Nitrox Scrubbing

[Steel Shootin']

I know you guys who took the Advanced Nitrox course looked at scrubbing as a way to enable you to make deeper dives and minimize surface intervals, etc.

What about the average guy who wants to spearfish within recreational limits (130 fsw)? It would seem to me that as long as your computer has the ability to change gasses on the fly, there would be benefit to either:

1. Hang a safety stop bar from the boat at about 20 fsw, clipping a high 02 tank to the bar, for the diver to scrub while doing his safety stop; or

2. Don't count on the boat being able to drop the safety stop line to you, and take a stage bottle with you with higher 02.

The downside I see to number 2 is you may not be able to use the stage bottle at depth for an emergency. Some would say, "if that's your purpose, it's not a stage, it's a pony."

Also, for any of you guys planning advanced nitrox deep water dives, have any of you decided to clip a stage bottle to yourself? If so, I'd be interested in knowing what configuration you came up with that least interfered with shooting fish.

If you are NOT clipping a bottle to yourself, what protocol will enable you to always be under the boat and find the safety stop line?

By the way, I have not taken advanced nitrox, so I am not advocating any of this. Just looking for input from anyone with more experience them me.

[Reef Raider]

Iam going to a 30 cf pony, 120cf steel hp , 1:80 al for travel gas and 1 lift bag . This should take me to 200fsw for a drop shoot and go! Also adv. nitrox and deco diving class.I have most every thing just need a lift bag whos got a good lift bag??? I need it in the next 2 wks?????????

[Steel Shootin']

You guys are friggen nuts! :D

[FredT]

Originally posted by Reef Raider
I have most every thing just need a lift bag whos got a good lift bag??? I need it in the next 2 wks?????????

http://www.carterbag.com/spearfish.html

http://www.carterbag.com/personalfloat.html

These are compact when deflated, won't spill air at the surface, and are built tough enough to take the abuse spearfishermen dish out. Of course for a REALLY tough bag you'll need to go for one of these!

http://www.carterbag.com/salvage.html

http://www.carterbag.com/boulder.html

Subsalve also makes good heavy duty salvage bags.

FT

[Reef Raider]

Thanks Fread T. thats just what I was looking for. Nuts are for bait I'am just crazy.

[FredT]

SHOOTING at 200' on any nitrox mix is something to be considered hard. I used to do regular dives below 200' on air, but not for hunting fish, just to do photographs. I'm just too stoned below about 150 to shoot accurately. Given the fish I prefer to shoot are large enough to hurt me in shallow water, a bad shot in deep water can trigger a USCG search. I'll go deep when hunting, but usally I'll have a finned DPV pulling me there or I stay out of that range.

Think really hard about going to a trimix or heliox breathe gas if you intend to hunt much below about 130. Even a little He in the mix can do wonders for your accuracy. It does mean an entirely new midset on ascent rates and deco tables though. He can sneak up on you is some strange ways if you're not careful about it's use.


Scott,

If you are doing nitrox bounces a deck deco breathing O2 will help purge fast and medium tissues, and you don't have to haul that green "T" bottle down with you. As a safety matter I do NOT figure the deck O2 time into the deco schedule, but do add it into the oxtox clock.

FT

[inletsurf]

Right on RR.

There's this 235 ft "cone" out here we do deep dropping at, VERY productive during certain times of the year. BIG grouper, even hit a 50 lb warsaw one time. The Cone is about 40 ft high...

I'd give my left testicle and maybe a pinky finger to just dive it one time with good vis and no currents (its gnarly because its on the gulf stream edge) for a drop and shoot dive. I find myself lately very consumed with the thought and I'm about an inch away to educate myself on whatever I have to do to get there. Have any of you done that kind of thing before???

[Reef Raider]

There are some wrecks in the 155fsw range that we do . I would like to see some of that deeper stuff though.Fred T you are making me rethink this I will get 2 PHs for my gun that should do the job.

