RDP vs eRDPml vs Dive Computer

[XS-NRG]

@Bubbletrubble

I've re-read what you were saying about the dive plan mode and now see how you're doing this. It didn't make sense at first. If it's an accurate way to get the pressure group then I can see its merit, however I still maintain my view on conservatism. If there is any doubt then I will not hesitate to yank the cord for the day. :cool2:

 

[Bubbletrubble]

This method has some merit, BUT .... the results could be greatly affected by the type - and settings - of dive computer you are using and by which depth you are considering.

@DiveNav: Yes, the "backed out" pressure group will depend on the dive computer used (algorithm employed) and level of conservatism. But really...we are just talking about OW recreational diving here with modest nitrogen loading. The OP has a Suunto computer, which as we all know, implements a rather conservative deco algorithm. The OP would be fine using the method I described with the PADI RDP.

The only requirement is to know what your NDL was at the time your computer failed. That's an issue of situational awareness. Divers should know what their NDL is, at any given time.

Exactly.

Maybe they are and I am too. But how bout the people that don't own their own gear and use rental equipment. The auto-on example I mentioned was on rental gear used by a tourist. Andy, you are right that is avoidable. This whole subject really does come down to whether or not you own your own gear and also take care of it appropriately and also know how to actually use it vs the rental divers and/or table divers. Clearly you have much more control over situations if you own the computer yourself and have it serviced properly and at regular intervals. It really goes without saying.

@XS-NRG: No, it comes down to the diver being familiar with whatever computer he is using -- whether it's one of his own computers or one that he's rented.
If I rented a computer from a dive shop, I wouldn't leave the shop without first figuring out: (1) how to read NDLs, total dive time, depth (2) what the deco screen looks like, and (3) how to access Dive Plan mode.

What exactly are you getting from your buddies computer? Will the dive plan be accurate? What if your buddy was a few feet deeper than you the whole dive? Or shallower? The profile would be different. How can this be accurate? Isn't this why we're taught never to share a computer underwater??? If the plan mode and the info displayed is the same regardless of the dive then it wouldn't matter and your technique should work.

Dive plans are neither accurate or inaccurate. They are what they are.

I would attempt to derive nitrogen loading status from my buddy's computer.
My method is predicated on the assumption that my buddy's nitrogen loading status is very similar to my own.
For me, this assumption is reasonable since I typically keep the same buddy for the entire repetitive dive series, we always stay within a few feet of one another during a dive, and we always begin/end a dive together.

For OW recreational diving with modest nitrogen loading, being a couple of feet higher/lower in the water column than another diver really shouldn't be changing nitrogen loading status significantly. You'd probably observe greater variances in NDLs if you strapped one Suunto computer and one Oceanic computer to the same forearm.

You keep using the word "accurate." It's inappropriate to be using such an adjective when discussing nitrogen loading status.

Think about why a diver is taught not to share one dive computer with one or more other divers. One issue is whether nitrogen loading status is similar among the divers involved. Another issue is redundancy (buddy as backup). Yet another issue is contingency planning with regard to buddy separation. If you are cognizant of these issues and think your buddy's computer reflects a reasonable approximation of your own nitrogen loading status, then I don't see a problem with my method at all.

Really? I'm surprised you even asked that. Conservatism is up to the individual and if you remember back to your OW class you'll remember that there are secondary factors. I happen to fall into a couple of those. Also (as mentioned earlier regarding dehydration) everyone is different, everyone will differ from day to day and every situation must be looked at on a case by case basis. If I know I'm doing 10 dives on a trip and I happen to miss 1 then big deal. Same applies to a live-a-board, you miss 1 dive on a week long trip, who cares. Sure you'll be pissed off you're missing one but in the grand scheme of things it really doesn't matter. I'd rather chill out and relax on the boat knowing I can dive another day than be air lifted to a HBOT chamber and screw up my whole holiday because I took it too far. If you choose not to be as conservative then go nuts, that's your decision. Why do I choose to be so conservative? Because I can, and because it's my choice.

