Tech1 Ratio Deco - Explained

[GLOC]

The other thing to bear in mind is that 40 mins is getting close to the maximum deco you can do on a Tech 1 dive with regards to backgas minimums.

Min gas from 45m is around 90 bar which gives you 120ish bar to use on the bottom (use some on the descent and SAC slightly higher on the descent until stabilised at the bottom). A SAC of 15L/min at 45m is nearly 3.5 bar per minute which gives you 35 mins on the bottom. 45 mins at 45m would require a fill of 245 bar using 90 bar min gas.

The numbers for T1 level RD all slot in nicely, fortunately.

[Howard Payne]

That Mal seems sensible - he's gonna tell me how long I'll be at 21m before we even get there - can't we take him along for redundancy along with the Vytec?

We're all going to diieeeeeeeeeeeeeeeeeeeeeeeeeeeeeeee

[Garf]

Originally Posted by Howard Payne

That Mal seems sensible - he's gonna tell me how long I'll be at 21m before we even get there - can't we take him along for redundancy along with the Vytec?

We're all going to diieeeeeeeeeeeeeeeeeeeeeeeeeeeeeeee

Frankly, if you weren't such a lazy chimp, you'd know how much deco i was gonna before we got to 21M

[A-M]

Clear explanation!!

[ardhill]

Nice one

My head is swimming with a flu thingy and I still understood your post (well I think I did)

Well, apart from that 'rounding up to the nearest 10 minutes' bit - what 10 minutes?

Thanks

[GLOC]

Originally Posted by ardhill

Nice one

My head is swimming with a flu thingy and I still understood your post (well I think I did)

Well, apart from that 'rounding up to the nearest 10 minutes' bit - what 10 minutes?

Thanks

10 minutes makes it easier to divide into 2 segements without having numbers left over.

Eg

30 mins deco would be split, 3@21, 3@18, 3@15, 3@12, 3@9 and then 15@6m.

26 mins could be split 3@21, 2@18, 2@15, 3@12, 3@9 and then 13@6m.

For the sake of 4 mins on what is potentially a 52min dive (26 mins bottom
time at 45m using the example above and 26 mins deco), why not just round the numbers upto 30 mins deco and make the dive 56 mins long (excluding the ascent from 6m to the surface)?

RD doesn't have to be hard if you understand what it is trying to achieve.

HTH

[ardhill]

Originally Posted by GLOC

10 minutes makes it easier to divide into 2 segements without having numbers left over.

Hmmm, but if you had say 18 minutes deco, so decided to round it up to 20mins.

10mins intermediate & 10mins shallow stops.

21 - 3min
18 - 2
15 - 1
12 - 2
9 - 2

Which isn't very even. See what I was confused.

I have no problem adding on deco to make calculations easier. I just didn't think 'that' was the 10 minute thing he mentioned as it didn't always work in my mind.

Thanks

[GLOC]

Originally Posted by ardhill

Hmmm, but if you had say 18 minutes deco, so decided to round it up to 20mins.

10mins intermediate & 10mins shallow stops.

21 - 3min
18 - 2
15 - 1
12 - 2
9 - 2

Which isn't very even. See what I was confused.

I have no problem adding on deco to make calculations easier. I just didn't think 'that' was the 10 minute thing he mentioned as it didn't always work in my mind.

Thanks

You are right, it doesn't always work, and I can see where the confusion has come from. I suppose most of the time 30mins is the average deco we would do for T1 limits (45m for 30mins, 48m for 25mins, 42m for 35mins) because gas usage at approx 17-20l/min for these scenarios is what you can get from a set of twin 12's and a single deco bottle. Admittedly if the dive was cut short, for whatever reason, then we would have to think about how to split the deco but your example is what I would do if I were running deco.

I know Garf is battling his way up the M23, M25, M1 to York after a nice day on the Moldovia so he might not be on until tomorrow to clarify if I was talking from a different point of view.

Regards

[ardhill]

Thanks Gloc, I do like the idea behind it though. If the numbers are fiddly, add deco time till they work out neater for your poor dive worn brain

[GLOC]

Originally Posted by ardhill

Thanks Gloc, I do like the idea behind it though. If the numbers are fiddly, add deco time till they work out neater for your poor dive worn brain

This is okay for T1 levels, but if you start adding numbers for T2+ dives, you are going to run out of gas. Once people get more attuned to what they need to do for real, ie what their bodies need, then they can change the numbers but to start with T1 level RD is relatively nice and easy.