Help with Planning a 100m Dive?

[Ainsleyberryman]

Im planning a 100m dive and wondered what everyone else would use for bottom mix and deco mix and why.

Im diving in the Red Sea over Christmas, OC Tmx and would be happy with up to three deco tanks. Bottom time of up to 20 mins, dont mind how long the hang is as it will be against the reef and I will be in my drysuit.

Im pondering the following:

Using Tmx all the way up to my O2 stop and keeping the Nitrogen at the same percentage.

Using my Tmx bottom gas up to say 60m then a weak Tmx then normal Nitrox.

Using my Tmx bottom gas up to say 60m then nomal Nitrox.

Using a lot or little Helium, a lot or little Nitrogen.


There are lots of possibilities using various gasses, but I need someone with actual experience to point me toward or away from some. Im comfortable when slightly narked and will be using my VR3. Previously been happy to 86m on twin 12's and just Nitrox 36 and 80. Ive done the various mixes using V-Planner as its easy to make changes to for comparisons.

Cheers, Ainsley

[Mark Powell]

Some questions to ask before planning a dive like this.

What level of narcosis are you prepared to accept?
What is your breathing rate?
What failures are you going to plan for?
What level of PPO2 are you prepared to accept for back gas and deco gas?
Are you planning on incorporating back gas breaks?
What do you consider the biggest risks in the dive? Narcosis? DCI? CNS? Gas?
What kind of support and backup do you have available?
Who is your buddy?
What decompression model are you going to use?
Do you want to make any changes to that decompression model?
Do you use deep stops?
Do you have a p-valve?
How much conservativism do you want to apply to your deco?
How old/fit/overweight/etc are you?

Everyone has a slightly different set of answers to these questions and your own answers will help cut down planning process.

[Mark Chase]

Hi Ainsley

Where are you planning to do the dive?

Andrew and I did this in January and we are out there again this Christmas so might be able to help out.

First things first:

You will need a minimum of two divers to do the dive

You will need shore cover if you’re not on a boat and the shore cover must include a safety diver to go in the water with a drop tank if required.

You will need two sources of buoyancy either dual wing or dry suit and wing.

You can normally only get 10ltr stages and the Ali ones float big time when breathed down

You will have very little / no chance of doing a 20min bottom time with the 180-200bar fills available. You will have nowhere near enough back gas and be very tight on deco mix as well.

We used a 10 of travel gas 21/25 down to 60m and back from 60m and twin 12s on the bottom and we spent a total of 15mins below 90m, 102 max depth little exertion ie mild fining no current and I gas switched back to 21/25 with about 70 bar to spare.

My planned SAC was 15

Using 32 % and 80% for deco in 10s with a 50bar reserve you will need 225bar fills for a 20min bottom time based on a SAC of 15. You’re unlikely to get this and it’s not wise to plan deco on a lower SAC as something might put your sac up a bit.

I did the plan using Decoplanner on 20/85 which I find similar to my VR3 set on 0 safety.

Post or Email me a deco plan and gas plan including ascent rates and include a pre dive preparation plan so I can see you know what your doing. If its cosha I am happy to offer further assistance. If it’s in Dahab we could help out as safety divers between Dec 26 and 01/01.


PS allow about £350 for gas

ATB



Mark Chase

[Ainsleyberryman]

OK, In response to those questions then:

What level of narcosis are you prepared to accept?
- Up to 40m - but less on the bottom

What is your breathing rate?
- 12 for the bottom, 9 for deco (im not planning on swimming anywhere)

What failures are you going to plan for?
- loss of one or more deco tanks - Yellow blob + slate to send down more. I use a double wing, two DSMBs, two reels, two computers, two masks, Manifolded twins with a slobnob, bailout slates.

What level of PPO2 are you prepared to accept for back gas and deco gas?
- Up to 1.6 for either, finally depends on total CNS

Are you planning on incorporating back gas breaks?
- yes

What do you consider the biggest risks in the dive? Narcosis? DCI? CNS? Gas?
- Equipment failure. The Narcosis will be within my tolerable level, DCI and CNS will be within accepted and practiced risk levels and loosing a gas will be catered for by longer deco and help from the surface. I will use 12L tanks for all.

What kind of support and backup do you have available?
- surface cover to be confirmed, but I want to be capable of doing the dive without needing their assistance - perhaps a hang tank of O2. They will be rebreather/OC Tmx trained and ready.

Who is your buddy?
- no one

What decompression model are you going to use?
- VR3, with bailouts using Proplanner or V-planner

Do you want to make any changes to that decompression model?
- I may depending upon others advice maximise my O2 window, last stop at 3m. But will intend to use the actual from the VR3 on the dive. The bailouts would only be used if both computers went wrong.

Do you use deep stops?
- Yes

Do you have a p-valve?
- Yes, and would hydrate on the stops.

How much conservativism do you want to apply to your deco?
- 20% VR3 / + 2 on V-Planner

How old/fit/overweight/etc are you?
- Never smoked, 82kg, resting heart rate of 52, fit.


What mixes/tables would you use and how would you answer those questions.

Cheers

[Ainsleyberryman]

Hi, Mark (Chase)

Just read your reply after responding to the other Marks. Thanks for the advice and offer of further advice. I have only just started to look at gasses and deco schedules using V-Planner as its easy to play with. But I would prefer to use somthing that was more similar to my VR3.

I previously used 12l for all my tanks and would be there when they mixed them up. I will be doing it with Emperor as i use to work for them and know some of the staff. One of my close diving friends is currently there and Ive met their technical guy Arron at the dive show.

My ascent rates will be around 8 to 10m/min as I will reel off from as deep as I can and use that as a control.

