reason for two computers??

[Boogie711]

I'd probably just shoot for the surface, blow off all my deco stops and prepare to die.

You know - you have a point - If I lose both a buddy AND a BT on the same dive. But on the other hand, I can envision scenario after scenario too... What if my tank blows up? What if all four of our regulators simultaneously fail? What if we get attacked by giant space blobs underwater? (Relax, I'm just being facetious.)

I just don't plan in advance on losing my dive buddies. Losing a dive buddy is a diver error, not a computer error. As a good rule of thumb, never use equipment to compensate for a lack of skill issue.

Have I lost buddies? Heck yeah... but I'm working on preventing it in the future.

 

[jagfish]

At my Solo diving training, one of the pieces of redundant equipment required was computer, so we had 2. Now remember, this is SDI, and I think they teach computer and not tables for OW cert.

Anyway, he asked me what I would do if my first computer crapped out. I said keep diving with my backup. He said, "Wrong, you abort the dive when you lose your primary." We had along discussion about this. He was comparing loss of a computer to loss of a primary reg. I argued how they were two way different things. If I lost my secondary air, I would be hosed, but if I lost my second computer, I could just surface at a leisurely pace, or even take more time if I thought I was close to NDL limits. He was the instructor, so I just went his way for the course.

But, if you second computer went, you just go the surface anyway. Presumably, you have been keeping an eye on your time and NDL limits along the way, so if it goes, you should have seen it in the last few miutes anyway.

 

[Vie]

BTW, I don't use a computer. I use a Suunto D3 in gauge mode and an Uwatec digital gauge for the backup.

just out of curiosity, are you getting slightly different depth readings? Back when I was using a Cochran, my computer would be reading shallower than everyone else's. I have also seen Suunto Cobras showing slightly shallower depths than Pelagics at identical depths.

 

[keyshunter]

just out of curiosity, are you getting slightly different depth readings? Back when I was using a Cochran, my computer would be reading shallower than everyone else's. I have also seen Suunto Cobras showing slightly shallower depths than Pelagics at identical depths.

I am not sure about the modern computers (I have never noticed it in my my Vyper manual), but in the manual for my old Aladin Pro, it clearly stated that the computer was calibrated for fresh water. This, of course, would give a slightly deeper than actual depth reading in salt water.

 

[DA Aquamaster]

I normally use a dive computer as well as a bottom timer when diving. On deep dives, the deco schedule for the planned dive as well as the contingency deco plans are on a slate and the computer is essentially the backup. If you are doing deco, dives, placing all your faith in a computer will get you bent or dead at some point. Similarly, I am not a proponent of relying on a buddy to bail me out. Stuff happens, buddies get separated and you are far better off being self sufficient when your computer fails while the buddy is AWOL.

I have noted differences between bottom timer and computer on occasion. They are normally within 1 or 2 ft at sea level and at altitude, but for example this weekend I noted that the computer read 150' and the bottom timer read 156' at depth. This appears to have been due to the computer deciding we were at sea level and working in FSW while the bottom timer decided we were at altitude and figured things in FFW. We were in fact around a 1000' and both on the edge depending on barometric pressure and the software involved.

In this case I assumed 156' used the 160 contingency and deco'd accordingly which also kept the computer happy. Assuming you have the gas for it, (and you should) following the more conservative of the two (whether they are both computers or bottom timer and computer) is a good idea.

I have had 3 computer failures in about the last 500 dives so they do die at inopportune times - but not all that often. When this occurs you either need a backup in the form of another computer or a watch/bottom timer and a contingency plan on a slate or need to remain within the NDL's and be monitoring things close enough to both notice the failure and to maintain an awareness of your N2 loading so that you can initiate your ascent before you exceeed the NDL.

For recreational dive trips a backup computer makes a lot of sense. If you have a backup computer, your week long dive trip will not be interupted by a required 12 to 24 hour surface interval as you can safely keep diving on the backup computer as long as it has bene along with you on all the dives.

