Underwater Navigation .. any ideas where to start?

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I want to make some sort of navigation aid for me when I go diving. I use a compass at the moment, but it is pretty easy to get lost and worrying about this takes away from my enjoyment. I have 2 ideas so far and I am hoping some of you may have some suggestions on which would be the easiest to do and where to start with the design.

Idea 1/ Something that tracks the direction and distance I swim and will then calculate a return journey when needed. Problems to overcome with this would be that currents will effect distance and speed travelled. Maybe an accellerometer and a digital compass would be enough to work all this out?

Idea 2/ Some sort of beacon system. Place a beacon where the dive starts and then have a handheld device that will point to the beacon and display distance. I like this idea, but how I would do this? I am not sure.

Any ideas, thoughts would be greatly appreciated.

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I certainly wouldn't rely on ANY electronic device (even if it had a 100% guarantee) to protect my life (as much as it's worth these days) and there would be an inbuilt problem in that you may well come to rely on it to your own peril.
Apart from all the problems that can go wrong in a lab/home environment (particularly finger trouble), you would also have to compensate for shock, pressure, water ingress, salt corrosion etc.
...ex sailor and scuba diver.
DANGER, WILL ROBINSON!

Assembler and MCU hobbyist.

Last Edited: Sun. Mar 4, 2007 - 08:20 AM
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Hmm that's a nasty one. Typically I'd say the combination of 3 axes gyro, 3 axes accelerometer, 3 axes magnetometer , and a GPS would be best. But you'll be underwater - so that wouldn't leave any way to correct the accelerometer's drift. Maybe throw in some sort of flow sensor or something - but then you have to worry about ocean currents. Gahhhh.

OK - on second thought - how about having three floating buoys or something that are at set offsets from each other that send out a low frequency ping every second? Should work pretty well as long as you're careful to filter out all the echoes.

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Holmes wrote:
I certainly wouldn't rely on ANY electronic device (even if it had a 100% guarantee) to protect my life (as much as it's worth these days) and there would be an inbuilt problem in that you may well come to rely on it to your own peril.
Apart from all the problems that can go wrong in a lab/home environment (particularly finger trouble), you would also have to compensate for shock, pressure, water ingress, salt corrosion etc.
...ex sailor and scuba diver.
DANGER, WILL ROBINSON!

I take your point on the safety issues, and I certainly wouldn't be relying on it as a life/death type gadget, more as a navigation aid. Most of the time I can find my way OK, and on deep dives we usually use lines etc, but I have been on boat dives where I ended up a long way from the boat, when I could have sworn I was almost back at the boat.

From the sounds of it it is way too complex for me to do anyway. I really like the beacon idea, but using 3 beacons is not really feasible. I would be trying to find some way to use a single beacon. I have seen a commercially available device that does just that, a single beacon with handheld devices that point to it. Just wondering how they would have done it.

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Taipan wrote:
I take your point on the safety issues, and I certainly wouldn't be relying on it as a life/death type gadget, more as a navigation aid. Most of the time I can find my way OK, and on deep dives we usually use lines etc, but I have been on boat dives where I ended up a long way from the boat, when I could have sworn I was almost back at the boat.

From the sounds of it it is way too complex for me to do anyway. I really like the beacon idea, but using 3 beacons is not really feasible. I would be trying to find some way to use a single beacon. I have seen a commercially available device that does just that, a single beacon with handheld devices that point to it. Just wondering how they would have done it.


Well - you could use a pressure sensor to sense depth, and magnetometers + accelerometers + gyro to get heading (using a kalman filter to correct the data). You could thenuse the change in distance from the beacon as a measurement of velocity, and use that to correct velocities that are being calculated from integrating the accelerometer data.

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If the boat had speakers on poles sticking out each side, each speaker would emit a tone burst at different freq for port and starboard side. Receiver box on your wrist has 2 hydrophones. Arrival time difference between two diff freq beeps at receiver gives bearing to boat. I think since the spacing of the speakers is knowm, distance could be calculated? If speakers were 90 deg from you, arrival times would be the same, lo freq on left means you are behind the boat, etc. Need simultaneous sampling on the mic preamps to keep the received beeps in phase. (External a/d needed)

Imagecraft compiler user

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Hello,

After five full minutes of couch potato fantasy! How about an autonomous flotation platform with positioning thrusters and a VLF directional antenna focused straight down. The platform could be solar/battery powered and could constantly adjust position to be directly above you. Then, could constantly update your GPS position and emit your long/lat position in morse code chirps that could be picked up and heard/displayed by either a headset (assuming you know morse code) or could be received by an AVR controlled device and converted for display on a backlit LCD.

