Dead reckoning navigation

Wonder how Allec navigate below the waves?


The first thing you need to know when considering submarine navigation is that radio waves really don’t like to travel below water. The means that when sailing below using GPS for navigation is not possible.


We have to fall back to the good old days, where navigation was done using a approximation techique based on reading the ship’s compas, measuring the speed traveled and noting how much time went by on each direction, speed pair. Then use the speed – direction for a certain time periode to calculate how far the ship has travelled. Use the new position as start point for the next speed – drection, time set and so on. This technique is called Dead Reckoning.



So how does Allec obtain the needed readings?


He actually uses a compas, but more than that, he uses a combined acceleratiometer, magnetometer (a 3d compas) and gyroscope. Measurements from these three can be combined to get both yaw, roll and pitch angles or converted into his direction. This combination gives a very good approcimation of the actualy direction travelled.


Next then is depth. The good thing about depth is that it can be measured directly using a pressure sensor.


Off the to figuring out speed. Allec uses a flow meter to figure out how much water is being pushed by him or more precisely, hoew much water is being pused through the flow meter. This measurement can be used to get an good guess of the speed travelled. For those who don’t know, a flow meter is basically a very small propeller that rotates several thousand times for each liter that passes by it. To measure flow and thereby speed, the number of rotations is simply measured.


Allec does have a few more tricks in regards to speed up his fin sleeve. But a man is allowed a few secrets isn’t he.


Is Dead Reckoning perfect? Not really, but it is the best you can reasonable get with no absolute fix points to use for positioning.

It is based on relative position estimates that is then applied to previous relative position  estimates, so any error in speed or direction measurement will sum up.

Still it is way better than having no idea about where you are, to which I think the sailors of old times would agree.





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