Stage planning in caves

[limeyx]

That is probably one of the best posts I've seen in months

Right, you do have to recognize at some point that it might have been a better day to go play golf than tech/cave dive

 

[limeyx]

First, I can't imagine a scenario where you would need a 70' bottle and would only have one stage in a cave. Second, given how little gas is actually used on deco relative to on the bottom, it really doesn't factor into the reserve. If both you and teammates are so low on gas that completeting deco if you lose an O2 bottle is an issue, you either just had the worst cave dive in history or your planning was bad.

Open water is different. Reserve gas planning is basically for an immediate ascent wherever the problem occurs. So, getting to useable gas is the primary concern. I don't know exactly what GUE teaches, but I generally plan to have enough gas for some amount of back gas deco (even if it is abreviated). Now, if the dive went sideways and you used reserve gas getting to the bottles useable depth this might not be the case since you can only plan for so many failures before it gets ridiculous.

GUE/AG are basically teaching 1 major failure (complete loss of backgas)
For T1 type dives, planning can also encompass loss of 2 deco bottles (but not any backgas) -- just double the deco and as it's shallower(exponential curve not S-curve), your rock bottom gas gets you probably 80% of the way there.

For tech1.5 (30 mins @ 200) basically plan is 1 lost back gas or 1-2 lost deco bottles with similar doubling of deco and allowing enough backgas for double deco of one bottle per person.

What if (say) you had a cave that drops almost vertically to 150 and then goes along flat at 150 (maybe such perverse caves do not exist) -- then you'd be spending a fair amount of time on the 50% bottle. You might need to plan 1.3's to 70 feet + back gas for lost/failed deco scenario ?

I am a baby in gas planning for caves, so for me it's more questions than answers at this point !

 

[rjack321]

First, I can't imagine a scenario where you would need a 70' bottle and would only have one stage in a cave.

Really, even in Eagle's Nest? That's a ~270ft dive right? I can certainly see using 2 deco gasses although I don't know enough about the profile to know if you need more than one stage.

Open water is different. Reserve gas planning is basically for an immediate ascent wherever the problem occurs. So, getting to useable gas is the primary concern. I don't know exactly what GUE teaches, but I generally plan to have enough gas for some amount of back gas deco (even if it is abreviated). Now, if the dive went sideways and you used reserve gas getting to the bottles useable depth this might not be the case since you can only plan for so many failures before it gets ridiculous.

Most dives can be completed on backgas if the deco bottle's unusable OR you use the backgas reserves to get up to the deco bottle. One or the other, not both.

 

[do it easy]

What if (say) you had a cave that drops almost vertically to 150 and then goes along flat at 150 (maybe such perverse caves do not exist) -- then you'd be spending a fair amount of time on the 50% bottle. You might need to plan 1.3's to 70 feet + back gas for lost/failed deco scenario ?

Yes, there is such a cave in Missouri that does that. It has a short tunnel at 45' right after the cavern zone. Then there is a vertical silo to 150' and a tunnel that bounces around between 130'-160' for a while. Water temp is about 50f. They say the river ices over in the winter time, so you can also do an ice dive

 

[RTodd]

Cave dives are a nice stable environment where the risk of needing to blow off part of your 20' stop is much much lower than open water. Therefore, oxygen is the first deco gas of choice. Getting as clean as possible prior to 20' (while always best case) isn't as big of a deal. So, generally only start using a 70 bottle when it has a meaningful effect on deco time.

Deep caves mean scooters. Swimming at those depths is bad for the joints. So, this means you need extra gas. The logistics of all of this and only using a single stage on most deeper dives are silly.

On all but the most extreme of dives where there would be support divers available to supply any needed deco gas anyway, the back gas reserve necessary to ensure a safe exit on a cave dive will usually allow you to deco out upon loss of deco gas.

 

[MikeFerrara]

Yes, there is such a cave in Missouri that does that. It has a short tunnel at 45' right after the cavern zone. Then there is a vertical silo to 150' and a tunnel that bounces around between 130'-160' for a while. Water temp is about 50f. They say the river ices over in the winter time, so you can also do an ice dive

The drop is a little over 400 ft in. We usually do the dive on 21/35 with one stage. We use use a 70 ft bottle and O2. The temp varies from high 40's in the winter to mid 50's or so in the summer. Especially considering the temp, the 70 ft bottle is woth bringing, IMO. Even when we do a shorter dive without the stage we use the 70 ft bottle.

The guys who are pushing the cave are, of course, using scooters, lots of bottles and heated underwear.

 

[RTodd]

The drop is a little over 400 ft in. We usually do the dive on 21/35 with one stage. We use use a 70 ft bottle and O2. The temp varies from high 40's in the winter to mid 50's or so in the summer. Especially considering the temp, the 70 ft bottle is woth bringing, IMO. Even when we do a shorter dive without the stage we use the 70 ft bottle.

The guys who are pushing the cave are, of course, using scooters, lots of bottles and heated underwear.

This is the problem with explaining this stuff on the internet. In 40 degree water, shaving 5+ minutes and being able to relatively safely blow off part of the 20' stop if there is a suit flood is important. But, not many cave dives like this.

 

[MikeFerrara]

This is the problem with explaining this stuff on the internet. In 40 degree water, shaving 5+ minutes and being able to relatively safely blow off part of the 20' stop if there is a suit flood is important. But, not many cave dives like this.

I agree. I've rarely used a 70 ft bottle in Florida but there is plenty of shallow cave and the water is almost 70 degrees. We get lots of bottom time with little decompression. I drop an O2 bottle and let it go at that.

 

[rjack321]

Cave dives are a nice stable environment where the risk of needing to blow off part of your 20' stop is much much lower than open water. Therefore, oxygen is the first deco gas of choice. Getting as clean as possible prior to 20' (while always best case) isn't as big of a deal. So, generally only start using a 70 bottle when it has a meaningful effect on deco time.

I have heard of the lesser emphasis on deep stops in the cave program vs. open water deco profiles. I'm curious how this plays out in practice and if its substantive though.

My observation was more along the lines of "we plan for one major failure in OW" and reserving backgas for every stage and/or deco bottle is a bit more conservative than this.

 

[RTodd]

I think you have lost something in the explanation. Carrying enough back gas for a failure of all stages and deco is often not practical. But, a great general rule of thumb is that if a complex dive goes well, you should have enough gas on you at the exit to do the whole thing again (i.e. half the gas or slightly less but with fewer bottles). It is the concept of building a bigger reserve gas cushion than thirds as the complexity of the dive increases that is important.

Also, deep stops are arguable done better in caves. But, it isn't as regimented since more often than not the profile of the cave on the exit provides you with a significant portion of the deep stops that need to be done. For instance, if you are doing a dive to 220 and then have a 1,000' ride back at 120, you are going to spend far less time getting to your O2 bottle from 120 than you would if you started a direct open water ascent from 220.