Twin CCR for deep cave exploration

Drmike

So shes almost finished-


As anyone doing deep diving especially deep cave diving will tell you one of the biggest headaches is the need to have to stage tanks many tanks - sometime a huge number of tanks in the cave.

For next weeks expedition we will have around 20 stage tanks in the cave!!! for one dive!

I kinda decided we had almost reached the practical safe limit for staging in our exploration of Sra Keow, plus other deep caves we are exploring.

So twin Rebreather was the way to go .

My initial brief was;

1) Twin Rebreather
2) Primary ECCR back up MCCR


Then after checking out the available side mounted bail out breathers I decided they breathed like crap so I added a requirement that the back up Rebreather have;

3) Back/chest mounted Counterlungs

In order to have a good WOB

As many of these remote caves have to be swam (difficult getting scooters in) I added a tough one;

4) Overall profile in water must not be bigger


I looked for a long time at the twin back mounted Meg Idea. Spent many an hour while side scanning the Java sea discussing twin meg possibilities with Craig C who along with Steve and Fred (RIP) are/have been building a twin meg for their deep dives.

However twin meg would need side mounted tanks making the profile bigger
and there was the cost factor (having to buy/build 2 Megs) The big issue for the twin meg was also the counterlungs. I could put rear lungs on it for the back up Rebreather but the breathing hose routing is a real mess. The deciding factor against the twin Meg was that I really hate OTS CL so


5) Chest kept clear (No OTS CL)



There is no doubt (Im not even going to waste time saying 'IMO' because its obvious to all, that Boris is the best deep/exploration Rebreather out there - so I thought it would be great to have a Twin Boris!


So

6) Twin Rebreather would incorporate Boris.


So my specs were

Twin Rebreather
No OTS Lungs
No increase in profile
Incorporate Boris


sh1t that was a tough spec.


But actually shes finished and its all been achieved.

The beauty of using Boris as a starting point for a twin Rebreather is the fact its already got rear mounted lungs so simply by adding another set of rear lungs (thanks DaveT/Phi/Peter) I could keep my chest free and have better breathing than a sidemount Rebreather.

The next step was to build a scrubber. I looked at the design of YBOD/Meg etc. but inthe end designed my own because it was cheaper/faster and I could optimize the shape/size. I built initially an axial scrubber (can be fitted radial also) fairly big with good water traps.

The scrubber can is anodized alluminium - rest is all Delrin.

The scrubber is attached to the base of Boris and the hoses run up either side and connect to the BMCL T pieces. The hose routing is neat and tidy.

The unit has a single cell at the moment but can take 3. Haven't got the display yet but it will either be a Hammerhead secondary courtesy of Kevin or an integrated VR3 courtesy of the other Kevin (Depending on which one gets here in time before the trip)

When shes on you dont know its there. The scrubber is the same width as the Boris (when Boris tanks are fitted) and so drag should be practically the same.. Other than having a 2nd mouthpiece under my chin I cant tell its there.

Ill be testing her for real next week then if all goes well seeing how she performs sub 210m

The attached pic is of the unit during testing (pre-anodizing of scrubber)

Im thinking of manuafcturing a bunch of these (see DaveT for the lungs) so if anyone wants one drop me a line (after Sra Keow)




PS - Jerome you are going to want one of these!!!!

Attached Images

twinboris.jpg (14.8 KB, 954 views)

__________________
Cave diving is a sport
Wreck diving is a sport
Diving in general is a sport

'Rebreather diving' is not a sport
its the delusional obsession with a highly dangerous and often inappropriate piece of equipment

DeepBlueInnovation

Thanks for the run through your design process, I am looking forward to the post dive report. If possible can you post some pictures with another diver in the frame when rigged so we can get a profile comparison.

Cheers,

Ben.

Drmike

Sure. Its the same width as the Boris. (profile is same)

A real comparison would be a diver wearing Boris and carrying at least 4 x AL80s!!! because thats what I normally dive with on big dives (rest are all staged) SmugMug - Drmike : France (LOT) cave diving - Sept 06

__________________
Cave diving is a sport
Wreck diving is a sport
Diving in general is a sport

'Rebreather diving' is not a sport
its the delusional obsession with a highly dangerous and often inappropriate piece of equipment

SteveL

Mike,

Where have you got the ADV of the second loop?

