Underwater Navigation

[DepthJunkie]

Is there a simple,on the fly formula to calculate pt. to pt. navigation.
Ex. Point A (dock) to B (known heading), A to C (known heading), B to C (?).
Any help would be greatly appreciated.

 

[String]

Pythagoras and geometry. Yes there is.

 

[Charlie99]

You also need to know the distances between the points.

Considering the inaccuracies in underwater navigation, rather than formula, I just use a simple mental map to figure things out.

Or just sketch it out on a sheet of paper. The result will be accurate enough for underwater navigation, particularly considering that our estimates of distances usually have large errors.

 

[The Kraken]

Not without knowing either the distance or the time between the first two points.

The heading from B to C is predicated not only on the azimuths of the AB and AC, but also on the lengths of each line segment.

As String said, Pythagoras and geometry.

You can also employ a "Nav-Finder" card.

 

[RonFrank]

UW Navigation with just a compass is an inexact effort at best. If you are going from A to B, as long as one stays the course, it is generally manageable. If you are trying to go from A to B to C, one generally needs visual references, or depth references in low vis.

One can count kick cycles to attempt to judge distance. The bottom line is that unless someone knows the area, it's difficult to do this accurately especially in low vis.

I navigate in low vis, and depth references, and site topography is the only way I ever manage to get things right if I'm doing anything beyond a straight line. With huge vis, things become a LOT easier, assuming again one knows the area.

 

[diver 85]

wait till we get GPS, will be a breeze then........

 

[Sinbad the Diver]

and don't forget to calculate magnetic declination if you are taking your start and end points off a map or based on gps points.

Here is a Wiki description of it if you don't know...over a long distance it can get you pretty out of sorts.

Magnetic declination - Wikipedia, the free encyclopedia

 

[b1gcountry]

I can think of two things you can do:

If you know the bearing to two objects from a common point, you can swim back to the common point after going out to either using your reciprocal headings.

If you have a pretty good guess at the bearing between your two Points (B and C) , and if you know the depth Point C is in, then you can swim to either side of Point C, and then follow the depth contours back to Point C...
So if a boat and a car are sunk off a dock, the car is in about 45', and the bearing from the boat to the car is between 25-40*, swim at 50*from the boat and turn left once you hit 45'.

This obviously doesn't work well on flat or undulating bottoms.

 

[String]

Magnetic variation shouldnt be an issue over the tiny distances typically covered underwater on a dive.

 

[MXGratefulDiver]

It's an inexact science (e.g. "naviguessing") due to the variables involved ... current being a major factor because it provides a moving point of reference with respect to both your starting and ending points. In other words, you have to account for the effect that current will have on your body as you travel across the bottom.

I teach a method I refer to as "mental mapping" which, as pointed out by Charlie99, means that you build a mental picture in your head as you execute your dive. To do this you need the following pieces of information ...

- an imaginary "starting line" depicting headings for "out" and "in"
- an X on that line depicting your starting location (e.g. a buoy or anchor line)
- the depth you start your dive from

To navigate your way around, you draw "vectors" representing your heading relative to the starting line. I don't use kick cycles, as they're not a practical way to dive in the real world. I use my bottom timer to approximate the length of the vector ... and compass headings to represent the direction ... and build a "map" of the dive as I proceed from point to point. When it's time to return to the buoy line I know two things ... which side of the "starting line" I am on at the moment, and the depth I want to be at when I conclude the dive. And I also have a fair idea where I am at relative to that starting location. So depending on the terrain I can do one of two things to return to the line ...

- if there's a reasonably consistent slope, I'll simply swim to the starting depth and either turn left or right, depending on which side of my "starting line" I happen to be on.

- if there's an inconsistent or relatively flat bottom topography, I'll swim in a vector that best represents the return based on the mental "map" I have been building as I do my dive.

This sounds more complicated in writing than it really is in practice. I teach it in my AOW class by having my students follow a series of flags ... each marked with a heading to the next flag. The final flag simply says "Home", and at that point they need to make their way back to the buoy line. Most times they get it on the first try. The key is to build that "map" as you go and keep track of which side of your starting line you're on at any given time.

... Bob (Grateful Diver)