dpv or rebreather? Or at least Dpv then rebreather?

[Errol Kalayci]

I am a passenger being driven home to S Fl from cave country as I write this so excuse typos. Today's dive was conducted as 3 man team each equipped with a bottom stage, oxygen bottle, Suex Dpv (xk1 or joy 37) and 104's on the back. We dove for a 80' bottom time starting time when we finished tie off into main line and hit trigger. We only used our stage and never touched back gas. Having not been in this cave in a decade, I took the lead and a team mate called it when we were at 3,900 feet into the cave. Total bottom time was 80' to beginning of ascent at 50' and we were on trigger the whole time. Our avg depth was 80 feet. We stayed on bottom stage until O2 switch and had 700psi left (started with 3,000) when we loaded truck. During the dive we saw side mounters swimming in of passage, rebreather divers, etc.

Thinking of the dive, I realize that we only used 66 cubic feet for 80' bottom time plus ascent to 02, including wing and dry suit inflation. To determine our scr simply divide 66 cubic feet used by 80 minutes x 3.4ata) and you come out with .25. Therefore, with a Dpv in a flow cave using only 66 cubic feet we covered 7,800 feet round trip, had 80' bottom time at avg depth of 80 feet. This is a huge gas savings over the average swimming diver's scr of .75, where that diver would need to use 205 cubic feet of gas to dive for 80 minutes at 80' ( .75 x 3.4 is 2.55 cubic feet per minute times 80 minutes bottom time is 205cubic feet needed). So we had an immense gas savings and was able to cover way more ground than a swimmer would during same amount of time. As you can see, a Dpv gives you a huge distance and gas leverage advantage and thus you get Speed plus a somewhat like rebreather gas advantage without the inherent risks associated with rebreather's. Historically, divers find about a forty (40%) percent reduction in gas usage while using a dpv vs swimming on open circuit with the addition of being able to move more gear effortlessly and quicker without raising work rate or travel much further (Dpv is typical 300-400%) distance advantage as well as gas leverage advantage. With all this said, why do many divers choose a rebreather over a Dpv? It seems logically that a diver should choose a Dpv as next step in the evolution and then add a rebreather as a tool when further gas savings is needed to to extreme depth or real logistical concerns. Probably, most rebreather divers would be better served with choosing a Dpv instead of a rebreather or if they need the rebreather most all would need or should certainly use a Dpv (or two) as well.
The point of this post is not rebreather bashing but to reflect that a Dpv is a wonderful tool used in cave as well as ocean to reduce gas consumption by 40%, increase distance by 3-400% potentially, add some further safety and just have a whole lot of fun!

 

[tstormdiver]

I got asked this question by a friend a couple of weeks ago. The question you should ask yourself is,... what are your goals? Do you want speed/ distance? (DPV) or do you want bottom time/ distance? (rebreather). 2 different tools for 2 different goals.

DPV's get you further faster & don't require a huge amount of maintenance. However there must be greater awareness, as they can get you into trouble faster.

Rebreathers will let you stay down longer both gas & NDL's (you are breathing the best mix for the depth). They also require greater awareness of the machine workings & what is going on in your own body. There is also a lot of pre & post dive maintenance that MUST be done religiously.

 

[sea_ledford]

Historically, divers find about a forty (40%) percent reduction in gas usage while using a rebreather with the addition of being able to move more gear effortlessly and quicker without raising work rate or travel much further (Dpv is typical 300-400%) distance advantage as well as gas leverage advantage.

Huh? I'm assuming something was lost in the phone/car translation... But a CCR will provide a hell of a lot more than a 40% reduction in gas usage. The rate would depend on depth, since you use the same amount of gas on a ccr regardless of depth, well aside from dill addition on the way down. Otherwise people wouldn't be able to do 100m dives with less than 40 cuft of gas used.

Or are you referring to metabolizing 40% less O2 due to decreased drag or something else?

