underwater navigation

[TSandM]

Beautiful post, as usual, from Diver0001 . . . For me, the single most important thing is to go all the way to the anchor, and note depth and the characteristics of the spot where it has lodged. Getting off the anchor line on the way down has been a pretty good recipe for not finding it on the way back

That said, one of our most challenging sites is an artificial reef on a nearly flat bottom. Every piece of rebar looks like the next, and there is no depth contour to follow at all. Even using a compass is not very helpful, because the structures of interest are spaced sufficiently far apart that it's impossible to follow a straight line. Visibility is typically 10 to 20 feet, too, so you have to get very close to the anchor line to find it.

I have found the answer to that site, though, but it costs about $4000 . . .

 

[Hatul]

Most of my diving is shore diving, but my system of compass navigation is to take a bearing to shore and then leave the compass alone. Whenever I travel I look at my compass and I form a mental map of the site and where I'm am in my mental map. If you recognize landmarks it's a big help, otherwise you're navigating by dead reckoning.

On the way back I do the safety stop and continue until I'm at around 10 feet deep. Now I correct for dead reckoning. I surface and take another bearing to where I want to exit and if I veered far then I descend and swim opposite to the exit point. Again I surface and swim on back to exit.

Ada.

 

[knotical]

Everybody goes in the water including the captain.

This bothers me more than any navigation issues. What happens if the boat slips anchor, or ... ?

 

[USVet96]

This bothers me more than any navigation issues. What happens if the boat slips anchor, or ... ?

LOL. I was thinking the SAME thing haha.

 

[RTee]

First of all...30 ft ain't bad at all. Secondly, in addition to all the points brought up so far I think one element is how you approach the dive. Sure you can apply the rules of third...go one third one direction (and timings in no current location), then one third to return and then attempt to relocate the line before coming up. However, when diving unfamiliar, reduced visibility and featureless dive spots I will rather attempt to dive a + pattern...ie go for a short while in one direction, return to the line then explore another direction, return and repeat the process. That way you are never too far from your reference line.

If diving in such conditions and in doubt...follow the mooring line to the bottom then run a line from your finger spool.

Last Feb in the Bahamas, I did 20 dives on unfamiliar sites where the vis was generally good but not always especially in the shallow. What I did was start from the anchor or mooring at the bottom and then swam clover leaf patterns after noting depth, features, and taking a compass heading before venturing in one direction...even if I had great features I could follow both ways.

I even recalled one very experienced diver who ran his spool from the anchor to a nearby coral bed in 20 ft of water or so (horizontal vis was at best 20 ft and the coral bed may have been 25 - 30 ft away). He basically left his spool just beside an easily recognizable feature and retrieved it on his way back.

Compass...will usually work very well except in close proximity to steel structures in which case you need to rely on the other cues or tools you have at your disposal.

 

[MXGratefulDiver]

Beautiful post, as usual, from Diver0001 . . . For me, the single most important thing is to go all the way to the anchor, and note depth and the characteristics of the spot where it has lodged. Getting off the anchor line on the way down has been a pretty good recipe for not finding it on the way back

That said, one of our most challenging sites is an artificial reef on a nearly flat bottom. Every piece of rebar looks like the next, and there is no depth contour to follow at all. Even using a compass is not very helpful, because the structures of interest are spaced sufficiently far apart that it's impossible to follow a straight line. Visibility is typically 10 to 20 feet, too, so you have to get very close to the anchor line to find it.

I have found the answer to that site, though, but it costs about $4000 . . .

Not to mention that compasses are generally not useful around much of the structure due to the metal content. Fortunately, it's not a particularly deep site ... but I've never found a way to reliably navigate my way around that place ...

... Bob (Grateful Diver)

 

[ClumsyCuttlefish]

To Knotical
"This bothers me more than any navigation issues. What happens if the boat slips anchor, or ... ?"
I agree completely, but I have no other choice. Unfortuunately we live in the area where there is only ONE dive shop (whose boat we use). This is also the reason why I didn't take the navigation class - the closest one is 500 km away.

Thanks to everybody for yuor advice. I am eager to try next time!

 

[Bob DBF]

Beautiful post, as usual, from Diver0001 . . . For me, the single most important thing is to go all the way to the anchor, and note depth and the characteristics of the spot where it has lodged. Getting off the anchor line on the way down has been a pretty good recipe for not finding it on the way back

I was actually paying attention to my navigation, for a change, and had not found the anchor where I knew I left it. I started looking around, kicking myself in the butt, and deciding how much more air to waste before a peek when the boats recall sounded. I hoped no one had screwed the pooch as I surfaced to find the boat had dragged the anchor and was a good 100 yards from it's former position. The good news was getting a Zodiac ride back to the boat.

Bob
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Even a blind pig gets an acorn once in a while.