Navigation

[Carribeandiver]

The only navigation course I have had was the course included in the AOW course. I can read a compass and swim to a point and back with no problems -- when there is no current causing drift.
My question is, how does one ascertain drift? Swimming wth current pushing you sideways causing a deviation that cannot be corrected on the return because the return finds the current pushing you farther off the line.
Since it seems impossible (to me) to determine how far off the current is pushing me, how do I know how much correction is necessary to get back to my starting point?

 

[skdvr]

As far as I know there is nothing you can do about current except to intentionally aim to the right or left of where your intended target it and then once you get out to the distance you are supposed to swim then you can turn and head directly to your target. Of course you would have to know the distance you are supposed to travel and have a good count on your kick cycles or your time. That is the only way that I know of...

Phil

 

[TSandM]

Well, if you're in midwater, I don't think there's any way to know how much drift there is. But if you're swimming over the bottom, you can add some natural navigation to your compass work. If you take a compass heading and look ahead of you, you can pick an object that's on your line and swim to it, and then take another heading and repeat the process. That will minimize drift. You can do something similar with contour lines, depending again on the topography of the bottom.

If the bottom is even and featureless, you're out of luck. Then you have to hope that you don't need to be precise in your return course.

 

[MSilvia]

To add to what Lynn said, if you can pick an object and swim to it, you can set a "best guess" course correction and see if following it (rather than swimming at the object) brings you to the object. Making corrections as necessary, you can figure out the heading that seems to take you back past the objects you noted on the way out.

 

[Carribeandiver]

Thanks skdvr, Lynn and MSilvia.

 

[jscott099]

For something interesting, try this web site.
http://www.sailingusa.info/current_deviation.htm

Its for sailboats and calculating the course deviation a current causes. I plugged in a 2 knot current hitting a typical diver at 90 degrees who was swimming .5 knot speed. A really fast diver might make 1 to 1.5 knots. It that scenario the calculator showed it blew me off course an amazing 76 degrees. Its got all the math on the web page. You could then take that and apply it to the distance of the swim just to see how far off you would be. All this assumes you know the current speed and your speed of course.

 

[Charlie99]

If you are swimming back to a boat or exit point in midwater (for either decompression or gas conservation reasons), then one tactic is to purposefully overcompensate by aiming well upcurrent. It's a lot easier to drift down onto a boat or exit point than to swim upcurrent.

It's kind of like the old orienteering trick of purposefully deviating one way or another so that when you hit a river/road/railroad you aren't wondering whether you should turn left or right to get back to your target.


Theoretically you can also make a guess at what heading you need to swim in midwater, by doing a few point to point jumps while still on the bottom and noting how much of an angle you need to crab. In practice, this doesn't help all that much because it's common for midwater currents to be much stronger (and sometimes even different direction) than the bottom currents --- but it's just one more tidbit of info to consider.

Charlie

 

[MauiScubaSteve]

The bottom line underwater is; unless in a static body of water, without seeing the bottom you are not really navigating, compass or not.

 

[1_T_Submariner]

We need a small inertial navagation device!!! It would not show your true heading. In fact I think it would work in caves etc... Price ummm that might ba a problem.

http://www.inertialscience.com/dmars_r.htm

Any Ideas on adapting this to underwater?

 

[tomcat114]

How about this little wrinkel to the mix.

Up here in Minnesota and Wisconsin quarry diving with Iron ore all over. I have thought about taking the nav class. I would guess that makes for alot of headaces.