navigation back to the boat

[MXGratefulDiver]

And sometimes things just don't work out! Case in point -- several of us, all pretty experienced divers (I probably had the least experience at 800+ dives) dropped off the boat to a dive site that was new to most of us. What we knew was that there was no significant current, there were rock piles scattered here and there and there was other rip-rap that had been dumped.

We went down the anchor line and found the anchor on a featureless (silty) bottom with the nearest thing maybe 20 feet away.

My buddy and I take a compass reading and head off.

We wandered around heading north, south, east and west and realized the depth never changed more than about 4 feet! By the time we decide we needed to get back to the boat, I had absolutely no idea where the anchor was -- and it turned out neither did my buddy! We headed towards where we thought was right, shot an SMB and did our ascent.

As it turned out we weren't that far from the boat but far enough that other divers, who had scooters, picked us up and towed us back.

Moral of the story? Always take a scooter?

I think I remember that dive ... Hat Island?

I teach navigation in sometimes challenging visibility conditions. The method I use is something I call "mental mapping". Think about building a "map" in your head of where you're going relative to your starting position. Or if you choose to, you can always just draw it on a slate.

You start with a reference line. For most diving, consider the line to run along an "out and in" direction ... with "in" being toward a shore. For boat diving in areas where shore isn't visible, establish a "north-south" reference line. Your anchor is an "X" on that line that designates your starting point.

When you initially descend down the line, immediately take note of your depth. If you're not good at remembering numbers, write it down on a slate. In fact, for initially learning this process, a slate can be very useful. Also look around and take note of any natural features that you would recognize on your return ... because compass navigation is not a precision measurement, and being off by only a couple of degrees can put you well away from the ending point when you return. Look in all directions and pick out two or three things that you'd recognize if you should see them again.

As you proceed on your dive, use the direction and time of travel to "draw" connecting vectors. Travel time will denote the length of the vector and compass heading relative to your reference line will determine its direction. Remember that you're only using travel time ... when you stop to look at something, you end one vector and begin another one when you leave that spot. Connect the dots.

When it's time to return to the anchor line, you should have a pretty good idea which side of your reference line you're on. In most cases, getting back will be a simple matter of swimming to the depth of the anchor and then turning left or right to follow that depth until you run into the anchor.

But as we all know, bottom topography isn't always even ... and so having an idea of where you are at relative to the anchor often means just "guesstimating" the proper heading and then keeping an eye out for those recognizeable features you noted when you first descended.

The key, really, is paying attention to starting depth and what's around the anchor line that you'd recognize, and then paying attention to which way you go when you leave that spot. And like all your other skills, it gets easier with practice.

... Bob (Grateful Diver)

 

[Bubbletrubble]

I use a mental mapping method similar to what NWGratefulDiver describes. Most of the dives I do from a boat are out-and-back profiles. I pay attention to the direction in which I'm heading and the depth at which landmarks are located. Occasionally, I'll look back to familiarize myself with the "return perspective." When I reach turn pressure, I simply retrace my steps from landmark to landmark. Sometimes I'll return by a slightly different route but, depending on vis conditions, I may still reference the same landmarks. By the end of the dive, I could easily write down a fairly accurate depth profile and rudimentary map of the area from memory. I use the same method whenever I'm driving a car in an unfamiliar city/town. Some people naturally do this, but I think the skill can be learned with a little practice.

I got used to making a mental map when I played competitive golf in high school. After the round was over, I'd "replay" the round in my mind to make sure that the number of strokes recorded on the scorecard was correct.

 

[Teamcasa]

Underwater navigation requires practice. Successful navigation includes both compass work and pilotage. First off, using a compass while holding onto or very near the anchor chain/anchor is not a good idea.
Here's what I generally do:
Move away from the anchor line and swim a circle around the line at 15' or so away from it.
After I decide on a direction, I note all of the surrounding features including the boat shadow (where possible) and sun position relative to the anchor.
I determine the depth and slope relative to shore and current direction.
And only then do I take a heading and mentally note the reciprocal heading.

Inevitably we get off course. So, relying on the reciprocal gives me general direction back but it's all the other information that gets me back on the line.

 

[Krazytomdiver]

As a dive guide, There are several ways to navigate underwater and most takes a lot of experience,training and a sixth sense. It becomes more challenging depending on type of dive,what happens during the dive, and weather/current conditions. Also night diving is a whole different senario. Repeatition of course is the best technical strength but proper use of your compass,landmarks,level thinking,and reference string/markers. I normally use a right angle travel direction from the mooring sight to the wall,affix a bright reference string at a set depth,decend down the wall,right or left depending on the current/profile,appoximate half tank,acsend to my set depth,reverse direction,locate the reference string,then go 90 degrees from that point. This has always been a good safe dive profile which incudes a multi-level dive with a variety of underwater enjoyment. Night diving is a lot simplier; I affix a glow stick at 15'/3m on the mooring line, pair up my divers,instruct them to do a spiral outward diving around the mooring until the glow stick is barely visible then reverse spiral inward back. In either situation (if lost) the guide can always group his divers at a safe depth/location,acsend to the top & get a compass reading to the boat,desend,rejoin the group,then receive a good 'ribbing' back on the boat during surface interval. Shore diving to me is just common sense;get a compass reading from shore, note landmarks on surface before you desend and reverse direction & resurface. These are just a few ways of navigaeting that have worked for me the past ten years.

