Multilevel diving and rock bottom.

[amascuba]

We need some more conversation in here. I'm curious as to how many of you guys treat rock bottom when you have a multilevel profile. It's geared more towards a simple single tank dive and not necessarily a thoroughly planned technical dive.

Do you treat your rock bottom pressure as static or dynamic?

Personally I treat it as dynamic based on the profile I'm diving. For example, a dive on a live aboard in turks and caicos. The dives typically start out at around 50-60 feet. We'll typically follow the ridge of the wall away from the main dive site to where the reefs are healthier until we reach 2000 psi, turn the dive and head back until we are back under the boat. By this time we are at around 1000 psi and at rock bottom for our depth. At which will typically do a minimum deco ascent and goof off under the boat at around 10-20 feet until we get bored and get back on the boat. I've been known to get back on the boat with around 300-500 psi after this. If I treated rock bottom as static then we would have planned the dive so that we were back on the boat with 1000 psi left, based on rock bottom for our maximum depth. Thoughts?

 

[Peter Guy]

"I know not what others may do, but as for me...." -- I treat RB as dynamic. At a local site we often go down to about 100' where RB is 40ft3 -- but then we come upslope and spend a lot of time above 40ft where RB is 500PSI. None of the people I dive with need 20ft3 to safely ascend from 40ft to the surface on a minimum deco dive.

 

[LeadTurn_SD]

We need some more conversation in here. I'm curious as to how many of you guys treat rock bottom when you have a multilevel profile. It's geared more towards a simple single tank dive and not necessarily a thoroughly planned technical dive.

Do you treat your rock bottom pressure as static or dynamic?

Personally I treat it as dynamic based on the profile I'm diving. For example, a dive on a live aboard in turks and caicos. The dives typically start out at around 50-60 feet. We'll typically follow the ridge of the wall away from the main dive site to where the reefs are healthier until we reach 2000 psi, turn the dive and head back until we are back under the boat. By this time we are at around 1000 psi and at rock bottom for our depth. At which will typically do a minimum deco ascent and goof off under the boat at around 10-20 feet until we get bored and get back on the boat. I've been known to get back on the boat with around 300-500 psi after this. If I treated rock bottom as static then we would have planned the dive so that we were back on the boat with 1000 psi left, based on rock bottom for our maximum depth. Thoughts?

Dynamic. Since I'm strictly a rec diver with no deco or overhead, I use my current depth to estimate Rock Bottom "on the fly".

I do almost exacty what what you described in your example. I typically reach the exit point (the boat, or an anchored dive float for a shore dive) with plenty of air remaining (usually about 800-1,000 in 30 feet of water), so I'll typically use it up goofing around in the shallows until I'm down to 300-500, or bored, whichever is 1st .



I'm interested to see what others do.

Safe Diving!

 

[Randy43068]

I'm with you. Dynamic and pretty much all gas is usable on a dive like this. That's how I recall it. I'm glad I'm not the only one who does what you do. Thanks for sharing it.

We need some more conversation in here. I'm curious as to how many of you guys treat rock bottom when you have a multilevel profile. It's geared more towards a simple single tank dive and not necessarily a thoroughly planned technical dive.

Do you treat your rock bottom pressure as static or dynamic?

Personally I treat it as dynamic based on the profile I'm diving. For example, a dive on a live aboard in turks and caicos. The dives typically start out at around 50-60 feet. We'll typically follow the ridge of the wall away from the main dive site to where the reefs are healthier until we reach 2000 psi, turn the dive and head back until we are back under the boat. By this time we are at around 1000 psi and at rock bottom for our depth. At which will typically do a minimum deco ascent and goof off under the boat at around 10-20 feet until we get bored and get back on the boat. I've been known to get back on the boat with around 300-500 psi after this. If I treated rock bottom as static then we would have planned the dive so that we were back on the boat with 1000 psi left, based on rock bottom for our maximum depth. Thoughts?

 

[b1gcountry]

As long as it's a multilevel dive, I have different RBs for different depths.

I like to keep it simple. Memorize rock bottom for 100', 60', and 20', then just round my depth up. It pretty much takes all the calculations out of it for me

Tom

 

[Gombessa]

Dynamic as well. Our simple shore dives usually start at 30ft, drop down to 50-80ft, and then end at 20-30ft. By the time we hit RB, we're usually already in the shallows, so we automatically adjust to account for reduced depth. By the time we ascend, we're sometimes breathing the RB supply as calculated for the shallower depth (which in doubles is invariably 500psi).

 

[Reg Braithwaite]

My understanding of RB is that it is always dynamic. In a non-overhead environment there is RB for a particular depth, so yes you descend to 60' and turn the dive at your 60' RB. But if you ascend to 20', you may find you are ahead of your 20' RB.

That being said... I would always consider 500psi to be RB or any depth, even 20'. It would be unpleasant to share air with an OOA buddy and then discover that the pressure gauge is 10% out of whack and we really only had 200psi in the tank. Probably not life threatening, but unpleasant.

 

[Blackwood]

Rock bottom is a dynamic function of Current Depth, Current Ascent Requirements, and Gas Consumption.

 

[do it easy]

Now we have MGOTF - Rock Bottom On The Fly.

Anyone can call Rock Bottom at any time

 

[rjack321]

Basically 2 numbers for me, above and below ~60ft.

And then just stupid shallow where I am willing to run the tank down to 300-400psi for weight checks and such.

"Fixed but dynamic"