underwater navigation

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ClumsyCuttlefish

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Location
Canada, QC
# of dives
25 - 49
Since my OW and AOW certification I dived with groups that were led by a guide (dive master). Recently I’ve started diving from a charter boat with my husband who is my buddy. There are no “group diving” there. Everybody goes in the water including the captain. And … here is the problem …everybody is able to find the way back to the boat, except us two. It does not mean that we swim in an opposite direction. Usually we surface somewhere near by (apx 30 ft) but still can’t manage to find the line. I reviewed the underwater navigation section of my AOW class, but diving with the compass seems won’t be working here. There is no reef or wall. There are boulders of different sizes and you can never swim in a straight line. Plus the visibility is not good so you can’t see far away. I observed the other divers, and they don’t use any paraphernalia to navigate. What is the secret?
 
When you take your compass reading, look for three landmarks along that line. Swim up to the first one, then looking over the next two, find another one. Continue this process until it's time to turn around, repeat until you return to where you started.

Also, make a very careful note of the exact depth of that anchor.

Lastly, PRACTICE! Lots.
 
Or have one of you use your compass to stay in a straight line while the other looks for the line.
 
I recommend turning back and making mental notes of what you see every now and then. What you see going out is NOT what you'll see on the return. If you're getting within 30 feet of the line or the boat, pat yourself on the back for a job well done.....unless you're diving with 100 ft of visibility. In the conditions you're describing, even more of an accomplishment. Here in So Cal, if I'm within a boat length, I'm happy as is any dive buddy I've been with. My original mentor a few years ago was like Magellan underwater. Every once in a while, he'd surface 30 YARDS from the boat. Can't win 'em all. :cool2:
 
If you are in a spot with not too many rocks or obstructions and not too bad visibility (10-15 feet?) you can use "point to point". You set the lubber line, etc. and find an object and go to it (or go to the left or right of that object). Then find something else that lines up with the way you want to go. But conditions must be pretty much as i described.
 
Plus the visibility is not good so you can’t see far away. I observed the other divers, and they don’t use any paraphernalia to navigate. What is the secret? (bold added)

Ah.... but they DO. You're just not seeing it.

Navigation becomes a lot easier once you start using *all* of the cues available to you. The navigation section of your AOW course is, unfortunately, a very poor introduction into what you really need in order to navigate confidently.

So what cues can be used?

1) time (tempo and air-supply/planning)
2) depth
3) compass direction
4) familiar objects and/or cues on the bottom
5) current / tide
6) light and shadow
7) sometimes sounds like anchor chains.
8) I'm sure some people have other cues they use too...

I'll deal with all of these topics briefly. If you have any questions, ask them.

1) Time, tempo and air-planning: This is your biggest tool for navigation much of the time. Simply put, in many cases if you swim for (say) 20 min in one direction and then turn around and swim at about the same tempo for 20 min in the other direction then you should be about where you started. This assumes that there are no heavy currents and that you have enough cues to know that you're swimming in a reciprocal course. I would say in most cases where you see divers navigate accurately but without any "paraphernalia" then what you're missing is that they picked their "turn around" point to correspond to a certain time or air-pressure.

2) Depth: The bottom is very seldom completely flat. If it is, then you need a compass. However, almost everywhere you dive there will be some depth change as you go even if it's only a metre or two. Even that amount of depth change is enough that you can pick a certain depth and swim along that (virtual) "depth line" from point A to point B. In your case, for example, you could descend from the boat to the bottom and record/remember the depth at the anchor. Then start swimming in the "out" direction. At some point you turn around (time/air cue) and ascend to your "depth line" as you swim back so you're at the depth where the anchor should be at about the time (or shortly before) that you expect to see it. I would say that probably 90% of "natural" navigation in practice is done by watching "time" and "depth". Oddly, that's not stressed the book.

3) Compass: For straight forward dives you only ever really need a compass if the bottom is completely flat or visibility is so horrendous that you can't see the slope of the bottom. Having said that, even if conditions are good you should always have a compass with you so you can answer questions like "which way am I swimming", "did I really turn all the way around" or "which way is the shore". However, in terms of navigation, the compass is generally a much less useful instrument than "time" or "depth". Also, when using a compass in a team, it works best when one diver generally controls "direction" and the other diver controls "tempo" and "depth". Assign or "delegate" tasks for best results.

