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Friday, 19 December 2014

Finding your Path- Underwater Navigation in Scuba Diving

So, last week we started a blog series with regards to underwater navigation. Essentially, the concern is that we are training Scuba Divers to go Scuba Diving with a similarly qualified diver but, with the very limited Navigational Skills training on the initial training course, can we really say we have given them the tools they need to dive without a guide!

Now we will start to look at Navigation techniques that divers (of all level) can employ to find their way around a dive site, starting with the most common tool... Underwater Compass!

Underwater Compass

An Underwater Compass is usually liquid filled and the important elements you need to know about include; the Bezel, the Lubber Line, and the Card, which has graduated degree markings and the North Arrow.

Although it appears that the card moves, it doesn't. This is why the North Marking will always point North. The Compass housing actually moves around the card.

How do we Set a Heading

We like the Suunto SK-7 model, as it is very easy to use, so the instructions below are for this model. It is an indirect reading compass, which means it has degree graduation markings arranged clockwise on the Bezel, with 0 degrees (North) coinciding with the Index Marks. The card itself will show 180 at the top of the North needle... hence indirect!!

To use the compass, a diver simply turns the Bezel so that the direction heading we want to take sits at the top of the Lubber Line (which shows our direction of travel). You would then turn yourself with the compass so the magnetic needle sits between the index marks again and the Lubber Line remains aligned with the centre of your body.

So, if you want to take a 30 degree heading, turn the Bezel so 30 sits at the top of the Lubber Line (furthest away from you). Then turn yourself and the compass together until the North needle on the card sits between the index marks.

If that all sounds too complicated to you, you are probably over thinking it. The biggest problem I find with students learning to use a compass is that using it is simpler than they think. So, even though we spend ages practising on land before getting in, add water and they think they must be doing it wrong because it is too simple!

For a reciprocal heading, turn the bezel 180 degrees to head back the way you came.

To Navigate a square, the bezel turns 90 degrees (add or subtract depending on whether you want to turn left or right) while for triangles make 120 degree changes.

Things are even easier now with the advent of digital compasses that many modern computers
include. The newest of which is the new Shearwater Petrel 2.

It doesn't get much easier than this!

Some tips for using a compass for navigation on your dives
  • Trust your compass. It is more likely that you are wrong than it is
  • Hold the compass level 
  • Be prepared to navigate around obstacles and account for currents etc
  • Don't forget other essential skills such as buoyancy and air consumption. It's very easy to get transfixed by the compass to the detriment of all else.
  • Practice with it so you are confident

A very handy tool to use but not the be-all and end-all of navigation, especially in clearer waters. Still, it is essential all divers know how to use a compass to find their route.