Gas switching computer

[Finless]

Originally Posted by TonyD

I liked my Cochran until the batteries went flat (cannot download or change date/time or ppO2), now its just a bottom timer. At least the later models don't trash the stored data if the batteries go flat.

I'm confused, I could understand you losing your dive history but why should changing the battery cause the other problems? Which one have you got; the Commander Nitrox?

When you say you can not change settings do you use the side contacts or the Analyst software?

I found the Cochran people really helpful (I phoned them up in America) when I had a problem. Per their web site their UK dealers are:-

Comparison Results

Having said that, I don't remember either being the business name I was given when I went up to the Cochran stand at LIDS.

Apparently there is a new single battery unit for the Cochras which lasts 6 times longer than 'ordinary batteries'.

[DevonDiver]

I originally bought an Apeks Quantum when I first started with my TDI Advanced Nitrox course. I had to send my first one back to Apeks because the buttons stopped working and they replaced it (no quibble, good customer service). The replacement seemed fine, but I've had three startling occurances where the depth gauge has gone banzai and started alternating between random depths...with associated annoying ascent alarms. I am sure that I was not inadvertantly bobbing between 14m and 6m....so I guess that the Apeks Quantum reliability issue has raised its ugly head again.

A few months ago, I bit the bullet and purchased a Suunto D9....this has proven to be great. It's fabulous as a day-to-day instructors watch, has a good algorthym and allows 3 gas switches (compared to the Quantum's 2)...which means I can dive and teach the DSAT tec deep courses using air, o2 and an intermediate nitrox deco mix (which is the logical next step after the basic advanced nitrox course). The Vytec also offers 3 gas mixes, but I've heard a few people slag it off because the depth gauge has proven reliable on deep dives.

[Mark Chase]

Originally Posted by videogirl

I'm currently doing a Nitrox Decompression course and may look at upgrading my computer to one that does gas switching in the near future. Can anyone recommend a specific computer?

The problem with cheep gas switching computers is they dont show TTS (time to surface on all available gas) and / or dive planning on PC.


As a result i found my Vytec a tad useless. Id be at 45m with it telling me i ha two hours of deco on the 21% I was diving. Fortunatly i had a rough idea that i only needed 45mins deco if i did 45mins on the bottom so i could ignore it and it then becomes a very expensive depth and bottom timer.

You go to 36m and switch to 36% and it drops to say an hours deco which is still a mile out

Then you go to 10m and switch to 80% and at last it gives you a good TTS time. But it dosetn like you being at 10m and asks you to go to 6 or it extends deco.

So you see basicly they are crap at doing deco dives.

I ended up running tables and just clearing the 6m stop on the Vytec.


So my 2p is if your already doing accelorated deco, invest in a proper deco computer now.

For 250-350 look out for a Nitrox or OC trimix version of the VR3 mono screen V2.1 or above.

For £500 you can get the Shearwater GF S/H. Stunning computer but its a bit of a brick.


If not then look at doing ratio deco and just use a depth and bottom timer. For Back gas an single deco gas dives to max 55m it works realy well.

As previously mentioned Computers fail so you need some form of redundancyy and ratio deco and a simple depth and bottom timer works out the chepest way to go about it.


I had a Vytec, then two VR3's, Sherawater GF and now I have a Shearwater Persuit and use ratio deco for redundancy.


ATB

Mark

[GLOC]

Originally Posted by Mark Chase

If not then look at doing ratio deco and just use a depth and bottom timer. For Back gas an single deco gas dives to max 55m it works realy well.

As previously mentioned Computers fail so you need some form of redundancyy and ratio deco and a simple depth and bottom timer works out the chepest way to go about it.

Mark, I would like to jump on your band-wagon if you don't mind

You are always going on about the GUE crowd recommending RD as a panacea without explaining the limitations/risks. We counter it by saying that you really need to know the whole picture about doing RD (mixes, ascent rates, deco gases etc). Please do not undertake RD unless you have a good idea of everything that goes into RD.

In your case videogirl, I would recommend using a bottom timer and tables to start with (as that is what you are going to do on the course) and then once you have an idea about where you are going in deco diving, then choose a computer to match your aspirations ie single gas, 2 gas or a full blown VR3.

Regards

[The Duck]

Actually a variant on GLOCs reccomendation.

V-Planner (other dive planning software also available ), printer, laminator and a bottom timer. Print and laminate tables and stick to a wrist slate or scrawl in your wetnotes (or any other way that you can think of to attach them to yourself).

