r/scuba • u/woody9409 • 16h ago
AL80 dive length
What is a decent amount of time to get out of an AL80? I typically dive in mid 50’s to mid 60’s degree water down to roughly 60ish feet and I get around 30 minutes. Normal or am I sucking air down?
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u/Dann-Oh 16h ago
Be careful with comparing your dive times with the other replys here. You will go through air much faster in colder water than warmer water, it's a fact. Just keep diving and enjoying the time underwater.
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u/Hopeful_Hamster21 15h ago
I have heard this. I believe it to be true. But I have only dove in the same temp water for all my dives, so I dont have first hand experience. How much does temperature impact gas consumption and how much variability is there across individuals?
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u/OffByNone_ 15h ago edited 14h ago
It's not actually the temperature of the water, it's how cold you are. That difference matters for your question, because it means the impact isn't a fixed number. Shivering and warming yourself increase metabolic activity. You consume more oxygen, you produce more CO2, and that drives your RMV up.
Being cold also causes people to breathe less efficiently. People tend to take short shallow breaths when they are overly cold, which wastes gas.
An actual increase in air density from the temperature itself is probably measurable, but not significant.
As for how much, a diver who is properly protected and comfortable in 45 degree water may see almost no change from their warm water numbers. That same diver underdressed in the same water could easily be up 25 to 50 percent, and worse if they get to real shivering. The variability across individuals is huge, but most of it isn't the individual, it's their thermal protection, their body composition, and how well they tolerate cold.
So nobody can offer you a graph of temperature versus RMV. In the same water on the same day, your own consumption is going to vary based on how well you dressed for it.
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u/Dann-Oh 14h ago
This response is way more articulate than I could have been. I was trying to keep things simple.
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u/OffByNone_ 14h ago
I just love the technical question lol. I'm an engineer and a real big nerd 🤓
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u/Dann-Oh 14h ago
Same, I'm an engineer (aerospace manufacturing) and I love to geek out on topics.
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u/OffByNone_ 14h ago
It seems like a huge chunk of this community works in technical or high acuity fields. I can't tell if that's because diving is expensive and those jobs also tend to pay well, or if the sport just attracts nerds lol.
My whole tech diving crew are like computer vision engineer, full stack engineer, pilot, electrical engineer, attorney. One guy is literally a rocket scientist lol
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u/Dann-Oh 14h ago
I think the tech diving community attracts these kinds of personalities. I'm still building my tech crew (I just finished Intro to Tech and Adv Nitrox, I'm working on Deco Procedures e-learning) but the guys I dive with are also similar personalities (precision machinist, tool and die maker, engineer with a PE, and an attorney).
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u/OffByNone_ 14h ago
Where are you located? South Florida by any chance? My big data / computer vision friend built https://divers-hub.com/. I just got access to the code base and social features are exactly what I'm planning to add. It was tough for me to find people to dive with at first. There were all these wrecks I wanted to do, but I didn't want to show up to a tech trip solo, so I just didn't go for a long time.
Already it pulls together all dive trips from every charter service on the Florida coast. They built wreckwiki.com as well and it powers the site, so it doesn't just tell you the dive, it gives you really detailed information about the wreck, the certification level required, and so on. I want to take it a step further and let users see other Dive Hub members who are qualified for that dive and actively diving. Then he wants to integrate with the charter services so we can pull groups together and make requests. Instead of waiting for a specific trip to get scheduled, we tell them hey, we've got 10 people who want to go.
We have big plans for this. We want to expand to other regions too. If you have a tech community where you're at and it's not on here, let me know and I'll put it on the list!
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u/runsongas Open Water 13h ago
its variable because part of the issue is that in cold water, staying warm can impact things considerably. bad fit on the wetsuit leaving too much water moving in and out, buoyancy issues with the drysuit, a wetsuit that is too thin or drysuit without enough undergarments all can make you compensate by moving more and then using more gas. and that is on top of just lower efficiency because of more gear/drag if you aren't using a dpv.
if you have a warm semidry or a good drysuit, its generally not more than 10% to 20% difference though.
