How to Know When To Start Heading Up

[fnfalman]

Did you teach them gas management and how to calculate their turn pressures? Did you explain the all use, 1/2, 1/3 rds rules?......If you say you did, great....I think it's a shame that OW students are not given the tools to safely plan a dive with reserves for their buddies.

Yep. We sat down and whipped out my handy dandy cellphone as a calculator and went through their gas planning as part of planned bottom time. Mapped out the areas we wanted to cover, pre-shoot the compass headings and wrote them down on their slates. They didn't have kick cycle/distance, so I was going to keep the travelled distance.

They commented why they didn't learn things like these in class and I didn't want to bad mouth the training program, so I told them that they've done grade school and now they need to step up and learn high school education.

When we went down, I purposely headed in the wrong compass heading and they reeled me in. When one of them hit turn-around pressure, he signaled me and his buddy, I gave him the OK back and kept on going, he reeled me in. If there's one thing that they got out of the dive was that you don't deviate from your plan and that's what I wanted them to learn even more than fancy gas management calculations, equipment rig-out, proper trim, and all the other fancy stuff.

PS I wanted to add that during gas planning, we used my SAC rate because they don't have SAC rates yet. I figured they are both young, healthy, in shape fellows and I'm a fat old bastard, it's fairly safe to use my SAC rate for calculation.

 

[Doc Harry]

Have you done the math to the graduation quiz yet?

100 feet: rock bottom =1300 psi

Available gas = Fill Pressure - Rock Bottom Gas
Available gas = 3,000 - 1,300 = 1,700 PSI

Thirds = 1/3 * 1,700 = 566 psi (round to 550 psi)

Turn pressure = 3,000 - 550 = 2,450 psi

How fast will you be using gas at 100 feet?

Assuming a SAC of 0.6 cubic feet per minute, that means at 100 feet (4 atm) you will be using:

0.6 x 4 = 2.4 cubic feet per minute

How many cubic feet is 550 psi? Using a conversion factor for the AL80 which is 77 cubic feet/3,000 psi:

(550 psi) * (77 cubic feet/ 3,000 psi) = 14 cubic feet

How long will it take you to breath through 550 psi and reach turn pressure?

14 / 2.4 = 5.8 minutes (about 6 minutes)

Dive Plan:

1. Leave the boat with 3,000 psi
2. Descend the mooring line and head up current to explore the wreck
3. Turn around when you reach 2,450 psi (you've used 550 psi after about 6 minutes)
4. Get back to the mooring line with 1,900 psi (you've used another 550 psi, another 6 minutes)
5. Explore the wreck in the vicinity of the mooring line for another 550 psi (about 6 minutes)
6. When you reach Rock Bottom Gas (1,300 psi), ascend the mooring line

If your buddy runs out of gas at your turn point, you should still have 2,450 psi remaining. This gives you 550 psi to return to the mooring line, 550 psi to get your buddy back, and 1,300 psi for both of you to safely ascend together with all required stops. (550 + 550 + 1,300 = 2,400 psi) You get back on board the boat low on gas but you are both safe.

What happens if you used an absolute 1/3 (1,000 psi) instead of 1/3 of available gas (550 psi)?

You would plan to turn at 2,000 psi, and return to the mooring line at 1,000 psi. As you can see, you arrive at the mooring line at 100 feet with 1,000 psi. You're already below Rock Bottom Gas.

If your buddy ran out of gas at the turn point, you would have 2,000 psi remaining in your tank. You would need 1,000 psi to get you back to the mooring line, and another 1,000 psi to get your buddy back. You would arrive back at the mooring line at 100 feet with ZERO psi remaining.

Why do so many people get into trouble on the Spiegel Grove?

On a single AL80, you've got only about 5 to 8 minutes to explore the wreck before it's time to turn around (depending on your SAC).

