too soon for twins?

[peterpan]

hello all,
im about to finish off my sports diver soon and am looking forward to a good summer of diving. i've around forty dives done, with slightly less than half of those in the sea. im considering doing the TDI advanced nitrox and deco procedures and the end of summer. would i be better off waiting till then to get a twinset or should i get it sooner and build up experience? also the cost would be more staggered taking into account ill prob need a stage and more regs for the above course? what you think?
cheers in advance
pp

[Mark Papp]

what you think?

I think that the time to consider changing is when you get frustrated that your single tank doesn't give you enough gas to do the dives you want to do with sufficient reserves or redundancy.

[Nigel Hewitt]

As Mark said it really depends on the sort of diving you want to do.

If the things you want to see are deep and require longer run times then move to the sort of equipment that enables you to see them but, I assure you, dangling on a string doing deco for an hour is incredibly booring so you need a good reason to be down there.

Of course dive shops would just love you to throw your money away...

[peterpan]

cool cheers for the replies,
i know it may be a bit soon but given that i have the opportunity to do these courses now and even if there is no need for me to go deeper it still gives me the opportunity should i want to i.e. not limiting myself to 35m. by the bye where is the best place to get twins (ebay not really an option unless seller is close to me) godive?
pp

[Steve Pearson]

hello all,
im considering doing the TDI advanced nitrox and deco procedures and the end of summer.pp

And what's wrong with doing BSAC ADVANCED NITROX :(

[peterpan]

is there something wrong with doing the tdi course?

[PeteM]

I think that the time to consider changing is when you get frustrated that your single tank doesn't give you enough gas to do the dives you want to do with sufficient reserves or redundancy.

I would add to that "and you are relaxed enough so that your breathing rate is about the same as others"

Too many people buy twinsets as a solution to high SAC

[peterpan]

yeah youre right there! my high SAC (ca. 27l/min) does seem to be the limiting factor on most dives. would i be right in saying that widening my experiences to deeper depths would aid (im under no illusions as to the fact that more diving at any level would ameliorate the issue, along with giving up smoking) a reduction in SAC?
but should a lower SAC be a prerequisite to advancement, when in all likelihood i can expect a reduction anyway?
pp

[PeteM]

yeah youre right there! my high SAC (ca. 27l/min) does seem to be the limiting factor on most dives. would i be right in saying that widening my experiences to deeper depths would aid (im under no illusions as to the fact that more diving at any level would ameliorate the issue, along with giving up smoking) a reduction in SAC?
but should a lower SAC be a prerequisite to advancement, when in all likelihood i can expect a reduction anyway?
pp

Diving deeper is likely to make it worse not better due to the increased stress.

Lower SAC of itself is not really a prerequisite of advancement but removing the reason for the high SAC is. The biggest reason for a high SAC is not relaxing enough. Other reasons include poor buoyancy, poor technique etc. All of these are good reasons not to be doing deeper, more challenging diving particularly involving deco.

When you have a significant stop to do you have a glass ceiling over you, breaking that ceiling will get you hurt.

[Turtle Dude]

As said already, it depends on the diving you are doing. I have just moved to twins after 20 years! Happily dived (my kind of easy diving) on singles and pony.

I moved to twins (300bar 7Ls) primarly becuase of the "feel" set up on my back, compared to 15+3L pony. Not becuase I wanted to push any more envelopes.

The main question is not so much the cylinders (you could operate a manifold twin like a single cylinder) it is the type of diving you choose with limited experience. There are plenty of other errors and dangers besides just sucking out all your air.

This is a dangerous sport - building up skills and experience is more valuble than any particular equipment set-up. Go for the training, just ease yourself in, and then come to the decision on twins based on your experience and judgement.

ps: and in all of this, spare a little thought for your back and phsyical health - I am proud (and I will brag now) that I have done 20 years of diving, with the intention to do another 20, with no back problems or injuries (unlike my motorbiking - doooh!); primarly, becuase I have got my weighting right, picked up and carried things right and not taken dumb macho risks.

