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Walle · 01-11-11, 01:37 PM

Well, it's really just a combination of different basic navigation techniques.

There's several different ways to know the position of OwnShip for example.

You could either get a "fix" by means of taking bearings to different navigational aids (lighthouses e.t.c.) or landmarks (church towers, tall buildings, special cliffs, e.t.c.). Taking two bearings and drawing them as lines, you would be near where the lines intersect. Taking a third bearing increases the precision.

Another way is to use celestial objects. Then you would have to take inclination readings to at least two objects in different directions. This technique involves a lot of math, since you also need to calculate the inclinations for the date and time you take the reading. The absolutely simplest and crudest form of navigating "by the stars" is having a stick that you hold out against north. As long as the ends of the stick is at the horizon and the north star, you are on the same latitude. If the star is below the end of the stick (when the other end is at the horizon), you need to go north, if it's too high, you need to go south. This is like the grandgrandfather of the sextant

Then when you have a fix, you would use dead reckoning. I.e. you keep track of the time you go in a certain direction, and at what speed. Then you can draw a line on the chart for the direction, and make markings for distance traveled. When you turn, you make a new line, and so forth.

You need to know your own position to be able to determine the (absolute) position of another ship. The relative position can always be found of course.

To get the position for another ship using the sonar, you would start off by getting his direction by taking three bearings from the sonar at constant interval. Edit: You need to be stationary. (well, actually you don't, but then it get's yet a little bit more advanced.) This will give you the targets course, but not speed nor position. Then you would extrapolate, i.e. add another interval and draw a fourth bearing line. This line is where the target ship will be on at a specific time. But before that, you move your ship, so when it passes the fourth line you take yet another bearing reading from the sonar and draw a line. The target ship will be where that line intersect the "extrapolated" line. Once you know where it is, you also know where it's been (the other three lines) and where, so calculating the speed won't be much of an issue there. I won't get any deeper in this technique, since there's already great tutorials on the forums(fora) covering that.

Using active sonar, you'd just take target ships bearing and distance, no fuzz.
With scope same thing, bearing and distance (using stadimeter). Or time how long it takes the ship to pass the line in the scope, if you know the length of the ship. But it's still the same principle, distance over time.

And then of course, you need to do it twice to get two different positions. Then just calculate the speed as distance divided by time.

01-11-11, 01:37 PM	#7
Walle Watch Join Date: Aug 2009 Posts: 26 Downloads: 7 Uploads: 0	Well, it's really just a combination of different basic navigation techniques. There's several different ways to know the position of OwnShip for example. You could either get a "fix" by means of taking bearings to different navigational aids (lighthouses e.t.c.) or landmarks (church towers, tall buildings, special cliffs, e.t.c.). Taking two bearings and drawing them as lines, you would be near where the lines intersect. Taking a third bearing increases the precision. Another way is to use celestial objects. Then you would have to take inclination readings to at least two objects in different directions. This technique involves a lot of math, since you also need to calculate the inclinations for the date and time you take the reading. The absolutely simplest and crudest form of navigating "by the stars" is having a stick that you hold out against north. As long as the ends of the stick is at the horizon and the north star, you are on the same latitude. If the star is below the end of the stick (when the other end is at the horizon), you need to go north, if it's too high, you need to go south. This is like the grandgrandfather of the sextant Then when you have a fix, you would use dead reckoning. I.e. you keep track of the time you go in a certain direction, and at what speed. Then you can draw a line on the chart for the direction, and make markings for distance traveled. When you turn, you make a new line, and so forth. You need to know your own position to be able to determine the (absolute) position of another ship. The relative position can always be found of course. To get the position for another ship using the sonar, you would start off by getting his direction by taking three bearings from the sonar at constant interval. Edit: You need to be stationary. (well, actually you don't, but then it get's yet a little bit more advanced.) This will give you the targets course, but not speed nor position. Then you would extrapolate, i.e. add another interval and draw a fourth bearing line. This line is where the target ship will be on at a specific time. But before that, you move your ship, so when it passes the fourth line you take yet another bearing reading from the sonar and draw a line. The target ship will be where that line intersect the "extrapolated" line. Once you know where it is, you also know where it's been (the other three lines) and where, so calculating the speed won't be much of an issue there. I won't get any deeper in this technique, since there's already great tutorials on the forums(fora) covering that. Using active sonar, you'd just take target ships bearing and distance, no fuzz. With scope same thing, bearing and distance (using stadimeter). Or time how long it takes the ship to pass the line in the scope, if you know the length of the ship. But it's still the same principle, distance over time. And then of course, you need to do it twice to get two different positions. Then just calculate the speed as distance divided by time. Last edited by Walle; 01-11-11 at 02:22 PM.