If you're on a cattle boat with bunch of idiots who don't know what they're doing, you may get stuck behind a bunch of slow pokes who are descending the mooring line very slowly. You may get to the bottom of the mooring line on the wreck with only 2,300 psi remaining. You've got to completely change your turn pressure and game plan underwater. Do you have a contingency plan for this?

New available gas = 2,300 - 1,300 = 1,000 psi
New thirds = 1/3 * 1,000 = 333 psi (round to 300, about 3-1/2 minutes of gas)
New turn pressure = 2,300 - 300 = 2,000 psi

If you don't plan your gas correctly and something goes wrong, you're gonna run out of air at depth.

 

[dj10022]

I usually follow the rule of thirds: one third to go down to your dive site and explore, one third to get back to your safety stop, one third in reserve. As long as you stay within the NDL for the depth you're diving, watch your gauge, and ascend no faster than 30ft/min you shouldn't need complicated air consumption calculations. Remember: plan your dive and dive your plan and always err on the conservative side. Better safe on the boat sooner, later with the bends.

 

[ScubaInChicago]

why do so many people get into trouble on the spiegel grove?

On a single al80, you've got only about 5 to 8 minutes to explore the wreck before it's time to turn around (depending on your sac).

If you're on a cattle boat with bunch of idiots who don't know what they're doing, you may get stuck behind a bunch of slow pokes who are descending the mooring line very slowly. You may get to the bottom of the mooring line on the wreck with only 2,300 psi remaining. You've got to completely change your turn pressure and game plan underwater. Do you have a contingency plan for this?

New available gas = 2,300 - 1,300 = 1,000 psi
new thirds = 1/3 * 1,000 = 333 psi (round to 300, about 3-1/2 minutes of gas)
new turn pressure = 2,300 - 300 = 2,000 psi
.................................................................................
If you don't plan your gas correctly and something goes wrong, you're gonna run out of air at depth.

and "DIE"

 

[Doc Harry]

I usually follow the rule of thirds: one third to go down to your dive site and explore, one third to get back to your safety stop, one third in reserve. As long as you stay within the NDL for the depth you're diving, watch your gauge, and ascend no faster than 30ft/min you shouldn't need complicated air consumption calculations. Remember: plan your dive and dive your plan and always err on the conservative side. Better safe on the boat sooner, later with the bends.

If you're getting to your safety stop with 1/3 remaining, good for you! Very conservative.

 

[highdesert]

My apologies if someone already posted this ...

Some AI (air integrated) computers will give you "dive time remaining", as opposed to "air (gas) time remaining". They will take into account your dive profile up to a given point, your breathing rate, and gas comsumption rate. Then they will look at your gas remaining, nitrogen load, and oxygen load, and determine which is the most limiting factor. Then they will compute the time at which you must start your ascent from current depth, complete any/all required deco/safety stops, and arrive on the surface with "x" psi remaing, a value you have previously programmed in, typically 500 psi.

NOW, HAVING SAID THAT ...

This is not a fail-safe plan to use, ignoring your training and disipline. It is a guide, to use in addition to your training. Just a thought ...

 

[Buoyant1]

Locally, 1000psi is always noted for our dives...first person to reach 1000psi let's everyone know even if we are in an area where we know that our exit point is near because we can always do an "option b" and continue to another part of our quarry, even if we DO venture to that option, it's still good to have a gas check.

Abroad (which for me usually means the Florida Keys) It depends upon the site and depth (or dive op's plan...usually an hour for reef dives) IF we have all the time in the world on a shallow reef, then 1000psi applies also since it means we need to find the boat. Deeper dives are usually NDL based depending upon which gas we are breathing.

It's always good to talk this over with the person that you are diving prior to descending.

 

[H2O 70]

Why do so many people get into trouble on the Spiegel Grove?

On a single AL80, you've got only about 5 to 8 minutes to explore the wreck before it's time to turn around (depending on your SAC).

