Rebreathers... why are they not more popular?

[wedivebc]

Thanks to all for the information...especially the detailed answers from caveseeker.

One other question. Caveseeker mentioned electric vs manual rebreathers do manual rebreathers offer more safety since electric can go haywire?

Dan

Not really since the electronic RB can be flown manually in the event of trouble. What causes more problem is electronics can promote complacency and they tend to check their PPO2 less often than us manual guys. The electronic guys can generally go deeper, 300ft+ My particular system stops delivering O2 at about that depth

 

[peterbj7]

The difference is that you can typically tell when something is wrong in an aircraft. You can also tell when your OC SCUBA isn't working (you're not breathing).

Although I've never used one, there have been a number of posts here regarding people who have died without ever knowing anything was wrong.

Terry

I agree with both BJD and CS. I've read the fine print of most CCR accident reports I've been able to get hold of, and "driver error" really is far and away the biggest factor. People not assembling their unit properly and because of "getinthewater-itis" haven't done the checks that would have revealed the problem, people who've ignored warnings given by the machine to warn that something's wrong to the extent of hammering the "offending" component on a boat rail until it shuts up, people who've deliberately removed their only OC access to the on-board diluent tank and haven't bothered to take a side-sling because "it's only a shallow dive", people who've failed to brief their OC companions on what constitutes an unusual situation with a CCR, so that even when they see an emergency taking place they don't recognise it as such.

The list goes on. Complacency is what kills most CCR divers (and most advanced OC divers too, come to that). Lack of training isn't the factor it once was, but it really is incumbent on the diver to ensure (s)he really does understand what is going on inside the black box (bright yellow in my case) and goes onto the water with his/her eyes open. You're on your own down there, no matter who may be with you.

On the subject of cost, I find CCR diving rather more expensive than OC at air depths, and vastly cheaper below that. But at any depth you see much more as sealife isn't scared away by the noise and bubbles any OC diver makes.

 

[caveseeker7]

You're welcome, Dan.

One other question. Caveseeker mentioned electric vs manual rebreathers do manual rebreathers offer more safety since electric can go haywire?

Manual rebreathers obviously have less electronics and less battery powered components to fail.
That doesn't make them fail safe, nor does it mean they have neither electronics nor batteries.

The manually controlled Classic and Sport Kiss still have the three O2 sensors (which generate a current that is measured in mV and displayed as pO2), three separate digital displays each containing a battery to supply the power. Therefor there is tripple redundancy when a cell or battery fails. Afaik Jetsam doesn't use waterblock cables, and I'm not sure how a unit would respond to cable damage or a short.

What the Jetsams don't have are solenoids, setpoint control computer and the higher output battery power needed (mostly for the solenoid). With eCCRs things get more complicated as the implementation of electronics has a vast variety with huge differences. One or more setpoint controllers, with or without integrated deco, digital primary displays, digital or analog secondary displays, HUD and tertiary displays. In addition, the location of these components and the interaction between one another also influences the way they work and the safety and redundacy they actually provide.

With so many different designs available one could write pages on that subject alone.
Let me give you two extremes: The SMI PRISM Topaz and the Cis-Lunar MK-5P.
They are at opposite ends of the scale, everything else falls in between.

The PRISM has a single setpoint controller located in a compartment outside the loop. The electronics are potted, as is the depth sensor that allows the electronics to switch from low to high setpoint and back at 18 fsw. On top of the potting are the primary and secondary calibration pods, which have their own seals. The 9V battery is in the same compartment. The primary display is a HUD with three multicolor LEDs, giving info on setpoint and system as well as battery and cell warnings. Power between battery and electroncs can be cut with the power switch, so no current can eschew the sensor readings in case of a short.
The secondary is an analog gauges that doesn't need a battery, instead running directly off the current generated by the sensors. The mV meter with the pO2/battery scale is potted and displays output of the three cells, and with the electronics switched on the setpoint and battery condition. Setpoint can be monitored without any battery powered electronics, hence battery or electronics failure is not an issue.
Overall a very simple, transparent and safe implementation of electronic control and completely independent and separate analog backup.

On the other end of the scale is the MK-5P. It has a rather large electronics box in the shell that contains two separate setpoint controllers, two separate audio alarms, a depth sensor and three separate batteries to power it all. Separate means that all those components have their own compartments. On top is are two LEDs, tertiary displays for safety divers or dive buddies. The large primary display, which contains the digital display, another setpoint controller, depth sensor and yet another battery. All that is connected to the rest of the electronics by a cable, and the three controllers communicate with one another. Either of the three can run the CCR. There are also pressure sensors for the onboard tanks, so contents are displayed on the primary as well. Two seven liter external tanks can be mounted and also hooked up to pressure sensors and displayed. While at it decompression is calculated, for several different divers if needed. A HUD gives info on deco, system status/warnings and setpoint. On the backsite of the primary is a digital secondary display that reads the analog cell output, is connected by it's own cable and has its own battery. As you can tell by now, there's a reason the price for one of these CCRs was between $15,000 and $18,000.

Different divers have different preferences in the setpoint control, manual or electronic, and in case of the latter in which implementation. I would prefer a manually controlled unit over some electronically controlled units, but not over others. The PRISM's electronics were one of the major factors I decided on that unit, and one reason why the SM1600 (MK15.5) would be my second choice.

Other divers wouldn't dive either one because of the electronics.

 

[wedivebc]

Afaik Jetsam doesn't use waterblock cables, and I'm not sure how a unit would respond to cable damage or a short.

Jetsam (KISS) uses ambient pressure so if the cable severs both handset and loop would get wet.

 

[caveseeker7]

Thanks Dave.