"living life without a hard bottom"
KT

 

[TSandM]

I think I remember that dive ... Hat Island?

I teach navigation in sometimes challenging visibility conditions. The method I use is something I call "mental mapping". Think about building a "map" in your head of where you're going relative to your starting position. Or if you choose to, you can always just draw it on a slate. . . The key, really, is paying attention to starting depth and what's around the anchor line that you'd recognize, and then paying attention to which way you go when you leave that spot. And like all your other skills, it gets easier with practice.

Lovely essay, Bob . . . but as I recall, you guys were as lost as Kirk and I were on that Gedney Reef dive!

It really is very interesting to read all these answers, because what you use for navigation can be so different, depending on where you dive. In blue water, or on well-defined reefs like we dove in the Red Sea, there are so many clues to use that are unavailable in 10 feet of viz on a silty plain. It's good to have a big back of tricks, because sometimes running a star pattern with a reel is the only way to stay remotely organized.

 

[MXGratefulDiver]

Lovely essay, Bob . . . but as I recall, you guys were as lost as Kirk and I were on that Gedney Reef dive!

You recall correctly ... I was Peter's dive buddy. That place is a navigational nightmare ... depths don't change, there are many similar looking "reefs" in close proximity to each other, and vis is often roughly a body length ... as it was that day. Oh ... and compasses don't work so well around all that metal.

At times and in places like that about the best you can do is enjoy your dive, ascend when you're ready, and be prepared for the possibility of a longish surface swim back to the boat ...

... Bob (Grateful Diver)

 

[rddvet]

I like this thread. I've been diving for many years, but only a couple times a year, and everywhere I dove typically was set up with a DM giving you a tour. As of late, I am diving very often, and trying to hone my skills. The boat I dive from now has a DM, but you're typically out on your own, and the DM is just a safety measure. Most spots my navigation is pretty good. But there is one place that sucks. It's just a featureless, flat sand bottom with hundreds of "fish pyramids"(metal structures put out by local gov't to make a reef) stretching over acres. They all look the same, and there really isn't a way to navigate by landmarks. The thing I hate is that I use out and back or square patterns with my compass, but I often still feel lost. I haven't gotten lost as of yet, but I often start to doubt my compass. Someone wrote, don't doubt your compass. That's good advice, because in those situations eventhough I doubt the compass, it hasn't wronged me yet.
Really the best part of this thread is the sense that I'm not an idiot, and everybody else has some of the same feelings too. I've doubted my skills a couple of times, just cause I was thinking that after all these years I should have ym navigation down perfect. I'm also a private pilot, but I can tell you for sure, navigation underwater is way trickier. I think sometimes it's simply a matter of getting too excited to see everything and moving too fast. I've had to teach myself to slow down

 

[James O' Mahony]

Depending on where you are diving (ie reefs etc ) in Ireland where viz at depth may be a problem its very common place and highly recommended (if not insisted on) to carry a tie off line of 70m or so which clips (not ties) onto the base of the shot line, simply spool out and reel in ! guaranteed to get to percisely back and you are free to concentrate on the sourounding life and go in any direction you wish. Mind you we also carry SMB's for those "just in case moments" of line breakage etc. Never experienced a problem even if multiple lines are clipped off at the same time. Peace of mind is great diving.

 

[WetBoy101]

It might seem obvious, or maybe I'm reading it into everyone's posts, but the one tip that goes with all of the advise above is to look at your compass as much as you are looking around. You want to make sure you make corrections before you get too far off. Start with out and back dives, then as you feel more confident you and your compass can get you back to your start point you can add a little variety to the dive. Do a square, a teardrop or a triangle, but start small, then increase the size when you always hit your mark, etc...

Happy Diving, Rick

 

[Akimbo]

There is a lot of good underwater navigation advice here, but nobody has mentioned the nearly continual dedication to the compass required to give you any chance of getting back to the anchor line. Lots of work and not much fun.

In the real world or recreational diving/exploring, you hit the bottom, perhaps with the intension of keeping an up-current heading, and soon get side-tracked following what interests you. Let’s see, nothing but sand at my 047° up-current heading and pinnacle to the left… hmm, screw the compass. After a few minutes of playing with a sea lion I am lucky to know which way up is, let alone the heading to the boat.

It is not often that I can see the boat from the bottom. I often surface to take a return heading at about half empty, but that rarely gets me back due to other distractions. The heading I take at around 500 PSI usually gets me right to the ladder due to the imposed discipline. There is a lot less distraction when the return swim is at 20' compared to on the bottom.