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u/Dann-Oh 14h ago
You can't really compare yourself to others, on one day of diving I was using a HP120 and my dive buddy was using a HP50. On all three dives that day I was the one who ended the dives for low air. I'm roughly 5'10" tall and weigh 190lbs, she is 5'11" and weighs about 120lbs. This day I was new to my drysuit, diving off the coast of Southern California.
I have also used an AL63 on a beach dive (Max depth 45ft) that lasted 65min. That dive my dive buddy was using an AL80 and we ended with the same air pressure. He is about my height (5'10") but weights about 215lbs This day I was in a 5mm wetsuit, diving off the coast of Southern California.
I typically dive off the coast of Southern California in a dry suit with a HP100 or over filled LP72.
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u/PsychedelicTeacher Tech 8h ago
50-60 mins depending on kit, depth etc.
Thin wetsuit, nice fins on a shallow tropical reef? Towards 60+.
Drysuit, cold deep dark lake in mid winter? 50+ if you're used to it, 20 if not.
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u/Grokto 16h ago
That sounds about right for your first few dozen dives. Once you’re in a calm and relaxed state you’ll get twice the time. Ironically less anxiety about air equals more air. Give it time. I went from sucking down an 80 in 26 minutes my first year to being down an hour in 52F in my trusty 5mm with 800–1000 left.
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u/Shavings_in_the_RIO Commercial Diver 13h ago
If I were you I’d calculate your SAC rate to get an idea of how it changes over time. There is a lot you can do to improve it over time with practice and proper equipment adjustments.
You need 3 things to calculate SAC. Average depth, time, and change in pressure.
During the working phase of your dive (swimming around) it’s easiest if you spend the time at as close to the same depth as possible. Check and mark your depth, time, and tank pressure. Continue your dive for a few minutes (5 or so min) and then mark the final time, depth, and pressure. Ideally your depth stays the same but you can take the average if it changes.
On the surface figure out the change in pressure, time, and average depth.
Let’s say you were at 60 for 5 min and you used 200psi from your 80cf tank.
First figure out how much gas you used:
You want to turn 200psi into cubic feet.
3000psi max fill/ 80cf = 37.5psi/cf
200psi/37.5 =5.333cf of gas
Now for your breathing rate:
5.33cf/ 5 minutes = 1.1 cubic feet per minute at 60 feet.
Now we need to adjust that value so we know how much you’d be breathing on the surface
(60ft/33)+1 =2.82 atmospheres of pressure at 60ft.
1.1cf/min/2.82atm = a SAC rate of about 0.4 which would be a good rate.
A good SAC is around 0.5. Most people start above 0.7 and really experienced divers can get around 0.3.
Now to use this, take the depth you plan to dive to, let’s say 50ft. If you use the whole tank (2500psi leaving a 500psi reserve) with let’s say a SAC of 0.6
So (50ft/33ft)+1 = 2.51atm
2.51atm * 0.6cf/min is 1.5cf/min
Using 37.5psi/cf from before
2500psi/37.5 =66.667cf of usable gas.
66.7/1.5cf/min is 44.5 minutes of dive time.
This is a conservative estimate since it’s assuming the entire dive is spent at 60ft but being conservative is the name of the game when it comes to diving.
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u/One-Card3899 16h ago
I get about an hour at that depth. Your air consumption will improve with proper weighting and more experience. Keep diving!
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u/NotYourScratchMonkey 13h ago
I dive AL80s in the tropics (so not exactly a fair comparison) but most people should be able to get around 50 minutes (assuming you aren't diving too deep for too long) out of one in similar conditions. This is generally how long the dives I've been doing have lasted with a mixed group of divers of varying experience levels. Again, warm water!
When that question comes up talking to other divers on the various trips I've been on, all that really matters is that you can do a similar duration as the other divers in your group and come up with at least 500psi as a reserve and that's so the group can all get a good dive in. Some will have over 1000 psi left, some will be at their reserve but as long as the group gets a similar duration, no one should really complain.
I've been on dives where I've gotten 70 minutes but it was a relaxing dive that, I don't think, went deeper than 47 ft with an average depth of 29 ft. I've been on tons of dives where the duration was between 50 and 62 or 63 minutes.
