Underwater navigation

[DevonDiver]

What is the trick to determining distance underwater?

Where possible, I use depth. Make a note of the depth at your start point, upon return swim until you hit that depth. It works well in any area where there is a constant slope (i.e. shore diving and some off-shore sites).

Otherwise, utilise natural navigation; marine life, bottom composition.. even noise. Conduct a brief awareness survey before you start off - know what the surroundings look like, if there are any noises nearby, what the bottom type is etc etc

Other than that, you have to rely on one of the common distance measuring techniques; kick-cycles, time etc. If water movement (current, surge etc) will be likely to disrupt your distance approximations, you need to make necessary adjustments. This comes with practice.

In really bad vis, on a flat bottom, with no differing natural signs, you can run a guideline

 

[MXGratefulDiver]

I'm not a big fan of kick cycles ... they tend to take your mind off what you're doing, or else you lose track. I prefer (and teach) a method I call "mental mapping". Think of it like in those old movies where someone would be driving and the camera would pan back until all you'd see is a dotted line being drawn on a map as the driver progressed.

You're doing a shore dive ... so start out by establishing a reference line ... "out" and "in". Set your compass bezel along that line. You mentioned a buoy ... if that's your starting point, think of the buoy as an "X" on the reference line. You begin building your map there.

You drop down the buoy line to begin your dive. Before you go anywhere, check your depth. Remember, diving is a three-dimensional activity ... depth is the third dimension, and an important piece of information if you intend to return to the buoy at the end of the dive.

As you begin your dive, look at your direction in relation to "out" on your reference line ... and mentally draw a line starting at the "X" that marks the buoy. Point your compass toward "out" and mentally draw a line at the angle between "out" and your current heading. The length of the line is determined by the time you travel in that direction.

Each time you change directions, add another line to your map, abutting it to the end of the previous line.

When you are ready to return to the buoy, the "map" will be an indicator which side of your reference line you are on. In most cases ... particularly on shore dives ... returning to the buoy is a simple matter of swimming upslope to your starting depth and either turning left or right ... depending on which side of the reference line you are on ... and swimming at that depth until you reach the buoy.

This method doesn't rely on keeping track of kick cycles ... it relies on keeping track of depth, bottom time, and direction of travel ... things you would be wanting to look at anyway. With a bit of practice you can learn to adjust for currents (you'll go faster with the current and slower against it) as well as using topographical features that will provide visual clues to where you are. But those are more advanced applications of the technique. Initially, just try building a simple "map" in your head of where you're going relative to your starting point (the buoy) and the "out/in" reference line. You'll be surprised how easy it is to figure out where you are that way ...

... Bob (Grateful Diver)

 

[Nwcid]

Bob that sounds like a great way. For a beginner maybe even get a slate and actually draw the map or make notes while you move. I like it.

 

[MXGratefulDiver]

A slate would be very helpful for learning this method ...

... Bob (Grateful Diver)

 

[FinnMom]

My diving club usually sets up a navigation course in a large, relatively shallow quarry. We have plastic jugs on the surface with rope going straight down from the jug with a good, solid weight on the bottom. No extra rope because you want the jug directly over the weight and you also don't want an entanglement risk.
About 3' off the bottom is a plastic sign threaded through the rope that tells you the compass heading to the next jug in thick, large numbers (remains visible even after 8 mos underwater).

You take compass heading on to the 1st jug before going under, then try to navigate the whole course of 3-5 jugs w/o having to surface. Since you're only in 5-6m of water you can surface w/o much trouble/time/risk. As often as necessary you can surface and take a heading to the nearest jug.

It's an excellent way to make an overly familiar dive site more entertaining.

 

[Malpaso]

Using those stupid compasses on the consoles is a surefire way to get lost though.

Could you expound on this please?

 

[Juardis]

Curious to know, how often is underwater navigation used on boat dives and under what scenarios would you need to use it? My only diving experience to date has been in a quarry and on boat dives where the boat comes and picks you up wherever you surface. I've been practicing some using the compass on my D6i, but it's been more to figure out how to use the compass vs. using it effectively. I figure at some point in my diving career I'm going to need to use it, or at least wished I knew how to use it.

 

[Hatul]

Gauging distances is a problem underwater especially on a deeper dive where you don't want to surface just to get your bearing. I wish someone would invent a GPS device that you could shoot up on a line to get your bearing.

 

[DevonDiver]

..how often is underwater navigation used on boat dives and under what scenarios would you need to use it? My only diving experience to date has been in a quarry and on boat dives where the boat comes and picks you up wherever you surface.

What do you do when underwater... hover in the same spot? If not... you're using some navigational techniques

 

[Akimbo]

Curious to know, how often is underwater navigation used on boat dives and under what scenarios would you need to use it? ...

There are several options. No navigation means the boat will either pick you, which is a really nice option, or you have a long and boring swim back on the surface after running out of air.

I suppose the most common is to head down the anchor line unless you can see the bottom. You are usually briefed where to find the best spots and which direction to head. If not, you might as well swim up current and turn around about halfway into your planned air supply. Since your path has likely been determined more by what you saw than your compass needle, a reciprocal course is usually approaching useless. That is why a lot of divers will surface for a compass heading back to the boat.

Naturally the swim back is probably also full of interesting stuff that isn’t in the direct line of your heading, there are currents, and you will only glance at the needle occasionally. Unless you are really lucky or visibility is like 200', there’s a good chance you will get closer but not run into the anchor. You can poke you head up and take another bearing or surface swim back. Repeat as air supply allows.

Great visibility allows choosing way points along your compass path, taking another bearing to choose the next waypoint, and repeat. This gets pretty boring with 15-30' of vis.