I asked you why you were being so conservatism not to be outright critical...but to see whether you had a reason for being that conservative.

FWIW, there are many, many other ways to increase the level of "conservatism" for a given repetitive dive series.
It's certainly your prerogative to be as liberal or conservative as you want. I just hope that whatever you decide...it's an "informed" choice.

@Bubbletrubble

I've re-read what you were saying about the dive plan mode and now see how you're doing this. It didn't make sense at first. If it's an accurate way to get the pressure group then I can see its merit, however I still maintain my view on conservatism. If there is any doubt then I will not hesitate to yank the cord for the day. :cool2:

There's the use of that term "accurate" again.

I would recommend doing a few repetitive dive series with a dive buddy who uses a more liberal computer. Before/during/after each dive, compare your Suunto NDLs with his computer's NDLs. You'll be surprised by the differences you'll observe. Once you do this, I think you'll see why splitting hairs over one or two minutes at a slightly different depth is rather silly.

Have fun out there and be safe...

 

[Eddie W]

In answer to your questions,

Yes if a dive guide is taking a group out he/she knows the dive is safe, has he calculated.. not allows, don't assume. What might be safe for the guide may not always for you, we don't know your recent dive history, are you diving in the afternoon with us but have done 2 deep dives earlier in the day elsewhere ? Yes I always ask, however a guide/DM is just that, there to show you the reef and look out for your general safety not to hand hold. If that is what is required then book an instructor/refresher/one on one.

With your briefings for your OW/AOW.. that does sound shocking, a dive should always be briefed, training or otherwise, for safety reasons, enjoyment and if the guests know what to expect then they have a better time and to be blunt makes my life easier. Again don't assume, if you don't feel comfortable say something.

Prior to a dive, don't worry what everybody else is doing, you do what will make you feel safe and comfortable. If you have questions ask them.

FYI, out-side of certain areas, a dive guide doesn't have to be a cert DM, I work in Indonesia and know plenty of very good guides, guides being the word here, that are not DM's. Anybody that knows me, my two are DMs.

Dive comp/RDP, I would strongly recommend a dive comp, yes you can plan with an RDP/eRDP, however this limits your dive, should you deviate from your plan a comp will allow for this an RDP can't. Its a bit like driving a car without a speedo, you wouldn't do it. It doesn't need to be an expensive comp. As you become more experienced and want to get away from the group a little a dive comp allows you to do this.

There is nothing wrong with planning a dive with an RDP and then using the comp on the actual dive.

I would say it is the most important bit of kit you buy and I am always concerned/watchful of a diver that doesn't have one. Also learn to understand what your DC is telling you, when I teach I still teach with the RDP as I need my students to understand what their DC is telling them.

I hope this helps and if some of it sounds harsh it isn't meant to.

I don't think it frightens you. I think it excites you to be able to point your finger at someone.

All I meant is that, when the resort takes a group out for a 45-minute dive to 50 feet, followed by a 45-minute surface interval, and a 45-minute dive to 30 feet, they've calculated that this sequence is not going to exceed the NDL's.

Of course I take responsibility for my own safety. I'm religious about planning my dives, recording my dives, keeping track of pressure groups, etc.

As a beginning diver, however, I have noticed that nobody has ever asked me to verify that what we're about to do is safe. The instructor takes me out for my open-water certification dive, or my advanced-open-water certification dive, and doesn't go over the planned depths and whether they're safe. Since it's an instructor taking me out, I assume he knows what he's doing.

And when I was at Sunset House on Grand Cayman, and they took a group of 10 people out for 2 boat dives, they told us the depths and times. I saw nobody on the boat calculating whether they were safe depths and times. They just did the dives. After the dives, some of them filled out their log books (me included). The instructors did keep close contact with us, however, and made sure that we did our 5-meter 3-minute rest stops.

So I think that there is a danger of assuming that the people taking you on the dive are going to make sure it's safe, when it might not be. That point is well taken. I think from now on I'll get out my RDP before each dive instead of after, even when it's an instructor planning the dive.