John

Just some guy

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That's a cool idea. Does anyone know which freqs attract big hungry fish and which freqs repel?

Imagecraft compiler user

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bobgardner wrote:
If the boat had speakers on poles sticking out each side, each speaker would emit a tone burst at different freq for port and starboard side. Receiver box on your wrist has 2 hydrophones. Arrival time difference between two diff freq beeps at receiver gives bearing to boat. I think since the spacing of the speakers is knowm, distance could be calculated? If speakers were 90 deg from you, arrival times would be the same, lo freq on left means you are behind the boat, etc. Need simultaneous sampling on the mic preamps to keep the received beeps in phase. (External a/d needed)

I like this idea, but would really prefer a single beacon. I would use this on shore dives too, place it near my entry point.

This idea gave me a thought, what about a single beacon sending out a pulse, and the receiver having 3 sensors spaced around the outside pointing in 3 different directions. If the sensors were 2" apart, would the AVR be fast enough to measure the pulse arriving at one sensor before the others? It could work out the direction based on the time differences between the 3 sensors. Distance isn't quite as important but maybe the strength of the pulse could give some idea of distance?

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Well, if I remeber correctly, sound travels at around 1440 m/s in water.
Now you need to do some math :)

Edit: you can also think about putting more space between the sensors, like putting 1 sensor in one arm and another in the other arm, maybe on a leg; but of course, complexity comes in in the form of "sensor-sensor" communication.

Embedded Dreams
One day, knowledge will replace money.

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Holmes wrote:
I certainly wouldn't rely on ANY electronic device (even if it had a 100% guarantee) to protect my life !

hmm, i guess you never fly commercial airlines (electronic flight/engine controls) or drive a modern car (electronic drive by wire/anti lock brakes)

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Nuno wrote:
Well, if I remeber correctly, sound travels at around 1440 m/s in water.
Now you need to do some math :)

Edit: you can also think about putting more space between the sensors, like putting 1 sensor in one arm and another in the other arm, maybe on a leg; but of course, complexity comes in in the form of "sensor-sensor" communication.

problem there would be that your arms do not remain in a fixed position. Placing the sensors on the tank might be a better bet, as they will remain fixed in relative position. The further apart the receivers, the better, as you will be able to more accurately triangulate your position relative to the beacon. IIRC: With 2 sensors you can get bearing, with 3 you can also get distance.

Writing code is like having sex.... make one little mistake, and you're supporting it for life.

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My brother asked me about a 'prop detector' he wanted for his sailboat. Solo sailors put the tiller on heading hold and they go below to get some ZZZs... He wanted to trail a line with a couple hydrophones.... detect the rumrumrum sound of a freighter... compute range and bearing... if its on an intercepting path, wake up the skipper. I analyzed a couple of prop sounds recorded with a hydrophone, but I was completly stumped on how to do the sonar, even if I had a simultaneous sampling a/d with a gain controlled preamp. The assumption was, all props are a certain dB up close, and the amplitude gives range. Arrival time gives bearing. Anyone that likes this idea can have it, cuz I'm too stoopid to take it any further.

Imagecraft compiler user

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Interesting idea, however I'm not convinced that all props have the same amplitude at the same range. Amplitude will depend on the prop geometry, as well as it's rotational speed. It may be more consistent with larger freight-liners, but certainly for smaller craft, as a diver, I've heard pitch and volume all over the map as boats passed overhead.

Writing code is like having sex.... make one little mistake, and you're supporting it for life.

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Why not use two hidropones, one on each side of the head (like ears...), and measure difference in amplitude between both. Then a led bar mounted on the glass may point towards the loudest side. This would give some idea about heading, simply moving your head around.

Guillem.

Guillem.
"Common sense is the least common of the senses" Anonymous.

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Instead of difference in volume, a difference in phase can also be used, and give better resolution/directivity.

Guillem.

Guillem.
"Common sense is the least common of the senses" Anonymous.

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Two emitters allows 2 position solutions. You will need either a differential signal (so you can tell +ve angles from -ve) or a third emitter - or only dive where the alternate solution is on land :)

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I have a lot of playing to do, I was thinking of trying a single beacon, but have 2 or maybe 3 sensors on the receiver. Then work out direction base on which sensor receives the ping first. Something like that anyway. This is a long term project but I will post my results.