[Mark]

is there something wrong with doing the tdi course?

No, there isn't.

However BSAC run courses too... ;)

[Gordon]

I probably err a little too far on the 'taking it steady' side, but I'll describe what I've done:
I would suggest that you get good and happy with a single, which is (provided you and your buddy are paying attention) good to 20m. Then I'd add a pony, if you get a reg you could use on twins you spread the cost a bit and you'd get good and happy with that so that when you get your sports you are good to 35m (ish - depending on how happy you are with the amount of gas in your pony). This is about where I am atm.
Once you start wanting to stay at 35m longer than you can safely on 12+3, then think about twins.
This way you clock up plenty of experience and get happy with kit fairly similar to what you've used already.

Gordon

[peterpan]

with respect to the pony, which i already use, i was under the impression that those 3l were not to be included in any of the gas calcs or planning but merely as added redundancy given that a failure on the single cylinder doesnt allow for shutdowns etc.

[Nigel Hewitt]

I probably err a little too far on the 'taking it steady' side, but I'll describe what I've done:
Maybe I go the other way...

By dive 40 I had the twins and we did a lot of good diving together but by dive 100 I was on the rebreather.

That was eight years ago mind. I was only 50 then and I've grown up a bit since then and I'm not quite so hasty now.
There is still way to much diving out there I haven't enjoyed yet.
So little time and so much sea... <sigh>

[dunny]

with respect to the pony, which i already use, i was under the impression that those 3l were not to be included in any of the gas calcs or planning but merely as added redundancy given that a failure on the single cylinder doesnt allow for shutdowns etc.
Thats true but what I believe Gordon is saying is that if the worst happens then a 3l pony will only give you enough air for 5 minutes at 35m, bearing in mind you could have a fair bit of deco a 3 litre is not enough redundancy so you move to twins. And also consider that air calc is 5 minutes of air at 27l/min. A paniced diver can breathe more than 70 litres a minute.

Phil

[ChristianG]

I'll argue from another PoV. A 27 litre SAC is that of a novice diver, at best. You need to get that down and significantly so and the only real way to do that is to dive in the environment that you're comfortable in currently. On a single - you need to leave the fancy stuff for when you you have sorted your breathing pattern.

At a guess I'd say that a 15 litre SAC is relatively normal (anyone?) for a reasonably experienced diver. There are many divers with an SAC a fair lot less than that, myself included and I'm not small. The fact, though, as someone else alluded, is that in a stressful situation your SAC can, and will, balloon out to quite extraordinary levels, particularly if your experience is such that your panic level can lead to exactly that.

That's easy to do for an inexperienced diver. So, walk before you jog and jog before you run. Forget about sprinting altogether.

[Gordon]

Thats true but what I believe Gordon is saying is that if the worst happens then a 3l pony will only give you enough air for 5 minutes at 35m, bearing in mind you could have a fair bit of deco a 3 litre is not enough redundancy so you move to twins.

Aye - that's what I was trying to get at.
Cheers Phil


G

[PeteM]

At a guess I'd say that a 15 litre SAC is relatively normal (anyone?) for a reasonably experienced diver.

I think that depends a lot on the conditions and the diver. I do about 12lpm in warm water and about 18lpm with drysuit, twins and stages. I would say I am not great on gas but far from the worst.

[HEO2N2]

Another point of view -

First of all, understand what is required in the Adv. Nitrox and deco course, you will need to demonstrate -

Excellent buoyancy skills, sufficient to hold your depth while doing a valve drill, sending up an SMB, swapping stages, gas switching and buddy breathing.

Now, everyone will have their own reasons for wanting to do the Adv EANX and Deco course and that is purely a matter of personal choice. I dont think anyone should say categorically that you should not do it until (insert some number of dives or years of experience). However, YOU should be ready for it and you will waste your money if youre not able to demonstrate those skills properly.