[FredT]

Get your gas under control first. At those depths a 50% He mix wouldn't be totally out of bounds, depending on your tolerance of nitrogen. Drop on the upcurrent side and swim down HARD to get to your target depth. Take the ride to allow the current to bring you to the structure. Larger pelagic fish will often be on the upstream side of the structure anyway so drifting through that zone can be really productive. Send each fish as shot to the surface on a separate bag for your boat crew ot recover, and you ascend and deco on a bag marked for that purpose after you drift past the structure. In heavy current it's necessary to fight and subdue fish in the current lee provided by the structure or you'll end up gettting blown off the thing really fast.

FT

[Reef Raider]

Great tip Fred T that I will keep in mind, lets hear more I got the feverbad!! I like the buzz too. so thats not a problm. I used to do night dives in a sink hole just to get buzzed up we would do 2 dives the 1st to like 150 -160ffw 2nd to 100-110 I just drop like a rock and would get the buzz there every time . It was good training I have worked my way up to this and hope it turns out to be a blast!

[inletsurf]

I guess 240 fsw is pretty much out of the question with even trimix, huh?

[FredT]

Originally posted by inletsurf
I guess 240 fsw is pretty much out of the question with even trimix, huh?
Trimix is in it's own at that depth, but gas management at those depths is a big thing.

FT

[johnhermes]

Too ****ing much for me

[100days-a-year]

I'm certified full-trimix.I did it just to be able to to do deep spearfishing.I've spearfished to 240' on mix,it's a lot of work.These are the problems we encountered.Air consumption really goes up due to depth and stress.This means doubles.If you miss the boat or lose a hang bottle ,you're in trouble ,this means stages for deco.While you're down there it's easy to get into serious hang time.This means either drifting or hanging in the current.I'll still do it ,but most of my best fish have been from 75' to 125'.Mix is also expensive to dive and requires training which ain't free.It also requires a lot of deck space.We dive 2 sets of doubles with 2 stages per dive that's 8 tanks each for 2 long dives or 4 bounces.I'm more inclined to the 150' to 200' range here which is the Ledge.That means a bigger boat as it's 50+ miles each way.This summer were heading to Ft Pierce to try some deeper stuff there as it's a lot closer.

[Dive4Blood]

Go with a 13cu ft aluminum stage of 80% nitrox. Anything larger is just a hindrance for spearfishing. With an average SAC rate of .5 cu ft/min it will give you five 3 minutes safety stops at 15-20 ft. The 80% nitrox scrubbing should allow you to do 8-10 Middlegrounds dives (90-130 feet) relatively safely per day so bring two stages, or use a transfer whip to decant off of a larger tank. Why would you hang needed deco tanks for spearfishing? The time consuming process of anchor diving in the Middlegrounds would slow the dive rotations to the point where needing deco stages would be moot. Not to mention the risk of losing the anchor line from currents or from chasing fish. The only way I would conduct a dive needing staged deco bottles off an anchored boat would be on a deep wreck in VERY good vis, and even then why not bring a stage with you for redundancy?

If you are using an LP or HP steel 120 for your tank, why are you even thinking of using a pony bottle? Discipline and proper gas management will eliminate running out of air. Even with equipment failure you should have, in most circumstances, enough time to reach the surface safely or get shallow enough (30') to breathe off your 80% nitrox stage.

[Steel Shootin']

[i]If you are using an LP or HP steel 120 for your tank, why are you even thinking of using a pony bottle? [/B] Well, if your HP hose ruptures and you've got 500 psi in your 120, that's not a lot of air regardless of the size of the tank. I realize a ruptured line is unlikely, especially at a lower pressure, but anything could happen. Hell, the o-ring on your tank neck could blow. Unlikely, but has happened. I wasn't suggesting using a pony in case you run out of air due to forgetfullness.

How are you going to carry that stage? Are you going to just attach it to your 120 on a bracket or strap, or are you going to carry it more like a typical stage, clipped to your BCD. I tend to agree on disliking the 30s. If I was going to carry a second bottle that big, I'd just dive twin 80s and have total redundancy in everything, including my first stages.

