Which model - VPM, RGBM

[Janos]

Originally Posted by aquayle

If no pre-planning on the dive, could you simply rely on the SUUNTO to give you safe enough deco?

For short amounts of deco (5 to 10 mins) Yes, but you need to do some pre-planning:

1) You need to plan your gas consumption carefully. You need to do it in more detail than the simple start ascending with 80 bar left in your tank. Not only do you need to work out how much gas you plan to use for the ascent, including deco, but you need to work out how much gas you will need if things go wrong (eg you get stuck in line and extend your bottom time by five mins - how much gas do you need, and how much extra deco do you do, and how much gas do you need for that deco?)

2) You also need to plan what you're going to do if you Suunto breaks. You know have some deco to do (but you don't know how much). I like BSAC tables for this as they are quite aggressive, but I plan on not using them that often, and normally it's easy to remember how much deco.

3) Be careful with your Suunto and understand how it works. Spend some time running profiles though it in plan mode, and with the Suunto Dive Manager. The Suunto likes you to get up to 6m quickly. A 10m/minute ascent is bloody fast when you're used to taking it easy and the Suunto will penalise you for going slower. This isn't a problem, IF you know BEFOREHAND that when your Suunto says 10mins of deco on the bottom it will say 15 minutes when you get to 6m if you're doing your normal ascent, and take about 18mins to count down [1] as you're not at 3m. Again SDM is your friend for working this out.

In general: Think through what might happen, and work our what the implications are for deco and for gas consumption.

Be careful of learning to dive on the internet.

Janos

PS - I haven't addressed any of the practical issues. But generally, for deco diving, I would expect you to be very comfortable switching to your bailout pony if that's what your using, and have good bouyancy skills (able to hold a stop, and to put up a DSMB in mid water without deviating by more than +- 0.5m.

[1] - All numbers are made up off the top of my head. Please don't believe them.

[nigelH]

Originally Posted by aquayle

I guess the 64K$ question is, can you do 'simple' dives on your computer.
If no pre-planning on the dive, could you simply rely on the SUUNTO to give you safe enough deco?

I do pretty much all my dives on the computers.
I have a set of tables in my pocket and I have pre-selected a bailout plan that can get me out of any dive I will do but although I have several deco-planners I bought and one I wrote I don't use them any more. The plan gets rewriten at depth. If seeing 20 minutes TTS makes my heart sink it is time to ascend. If it looks well worth it then give it another five and see what else we can see.

eg:

Yeah. I know the ascent from 6 was a bit abrupt but I hadn't hitched the p-valve up...

[Janos]

Originally Posted by Gledders

Are you aware what pattern of stops your computer will spring on you... the sunto for example jumps from 3 minutes to surface to 6 minutes to surface very quickly and makes no allowance for ascent time or stops below 6 metres (or something like that - I don't use one any more but seem to remember being surprised how quickly it mounted up and how slowly it came down again).

A lot of people get caught out when their Suunto's go into deco. The think to remember is that generally the first stop it will show is 4 mins which includes the optional 3 minute safety stop. It then goes very quickly to showing six minutes of deco and then seven. It then takes a little while to increase. However you're right. The pre-planning modes (including the SDM software) is very good for this.

Suuntos do count down below 6m. And if you deco at 6.1m it's not much different to 5.9m as far as Suunto is concerned. But they do assume that you will spend most of your time at 3m and this does make a difference.

It is only the last three minutes, which is the optional safety stop part of the 'deco' that won't count down below 6m.

Janos

[aquayle]

OK
so which course(s)
BSAC advanced Nitrox & then ERD; or
TDI Combined Advanced Nitrox & Decompression Procedures

Andy

[Scuttler]

Originally Posted by aquayle

OK
so which course(s)
BSAC advanced Nitrox & then ERD; or
TDI Combined Advanced Nitrox & Decompression Procedures

Andy

My money would be with TDI personally. No particular reason just that IMHO BSAC are not really a "techincal" diving oprganisation.

[chrisch]

Originally Posted by Scuttler

My money would be with TDI personally. No particular reason just that IMHO BSAC are not really a "techincal" diving oprganisation.

My vote too for TDI, BSAC are trying hard to address the more technical side and may well do so very well when the Tx course gets underway. Meantime I think the tech agencies like TDI, IANTD (or GUE for that matter) will give you a lot more info about the decompression theory discussed in this thread.

Some BSAC instructors will also cover this, but the basic avanced trox course still looks at the 88s and the deco stuff tends to kick in with ERD.

If you only have the BSAC basic trox there will also be a little catch up to do on Equivalent Air Depths.

Chris

[nigelH]

Originally Posted by chrisch

Some BSAC instructors will also cover this, but the basic avanced trox course still looks at the 88s and the deco stuff tends to kick in with ERD.

LOL

Even I'm a BSAC Instructor and Janos is a... what was that badge at LIDS again?

[chrisch]

Originally Posted by nigelH

LOL

Even I'm a BSAC Instructor and Janos is a... what was that badge at LIDS again?

But that's the thing about it if you can add value BSAC lets you. Its the only thing where it beats the "competition". The basic course is the 88s IIRC... Dammit now I've got to surf some more and work less again....

As to LIDS I think the big new thing is the PADI Discovery Channel Diver speciality where you get a cert for watching SKY.....

Chris

[chrisch]

See... I'm old and alcohol addled but teh memory is still there... The deco model stuff is in ERD http://www.bsac.org/techserv/syllabus/erdsyl.htm

"3. Theory Lesson - Decompression Diving - 45 minutes

* Tools – Tables, PC Software, Dive Computers
* Run Time Management
* Rich Nitrox mixes, Oxygen Tracking
* Good Decompression Practice"

Chris

[Mark Chase]

[quote]

Originally Posted by aquayle

I guess the 64K$ question is, can you do 'simple' dives on your computer. This is a bit like 'deco-on-the fly' I guess. I did a 35m dive (profile below) but with very slow ascent took a pony of air because knew it would involve deco - computer says 9mins at ceiling of 3m (and floor of 6m). If no pre-planning on the dive, could you simply rely on the SUUNTO to give you safe enough deco?

Deco on the fly is a term referring to a set of decompression rules that evolved around a very specific range of gases and a very specific set of decompression rules. A 35m dive would be carried out on Trimix 21/35 using 50% 02 for decompression. There is no other way to do the dive if your using DOTF.

Flying a computer is OK but unless you have a full on decompression computer like a VR2 VR3 Abyss Explorer etc you are going to get some very basic profiles using mainly Bhulman style get shallow quick ascents.

Fo short deco dives this is fine but you need to know what your deco commitment is likely to be and how much gas you will need BEFORE you get in the water. You should never go into deco without pre planning or at least enough experience to just know what you need.

I dived deep air and shallow trimix using a Sunnto Vytec. I used tables to generate the deep stops and I followed the Suunto on the shalow stops but i always knew what my deco would be and how much gas I needed before ever getting on the boat.

As for training I would personaly avoid the ERD course as it is a deep air course that is frankley out of date. Look tawards Advanced Nitrox and Decompresion procedures folowed by entry level Trimix or if you like the DIR
stile of diving and want to do away with your computer do DIRF and Tech1

Both will get you into the 50m range of diving with deco.

ATB

Mark Chase