 

[Errol Kalayci]

There was a typo which I fixed, the 40% reduction in gas usage was from Dpv vs swimming on oc.
I disagree with the post about rebreather's giving you longer no decompression dives or shorter deco. First, in my opinion if you are not doing a decompression dive then I can not see where you would need a rebreather unless the water is very cold or logistics very difficult. Second, using standard gases across the intended range the avg po2 on open circuit is 1.2 which is the same on a rebreather so deco schedule is very close. Since a DPV reduces my gas usage by 40% I get much longer bottom times or ability to travel over swimming. Swimming at depth is bad for you for many reasons. A Dpv is a gas extension devices due to its elimination of workload which decreases co2 as well, a rebreather is a gas extension devices due to its recirculation some or much of each breath that can increase c02 from work of breathing or swimming hard, failure of flapper, etc but the scrubber neutralized the co2 via the base sorb material. Decompression is a draw, they are both gas extenders Dpv gives you speed/distance in work free environment, rebreather gives you heat, less noise. Seems logical to extend time via Dpv and save work stress underwater then add a rebreather later when you need to further reduce usage but then you will already have device to minimize effort and allow you to go much further while being better on your body

 

[tbone1004]

CCR will give you a deco advantage if you are diving standard mixes when you aren't at their optimum depth, may not be by much, but if you're doing a lot of up and downs or multi profile diving they can cut deco considerably.

Most importantly, most CCR divers are diving in situations where a DPV wouldn't be useful. Most ocean diving and wreck penetration is not really prime DPV use at least from a gas savings standpoint, and what I would argue is "most" major caves in Florida, you can't take a DPV in. Madison Blue *unless you're on the survey team*, the whole Peacock complex, Cow, quite a few others you get a major benefit by being on CCR and you can't take a DPV in there. Twin cave you get to use it for the first thousand feet then you're done, so you take a 20 minute kick on one stage and make it a 6-8 minute zip in on a scooter, but with as shallow as it is there's no major benefit, JB/Ginnie/LR sure you get huge advantages, but if most of your cave diving is in Peacock or around other areas where DPV use is limited or restricted, CCR gets you a lot of advantages, especially if you're spending $6k+ on a new one.

Being the owner of the first Suex shop in the country, you are obviously HEAVILY biased towards Suex in particular, and being a WKPP diver you are also heavily against CCR usage unless it is mission specific, so you you should lay that out as you are making these statements, there's nothing wrong with any of it, but you should at least state that this is your heavily biased opinion being a WKPP diver that CCR's are mission specific tools only, and as general common courtesy at least put the link to your shop in your signature since you mentioned Suex specifically.

I'm in the current boat of CCR and DPV acquisition. It is interesting to see the different schools of thought between Marianna and High Springs, with Marianna being heavily biased towards DPV use, and High Springs generally having significantly more CCR divers. I think spending $6k+ on a scooter is insane and if you're going to spend that kind of dough, you might as well just bump up to $8k-$10k and get CCR mod1 training which is a more useful tool for more diverse locations. I will be getting a DPV first as my buddy is dragging me to caves like JB far more regularly than I had originally intended and spending $2k on a UV-26 is much more amenable and I wouldn't want to kick through that cave on CCR or OC, but if I was diving Peacock, Madison, etc on a far more regular basis, or if I was regularly doing dives that require trimix, it would be CCR in a heart beat, you just literally can't argue on the gas bill savings if you're diving helium regularly, especially if you follow GUE standard mixes where below 100' goes to helium, no one can afford to make OC dives to 200'+ anymore, CCR's will legitimately pay for themselves if you are diving to those depths regularly, a DPV does little to nothing for you on deep wreck penetration or most ocean diving for that matter, CCR's allow you more bottom time with generally less decompression schedules, as well as the silence around the fish which is nice for reef diving and photography. Different tools for different types of diving and if you're cave diving, shore diving, etc where a lot of your dive time is taken "getting there" then sure, DPV's are great tools, but if most of your diving is in places where you aren't travelling a great distance then they are heavy and expensive paper weights and you would get more use out of a CCR....

