Everybody loves lighthouses. They are picturesque buildings, beloved of artists and photographers. You can see them in fancy calendars, and seaside towns that boast one usually have it all fixed up for their tourist trail. When the authorities shut down a lighthouse, or replace it with an automated light on a tower, the locals usually try and raise the money to buy the building and maintain the structure. Trying to tear one down usually means the whole community will turn out to save it. There's all that history and romance, the light flashing its reassuring beacon to mariners, and it's usually taken care of by a salty old dude living in the attached quarters. Day or night, fair weather or foul, the light always is there, blinking faithfully, guiding the sailor safely to his destination. The old lighthouse keeper is making sure the lamp is topped off with oil, the clockwork mechanism that rotates the baffles is wound up, and the rest of the building is maintained Bristol fashion: vital tasks for a man alone.
Its a beautiful concept, but its fading fast. The lights are expensive to operate and maintain, and in today's age of shrinking budgets and fool proof electronics, even the fully automated lights are winking out one by one. Many have already been retired, and only the most famous and vital ones can be expected to be around much longer. It's only a matter of time before they will be no more: obsolete. The building will be converted to some new use, demolished altogether; or left to decay, covered by graffiti and defaced by vandals; locked up so the kids won't get hurt climbing the rusty old wrought iron spiral staircase. The magnificent Fresnel lenses, like giant jewels, will be hauled away to the local museum, blinded forever.
So how do lighthouses work, anyway? I don't mean their mechanical operation, I am speaking of their role in navigation. How do they guide ships through the night? Most folks just think they mark the entrance to harbors, or warn seamen away from shoals, reefs and other hazards. This is all true, of course, but lighthouses also worked together, in groups, as part of a constellation of navigational aids.
It was common for lighthouses to be built at regular intervals along dangerous coasts, spaced so that a ship sailing offshore parallel to the coast would always have at least one visible at any time, and preferably two or even three. Each light would be identified by a distinctive pattern of flashes of its beacon, a signal imposed on the beam by a rotating set of baffles and mirrors driven by clockwork. The pattern was marked on the chart (flashing, 3 seconds or occulting, 5 seconds) along with the light's carefully surveyed position. The navigator would always know exactly which light he was looking at and precisely where it was located. If more than one light was visible simultaneously, bearings could be taken to triangulate an exact position, telling the mariner how far offshore he was, and enabling him to determine his course, speed and leeway. In lonely stretches of coastline where only one light could be seen, running fixes and bow-and-beam bearings allowed the sailor to dead reckon himself down the coast to the next light. The next one down the line would verify his estimated position and allow him to update his track. I still remember the sequence in my old waters--Anclote, Egmont, all the way down to Sanibel...
Also marked on the chart was the height above sea level of the beacon, (example, 21 ft.) so the skipper could calculate roughly how far offshore he was: too close and he might go aground, too far and he might not see the next light. Along the Florida Keys, the salvagers used to knock out the lighthouses and build fires on the beach carefully placed to fool ships sailing up Hawke Channel at night. When they ran aground on the coral, the pirates would row out in small boats to the exact places where they knew the wrecks were, murder their crews and plunder their cargoes. There's an old story of one pirate who was a preacher and had built his church so he could look right out from the pulpit through the open doors to where the reef was. When a ship hit it, he would alert his crew in the congregation with a specific line of Scripture which they knew was the signal. One by one they would secretly slip out and get his boat ready so when the service was over he would have a head start over his competitors to get to the wreck. Eventually, the US Navy had to clean out the pirate nest and build a base there to protect the lights.
Its a fine feeling when, on a nasty night, that next lighthouse pops up over the horizon, right on time and right where you expected to see it, confirming your position. Its an experience that will soon be lost in these days of GPS.