Some deco divers use redundant computers to track deco obligations and in that case, if the "primary" computer failed, it would be cause to abort the dive as you coulkd not afford to lose the other as well. But in a recreational non-deco situation, if one of the two computers failed, I'd finish the dive on the remaining computer.

 

[matt_unique]

And even LESS necessary in technical diving, since your dive plan and contingencies are already thought through well in advance. If your bottom timer goes kaput, that's what your buddie's wrist is for.

I don't have the same confidence in buddy or "team" diving such that I would forgo redundancy planning.

I should clarify that I use a computer and a UWATEC digital depth gauge for deco dives. Both are used as a bottom timer and depth gauge. My profiles are on slates. The DDG is calibrated for fresh water and my Suunto computer is calibrated for salt so the DDG will always show a little deeper. 156' on my Suunto = 160' on my DDG for example.

--Matt

 

[BigJetDriver]

Oh my yes... if you need one computer then you probably need two! I remember in one of my threads on mutilevel diving without a computer or tables one fellow was adamant that you should have two computers.... in fact I think he might have been in favor of three and polling them to see which one was to be believed.

Aayy...Chihuahua!!!!!!!!!!!!!!!!!!!!

 

[ScubaDadMiami]

You know - you have a point - If I lose both a buddy AND a BT on the same dive. But on the other hand, I can envision scenario after scenario too... What if my tank blows up? What if all four of our regulators simultaneously fail? What if we get attacked by giant space blobs underwater? (Relax, I'm just being facetious.)

I just don't plan in advance on losing my dive buddies. Losing a dive buddy is a diver error, not a computer error. As a good rule of thumb, never use equipment to compensate for a lack of skill issue.

Have I lost buddies? Heck yeah... but I'm working on preventing it in the future.

While it is not highly likely to have both things happen on the same dive, we all know of incidents of electronics flooding or failing on a dive, and you already said that you have had separation incidents (Who hasn't?). So, it is not like I am planning for the nearly impossible here.

You are right that it is not highly likely that my scenario will happen, but it is not what I would call far-fetched. For another inch and a half on my wrist, I don't see a down side to preparedness in this case.

 

[ScubaDadMiami]

just out of curiosity, are you getting slightly different depth readings? Back when I was using a Cochran, my computer would be reading shallower than everyone else's. I have also seen Suunto Cobras showing slightly shallower depths than Pelagics at identical depths.

I was previously diving with two Uwatecs. At most, for a second or so here and there, I would get perhaps a one foot difference occasionally.

Now, I am diving with a Suunto D3 (in gauge mode) and the Uwatec. I got the D3 because I wanted a resettable stop watch feature. I just kept forgetting whether I was at my stop for 8 minutes or was it six. Now, I just reset each time I change to the next stop and I don't have to rely on my memory or write it down.

I think that one gauge is calibrated in salt water and one in fresh. So I am always a foot or two deeper on my Suunto than the Uwatec. Close enough for government work and deco.

 

[pt40fathoms]

Technical diving rules that will save your life!

Rule #1 Always plan your dive as if you were forced to complete it alone!

This means YOU carry what is necessary to accomplish this. To rely on your buddy as a backup is just asking for the grim reaper to pay a visit. Your buddy is your first choice, but never your only choice!

Rule #2 Always carry backups of life support equipment!

That includes dive computers, or at the very least a dive computer backed up by a bottom timer and bail out tables, or two bottom timers with run tables backed up by bail out tables. (get the picture)

Rule #3 Always plan your OWN dive!

Never rely on someone else’s calculations and dive planning, and NEVER “fly” a computer during a dive. This too will get you killed. (Flying a computer is the foolish art of just jumping in and letting the dive computer tell you when and how to end the dive. You may get away with it for NDL dives at shallow depths, but try that stunt in technical diving and you are playing with your life.)


Now why would you want two dive computers for recreational diving?

If one fails you can still enjoy your vacation.

Is it money well spent?

I don't think so, the odds are very remote that you will have a failure. Not impossible, just very remote.