If you're on a cattle boat with bunch of idiots who don't know what they're doing, you may get stuck behind a bunch of slow pokes who are descending the mooring line very slowly. You may get to the bottom of the mooring line on the wreck with only 2,300 psi remaining. You've got to completely change your turn pressure and game plan underwater. Do you have a contingency plan for this?

New available gas = 2,300 - 1,300 = 1,000 psi
New thirds = 1/3 * 1,000 = 333 psi (round to 300, about 3-1/2 minutes of gas)
New turn pressure = 2,300 - 300 = 2,000 psi

If you don't plan your gas correctly and something goes wrong, you're gonna run out of air at depth.

and "DIE"

I don't you that many people have died running out of gas on their way up the mooring line because it is crowded. A bit over dramatic. If they are on the mooring line which is crowded, there are plenty of opportunities for getting gas.

The Spiegle is deep, from a recreational point of view.. I've been out there on days when we were able to free dive. The shallowest thing we could touch was 62fsw. Most of the good stuff on the wreck is 70-95fsw. The sand and anchor look sooooo close at 140fsw.

The Spiegle can have a lot of current.

The Spiegle is very assessable. Look at all the cattle boats that show up. A lot of inexperienced divers have access to it.

The Spiegle has a lot of points of easy penetration.

Gas planning has defiantly contributed to deaths and accidents on the Spiegle, but saying you got to a crowed mooring line and didn't account for rock bottom gas is a small way in which you can die on that wreck.

Anyway, you could account for rock bottom gas and get stuck on the mooring line and still end up OOG is you don't know what the hell you are doing.

 

[Doc Harry]

I don't you that many people have died running out of gas on their way up the mooring line because it is crowded. A bit over dramatic. If they are on the mooring line which is crowded, there are plenty of opportunities for getting gas.

That's not what I said or inferred. You need to read more carefully.

 

[Buoyant1]

I don't you that many people have died running out of gas on their way up the mooring line because it is crowded. A bit over dramatic. If they are on the mooring line which is crowded, there are plenty of opportunities for getting gas.

The Spiegle is deep, from a recreational point of view.. I've been out there on days when we were able to free dive. The shallowest thing we could touch was 62fsw. Most of the good stuff on the wreck is 70-95fsw. The sand and anchor look sooooo close at 140fsw. yeah! it's SOOOO tempting also

The Spiegle can have a lot of current. As do most of the wrecks in that area...The Duane is particularly usually nasty! When I was on the SG last year it wasn't TOO bad, more current about halfway down the line than on the wreck itself

The Spiegle is very assessable. Look at all the cattle boats that show up. A lot of inexperienced divers have access to it. Another huge trend down there, that's why it's good to know which op you are diving with down there. (and why it's a good reason to "interview" your insta-buddy)

The Spiegle has a lot of points of easy penetration. As does the Vendenberg! WOW how many places you could wander off in those two wrecks! I'm glad I was there with someone that knew it inside and out. I can really see how people can get lost inside of it!

Gas planning has defiantly contributed to deaths and accidents on the Spiegle, but saying you got to a crowed mooring line and didn't account for rock bottom gas is a small way in which you can die on that wreck.

Anyway, you could account for rock bottom gas and get stuck on the mooring line and still end up OOG is you don't know what the hell you are doing. I guess I'm having a hard time wrapping my brain around this....you are on a CROWDED mooring line, and you die going OOG? Why not just reach for the closest reg and keep breathing?

I guess some of the "worst case" scenarios can get a bit far fetched, but come on...you're headed up the mooring line, it's crowded, grab another reg and live to dive another day?!?!? Better yet, carry a goodly sized pony bottle (Not a freaking spare air!) and have your own bail method?!?! If you are that stubborn and want to use an 80 on a deep and unpredictable dive like the SG, then you really need to think about what you are doing, and if you think that an 80 is sufficient (rock bottom planning or not) you have another thing coming! Sure none of this replaces actual dive planning, but those type of chaos contingencies keep you alive!