Is the Mk VI / SE7EN really that dangerous

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Who, diving and not diving this unit, have first hand experience a failure during a dive, be it in person or witnessed?

I have had a cell start to die during a dive, the unit told me which one and how it was failing, I elected to bail out and continue the dive OC (25m NDL wreck dive with an AL80 bailout and OC buddies). That cell was right at the end of it's rated life anyway so not a unit issue. I have had some pre-start tests fail, usually due to user error, I have never lost a dive due to it.

non-zero chance it will find a "problem" and prevent you from diving.

The only test it does are those you would do on any unit pre-dive, if it fails those should you be diving anyway? It makes normalisation of deviance a much harder concern, which would maybe have saved the lives of a few people we know.

Return to Factory for almost all maintenance, pre-packed scrubbers, lack of versatility due to the factory locked nature of the unit.
One of the issues was its ability to do mix gas diving. But there may well have been upgrades to the unit or available packages that negate this criticism.

There has always been a repack scrubber available, everyone I know dives with those for their own diving. Molecular have announced they are ceasing production, Poseidon is bringing out their own repack very shortly. The solenoids and gas manifolds are inside the head, those do require sending to the factory unfortunately. Customer service has not always been what it could be from Poseidon, sadly, especially in the US though I believe that is much better now.

As a disclaimer, I have not been trained on the unit, I have not used one, and I have not spent any time looking at them. So I might well be wrong.

Not a dig at you, Gareth, but that is what happens on a LOT of CCR discussions. People make their own assumptions based on their perceptions and then fight to the death on those.

I don’t like the automation involved, I don’t like their upgrade path, but I understand why they do both.

The upgrade path is purely to get the appropriate training, then get the appropriate battery. A full path is as follows:

Buy CCR in rec config. 40m NDL battery (green) is sent to your instructor, if you aren't certified.
Do Tec40 equivalent, get yellow battery (40m, deco enabled)
Do normoxic (either 48m or 60m trimix battery depending on agency and add MAV and inverted tanks)
Hypoxic (Deep battery (black))

It does suck that you end up with batteries you don't really use, but there is a 2nd hand market for them as spares and for people upgrading.

Simply blowing dil across the face every once in a while won’t necessarily show a problem.

It's not that simple. Every time the unit adds O2, that blows across the face of the primary sensor. The unit knows depth and temp and the gas, so it knows what it SHOULD read, and compares that to the actual reading. It also compares that to the reading of the 2nd cell which gets a dil squirt every time you add, and that then gives you an O2-high calibration and an O2 low calibration, continually compared to each other and to the theoretical comparison.

In practice, it means that all the maths we are doing on a "normal" unit (mV readings at 6m O2 flush, linearity check, dil flush etc) are being done continuously by the unit. It is one less thing for ME to get wrong...

The Poseidon methodology is simply to tell you to bail out.

In Rec mode, yes as that is the philosophy of Mod1. As you enable more features the machine holds your hand less and does more to enable you to safely stay on the loop.

If that’s possible with the Poseidon

For US versions, yes, as the valves on the tanks are all DIN. CE versions have the M26 O2 first stage so not possible.

hop on a unit that you have zero pedigree with just doesn’t give me the warm fuzzies

That is reflective of the type of diver you are, for those looking at recreational CCR diving, which is the point of the unit, all units that they see out in the wild will be the same. It is why mods are not encouraged. If you gave me a random Poseidon unit to dive right now, if it passed the pre-dive checks and a 5 minute visual inspection, I am confident that I can go and do a NDL, warm water dive with it. Deep, long deco etc? I would take my own, minus the tanks and auxiliary gear that I can get that side.

My main gripe with the MK6/MK7 is the number of courses and battery options that have to be bought after each course in order to dive 10M deeper. At a rough guess you'll spend more money on courses and special batteries as you advance to 100M dives, than the unit cost new at full retail price. Almost every other rebreather doesn't actively limit you in your diving after you buy it.

