I keep reading that lighthouses help sailors 1) be aware of dangers like rocks and reefs, and 2) navigate in the dark. I understand that lighthouses beam a series of flashes that a sailor can see from far away, but I’m not quite sure how seeing a series of flashes in the dark from a single point-source can accomplish point 1 and point 2.
In: 8
It’s an immediate warning to sailors that there is land nearby, so they should start minding their depth and location. Ideally, the sailors have maps/charts for the areas they are sailing in, so they can identify which lighthouse it is based on surrounding terrain (or rough estimate) and use that, along with their maps/charts, to find where the hazards are nearby.
So the lighthouse isn’t to tell the sailors anything except their location, with the sailors responsible to figure out the rest.
lighthouse = shore = reefs, rocks and low water.
it’s like a amber flashing light in traffic. it tells you that there could be danger but not what it is.
The flash pattern (and colour) identify which lighthouse it is. The ship has a map that shows where lighthouses physically are. The ship also has a compass so it knows what direction it’s pointed and what bearing the lighthouse is. With all that information, you can put a line on the chart through the lighthouse and your ship must be on that line.
If you know how fast the ship is moving (which you should) and you can measure how fast the lighthouse’s bearing is changing, you now also know (approximately) how far you are from the lighthouse. The closer you are, the faster the lighthouse’s bearing will change.
Combine all that, and you know where you are. And, crucially, you know where the lighthouse is, which is a place you don’t want to be because the lighthouse is built on top of something that you should not snuggle your ship up to.
With the aid of a map and compass, knowing where the lighthouse is helps pinpoint a location. It is simply a fixed reference point.
It doesn’t make it possible to navigate in the dark but with a precise location, it is much simpler to avoid known dangers like shallow waters or reefs (which are marked on maritime maps)
Well the first point is simple. You build the light house ON the dangerous rocks or reef (or right next to it. That way ships know to stay far away from the lighthouse to avoid getting shipwrecked.
And as for navigating in the dark, the majority of the time the ships captain and crew already knew the path they were planning on taken, and chances are had taken that path before. So the lighthouse just acted as a check point. You would keep track of where you thought you were on the map, and then when you were supposed to be passing a lighthouse check if you could see the lighthouse.
If you could see the lighthouse you knew you were on course, if you couldn’t see the lighthouse that meant soemthing was up, maybe the wind is blowing you off course, maybe you’re not moving as fast as you thought, etc etc.
The gap between each flash identifies which lighthouse it is, knowing what the lighthouse is tells the sailors where they need to sail and how much space to give the danger.
The lighthouse itself is always built on the shore (or atop a reef), so the first rule is that a sailor never wants to get too close, or else they will risk running aground and either getting stuck, or sinking.
The lighthouse itself will sometimes be painted with a unique pattern of stripes or colors, so that in the daytime sailors can identify the lighthouse and then determine their location relative to the lighthouse with a compass. (There is a chart or some kind of book which lists lighthouse markings IIRC)
At night time, a series of glass lenses rotates around the light which causes it to “flash” when viewed from a distance. The speed that these lenses rotate will change the number of times per minute that the light appears to flash. So for example, one flash every 10 seconds = lighthouse #1, one flash every 5 seconds = lighthouse #2 or whatever. There will be a code written on marine charts (aka maps) which tells a sailor which flash pattern corresponds to which lighthouse.
Additionally, other marine navigation lights and marker bouys have coloured lights on them which can indicate hazards. These will flash with a pattern of green, red, yellow or white lights and can be decoded by using the marine chart.
I would also add that when you’re sailing at night with no moon/obscured moon, you’re basically surrounded by blackness everywhere. You are really driving blind. In pre-gps days, this means that you don’t have your exact location, and you can’t see what’s ahead. Maybe you’ve got a light on your ship that will illuminate a short distance ahead of you, but big ships can take a really long time to stop. In the open sea, this isn’t a big problem because there isn’t much to crash into, but those coastlines can come out of nowhere if you’re not careful. So people decided that the easiest way to solve this problem was to put a goddang big light on the shoreline.
Lighthouses essentially mean “stay away from me” to sailors so they don’t run aground in bad weather/low visibility. That’s pretty much it.
Latest Answers