Question Search & Recovery vs Underwater Navigation

[Orso Raggiante]

I have always marveled at divers who basically show up at a dive centre, pick up their cylinders, and go off to dive at a particular site. I wouldn't know how to get to, say, a wreck, if I had dived that site just that morning! So I was thinking of doing either a Search & Recovery specialty or an Underwater Navigator specialty to help me locate myself and the things I want to see underwater. Does anyone have any recommendations as to how I can achieve this, or perhaps tell me the difference between the two courses mentioned? Both seem to teach some amount of measuring distance, knowing directions, and remembering features. Thanks in advance!

 

[BoltSnap]

Depends on where you are and what you are doing.

Where you are: magnetic declination varies greatly depending on your location. Variation in Seattle, Washington USA is +15.21 degrees, Key West, Florida USA is -1.88, Antigua is -14.99, Malta is +3.8

Depending on your location and visibility, not knowing about magnetic variation may not matter much. In locations with high magnetic variance and less than ideal visibility a 15 degree variance that is not accounted for could cause you to miss your mark (unless you and the person giving directions were both not accounting for variance.

What you are doing: Let's say you are on the surface and want to mark the spot below you for future reference. You shoot a number of back azimuths to trisect your position for later use with a map. In this case, you will need to account for declination when referencing the map to your azimuths. If you intend to share this data with someone in the future you will need to indicate whether or not magnetic variance was accounted for so that everyone has the same point of reference.

How much is this going to matter to a person swimming with fins, not much. It depends on the distance mainly. If you are using a boat to get to a site for a long distance, then it matters but not for short distance a diver using his fins to swim to a location.

 

[BoltSnap]

For what we are discussing it does not really matter at all. If an instructor does not know what it is nor how to find it then he is not much of a navigator IMO.

Captain, I am a little confused with your statement, on one hand you say it doesn't matter but then you say that the instructor is "not much of a navigator" if he doesn't know. As I have said above, it doesn't matter for the shorter distance we swim with fins to get to a location since the distance isn't enough to make a difference. I do a lot of surface swimming with fins (up to 1.2Km) and it doesn't matter at all. If I were to be on a boat, it may make a difference.

 

[Capt Jim Wyatt]

Captain, I am a little confused with your statement

If a purported "Navigation Instructor" does not know about magnetic variation he is not much of a navigator.

 

[KeelsonGraham]

I would have thought that, if you’re trying anything complicated such as fixing position, then deviation would be much more of a problem - with all that ironmongery in close proximity.

 

[clownfishsydney]

I think there are two type of people, those who have an innate sense of direction and those who do not. In my experience, those who have a sense of direction can navigate in the bush or in cities without trouble and are also good at navigating underwater. Those who have no sense of direction are hopeless at both.

Some people can never be taught navigation above or below the water.

 

[Capt Jim Wyatt]

I think there are two type of people, those who have an innate sense of direction and those who do not.

I tend to agree with that.

 

[inquis]

Can’t see the relevance of knowing the variation at a dive site, provided it remains constant

Maps and bearings derived from such are typically based on True North. Following a true bearing with a magnetic compass is a source of error. Whether it matters or not depends on the distance, vis, size of target, etc. It's easy to eliminate that error, so why wouldn't you?

 

[tursiops]

Maps and bearings derived from such are typically based on True North. Following a true bearing with a magnetic compass is a source of error. Whether it matters or not depends on the distance, vis, size of target, etc. It's easy to eliminate that error, so why wouldn't you?

The two most common uses of a compass I've encountered are:
(1) taking a bearing, and then following it
(2) using a map of the dive site with bearings on it to various objects

The first does not require one to know or use declination.
The second usually uses magnetic bearings, because that is how it was constructed, but you don't know for sure unless it is stated on the dive-site map, or perhaps YOU made the map.

A variant on both is what compass was used to take the bearing. If it was your own, OK, If it was someone else's, be careful; their compass might be from Finland or somewhere and "corrected" for its declination.

A final problem is deviation, an error introduced by nearby metal objects. I saw this once when someone took a bearing, set their lubber line to it, and then rested their compass on their big old 4xC-cell flashlight to see during a night dive. Whoops. The batteries in the light forced massive deviation.....no matter which direction they swam, their compass showed they were going North.

 

[Altamira]

While mag declination may need to be considered, if significant, for underwater navigation, I find current speed and direction more difficult to calculate and compensate for in less than good visibility. I have also given up on counting fin stokes because I find it too easy to lose track of the count if distractions pop up (not an unusual occurrence). So I use my watch for timing, but find myself guesstimating my underwater speed and drift if the visibility is not good. Navigating in jets at high speed and low altitude was easier!

 

[tursiops]

While mag declination may need to be considered, if significant, for underwater navigation, I find current speed and direction more difficult to calculate and compensate for in less than good visibility. I have also given up on counting fin stokes because I find it too easy to lose track of the count if distractions pop up (not an unusual occurrence). So I use my watch for timing, but find myself guesstimating my underwater speed and drift if the visibility is not good. Navigating in jets at high speed and low altitude was easier!

I always taught tricks to assess and adjust for currents as part of my Nav courses. There is not enough time to do that i n the single Nav dive for AOW, but there is time during the full specialty.