeded, it was noted that an actual course of 228 degrees was being made good. Bearings on Cape Charles and Cape Henry fixed the ship's position here at 23.24. The captain decides to change course and head for Chesapeake Bay entrance. At 23.28, with Cape Charles light bearing 343 degrees, and Cape Henry light bearing 275 degrees, course is changed to 283 degrees, and speed reduced to 15 knots. The navigator picks off the course through the channel 288 degrees. He wants to change course when in this position, at which time Cape Henry light will be on the port beam. On the bridge, he watches Cape Henry light, while the quartermaster watches it through the allodade, until it is on the bearing, sir. The ship changes course to 288. At 0005, he obtains these bearings, as before he plots them, and this is his fix. Note that in this fix, all bearings are abaff the beam. It is good practice when possible to have some of the bearings forward of the beam, so the navigator decides to shift to thimble-show light. It has these characteristics, on one second, off one second, and should bear 290 at 0010. Looking in that direction, he sees this flashing light. Again, the stopwatch comes into use, where there are many flashing lights in this vicinity, and he wants to be sure that he is taking bearings on the correct one. A good navigator always checks the characteristics of any light with the data in the light list. The quartermaster takes a round of bearings and records these data. So the savanna continues up the channel to Hampton Roads, picking up new lights ahead and dropping the astern ones, until she anchors in her assigned berth. The same method of anchoring will be used as before, except that at night, the navigator will not be able to use the tank for bearings, and he will therefore probably use this aero beacon in its place. In piloting, it is assumed that the navigator will have his compass accurately calibrated and the various instruments which he uses in precise adjustment. If he frequently fixes the position of his ship, and carefully plans his courses to the anchorage, he should have no great difficulty piloting his ship through inland and offshore waters. But the navigator in pilot waters must be continuously alert and always looking ahead. Only in this way can he ensure the safety of his ship.