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I remember seaing a story about a blind kid who would make a 'clicking sound' with his mouth and would be able to navigate using the reflections to figure out where he was going .

Never dived (saw Jaws) but is it possible to hear sounds and guess from where they came from or is sound underwater not directional ?

Pete

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digitool wrote:
I remember seaing a story about a blind kid who would make a 'clicking sound' with his mouth and would be able to navigate using the reflections to figure out where he was going .

Never dived (saw Jaws) but is it possible to hear sounds and guess from where they came from or is sound underwater not directional ?

Pete


Yes, I knew a kid that could do that when I was younger. He could even tell where the gutter in a street was. Amazing.

I haven't dived for a while, but from memory I think it is pretty hard to tell the direction of a sound underwater. I guess because the sound travels a lot faster in water than air it is harder to distinguish the direction.

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Hey,

At the most basic level - do you just need to figure out where to come up where the boat is?

If that's the case you might find this a bit easier. As then you can use the previously mentioned systems of two or three receivers to figure out direction.

Note if you have two sensors and one transmitter: you will have a line circle of solutions (draw it out on paper to prove yourself). Draw two dots for each sensor, connect them with a line. In the middle of that line imagine a plane at a right angle to that line. You could put a ping anywhere on that plane - it would always result in two pings being received at the same time. Similar problems occur for all measurements, not just measurements where both pings are received at the same time.

This also means that even if you just want a heading (don't worry about up/down) you will have a problem: there are two solutions, one pointing each direction. This all makes more sense if you draw it out...

So you'll need three pick-up sensors at least.

Regards,

-Colin

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c_oflynn wrote:
Hey,

At the most basic level - do you just need to figure out where to come up where the boat is?

If that's the case you might find this a bit easier. As then you can use the previously mentioned systems of two or three receivers to figure out direction.

Note if you have two sensors and one transmitter: you will have a line circle of solutions (draw it out on paper to prove yourself). Draw two dots for each sensor, connect them with a line. In the middle of that line imagine a plane at a right angle to that line. You could put a ping anywhere on that plane - it would always result in two pings being received at the same time. Similar problems occur for all measurements, not just measurements where both pings are received at the same time.

This also means that even if you just want a heading (don't worry about up/down) you will have a problem: there are two solutions, one pointing each direction. This all makes more sense if you draw it out...

So you'll need three pick-up sensors at least.

Regards,

-Colin

Yes, all I need is to find where to come up so I don't need to know depth, just direction. I am planning on using 3 sensors to give direction. As far as working out distance, I would ideally like to calculate the strength of the received signal, not just when it is received. Using the strength I could probably get a rough idea of distance. I gather the further the ping travels the weaker it will be when received.

Where to start with a circuit to transmit and receive an ultrasonic ping, I have no idea. I'll give google a good working over but if anyone has any suggestions I would appreciate it.

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glitch wrote:
Nuno wrote:
(...)

problem there would be that your arms do not remain in a fixed position. Placing the sensors on the tank might be a better bet, as they will remain fixed in relative position.


You're right.

c_oflynn wrote:
At the most basic level - do you just need to figure out where to come up where the boat is?

I was thinking. Maybe 1 sensor is enough. You would have a watch-like device and orient your wrist until you get the strongest signal. Then you know it's more or less into that direction.
Maybe a mechanical construction could help on this, if the sensor (a "mic") is at the center of some kind of "parabolic" dish.

Any toughs anyone?...

Embedded Dreams
One day, knowledge will replace money.

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All the divers I know like to keep it simple and robust, I suggest just one transmitter at home location. The diver carries a directional receiver. At about 50KHz this will be quite small, say about 10cm receive aperture. The diver has an intensity display to show how strong the signal is:- he heads for the strongest signal. Exact direction is not necessary because as he gets closer the angle sensitivity increases.

Possible fancy features:-
==The receiver can trigger the transmitter (ping it) to respond so that it only responds when needed. This way you get distance (time to respond plus 2 way transit time. Use a different response frequency so that you don't trigger on reflections from your own signal.
==Volume control at the receiver to accommodate a large dynamic range, not AGC because you want relative signal strength.
==Maybe a log response.
==Use 3 hydrophones, 1 forwards looking, 2 looking sideways with their own indicators. This will indicate extreme angle and to make direction finding easier.

