How to Know When To Start Heading Up

[ScubaInChicago]

I tend to follow the rule of 1/3's. 1/3 to get there, 1/3 to get back and 1/3 for whatever.

Since I'm not using the rule of 1/3's for cave diving, I make sure that the end of 2/3's a tank I'm back at the anchor line. Since I'm typically diving to my NDL or I end up with no more than 10min deco obligation. I'll end up getting back on the boat with 1100psi left using a HP130 in typical NC wreck dives.

Your tempting DEATH in any overhead environment, wrecks included by using your method of 1/3'rds....It's a pretty simple math to work out.....take your RB (Rock bottom &/or Minimum gas) calculation that gets you and your buddy from depth to the surface and subtract that from your 1/3'rds equation.

Once out of the overhead, you can use the extra 1/3rd near the upline however you like but never go below RB....

 

[H2O 70]

Your tempting DEATH in any overhead environment, wrecks included by using your method of 1/3'rds....It's a pretty simple math to work out.....take your RB (Rock bottom &/or Minimum gas) calculation that gets you and your buddy from depth to the surface and subtract that from your 1/3'rds equation.

Once out of the overhead, you can use the extra 1/3rd near the upline however you like but never go below RB....

To be clear I'm not doing extended penetration into wrecks, yet. Always keep the actual blue ocean in sight.

 

[Dr Wu]

Your tempting DEATH in any overhead environment, wrecks included by using your method of 1/3'rds....It's a pretty simple math to work out.....take your RB (Rock bottom &/or Minimum gas) calculation that gets you and your buddy from depth to the surface and subtract that from your 1/3'rds equation.

Once out of the overhead, you can use the extra 1/3rd near the upline however you like but never go below RB....

Let us all applaud ScubaInChicago for "going there" and threatening
DEATH to a fellow diver.

Good on you ScubaInChicago! You deserve the greatest recognition this board can offer.

You threatened a diver you decided was beneath you with the ultimate sacrifice. He/she is going to perish for the crime of not being as cool as you.

God help us all..

 

[ScubaInChicago]

Let us all applaud ScubaInChicago for "going there" and threatening
DEATH to a fellow diver.

Good on you ScubaInChicago! You deserve the greatest recognition this board can offer.

You threatened a diver you decided was beneath you with the ultimate sacrifice. He/she is going to perish for the crime of not being as cool as you.

God help us all..

To be clear, it's not an attack on anyone.....It's a fair warning that a penetration dive should be planned using the proper method of thirds....not a method of thirds for open water.....

Many people may be lurking and not engaging and could potentially walk away with with faulty knowledge that could jeopardize their safety. Why would you make it out as though I'm better than anyone else for that?????

 

[TSandM]

There are a number of different ways of calculating a safe reserve, and how to apportion the other gas you have. Bob's article goes into this in more detail, but basically, you should always have enough gas in your tank to get you and your buddy to the surface, wherever you are in the dive.

How you split up the gas outside of your reserve, depends on how you are managing the dive. If you are drifting, you can drift until you hit "rock bottom", and then ascend. If you are shore diving, and would LIKE to get back to your entry but CAN surface swim if necessary, then dividing your usable gas in two works. If you are in a situation where you MUST return to a given point, then you need to divide the gas that's left after you remove the reserve into thirds, so that you have enough to get your buddy back to the upline, and back to the boat. These dives are not beginner dives, though.

Using a gross "rule of thirds" for all dives will generally reserve a safe amount of gas, but in some cases may not be enough, and in other cases, is wildly overly conservative.

I would like to congratulate the OP for asking this question, because it is a very good one. The answer is the beginning of rational gas planning, and rational gas planning (understanding all the concepts that go into allocating the gas you are carrying) is a huge, and undertaught, part of diving safety.

 

[diver 85]

...actually most dive ops DO enforce depth limits, de facto 'scuba police'.

Not any of the ones I've ever dived with...Example, last Monday(5 days ago) we made our 6th dive of a CZM trip...Our 3 man group from Louisiana consisted of myself(certified in '85) 1400+ dives, my best friend in hs(certified in '00) 300+ dives, & his SIL(certified last Oct '09)-that was his 6th dive following his Oct. certification....Dive site: Maracaibo(see link)....

The SIL's max depth(I looked @ his computer post dive) was 119 feet, in fact, the below pic is one I took of him (& I read my computer just before snapping pic) @ 116 feet in the archway of Maracaibo---we were starting a slight ascent coming out of the archway.......

Cozumel - Maracaibo

 

[Diver Tim]

I'm partial to Lamont's article because it gave me the mathematical tools to be able to figure rock bottom numbers for myself...and, knowing my average SAC, to be able to get an idea of how long to expect my air to last for a particular dive. I guess I prefer math and science to "this has always worked for me" or "my rule of thumb is..."

 

[Troutmaster]

I give credit to the OP for asking! It is nice to see a new diver asking improtant questions, keep that up and you will do well.

I have to agree with Diver 85, none of the operations I have dove with enforce any kind of 60ft depth limit, including the one I would say is the most safety concious company I have ever dove with (Ocean Frontiers, Grand Cayman).

I held only a OW cert for 18 years and routinly dove below 100ft. And I think I was alot more qualified to do so than a guy with 15 dives total with an AOW cert.

As a recomendation to the OP, stay shallow and work your way deeper as your experience dictates.

 

[ianr33]

I guess I prefer math and science to "this has always worked for me" or "my rule of thumb is..."

Just to point out my "rule of thumb" was derived by plugging a reasonable range of SAC rates into V planner for different depths. Its not something I just dreamed up one day.

Maybe "field algorithm" would be a better term than "rule of thumb"

 

[Cave Diver]

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A ScubaBoard Staff Message...

Please remember this is in the New Divers Forum. If you wish to discuss gas planning as it pertains to overhead environment diving, please do so in one of the more advanced forums.

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