Quote: (Originally Posted by
Gill Envy)
with all this talk of WOB and skepticism, I have to ask Alex and Dave, when a test is done for WOB, is it on a machine or a human. there are so many variables to actual human performance which could be missed by a machine. for instance, what I've noticed is a huge variance of mouth piece thickness. the stock version that comes with the meg is super thin (my front teeth actually come together), the one that comes with the Evo is quite thick (holding my front teeth a good 1/2 inch apart) and I've seen everthing in between on other rigs. I can imagine that you could make a very capable rebreather in terms of WOB then make the mistake of putting a thin mouth piece on it that simply makes the teeth a barrier that add significantly to WOB in high respiration. I swapped out my mouth piece on the meg from the get go with a thicker one. Further, I've noticed that in the worst moment, we tend to bight down extra hard in current, potentially reducing the size of the air way. Are any of the WOB test taking this dynamic into account.
WOB is measured on a breathing machine with the equipment in salt water in a pressure chamber. This gives a result that can be reproduced at any time, that is objective and allows for direct comparisons.
In looking at the mouthpiece bite, we check the cross section is at least as large as the opening in the mouthpiece itself and record a problem in the results if it is smaller, and that we have had to change out the mouthpiece.
Humans are very poor at measuring WOB, but manned underwater tests do have a key roll in testing.
Human testing can check things like the ADV fires when the CLs are bottomed out in all positions, they feel they get a big enough breath or not, how the CLs affect trim, how water dumps work or interplay with the OPV and other ergonomic issues. Of course, if any changes are made, one has to repeat the machine testing all over again.
Alex
NB: Just one note on the recent divergence of this thread - the results of the under-funding complained about, are systemic in sports rebreathers. A new eCCR done completely properly costs vastly more than one would imagine. If there are 5000 rebreather users, who buy a Euro 3,500 rebreather once every 7 years, then that is just Euro 2.5mn of sales a year. Even if one spent every penny of it on R&D, it would take 5 years global sales to fund one new rebreather development properly. Given that revenue from sales has to be used to produce and support units, then there is simply not enough revenue potential in the sports market to fund a proper job. Some companies are better than other in avoiding the worst results of under-funding, and some have had larger budgets than others, but the result is still defects in products that would not be there in a commercial or military product, where the market is larger. The most expensive part is always that last 10%, and it is the most under-estimated.
One thing the accident list is for, and the Open Revolution initiative, is to enable some core information needed by everyone to be published, so each company does not have to reinvent the wheel. Lets return to that objective, to put the accidents here, and analysis on another thread. The WOB issue is a good point to debate, as its role in accidents is unclear, but saying unit A or B has underfunding problems is a statement that could be repeated many times on different units. There have been more than 30 companies try and make sports rebreathers.