After a while you will have a "library" of tables that you can select from. Plus by playing with the planning software you can start to recognise patters that appear in the deco schedules.

Also when you have bought a computer to suit your planned diving you can still take your tables with you - just in case your computer fails.

[Mark Chase]

Originally Posted by GLOC

Mark, I would like to jump on your band-wagon if you don't mind

You are always going on about the GUE crowd recommending RD as a panacea without explaining the limitations/risks. We counter it by saying that you really need to know the whole picture about doing RD (mixes, ascent rates, deco gases etc). Please do not undertake RD unless you have a good idea of everything that goes into RD.

In your case videogirl, I would recommend using a bottom timer and tables to start with (as that is what you are going to do on the course) and then once you have an idea about where you are going in deco diving, then choose a computer to match your aspirations ie single gas, 2 gas or a full blown VR3.

Regards

There is no diference running ratio deco to running any other sort of deco?
ALL deco is mix dependent and ascent rate dependent. Standard safety procedures like planning the deco bassed on max dpth as you do with tables are directly transferable to Ratio Deco. Standard deco gases are prefered but not esential

My point being in the 40-55m range 1:1 ratio deco with a single deco gas of 50% is simple and has very few problems of note.

Beyound 55m it gets a fair bit more complicated and can be problematic in terms of levels of agression.

I beleive your confusing my opinions on some of the dive planning systems used with "deco on the fly" as outlined by an number of GUE divers. I dont beleive this has any relevence to divers using ratio deco.

I use ratio deco and i dont folow those planning ideas and I dont use standard gases.

It still works, but my ratio deco profiles are likley to be a lot more conservitave than yours.


ATB

Mark

[Mark Chase]

Originally Posted by GLOC

then choose a computer to match your aspirations ie single gas, 2 gas or a full blown VR3.

Regards

Which two gas computer and why / how?

ATB

Mark

[GLOC]

What I was trying to say was the ratio deco which most people subscribe to is based around a standard set of gases, standard rates of ascent and standard deco deco gases.

Yes, you can create ratio deco tables for whatever mix and depth you like but I very much doubt that someone who is doing AN & DP will be at that skillset. Indeed the published RD profiles are based on Trimix so it would be out of the scope of this discussion.

However, I cannot see how your 1:1 profile can be more conservative than my 1:1 profile unless you are using a higher ppO2 because 30mins on the bottom equals 30mins of deco.

Can you also tell me the difference between RD and DOTF as I thought they were the same?

Computers wise, I only know of names but don't know capabilities as I just use bottom timers therefore I was just suggesting a variety of options.

Regards

[Steve S]

Hi Videogirl,

on your course you will probably have to follow tables either made yourself via v-planner etc with a bottom timer/watch even if you have a gas switch computer, but IMO it's also good to use a computer as well and see how they compare, I have had an Apeks quantum for 2 years now and can't fault it.

I wouldn't deco dive without a back up timer and tables though.

Safe diving,
Steve

[Mark Chase]

Originally Posted by GLOC

What I was trying to say was the ratio deco which most people subscribe to is based around a standard set of gases, standard rates of ascent and standard deco deco gases.

Yes, you can create ratio deco tables for whatever mix and depth you like but I very much doubt that someone who is doing AN & DP will be at that skillset. Indeed the published RD profiles are based on Trimix so it would be out of the scope of this discussion.

However, I cannot see how your 1:1 profile can be more conservative than my 1:1 profile unless you are using a higher ppO2 because 30mins on the bottom equals 30mins of deco.

Can you also tell me the difference between RD and DOTF as I thought they were the same?

Not much, just DOTF is generaly accepted as being the GUE version using the GUE standard gas list. Ratio deco can be calculated on pret much any gas list

My 1:1 profile will be based on max depth and run time will be from leaving the surface to starting my ascent.

I beleive yours is average depth starting your time from the bottom of the shot.

QED I will be doing more deco than you dispite leaving the bottom at the same time.

But i am old and fat and you are young (ger) and fit

ATB

Mark

Computers wise, I only know of names but don't know capabilities as I just use bottom timers therefore I was just suggesting a variety of options.

Thats what i thaught.

From what I have seen the only cheep alternative two gas computer to the VR3 is the VR2.

If there is a cheeper better computer id like to know what it is.

Unless the Vytec DS and the Marres have started giving out proper TTS info they are still crap.

ATB

Mark