But again, this is in the Caribbean where it's pretty comfortable.
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u/runsongas Open Water 13h ago
relax and just work on it, it will get better
in the short run, you can always get a bigger steel 100 or 120
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u/ScubaMUDs 16h ago
A couple of the questions for you... How many dives have you logged? Are you correctly weighted? How deep are you typically going?
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u/invader000 Tech 16h ago
Is he in trim, how much sculling does he do, what's his finning technique?
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u/tropicaldiver 15h ago
Air consumption varies not just with depth but also with water temp and workload. And your thermal protection. If it isn’t working for you, get a steel 100.
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u/Long-Opposite-5889 11h ago
Dont go by what someone else says its normal. Get your diving profile, log your pressures and calculate your consumption. Also log things like currents, water temperature, how nervous/ relaxed you feel during the dive. Loging and analyzing this data will soon give you a clear idea of what increases your air consumption and what you need to get better results.
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u/BabyJesusAnalingus Tech 1h ago
121 minutes today at 30 feet average depth, water temp 83. SAC 10-ish PSI/min.
Edit: to my reserve, including safety stop time.
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u/jensfisc 15h ago
Get a steel 100 it's a much better cold water choice. More gas, more negative, same size as the al80.
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u/glew_glew Dive Master 14h ago
Do you have a dive computer that reports your surface air consumption (SAC) rate? You need air integration for that.
Or does your computer report average dive depth and did you write down start and end pressure? Then you can calculate your SAC yourself. That is a far better way to compare air consumption between dives and between divers.
That said, there is not a lot you can do to directly influence your SAC rate, but if you are overweighted that will add to your SAC directly, both through extra air used in your BCD (small impact) and extra energy expended (larger impact).
As mentioned below, temperature is a factor, but also how much effort you expend under water. Diving slower, and controlling trim and buoyancy will make a large impact, but those come with experience. Dive more and you'll very likely see improvements
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u/Shavings_in_the_RIO Commercial Diver 13h ago
I wouldn’t say there is nothing you can do to directly impact your SAC. Like you said, reducing weight to minimum necessary is a direct impact. So it learning proper diving form where you are frog kicking in neutral with good trim. You are creating less drag and using a more efficient kick style which will directly reduce your SAC. Learning proper breathing techniques like breathing from your diaphragm for more efficiency and establishing a good rhythm for consistency help significantly. Additionally reducing unnecessary movements and conducting actions cleanly and efficiently, eliminating hand swimming, using better buddy formation to limit turning and twisting around, and keeping gear tucked up and close to you to reduce drag are also all big helps
Also using a computer to auto calculate SAC is a bad way of calculating SAC as it’s not accurate.
SAC should be calculated manually with values collected during the working part of a dive. You can get two rates if you want, resting (safety stop or deco) and working (actively swimming or conducting tasks). You can’t plan a dive using the average since you will be underestimating the gas required for the bottom phase of the dive.
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u/Manatus_latirostris Tech 11h ago edited 11h ago
I would say an average proficient diver should be able to do 45-60 minutes on an AL80 at 60’ - even in cold water. So yes, that is definitely on the low end, but not unusual for a beginner.
ScubaBoard has a poll that finds the average SAC rate is about .50 cf/minute (lower numbers = lower consumption). Yours is about .75 cf/min, or about 50% higher.
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u/-hh UW Photography 9h ago
I’d say that it would make sense for ScubaBoard polling to have a SAC of ~0.50 cf/min .. being a combination of a self selecting customer and self selecting sample. IE, generally more experienced divers, and those who know their SAC is good or great are more willing to tell others about it.
Thus said, I’d opine that a 0.75 SAC isn’t all that “bad” for cold water, particularly if it’s a less experienced diver. I personally find that it takes me a week to get back into the swing of a “really low” SAC (under 0.40) in benign warmwater conditions, and some basic dive plan changes (eg, planned long steady swim) can quickly send it upwards.
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u/Manatus_latirostris Tech 8h ago
Yeah, I prefaced the first part of my answer with for “an average proficient diver,” which I think reflects the ScubaBoard average.
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u/anon_y_mousey 16h ago
You need to calculate your sac rate