 

[Superlyte27]

There was a typo which I fixed, the 40% reduction in gas usage was from Dpv vs swimming on oc.
I disagree with the post about rebreather's giving you longer no decompression dives or shorter deco. First, in my opinion if you are not doing a decompression dive then I can not see where you would need a rebreather unless the water is very cold or logistics very difficult. Second, using standard gases across the intended range the avg po2 on open circuit is 1.2 which is the same on a rebreather so deco schedule is very close. Since a DPV reduces my gas usage by 40% I get much longer bottom times or ability to travel over swimming. Swimming at depth is bad for you for many reasons. A Dpv is a gas extension devices due to its elimination of workload which decreases co2 as well, a rebreather is a gas extension devices due to its recirculation some or much of each breath that can increase c02 from work of breathing or swimming hard, failure of flapper, etc but the scrubber neutralized the co2 via the base sorb material. Decompression is a draw, they are both gas extenders Dpv gives you speed/distance in work free environment, rebreather gives you heat, less noise. Seems logical to extend time via Dpv and save work stress underwater then add a rebreather later when you need to further reduce usage but then you will already have device to minimize effort and allow you to go much further while being better on your body

Sounds like you've got it all figured out and made up your mind. Next question....?


Oh, btw, you're wrong on a few points.

 

[danvolker]

CCR will give you a deco advantage if you are diving standard mixes when you aren't at their optimum depth, may not be by much, but if you're doing a lot of up and downs or multi profile diving they can cut deco considerably.

Most importantly, most CCR divers are diving in situations where a DPV wouldn't be useful. Most ocean diving and wreck penetration is not really prime DPV use at least from a gas savings standpoint, and what I would argue is "most" major caves in Florida, you can't take a DPV in. Madison Blue *unless you're on the survey team*, the whole Peacock complex, Cow, quite a few others you get a major benefit by being on CCR and you can't take a DPV in there. Twin cave you get to use it for the first thousand feet then you're done, so you take a 20 minute kick on one stage and make it a 6-8 minute zip in on a scooter, but with as shallow as it is there's no major benefit, JB/Ginnie/LR sure you get huge advantages, but if most of your cave diving is in Peacock or around other areas where DPV use is limited or restricted, CCR gets you a lot of advantages, especially if you're spending $6k+ on a new one.

Being the owner of the first Suex shop in the country, you are obviously HEAVILY biased towards Suex in particular, and being a WKPP diver you are also heavily against CCR usage unless it is mission specific, so you you should lay that out as you are making these statements, there's nothing wrong with any of it, but you should at least state that this is your heavily biased opinion being a WKPP diver that CCR's are mission specific tools only, and as general common courtesy at least put the link to your shop in your signature since you mentioned Suex specifically.

I'm in the current boat of CCR and DPV acquisition. It is interesting to see the different schools of thought between Marianna and High Springs, with Marianna being heavily biased towards DPV use, and High Springs generally having significantly more CCR divers. I think spending $6k+ on a scooter is insane and if you're going to spend that kind of dough, you might as well just bump up to $8k-$10k and get CCR mod1 training which is a more useful tool for more diverse locations. I will be getting a DPV first as my buddy is dragging me to caves like JB far more regularly than I had originally intended and spending $2k on a UV-26 is much more amenable and I wouldn't want to kick through that cave on CCR or OC, but if I was diving Peacock, Madison, etc on a far more regular basis, or if I was regularly doing dives that require trimix, it would be CCR in a heart beat, you just literally can't argue on the gas bill savings if you're diving helium regularly, especially if you follow GUE standard mixes where below 100' goes to helium, no one can afford to make OC dives to 200'+ anymore, CCR's will legitimately pay for themselves if you are diving to those depths regularly, a DPV does little to nothing for you on deep wreck penetration or most ocean diving for that matter, CCR's allow you more bottom time with generally less decompression schedules, as well as the silence around the fish which is nice for reef diving and photography. Different tools for different types of diving and if you're cave diving, shore diving, etc where a lot of your dive time is taken "getting there" then sure, DPV's are great tools, but if most of your diving is in places where you aren't travelling a great distance then they are heavy and expensive paper weights and you would get more use out of a CCR....