As above, its NOT every 10m. Its after very phase. So, the phases are : NDL 40m, deco 40m, 50m trimix and 60m trimix (that is agency dependent. You do NOT have to get both.) and then 100m+ full trimix. Those batteries are 250 USD so IF you got all of them, and did not sell your used ones, you would be 1000 USD in (you would get one with your unit). The CCR industry has always looked for ways to limit liability due to the huge impact of only one or two fatalities. They used to have PIN on the handsets, only sending a unit to an instructor who would then unlock it after training etc.

I do not believe that it is in the interest of the CCR manufacturers OR us as divers, to have someone be able to do a 100m+ dive on a unit they have just received in the mail and are not trained on. Others may have different opinions, and there are other units for them.

Poseidon CCR diving is a philosophy change from other units. That philosophy is not for everyone, sure.

In aviation, there was HUGE debate around autopilot when it first came out. Horror stories of how the machine would take all choice away and try kill pilots left and right. Same with fly-by-wire.

Now, all commercial flights are conducted with autopilot from 200' and above. The philosophy now is, let the machine do what it does well (maths, calculations, split second monitoring etc) and let the human do what it does well, which is monitor the machine and make choices of when the machine is not behaving and take over. That has resulted in an unprecedented level of safety since the human is almost ALWAYS the weak point.

In CCR diving, the Poseidon is a Dive-by-wire system. I know what causes failures, I know what failures look like and I know which I can recover from and how. For the rest of it, I am a fallible human. The machine does a WAY better job of monitoring the "boring" stuff than me, so I let it do that and I watch it.
 
Isn't it possible to buy a Seven in tech configuration and with the tech battery directly?
Yes, but they won't send the battery to you. They will send it to your instructor who will use it during the training and then hand it over on certification. At least, that is what is supposed to happen. There are always some batteries on eBay or wherever.
 
Isn't it possible to buy a Seven in tech configuration and with the tech battery directly?
Not really sure, but as far as I understand, the rebreathers are made up to the maximum certification of the diver ordering it. If your instructor orders a MK7 for his own use and then sells it to a student/ex-student , the end buyer could end up with a RB that has capabilitys that are inappropiate for the owner's skill level. This isn't usually a problem until the RB has to be returned for factory service. Getting it back in the same advanced configuration as the diver shipped it to Poseidon might not be possible, afaik.


Michael
 
Yes, but they won't send the battery to you. They will send it to your instructor who will use it during the training and then hand it over on certification. At least, that is what is supposed to happen. There are always some batteries on eBay or wherever.

The quote below does hint that it is possible to buy an unlimited unit at once when you start training.


CCR FAQ - Poseidon Se7en | Dive Gear Express®

"
What battery module should I choose?
The basic rechargeable smart battery Rec 40 (aka Green) supports sport limits of no-stop required dives to a maximum of {132 fsw | 40 msw} on air diluent. Poseidon offers a selection of other batteries (identified by their color) that each enable software features which allow progressively more advanced levels of diving. Because these batteries are expensive and time consuming to later upgrade, for divers who expect to exceed sport limits we recommend always initially choosing the Deep (aka Black) battery that unlocks all functionality and has no depth or gas mixture restrictions."
 
Not really sure, but as far as I understand, the rebreathers are made up to the maximum certification of the diver ordering it. If your instructor orders a MK7 for his own use and then sells it to a student/ex-student , the end buyer could end up with a RB that has capabilitys that are inappropiate for the owner's skill level. This isn't usually a problem until the RB has to be returned for factory service. Getting it back in the same advanced configuration as the diver shipped it to Poseidon might not be possible, afaik.


Michael
The only part of the unit that is specific to a certification is the battery. The rest of the unit will be serviced and sent back the same way it came. ordering a replacement battery if you weren't supposed to have the original one could be an issue.

EDIT: I see from the above post that that may no longer be an issue.

