Compass Navigation

[awap]

Originally Posted by Kimusubi

Yeah I've been reading compass dude's website. A lot of interesting stuff. I haven't gotten a chance to read the whole thing, but I get a hang of it of how it works. I'm definitely going to start practicing it on land before we go to California, and I'll eventually take the class for underwater navigation. The only problem with taking it now is the time constraint.

Let me get this straight though:

If I start at point A, and I go directly in a straight line to point B for lets say 10 kick cycles, then I go 70 degrees North North-West for 10 kick cycles to point C, and then I take a direct 90 degree south to point C for another 10 kick cycles. Now to get back, I would do ten kick cycles to 20 degrees North-North East, then take another 10 kick cycles at 70 degrees South-South East, and finally take ten kick cycles directly south.

I used no compass for this, simply because I just wanted to get a feel for how it worked. In retrospect, my directions don't really make sense, but if anyone can clear it up for me, I'd really appreciate it.

Here is a LOVELY paint image of how I went through with it. Excuse my poor paint skills and my absolutely terrible scaling.

You need to work out the azimuths from the turn angles. I never have been very good a counting kick cycles. I prefer working with transit times and my slow. steady constant swim pace.

So, it looks like your x-axis is the east-west axis. So you intend to travel at 0 degrees from A to B. Then you plan to turn to a heading of 340 degrees to point C. Then you plan to turn to 250 degrees and swim to point D. So the back azimuths are 70 degrees from D to C; 160 degrees from C to B; and 180 degrees from B to A. If the points A, B, C, & D are readily recognizable features, it should not be too difficult as long as you don't have to compensate for currents.

[cummings66]

I did google the scuba sextant because I couldn't fathom how a sextant which works by reference to celestial bodies could work under water and it turns out it's really a Nav-finder by Padi. Now what I find interesting about it is it makes life easy for the diver because you have a form of sorts to record your dive directions on.

To use it simply requires you know your kick cycle distance and pay constant attention to your heading. Pretty slick and I appreciate the posting talking about a scuba sextant because I would have never considered a way to do it with a tool.

I've done it the hard way by making notes on a slate, pretty common but I like the automated way, well, sort of automated. Thanks for the posting, I learned something new today and now I'm happy.

[navyhmc]

One other thing. While doing a compass course: Look Around! Don't keep your eyes glues to the compass. Unless you're in 1' vis muck, you'll miss stuff and if you notice things ahead of you and to the sides of you if you get off course, you have other things to follow other than the complass. Always have a back-up plan.

[sea princess]

Originally Posted by navyhmc

One other thing. While doing a compass course: Look Around! Don't keep your eyes glues to the compass. Unless you're in 1' vis muck, you'll miss stuff and if you notice things ahead of you and to the sides of you if you get off course, you have other things to follow other than the complass. Always have a back-up plan.

This is great advice..I am in the middle of doing my navagation class at the lake and i found myself looking at just the compass at first and missing out on what was around me and the natural navagation points. I was quite excited i did get back to my starting point which for me is a miracle. I suck at having a sense of direction so learning to use a compass is a long overdue skill for me to learn.

[bubbletrubble]

@Kimusubi: To elaborate on what awap has posted, whenever you refer to a direction in compass terms (heading in degrees), the standard convention is that zero degrees is due north, 90 degrees is east, 180 degrees is south, and 270 degrees is west -- no matter what your position is. The number that you read through the "window" on your SK-7 compass is the heading.

Compass navigation isn't rocket science. I really wouldn't suggest taking a formal course in it (unless the course is offered for free). It's nothing more than tracking distance (kick cycles), direction (degree heading), and using simple geometry to figure out where to go next. As someone else pointed out, compensating for currents can make navigation a little more challenging.

I completely agree that you should exploit the existence of natural and man-made navigational landmarks. For example, on my local shore dives, one swims perpendicular to the ripples in the sand to get back to shore. When I'm at a new site on a dive boat, I tend to use more natural landmarks, like a peculiar rocky reef formation, to help find my way back to the boat. YMMV.

When taking headings with your compass, constantly check that the compass is level by tilting it around. It should be moving freely within the oil. I've seen instructors leading their classes astray by following "stuck" compass needles. :-) You'll be happy to know that the SK-7, unlike some other compasses, can tolerate a fair amount of tilt.

Have fun on your dive...

[MSilvia]

Originally Posted by cummings66

Pretty slick and I appreciate the posting talking about a scuba sextant because I would have never considered a way to do it with a tool.

I've done it the hard way by making notes on a slate, pretty common but I like the automated way, well, sort of automated. Thanks for the posting, I learned something new today and now I'm happy.

Likewise! That's a pretty cool idea, and something I'd never heard of before.