[Dive4Blood]

Underarm slung stages are for psycho hole crawling cave divers. The best tank mount for a stage I've seen is a product called a Scuba Duba, Financial Advis has one, and I will be getting one very soon. Ask him to bring it to the Seals meeting on Tuesday.

If your HP hose ruptures with 500psi? Well shit, you can get hit in the head with a errant drive on the golf course and die also. :D

[Steel Shootin']

I've got the scuba duba too. It's nice because you don't need a seperate mounting bracket for each tank, since the bungee is always attached to the stage bottle. Just wrap the bungee tubing around the big tank, and you're ready to go.

[swimndive]

Scott It looks like this has gone off on a tangent. Let me try to answer your two questions. 1) Yes, accelerated deco or O2 scrubbing with 100% is a very effective way to add an additional safety margin for any recreational dives. 2) There are numerous variables you need to consider when planning this type of diving. Depth, weather, currents, the number of divers, emergency equipment considerations, time of day, etc… may all be critical. Here's quick set of deep diving rules taught to me by someone who's done a fair amount of it. Tri-mix in doubles for all dives below 130' (30/30 is also a very nice mix for strenuous dives @ 100'). Always keep deco times less than 30 min (sharks and weather can cause an abbreviated or aborted deco, keeping the deco short means you can survive it). No solo diving, always dive in teams, one shagger per gunner. Deeper hunting should be done with a scooter. Always carry min of 1.5 times the required deco gas at all times. No rodeo fishing ( powerheads mandatory). Hip clip deco bottles by the nose to keep them out of the way. Always have a surface support diver ready to go. If the boat is anchored, you need a chase boat and support diver geared up and in the chase boat (both must be ready to go). Proper planning will ensure success. There is much I have left out, but this should give you an idea of some of the things you need to have answers for before you get wet.

[100days-a-year]

Iran a bunch of options on V-plan for short repetitive dives at 200' and couldn't get away with less than 13 minutes of staged deco using a 10 minute BT of which 4 was descent yeilding a 6 minute bottom time.for a total dive time of 23 minutes .After a 2 hr SI you could repeat the same dive .Helium is very unforgiving about deco ascent rates,but it does help you to see straight.Do a search for Vplan and GAP to get some freeware to check out what kind of profiles are common.I still dive air to 150' or so cause He is a logistical PITA.

[bubblejunkie]

Damn I need a new job, you guys are spending silly money with this stuff.

[Steel Shootin']

accelerated deco or O2 scrubbing with 100% is a very effective way to add an additional safety margin for any recreational dives.Thanks. That's the key to the original question, which is scrubbing for recreational divers. I like Fred's suggestion to scrub and keep track of 02 exposure (w/o it affecting the dive profile of whatever your nitrox mix was, if I understood correctly).
There are numerous variables you need to consider when planning this type of diving. Depth, weather, currents, the number of divers, emergency equipment considerations, time of day, etc… may all be critical. Here's quick set of deep diving rules taught to me by someone who's done a fair amount of it. Tri-mix in doubles for all dives below 130' (30/30 is also a very nice mix for strenuous dives @ 100'). Always keep deco times less than 30 min (sharks and weather can cause an abbreviated or aborted deco, keeping the deco short means you can survive it). I'm staying within recreactional limits for a couple of reasons. First, diving, and specifically spearing, becomes increasingly more dangerous past 130'. Most importantly, for me, is that you don't need to go past 130' to get into great hunting.

No solo diving, always dive in teams, one shagger per gunner. Deeper hunting should be done with a scooter. Always carry min of 1.5 times the required deco gas at all times. No rodeo fishing ( powerheads mandatory). Hip clip deco bottles by the nose to keep them out of the way. Always have a surface support diver ready to go. If the boat is anchored, you need a chase boat and support diver geared up and in the chase boat (both must be ready to go). Proper planning will ensure success. There is much I have left out, but this should give you an idea of some of the things you need to have answers for before you get wet. Interesting stuff, although a little more conservative then I dive. I wouldn't fault anyone for adhering to those suggestions.