I can dive a 7 in full tech config with a Rec battery, no issues, no training required. the difference is the tanks are inverted (ignore after start-up) and there are MAV for O2 and Dil (disconnect and dive as normal.

All my settings and preferences and dive logs are stored in the battery so once I boot it up, the unit will behave exactly as my own.
 
Thanks for the in depth explanation, I’m sure you’ve explained this before but I keep forgetting the specifics. Let’s say you add O2 at 10m. So you’re saying (let’s go with air dil) that the primary cell goes, yep, 2.0, and the secondary cell goes , yep, .42, everything is good? And if the secondary cell is current limited at say, 1.0 it tells you to bail out? I’m assuming the unit tells you that the secondary cell has failed due to current limitation? How does this behavior differ on a rec battery as opposed to the deep battery? Will the unit let you continue the dive, now that it has made you aware that your secondary sensor is toast? How much of a failure state will it allow? Could you continue the dive without the unit doing squirrely things? How will the unit behave?

As to the tank thing, I physically cannot mount my tanks to either of my units incorrectly and have them physically connect where the required connections are. This is possible with the Poseidon?
 
If the issue is current limiting, the unit will reduce the set point to a max of 1.0 (known good) and allow you to continue the dive, with a warning that the SP is now reduced. If the primary cell is failed (erratic or unexpected readings) the unit will advise bailout, while attempting to use the secondary sensor to maintain a breathable gas should you decide to stay on the loop. You will have a continuous warning and red buddy light.

if the secondary cell goes, then you will get a warning, however the unit will allow you to continue as long as the primary, continually monitored, cell is still behaving. That will allow you to remain on the loop in a deco scenario etc.

If you remain on the loop, the unit will always attempt to give you a breathable gas, at the highest SP it is confident of.

One fatality early on occurred where a diver (untrained, never dived CCR before) put one on with a VERY low battery. It alarmed, warned him but he ignored it and continued diving. the unit load shed as the voltage dropped until eventually the only thing working on the unit was the solenoid and then that died, he went hypoxic and died.

If you go in the water with the unit switched off, it will switch on and alarm to tell you that it has not been tested, then go into life support mode and try to give you something breathable as long as it can.
 
If the issue is current limiting, the unit will reduce the set point to a max of 1.0 (known good) and allow you to continue the dive, with a warning that the SP is now reduced. If the primary cell is failed (erratic or unexpected readings) the unit will advise bailout, while attempting to use the secondary sensor to maintain a breathable gas should you decide to stay on the loop. You will have a continuous warning and red buddy light.

if the secondary cell goes, then you will get a warning, however the unit will allow you to continue as long as the primary, continually monitored, cell is still behaving. That will allow you to remain on the loop in a deco scenario etc.

So it will allow you to continue, but makes injection choices based on the lone viable cell, in the example I mentioned? Interesting. Will it continue to give you information if both cells have an issue? For example, how would it deal with running SCR, in the event cells are current limited higher than the PO2 of your dil at depth? Will they continue to provide adequate data? Do you still have access to raw sensor output?

I’m on my phone. This is annoying trying to type. I’ll revisit this later. I have more questions.
 
So it will allow you to continue, but makes injection choices based on the lone viable cell, in the example I mentioned? Interesting. Will it continue to give you information if both cells have an issue? For example, how would it deal with running SCR, in the event cells are current limited higher than the PO2 of your dil at depth? Will they continue to provide adequate data? Do you still have access to raw sensor output?
If you are on a 7 with the M28 computer as controller, then you have a display of both sensors and what they believe the current PPO2 is. On a paddle, no. In that case, the PPO2 field is replaced by a flashing Cx error, where the x is a number indicating how severe the issue is and which sensor is giving the problem.
 
Remotely related to the topic...
Are there any public figures regarding the popularity of different rebreathers worldwide?
Total number of units sold by each manufacturer is probably what I am looking for.
 
https://www.shearwater.com/products/teric/

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