So, where does that leave you? Well, my own opinion is that you will never get the experience of shutdowns unless you have a twinset and manifold. You will never get to practice your buoyancy while doing them unless you have dived with them and you will never get used to the different trim and characteristics of twins until you dive them. Getting a twinset a month before the course and finding that you are having problems reaching your valves is not good (especially if the problem is down to a poorly fitting dry suit).

Just because you dive with twins does not mean that you have to dive deep or go into deco. You do have a fairly high SAC rate and a pony is going to be next to useless on any 30m dive if you really need it (as has been said above, your SAC can rocket to 70+ L/PM and on a 3ltr 232 bar pony at 30m in a panic you will get about 2 minutes use out of it) so there is a lot to be said for the redundancy of twins.

If you are happy to fork out the extra expense (not only on the twins and two sets of regs, wing etc, but also doubling the cost of your gas fills) and you feel it is a good move for you and the diving you want to aspire to then go for it!

[builder_russ]

Quit Smoking first, before you do anything else!!!!!!

[diversue]

And the BSAC course will cost you heaps less ...

[Matt-75]

TDI Combined Advanced Nitrox & Decompression Procedures Diver
This three day course includes both the Advanced Nitrox and Decompression Procedures courses. It is more intensive, but more efficient. It includes 6 nitrox dives and covers all the topics required to use mixtures from 40% to 100% for decompression as well as the ability to perform accelerated decompression.

Includes: TDI Advanced Nitrox & Decompression Procedures manual & certification.

Pre-requisites: Advanced open water diver or equivalent, TDI Basic Nitrox or equivalent, 50 logged dives, minimum 18 years of age.

Cost: £380

Vs.

Advanced Nitrox Diver

AIM

To Introduce BSAC Sports Divers to the meticulous dive planning and practical skills required when diving and decompressing using enriched Nitrox mixtures.
To monitor time spent at different depths tracking different partial pressures of oxygen in order to avoid oxygen toxicity.
To teach the safe use of up to EANx 50 as both a diving and decompression gas.
To teach the safe use BSAC Nitrox Decompression Tables.
To teach the safe use of Nitrox and Air Computers.DURATION
Two days: Day 1 - Classroom studies, Day 2 - Two Open Water Dives
ENTRY GRADE

BSAC Sports Diver or similar (see BSAC SALT table) + 20 additional dives
BSAC Nitrox Diver (or equivalent)
Current evidence of Fitness to DiveFACILITIES

A suitable classroom for theory lessons, with enough space to spread Nitrox cylinders for practical analysing lessons.
A suitable open water site for practical diving on Day Two.
The following equipment will be required for the practical dives:
1 Nitrox cylinder per student (minimum 10 litre)
1 Pony cylinder (or doubles) per student
1 Delayed SMB per student
Oxygen analysers.Nitrox cylinders must conform to the BSAC recommendations: in test, in Oxygen Service and correctly labelled.

---

The differences between the two are above, but the OP probably already read them. The combined Nitrox seems to cost about £85 (in yorkshire), Advanced seems to cost £31 and whatever regional costs are required.

http://www.bsac.org/page/331/advanced-nitrox-diver.htm
http://www.dive-tech.co.uk/tdi%20courses.htm#advdeco

[peterpan]

good point but deco procedures (tdi), as i understand it lies somewhere between adv. nitrox and erd (bsac) and allows for accelerated deco with up to 100%.

[Richard Whitcombe]

And what's wrong with doing BSAC ADVANCED NITROX :(

The fact it doesn't compare to the TDI Advanced Nitrox maybe in terms of limitations and so on ?
Isnt the BSAC course basically just mid water DSMB and up to 50% on stops but not accelerated or have they changed it?

[Twinsetmad]

Quit Smoking first, before you do anything else!!!!!!
My thoughts too.... but do look around and talk kit to people.... Most like nothing more than show what they have and why they set it up that way.

[Gordon]

Isnt the BSAC course basically just mid water DSMB and up to 50% on stops but not accelerated or have they changed it?

That's about right atm - I'm sure its being rewritten as we speak.