Suunto cobra 2 compass

[Shellshocked]

My wife went to our local dive shop this week and they showed her the cobra 2. We currently have the standard cobra computers. The shop manager told her the cobra 2 has a new feature to help you return to your entry point. I looked at the manual and the electronic compass does have features to return you to a marked compass location. I am not quite sure this will really tell you the way back to the entry point - can anyone shed some light on this?

thanks Shellshocked

[Brandon]

It likely calculates a reciprocal course by computing vectors off the course headings you followed during a dive. For example, if you swam North for a quarter of the dive, then swam East for another quarter of the dive, it likely knows that you need to travel SW for the remainder of the dive to return to your origin.

Is it accurate? I'm sure in some situations it is, but what if you aren't using your compass during the entire dive, and its sitting down by your waist? There's no way its getting accurate compass info then, and I can see that greatly impacting how accurate its calculation would be.

It's going to have problems if you vary speed or stop often during a dive as well.

Just my thoughts... did you have another reason you wanted to upgrade? This alone doesn't seem like a great reason to drop $800 on a new computer...

[Shellshocked]

Brandon,
That is what I thought, the compass has no way of knowing how far you traveled in specific direction it only know that you went in a certain direction for a specific time. The only reason to consider the upgrade is if this really worked. My wife and daughter get paranoid about straying to far from the boat in an open water dive and having something that told them the boat was "that way" would reassure them (we have all taken a navigation course already). We primarily dive the caribbean with little current but we have had a few dives where the current was strong and you had to really pay attention to where you were during the dive. I use a manual compass and it provides a good general sense of which way to go. An underwater GPS would be ideal - I know there are some systems but they require a homing beacon.

Thanks Shellshocked

[Brandon]

Brandon,
That is what I thought, the compass has no way of knowing how far you traveled in specific direction it only know that you went in a certain direction for a specific time. The only reason to consider the upgrade is if this really worked. My wife and daughter get paranoid about straying to far from the boat in an open water dive and having something that told them the boat was "that way" would reassure them (we have all taken a navigation course already). We primarily dive the caribbean with little current but we have had a few dives where the current was strong and you had to really pay attention to where you were during the dive. I use a manual compass and it provides a good general sense of which way to go. An underwater GPS would be ideal - I know there are some systems but they require a homing beacon.

Thanks Shellshocked

They make locator beacons you can use underwater to find out where the boat is. Leisurepro sells them... I can't remember what its called.

Just spend some more time practicing with the compass, and all these electronic devices won't be necessary. Towel over the head in your yard or a big parking lot is an excellent way to practice. Just have someone spot you to keep you from tripping / wandering into traffic!

-B

[C Chris]

Check out www.desertstar.com (http://www.desertstar.com) goto the tab that says "Sport Diving". The unit transmits to approximately 300m with a 50 hour bat life - interesting. Has an LED readout (color coded) to tell you your distance from your entry (or chosen) point. At LeisurePro as Brandon mentioned. Search on Desert Star. Cost = $324.

[Jai Bar]

Brandon,
That is what I thought, the compass has no way of knowing how far you traveled in specific direction it only know that you went in a certain direction for a specific time. The only reason to consider the upgrade is if this really worked. My wife and daughter get paranoiazimouth d about straying to far from the boat in an open water dive and having something that told them the boat was "that way" would reassure them (we have all taken a navigation course already). We primarily dive the caribbean with little current but we have had a few dives where the current was strong and you had to really pay attention to where you were during the dive. I use a manual compass and it provides a good general sense of which way to go. An underwater GPS would be ideal - I know there are some systems but they require a homing beacon.

Thanks Shellshocked
I used to have the Uwatec digital compass. It had an option to set up to 9 bearings, so one could set a nine-legged course. Then, it could calculate the reverse azimuth for each stretch and help you backtrack to the origin.

That is nice in theory.

However, you need to know how much time you've spent in each direction, assume you kept diving in straight lines, at constant speed and that there are no currents whatsoever.

I found this feature impeactical after a few dives, and since you are looking for some reassurance that "the boat is that way" you may settle for something like a GPS.

I have tried- and occassional use- a regular GPS unit inside a clear watertight case. Search the forum for "underwater GPS" and you'll find some info. I use it for other reasons but it works.

In a few words- the GPS floats inside the case and is beeing towed using a simple spool/reel. Since it is not always comfortable (or safe) to tow something on the surface, you can do the following:
- On the boat, add a waypoint to the position where it is anchored. Close the case.
- You can either set the GPS to show the graphical display of the diving course, or set it to return to the boat/waypoint (and it will show you distance-bearing to the boat).
- You can either tow the GPS floating during the dive, or just keep it underwater near you and send it up once in a while so it acquires your current position.
- Whenever you want to see your position just roll it down and look at the display

A small clear watertight case is inexpensive (20-30$) , and you can buy at ebay a housing for zillions of obsolete digital cameras, or from friends who flooded the camera and don't need the housing any more since they usually upgrade to whatever is available on the market and the housing is useless. Unfortunately, there are plenty of these too :eyebrow:

You need also a basic GPS unit. Probably altogether it by far less than a new Cobra2 and you also have the GPS for other uses :14:

Again, even when tugged, if there are high waves or the housing gets underwater it will loose the track as long as it is immersed so don't expect for a continous tracking.
Of course- when you pull it down to look at the display it will loose signal and show you the last position so you'll have "gaps" in the course tracking. But it is enough for your needs.