[Steel Shootin']

Originally posted by 100days-a-year
Iran a bunch of options on V-plan for short repetitive dives at 200' and couldn't get away with less than 13 minutes of staged deco using a 10 minute BT of which 4 was descent yeilding a 6 minute bottom time.for a total dive time of 23 minutes .After a 2 hr SI you could repeat the same dive .Helium is very unforgiving about deco ascent rates,but it does help you to see straight.Do a search for Vplan and GAP to get some freeware to check out what kind of profiles are common.I still dive air to 150' or so cause He is a logistical PITA. Thanks. I'll see if I can find that shareware on the web. The Suunto Dive Planner doesn't allow those variables.

[FredT]

is WAY too long! Try this profile for size, and vary your mix in your planning software to see where it gets you. I use Abyss for running what-ifs but several other programs are out there that will do nearly the same thing. I find a 1.6 to 1.8 ATA peak O2 at bottom a good point for me, cause I'm NOT going to be there longer than 4 or 5 breaths max, others like a 1.4 to 1.6 ATA O2 limit.

Assumptions:
1. You hit the water with gun ready to go, so you don't have to load it on the way down.
2. Small footprint or midsize very isolated structures that concentrate fish.


Time line.
1. Roll off the boat negative, clear continuously and fin down hard to ~100'. Elapsed time ~ 20 seconds from splash.

2. Buddy bubble check for 2 breaths then down again. Elapsed time 60 seconds from splash.

3. Level at 70% of vis above structure (assuming 200 and 60' vis gives you a pause at about 160) and pause for 3 deep breaths while searching structue for THE fish. Once it is identified move to the best point above the structure to begin the stalk. Elapsed time 2:30 from splash.

4. Exhale enough to get negative, then hold and complete the stalk. Your next inhale is on the shot, then 2 quick purge breaths as you head UP to get the fish 20 to 30' above bottom before he wakes up, if he wakes up. Elapsed time should be less than 5 minutes from splash.

{If you blow the stalk head up again to your previous hover depth and retarget and stalk. You inhale when you turn the dive. Do this only ONCE on the dive. If you blow the second stalk the dive is OVER! Contingency plan for 7 minutes max, 3 at max depth, the rest at your hover depth.}

5. Continue ascent to first required stop. This should be about a 1 minute pause at about 100.' By this point the fish's swim bladder is working like a lift bag if you hit him correctly. Attach your bag to the riding rig or gun and shoot him to the surface for the boat to recover. You now start your "required" deco.

As you crunch the numbers you'll see that almost all the gas you've absorbed is in "fast" to "medium" tissues. Given a 5 or 6 minute ascent you'll hit the surface with almost no slow tissue loading. Total dive time should be 10 to 12 minutes max. Following this profile you should NOT get into a required deco liability. If you do juggle your mix and bottom time again to loose it. Seconds count when deep, so be sure your software allows you to split minutes at least into thirds. Your stops are then "safety stops" and you _should_ surface with less than a 70% gas load in your heaviest loaded tissue model.

If you blew the first stalk your worst case of 15-18 minutes including now required deco means you sit out the next dive while purging.

The deep rig divers will do 6 to 10 of these type dives a day, often with an hour or less between drops. Safety diver hits the water 10 minutes after the first splash unless the diver's bubbles show them back to shallow depths again. Deck deco helps them a lot, but chamber rides are possible at any time if you get just a little dehydrated.

HINT: Closing the dominant eye during descent adapts it to the lower light levels at depth MUCH faster at the hover depth fish finding stop!


FT

[Reef Raider]

More good stuff Fred T dully noted. I went with the dive rite pony mounts 2 of these that should keep it from moving around much at all. Also I can't see any way its coming lose and should be a snap to change tanks over.