Watch out for indirect reflections that will indicate the wrong direction.

Scan is manual (draw an arrow on the receiver to point the way home)

I remember seeing head worn receivers to allow the diver to perceive direction but they had to place them much wider than his head to account for the different sound velocity, not practical.

For this you don't even need a micro.

GK

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Now for the really stupid questions, how do I generate a ping of a specific frequency ie 40KHz? Can the AVR generate a ping or would some other circuitry be better?

I think it is about time I learnt a bit more about basic electronics. Can anyone recommend a good book or online tutorials?

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Taipan wrote:
I think it is about time I learnt a bit more about basic electronics. Can anyone recommend a good book or online tutorials?

See the sticky at the top of the forum list :)

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Do a google on
SSBL USBL LBL (underwater acustic position system)

But underwater acoustics isn't easy, but for a short range, low accurancy, you might be able to make something. Getting it watertight is also a challenge.

A dive often last up to an hour, and a low cost inertial system will drift a lot in that time.

btw, have you seen this: http://www.utc.co.il/web4.swf

BtC

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BillTheCat wrote:
Do a google on
SSBL USBL LBL (underwater acustic position system)

But underwater acoustics isn't easy, but for a short range, low accurancy, you might be able to make something. Getting it watertight is also a challenge.

A dive often last up to an hour, and a low cost inertial system will drift a lot in that time.

btw, have you seen this: http://www.utc.co.il/web4.swf

BtC


Thanks for those tips, every bit helps. That UTC device is excellent. I do like the challenge of making my own gadgets. If I can make a handheld device that can point at a beacon I'll be happy. All fun along the way too.

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A 'loop antenna' with 2 hydrophones spaced left and right should give a 3db increase when facing the sound source shouldn't it? Theoretically? If the spacing is a 1/2 wavelength, it should really cancel out at 90 deg off.. like a figure 8 mic.... hmmm.. I'd hate to swim a half mile off by 180 degrees following this bogus beeper....

Imagecraft compiler user

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bobgardner wrote:
A 'loop antenna' with 2 hydrophones spaced left and right should give a 3db increase when facing the sound source shouldn't it? Theoretically? If the spacing is a 1/2 wavelength, it should really cancel out at 90 deg off.. like a figure 8 mic.... hmmm.. I'd hate to swim a half mile off by 180 degrees following this bogus beeper....
lol .. spose that'll all be part of the fun. I was thinking of a 3rd hydrophone positioned in the middle and behind the left and right one. If it receives the ping before or after the other ones should tell me which direction.

I made a circuit ages ago when I was playing with a BX-24, it has a digital compass and a graphic lcd. I think it had about 8 memory slots where you pressed a button each leg of your journey, it recorded direction and then counted time. When you wanted to return you press another button and it would reverse all of the headings and start counting back. Thing is it doesn't allow for stops along the way, or drift in currents etc. I never did get it waterproofed for testing underwater. I could walk around my house without getting lost :D A much simpler beacon system would be so much better.

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I think that I would take a slightly different approach...although I would never depend upon someone else's actions to keep me safe (except my dive buddy).

I would use the boat's larger dimensions to provide a wider spaced receiver array to unambiguously triangulate the bearing to the diver from the boat. Have a single tx/rx on the diver (no need for triangulation by the diver)...there are more than enough things hanging off me when I go diving without adding extras.

Equip the diver with a transmitter that sends his ID number with checksum (allows for multiple divers in different directions). When the diver wants to know his way home, he broadcasts his ID. The boat receives, triangulates, calculates the bearing to the diver and broadcasts the bearing for the diver to use to return to the boat together with his ID and checksum. The diver's unit will ignore bearings for other IDs.

The diver can repeat the bearing request as often as he needs to allow for drift currents.

On the boat, the system could log repeated requests from the same ID and by simply plotting the bearings over time, find their intersection that would give approximate distance. A diver does not swim quickly so the uncertainty in distance would be relatively small...imho.

I might just think about doing this myself. Haven't had a good excuse for a dive for a while. :lol:

Ross McKenzie, Melbourne Australia

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Hello,

I have the following issue of NUTS & VOLTS (link) that has a small article on a simple oscillator circuit that can be configured down to 5hz!

http://www.nutsvolts.com/toc_Pag...

I was funnin in a previous post but this is a tough challenge! Once again, I immediately thought you were talking about salt water! Is that correct?