Regarding the ocean dives....I don't know that it is fair to say that a DPV benefit does not exist....this really depends on what you want to do for any given dive....if you were going to go photograph a jawfish that you know is right under the boat, no, the DPV is not going to help. But, on some other dive, you might want to find as many lobsters as you could---scooter divers tend to have exceptional results, covering so much more ground than swimming divers can....
I like to use scooters in an area I am fairly unfamiliar with, to essentially map the area out in my own mind, so that on future dives I will know where I want to concentrate with video--where I will want to look for great structure shots.

Palm Beach is a spectacular place for DPV's, as the reefs go for so many miles and the boat follows us....and because sometimes there is a very good reason to go up current when you see something, and with the scooter, this can be very effective--when swimming, this can waste huge amounts of gas, and not allow you to get too far ( even with a CCR).

Beyond Palm Beach, I like DPV's for the Bahamas....and I really wished I could have had my Gavin, or one of Errol's Suex scooters, for the time Sandra and I were in Fiji--a place with currents and some incredible visuals you could get --where the more ground you cover, the more wonders you see.

Since we are talking about MOST divers, most will not be doing big deco in ocean--most boats won't be allowing it, and most recreational divers are not looking to rack up an hour or more of deco ( which is of course, the place the CCR shines for having enough gas for the dive)....For a 90 or 100 foot deep dive, using a scooter can have a dramatic effect on air consumption....a diver like Sandra that can do a 6 hour dive at the BHB Marine Park on a hp100 ( that barely breathes due to resting pulse level workload in macro shooting), can have massive amounts of gas left in their hp100 after a 100 foot deep scooter dive for 40 minutes.....so you would question what they would need the CCR for here, and this person would enjoy the huge range they had from the scooter, all the sights they were able to see, and the lack or exertion would be appreciated as well.

 

[Superlyte27]

I don't see too many macro photographers with scooters clipped off. Lol

Especially at Bhb.

Also if you're doing NDL dives in the example above. You certainly don't need a suex. Buy a used Mako for 10% of the cost of a suex.

 

[Errol Kalayci]

I was not trying to sell scooters via my post, but as asked. See Technical Diving Solutions for any information relative to Suex or my dive services. I have been cave certified with DPV and a member of WKPP for over 20 years. I have maybe 5-600 cave dives, most were relatively deep and long as I was an active explorer and member of the Explorers Club. I am mostly an ocean wreck diver with 3,000+ trimix dives, dpv, etc. My last ocean dive was 6 miles long and possible only with dpv. I use dpv on almost every ocean or wreck dive unless I am teaching or have reason to swim. I am experienced and certified on various rebreathers and even taught them for years in the past but believe they are a tool to be chosen for use with care. I am also a competitive triathlete and coach in addition to teaching for GUE or working as COO for one of Florida's largest engineering companies. Hopefully that provides full disclosure that you seem to have wanted.

 

[tbone1004]

I know who you are and your reputation is quite impressive in the diving community, I wasn't questioning any of that, but for those that don't know who you are it does help to shed light on why you started this post. For the record, I do agree that DPV's are wonderful tools and are spectacular and allow for diving that can't easily be done on OC alone and while a CCR removes a lot of the bottle carrying or time due to gas used requirements in diving, they can't get you from point a to point b 3-4x as fast as you can swim and use essentially no gas because in a drysuit while being towed by a torpedo you might as well be laying on the couch as far as sac rate is concerned, but CCR's do have their purpose outside of deep long cave penetration and while you are lucky in the area that you are where DPV's make more sense, CCR's do make more sense for quite a few people which is why there are far more of them out there than there are DPV's.