On Fri, 2 Feb 1996, Richard Pyle wrote:

> Then why, among my stack of NEDU reports, do I find various evaluations 
> of the "Mk 15 1/2 Closed Circuit UBA"? (e.g., Rept. No. 10-84)

The military wasn't happy with some of the features of the Mark15 such as 
the small scrubber size which limited scrubber duration. They also didn't 
like the stainless center section. There were other minor things they 
grumbled about as well. BioMarine decided to build another unit that 
corrected the complaints of the military and built about 18 Mark 15.5s 
for the military to evaluate. The military evaluated them and liked them 
and wanted other features added. So BioMarine used the Mark 15.5 design 
and incorporated the new additons into the design and the Mark 16 was 
born. BioMarine made the Mark 16 for a while but during the process 
the government decided to reopen bidding on the contract to 
supply rebreathers and Carleton beat out BioMarine in a hotly contested 
race. So, the 18 Mk15.5 reverted back to BioMarine. BioMarine was bought 
by Don Rodocker who, as part of the deal, acquired the MK15.5s. He sold 
them to civilians including me and McKenney. There are now more than the 
original 18 Mk15.5s out there because all that needs to be done to 
convert a MK15 (of which there are a lot floating around) to a 155 is to 
replace the center section with a 155 center and viola a MK15 becomes a 
155. I know someone who has done just that. 


> 
> I don't know the history well enough, but I do know there are some
> fundamental differences in design concepts between the two units (you
> know, trivial things like counterlung placement, electronic and manual
> control principles, scrubber canister design, etc). What you suggest above
> might be akin to saying that the Mark 15.5 grew out of the foundation laid
> by the Fleuss Mask. My understanding is that the reason Stone started at 
> ground zero on rebreather design was that he wasn't happy with the 15.5 
> for cave diving.  He could have saved a hell of a lot of money by just 
> modifying the 15.5 to meet his needs.  Unless he's stupid (and I happen 
> to know that he's not), he must have had some reason for re-inventing the 
> wheel.

If I were building my own rebreather, I would change several things about 
the 155 that are made for the military but unnecessary for rebreathers 
in general. Basically, the military needs good units that are a. dumb 
proof, b. shake, rattle and roll proof and c. completely reliable in the 
hands of guys who could f**k up a steel ball. I mean, BioMarine was asked 
to remove the off-on switch and not put one on the MK16 because the guys 
were torquing them off (and the switch is not inconsequential). The 16 is 
turned off-on by removing and installing the battery. The switch can be 
found on MK15 and 155s. Remeber too that Stone-if I remember the history 
correstly- built two complete rebreathers in on Cis-Lunar until he 
realized that some things did not have to be redundant. He took one such 
unit and made two out of it and you now have them both. There is no 
question he looked at the MK155 and redesigned it to fit his needs- with 
the 155 providing a positive stimulus for the resulting unit.   
 
> On the other hand, what makes the 15.5 so attractive is the incredible 
> amount of testing that it has been subjected to.  Over the past year, 
> I've learned a lot about how important it is to have real-world test time 
> on units in a variety of conditions, and the 15.5 is near the top of the 
> heap as far testing goes for mixed-gas fully closed 'breathers.

This is one of the biggest points for BioMarine. They know rebreathers. 
The new CCR500 is further evolution of their knowledge about rebreathers 
and the price of $7000 for a fully closed circuit rebreather makes it 
very attractive. For redundancy you could wear one in front and one in 
back for $14K.

> > You know, biologists have known for a long time that if earthlings 
> > worshipped anything it ought to be the sun for providing the oxygen we 
> > breathe and the food we eat. In the same vein, rebreather fanciers ought 
> > to worship the MK 15.5 as the fountain of all rebreatherness and as such 
> > they ought to bow their heads when we MK15.5 owners pass by with our 
> > units. Rod 


> 
> Huh?  The sun provides the oxygen? wha...?  Did I miss something? I 
> always though that the sun provided electromagnetic energy.

Inside each particle of electromagnetic energy is a tiny bit of O2 which 
is released when the energy hits a green leaf and other particulates in 
the ocean.

> But on the rest of the stuff (e.g. head bowing, etc.), I fully agree.

BTW, I thought your explanation for the bailout procedure if you lose all 
three sensors in the Cis-Lunar ( the three sensor concept came from the 
MK155) was excellent. Unfortunately, it is probably lost on 
non-rebreather divers because you have to practice the concept 
with a rebreather for it to become second nature. For many divers, the 
only procedure to adopt if all three sensors fail is to place their head 
squarely between their legs and kiss their butt goodbye. Rod  


 > 
> Aloha,
> Rich
> 

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