4) Bottom cues: This can be anything that doesn't move. A few of them are mentioned in your AOW book but generally I would look for something really obvious like a foreign object (ie discarded junk, a net etc.). Also "surface" cues can be handy too if your viz is good. Perhaps you can see the boat or an anchored bouy. Alternatively, you can create your own cues by disturbing the bottom (if appropriate). In any event, the more you dive at a given site, the more likely you are to find things you can use for cues.

5) Current and tide: These will give you clear indicators of direction and can be either a help or a hindrance to navigation depending on strength and direction. My advice if you're unsure about navigating a site is to eliminate this effect by diving a slack tide until you "get your bearings"

6) If viz is good you can use light and shadow to determine direction. Sometimes, for example, you can see the position of the sun from your dive depth which can tell you which way you're going if you're not sure and/or don't have a compass.

7) Sounds: We're trained that sounds are a poor navigation aid because you can't determine direction from them. However, some sounds can be very helpful. A rattling anchor chain is one of those. If your boat uses an anchor you may be able to hear it from a distance. You may not be sure of direction, but if you listen carefully, you WILL be able to hear "volume" (ie how loud it is). This can sometimes help you decide "if you're there yet", or even "if you have gone too far".

8) Like I said, I'm sure that other people have cues taht they use that I haven't mentioned. Also, just to recap, the most reliable and accurate tools you have for navigation are "time" and "depth" provided your dive site isn't completely flat and you are able to swim "out" and "back" with about the same tempo. One last point to make is that awareness of your surroundings is very important to accurate navigation and it may require you (often does) to "slow down" and spend more time consciously observing your surroundings. A bit of advanced planning and having some kind of a mental map of your dive site doens't hurt either.... :)

Hope that helps.

R..
 
I have found the most important to me is the depth of the anchor or tie off. You can be very close but just up or down a few feet and miss it.
But 30 ft is pretty good in my opinion.

Cheers
Michael
:coffee:
 
Ah ... Rob posted pretty much what I would have. Depth is an important factor underwater ... you're now working in three dimensions rather than the two that we're used to ... so use that information to your advantage.

Before you descend, use your compass to establish a "reference line" ... if you know how the bottom slopes, sighting along "out" (downslope) is usually the best reference. Think of this as your starting line. Once you descend, note how deep the anchor is. Then go about your dive. What you use your compass for at this point is determining which side of your "starting line" you're on at any given point in the dive. Are you swimming to the left of it or the right of it? And how far? When you're ready to come back to the boat, swim to the depth that you noted the anchor is at, and then turn either left or right to follow that depth line until you see the anchor.

This method works very well in areas that are relatively evenly sloped. In flat areas, you can still use it, but then you must rely more on the compass.

Natural methods as described above ... when you get to the anchor, look around and make a mental note of whatever you see. Note where it is located relative to the anchor. When you return, if you see those objects, you will have a better idea that you are close to the anchor ... even if you cannot yet see it.

... Bob (Grateful Diver)
 
Since I can get lost in a one-chair barber shop I usually dive with shops which provide a DM at no extra cost. Two things you can do. One is to follow or keep in sight the Captain. The other is to notice a diver with some characteristic which stands out, like pink flippers or something , and keep him/her nearby, hoping that this particular person isn't lost also. Otherwise you could take a navigation course.
 
In addition to the excellent posts from a couple of people above, I can add only a little, but it should be useful:

1. Us the your compass properly- hold it level, use the bezel to set a course, etc.
2. Believe the compass. Most people who "can't do it" can do it if they just believe what the compass is telling them
3. Practice with your compass- practice all the time- on land, under the sea. Practice makes perfect. Start with out and back, then right angles, then triangles then irregular patters.
4. Compass navigation is vectors- that is, direction AND distance for each leg. So meaure not only direction, but distance. Distance can be measured in kick cycles or time, and frankly that is where the practice comes in. Distance is tougher to pinpoint than direction. The compass will be spot on on direction, but you have to do the distance factor yourself.
I am a navigation/compass nut- I think everyone at the advance open water diver level and above should have and know how to use a compass, and I am very glad you are getting into that area of competence now.
DivemasterDennis
 

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