Your right about the floaty ally tanks, I was considering that and will do weight checks to sort it.

As for travel gas and backup i could cope with four tanks if needed.

Bloody expensive gas bill !

I will have to do some more plans on Decoplanner first and then get back to you. I dont currently have a copy, is it freely available or do I have to buy it ?

Cheers,

[Mark Chase]

What level of narcosis are you prepared to accept?
- Up to 40m - but less on the bottom

Up to you but pushing it with three 12ltr stages IMHO

What is your breathing rate?
- 12 for the bottom, 9 for deco (im not planning on swimming anywhere)

Egypt is not like the UK slack is unpredictable so are up currents and down currents. My SAC is about the same as yours and plan 15 to allow a margin of error but again this is your choice.

What failures are you going to plan for?
- loss of one or more deco tanks - Yellow blob + slate to send down more. I use a double wing, two DSMBs, two reels, two computers, two masks, Manifolded twins with a slobnob, bailout slates.

Take your own slob knob but check what manifolds they have, as it might not fit.

What level of PPO2 are you prepared to accept for back gas and deco gas?
- Up to 1.6 for either, finally depends on total CNS

1.6 for back gas? Surely not it would make the CNS silly.

What kind of support and backup do you have available?
- Surface cover to be confirmed, but I want to be capable of doing the dive without needing their assistance - perhaps a hang tank of O2. They will be rebreather/OC Tmx trained and ready.

DONT use a hang tank without a diver on hand to protect it. There are so many scobydoos about and they do the strangest things

Who is your buddy?
- no one

They wouldn’t / shouldn’t let you do it.

What decompression model are you going to use?
- VR3, with bailouts using Proplanner or V-planner

Do you want to make any changes to that decompression model?
- I may depending upon others advice maximise my O2 window, last stop at 3m. But will intend to use the actual from the VR3 on the dive. The bailouts would only be used if both computers went wrong.

If your going to use the Buhlmann based VR3 for the dive your bail out must also be Buhlmann based so avoid Vplanner.

How much conservativism do you want to apply to your deco?
- 20% VR3 / + 2 on V-Planner

My 2p Run the VR3 on 0% and mentally add your own conservatism. You can add as much as you like but taking it away in an emergency will bend it and task load you.


We used 13/65 because we bounced the 102 bit so PP02 wasn’t a major issue. I would say 11/60 would be a better choice of your planning on staying at 100 for any period of time.

We used 21/20 travel and deep deco but in hind sight I would up this to 21/35
Then we used 32% Nitrox and 80% Nitrox for deco. 100% is going to mean short fills. and 50% put too much pressure on the bail out plans and the travel gas so we stuck to 32 & 80. Using 80 meant we didn’t need air breaks and didn’t have to factor the back gas into our bail out plans.

What’s the dive site and what are you expecting to do at 100m for 20mins?

Also note my Suunto computer craped out at 100m telling me I was at 116 m. These depths put quite a strain on the equipment. Fortunately I took three computers

ATB

Mark Chase

[db8us]

Be careful with the VR3 at that depth and Bottomtime. There were some pretty ugly bends in that range...
If other software does not match this profile question ALL systems, including the ones that you already have paid for.
20Min BT in 100m is a LOT of OC gas and with D12 i would say "unmanageable".
I will not comment on the solo-stuff etc...
Just: Be careful

I would use D18 or 20, 10/70 as backgas and 35/35, 50/25 and O2 for deco.
(and i am not saying that this is enough gas)

Divetime would be around 2-3h
First stop would be at around 80m.
IMHO equipment issues are rarely a problem compared to planning and execution...

Michael

[Mark Chase]

We paid about £150 for twin 12s of 13/65. but the 350 includes trimix and deco gas for the 50m & 80m build up dives. I think Emporor are charging us 0.05p / ltr for trimix. We are booked for a tec dive livaboard with Aaron in Feb 05

Here is our trip report or the blue hole dive we did it with Posiden Divers:

http://www.yorkshire-divers.co.uk/fo...ead.php?t=1257

ATB

Mark Chase

[Ainsleyberryman]

Great advice, thanks for the comment guys. Im going to continue to plan taking on board your points. Im not sure where I will do it. I was thinking of somewhere near Sharm as its closer to the chamber !! But will sort this as part of the plan.

I will spend some time fiddling with weight and four/three tanks first, but yes, END of 20 would be better and 1.4 to keep the CNS down is what Id plan. Afterall I will be doing a hang in nice surroundings, unlike mid channel. I will get some deco software that is Buhlmann based and use that.

Interesting about your poor old Sunnto. I use one as a bottom timer, but will be taking two VR3's along for the ride.

Any comments on diet before and during. I will only be drinking water for the preceeding four days, and may consider using some of those elecrolyte sachets during the dive.

How did you feel during and after the dive, and what temp do you think it will be over Xmass ?

Cheers.

[Mark Powell]

Hi Ainsley,

I think the biggest problems is going to be gas, especially with a 20min bottom time.

When planning a dive I usually plan for a consumption rate higher then my real average rate. Then you have some contingency if something goes wrong. Is there any contingency in your planned SAC rate?

I would tend to favour a travel gas with some helium and then an additional two deco gases. 32 and 80 as well as 50 and 100 as pairs of deco gases are popular choices although you need to consider CNS loading.

The biggest risk as I see it is loosing one of your deco gasses. You won't have anywhere enough to complete your deco. If you don't have a buddy then you will need a deep safety diver. What's the reasoning for not having a buddy (or two!).

Appologies for all the questions but I believe that if you are going to do a dive then you need to think through the various factors. If I just told you what I would do, it wouldn't really help you.