[JohnDiver]

Wow , you guys are ballsy. To much can change too fast while spearing. I will limit my dive to 130 140 ft max. These deep multi gas, dives are too complex for me to add the uncertainty of a large fish on the end of a spear. :eek:
Good luck to ya:D . I really enjoy hearing the stories. But you guys be carfull. Shit happens. Most of us have had things go wrong from time to time that cost us an extra few mins of botom time...now when that happens at 230fsw :eek: been nice knowing you

[FredT]

If you can't do that, and easily keep track of it, below 160' your dive is too long to be doing several deep dives per day.

Originally posted by JohnDiver
Most of us have had things go wrong from time to time that cost us an extra few mins of botom time...now when that happens at 230fsw :eek: been nice knowing you

When things go wrong on a deep hunt you immediately abandon all chattels not needed for life support and get your a$$ UP! Guns and gear can be recoverd later if possible, or simply replaced. I generally carry one or more "spare" guns to the boat just in case I have to abandon one. If you can't accept these constraints, don't go there. Busting the main dive plan is a big mistake, busting the contingency plan is often fatal.

BTW the dives I've described are generally done with ONE gas mix on a single bottle, often getting two or more dives per bottle. Purging is done on deck from a large O2 bottle.

FT

[100days-a-year]

FredT,I was talking about doing mix dives .On air I'd say I dive pretty much as you described unless the currents whistling.On mix,going up and down a whole lot +- 30' can really get you in trouble.We dive either LPs jacked up or doubles .AL80s don't really lend themselves to this,but I have several buddies who get 3600+ fills of 24-28% for doing 2 deep bounces per tank.We also try to dive big areas if there are several divers going down or if we're after lobster.This time of year we can rarely pull off everyone getting 3 dives and and all the moves in my boat .If just bouncing small marks 4 is possible per guy.Be careful with the 1.6 and above P02s,it's possible to Oxtox a lot easier at my advanced age esp. when working hard.

[Dive4Blood]

Fred T, could you explain the process of "deck deco" which I assume is the surface interval breathing of 80-100% O2 ? How does this affect your O2 clock, and how would you account for your "improved" deco status on your computer? It seems to me like you wouldn't be able to so basically you are just adding a safety margin to your dives. I would be interested in seeing the increased O2 level "risk" vs. offgasing "reward" of the whole process.

How much hydration to you guys do on deep bounce dive days?

[FredT]

The diving I described works on rigs, and isolated wrecks. As I said before what is suitable here may not be even close to the correct approach around the corner. He outgassing is a problem during rapid ascents, provided you have been down long enough to suck it into tissues. SHORT bounces with very short excursions to max depth do not present a significant offgassing risk since there is little time for the gas to uptake into the system. Again it's time to use the gas behaviour to your advantage by keeping max depth excursions very short relative to the time spent at "hover depth". Slower ascents form the hover depth make excellent sense. If the water is clear enough to do this type of hunting that hover depth shold be significantly above the bottom and enough so the the swim bladder of the fish expanding to the point they dont' swim well.


Deck deco is breathing 100% O2 on deck either through a reg with your mask on or thorugh a full face mask. It has little effect on short tissue saturation on repetitive dives, but it will pull the dilutent gas out of your middle rate tissues so you can start pretty much "clean" on the next drop. It is not figured into the puter but is used as adding an appropriate DCI fudge factror. It adds to the oxtox clock as 1 ATA exposure time though.

To determine if the effects of deck deco is inside your tolerance band (both hassle and financial) it's necessary to do many days of simulated dives on software both with and without it during SI. Generally after about the 4th bounce dive of the day this starts to add significant safety margins to the DCI side of the equation as the slow tissues load much less than the dive puter thinks they are loading. After the 5th or 6th dive the middle to slow tissues are what is statring to control the gas loading algorithm.

FT

[100days-a-year]

FredT,you could run that SI as a long deco at 2-5 ft to get O2 and tissue loads esp on GAP which has a graphic representation of each compartment.That's way to much freetime for me tho.:)