John

Just some guy

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johnrk wrote:
Hello,

I have the following issue of NUTS & VOLTS (link) that has a small article on a simple oscillator circuit that can be configured down to 5hz!

http://www.nutsvolts.com/toc_Pag...

I was funnin in a previous post but this is a tough challenge! Once again, I immediately thought you were talking about salt water! Is that correct?

John

Yes, I have been talking about salt water.

This is definitely a tough challenge for me, especially considering my limited knowledge of electronics. But I have been thinking about this for a long time and I need a new project so I will keep at it and slowly piece something together ... I hope.

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Taipan, My apologies, the circuit can be configured for 5"K"Hz not 5Hz. That is my first mistake ever :D

John

Just some guy

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johnrk wrote:
That is my first mistake ever :D

John

WOW - mine was buying a pencil with an eraser :)

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Taipan, I think this is a neat idea and would be quite useful with many applications if the cost was kept to a reasonable level. However, if your field is not electronics and you are serious you might want to enlist the help of a knowledgeable electronics person willing to devote the time and energy (Depending on if this is just a 'wim' or a more serious idea of yours with marketable value). This is definitely not a beginner project. I am a newbie myself and would need lots of help on this device.

Good Luck!
John

Just some guy

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johnrk wrote:
Taipan, I think this is a neat idea and would be quite useful with many applications if the cost was kept to a reasonable level. However, if your field is not electronics and you are serious you might want to enlist the help of a knowledgeable electronics person willing to devote the time and energy (Depending on if this is just a 'wim' or a more serious idea of yours with marketable value). This is definitely not a beginner project. I am a newbie myself and would need lots of help on this device.

Good Luck!
John


Thanks for the advice John, this is a project I have been thinking about for quite a few years now, so it is not just a whim, but whether it is an easily marketable idea would remain to be seen. I have been considering getting some help with the electronics design but to begin with I have a stack of books I got from my local library about electronics and I am studying these at the moment. I am playing with a few other simpler electronics gadgets so the learning will not be lost. I am not sure how far I will get with this project before I realise I will need some serious help. I am hoping I'll figure it out as I go. I will post my progress as I go but this is going to be a long term project. I appreciate all the advice so far.

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Do you live near salt water? This is a project that will require testing and experiments.... I thought maybe a tank in the lab would help.... no, echoes from the sides... What does an anechoic water tank look like? Non parallel sides? To simulate testing hydrophone receivers and transmitters at range, maybe we could add some goop to the water to increase attenuation to simulate long range? Jello? I'm still not sure if pinger on the boat or pinger on the diver is better... both will have to deal with bottom reflections where the distance from diver to boat is about the same as the depth. Maybe an active system with pinger at both locations? Marco! Polo! About the only hw item we need is an external a/d with simultaneous sampling and programmable gain. There are recent Linear Tech data acquisition systems chips that have this. The rest seems like programming!

Imagecraft compiler user

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bobgardner wrote:
Do you live near salt water? This is a project that will require testing and experiments.... I thought maybe a tank in the lab would help.... no, echoes from the sides... What does an anechoic water tank look like? Non parallel sides? To simulate testing hydrophone receivers and transmitters at range, maybe we could add some goop to the water to increase attenuation to simulate long range? Jello? I'm still not sure if pinger on the boat or pinger on the diver is better... both will have to deal with bottom reflections where the distance from diver to boat is about the same as the depth. Maybe an active system with pinger at both locations? Marco! Polo! About the only hw item we need is an external a/d with simultaneous sampling and programmable gain. There are recent Linear Tech data acquisition systems chips that have this. The rest seems like programming!

Yeh, I'm 5 minutes drive from the ocean. I was thinking of starting by working with audible sound so I can use standard speakers and microphones to see how I go getting the basic principle working. I wouldn't worry too much about range to begin with. Then I would look at the ultrasonics and increasing the range. Do you think that is a reasonable approach .. or way off.

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Hey,

Just as a note, something I saw recently:

http://appft1.uspto.gov/netacgi/...

From http://www.newscientisttech.com/...

Regards,

-Colin

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Taipan,
Dive another 50-100 dives just using the compass and keep an eye out for any notable features of the reef/bottom where you go in, and you'll eventually have no problem navigating.
It's just a matter of experience.

/Jesper
http://www.yampp.com
The quick black AVR jumped over the lazy PIC.
What boots up, must come down.