Years ago before AP valves and Bob Howll made advs for the ybod we tried mounding a reg in the bottom of the scrubber canister - and it was crap - to much hydrostatic pressure difference - between lungs and the bottom of the canister.

On the scond loop as long as it adds gas on decent even when you are not breathing off it is probably the most important thing but just thought Id mention it for due consideration.

Steve

Drmike

Im using inspiratation T pieces (With ADV) ADV is plumbed into same source as primary unit ADV so it will always fire on descent.

What you can see on the side of the scrubber lid is the manual O2 inject button

__________________
Cave diving is a sport
Wreck diving is a sport
Diving in general is a sport

'Rebreather diving' is not a sport
its the delusional obsession with a highly dangerous and often inappropriate piece of equipment

schford

How / where do you mount the diluent & O2 for the second breather - I am guessing you would not use the same o2 and dil for the Boris ....

__________________
Bailout and Kit Management account for Murphy's Law

The only bad question is one you did not ask and later wish you had.

Use of Rebreather World is subject to the Rebreather World Terms & Conditions of Use

dave t

Well done Mike, looks great.

I have some experience with twin ccr's so couple of points I would mention, run three cells not one, my belief is the secondary should be as good if not better than the primary ccr!

dont assume that at the depths you are talking about the secondary scrubber will start working as soon as you get on it. I have tried switching to a cold scrubber at 80m without any troubles but at your planned depth...........velcro the second mouthpiece to your chest otherwise it will float about and drive you nuts!! make sure youi keep the po2 in the secondary at least the same as your dil po2 at depth. consider you may have to go OC for a few mins before getting on to the second breather.

I am sure you have thought of all this anyway but its worth saying, good luck and stay safe

Dave

tecdivertraining

looking forward to seeing it next week. how do you think it will work with my meg?

PS did you sort out the sofnolime and how much was the excess.

cheers

__________________
Mathew Partridge
Technical Director
Pro-Tech Dive College
www.protechdivers.com
www.tech-ccr.com

Drmike

Hi Dave,

Thanks for the advice and info.

I studied the failure mechanisms and risks etc and concluded the best thing to do was:

Primary Rebreather and Back up ADVs both from same dil source (big dives - so thats offboard dil. (The reason same source is you know that the dil supply to the back up adv is on - obviously no flow stop on back up ADV. This avoids the risk of crushing/flooding the back up due to lack of ADV firing and you know that at depth your ppo2 is practically setpoint anyway as soon as you bail.
Three cells will be the norm but only if the parts get here in time. Having the VR3 plugged in gives deco - which is nice to have - I may do both

On long dives backup Rebreather will be breathed occasionally and in long or short dives the initial bail to back up Rebreather will initally be SCR to help the scrubber warm up.

The backup mouthpiece is on a short hoses and tucks under the two manual inject connectors on Boris - fits nicely!

Cheers
Mike

__________________
Cave diving is a sport
Wreck diving is a sport
Diving in general is a sport

'Rebreather diving' is not a sport
its the delusional obsession with a highly dangerous and often inappropriate piece of equipment

Drmike

Big/long dives so you need off-boards anyway (to get the volumes)

With a twin Rebreather big risk is losing all the O2 so I like tp carry small backup O2. So I run units from same offboard O2 and keep on board O2 and Dil as backup.

Benefit of using same dil and O2 supply is its always on and always ready to go. Dont want to bugger around connecting hoses turning on valves ect at depth. Just bail and go. The other benefit is you wont cock up and have either dil or O2 turned off.

Risk is that you have more failure points where you can lose O2 or dil - well I have back up (2L onboards) so thats not really a problem - also benefit outweighs risk

__________________
Cave diving is a sport
Wreck diving is a sport
Diving in general is a sport

'Rebreather diving' is not a sport
its the delusional obsession with a highly dangerous and often inappropriate piece of equipment