Tank sizes when diving

[Mustard Dave]

You can never have too much gas. Not having enough gas can be a bit of a problem though.

Here in the UK, the most popular size seems to be 232bar 12 litre steels (roughly 100 cubic feet). For deeper dives within recreational limits, many use 15 litre cylinders (120 cubic feet). Often you see women and kids with 10 litre (80 cubic feet) as they are a little easier to handle.

Most the lads at my club dive twinsets (me included) and again, 12 litres seems to be the popular size. One bloke has a set of twin 15s in his garage. He borrowed them off another fella who ditched them as they are too heavy. Twinsets work well in the UK. I would not want to be deeper than 30 metres in cold water without a redundant air source. If I'm just doing a sedate bimble at one of the inland sites with a buddy on a single, it just means I don't have to put it in for a fill after the first dive like they do. It is a pain in the arse on a RIB though.

When we go to Malta (an annual trip at my club), most of us ask for 15s. They usually have to borrow them, but the dive centres there tend to help each other out so it isn't a problem for them if we give them notice. The simple reason for this as it gives us longer in the water. There's no harm in strapping the biggest cylinder you can handle onto your back, whatever your SAC is like.

 

[TSandM]

Well, you asked the question of whether it's better to use the lever of short divers to make new divers work on their consumption, or just to give them bigger tanks. I look at it another way -- a new diver, enthralled with his new sport, may be much more tempted to push his air supply to the limit, if he has to do it to get a long enough dive to feel satisfied with.

In addition, if you run dives where the whole GROUP has to surface when the first person runs low on gas, I'd much rather you give the new divers bigger tanks.

They will only run an increased DCS risk in the sense that they are able to stay down longer, but if they're still huffing through gas at a rate that requires larger tanks, they probably still won't be pushing NDLs.

Economics undoubtedly plays a role as well. It's one thing to get a 20 minute dive from shore, where your entire cost is the $10 air fill. It is quite another to spend a couple of hundred dollars for a grand total of 40 minutes underwater.

High gas consumption was never one of my issues, and it has dropped with time. But my very, very favorite way to dive warm water is with double Al80s. They dive well, and with that gas supply on my back, the ONLY thing I have to think about is deco (and requested maximum dive time, if the boat has one).

 

[Searcaigh]

Most of my holiday diving to SE Asia always involves using AL80s. On a recent trip to Puerto Galera I managed to obtain an AL100 for one of my friends that is a real gas guzzler and he managed to stay under longer with myself and my other buddy on the trip using AL80s.

Personally at "home" I am diving AL80s with Nitrox for most dives, although I have an HP100 and a set of doubles (7.9Lx2) that I use for specific dives such as a 30M wreck as well as long dives on a specific site where I go for critter photography (90 mins is not unusual for me and my buddy here). My usual buddy is also a small built lady who can last almost 2 hours at 16M on an AL80, and I match her bar for bar using an HP100.

Choose the tank to match the dive is my preference, I also use S63s on occasion for shallow dives (10M) plus my daughter likes these too mainly because of the weight, but also suits her gas consumption too.

Horses for courses

 

[Bonairetrip]

You can never have too much gas.

Yes and no. Nothing bad has ever happened from surfacing with too much air. But carrying more gas imposes additional costs of one sort or another. Larger tanks tend to cost more. Larger tank are more unwieldy on the boat -- even more so for a shore dive. Smaller tanks are simply easier and that difference is noticeable -- above and below the water. Otherwise we would all be diving doubles with an iso bar -- or surface supplied.

I am a big guy (with a decent SAC) and can easily handle the weight of HP 100 -- yet on some tropical dives I use an AL 63. Why? It is enough air (including a reserve) to do the job and it is a tad bit easier to handle in or out of the water. I know some very small females who do well with (I think) a 40. On the other hand, for a cold water dry suit dive, I would likely go with either an al 80 or (if available) a HP 100.

In other words, the right tank for the unique combination of diver and dive. (And, when in doubt, got to a larger tank).

As a customer, I appreciate it it if the operator offers me (as a customer) some choices -- IMHO there is no good reason to make the air hog use a small tank nor to make the 4'11" gill breather fight with an 80 or 100. For your pros, I would upsize the tanks from what they might use as a customer (the margin to chase a wayward diver who unexpectedly went deeper).

 

[Nemrod]

Lately I've seen more and more divers, usually newer divers, request for larger and larger tanks. AL80s are the 'standard' by and large. Requests come in for 100s and now 120s and 130s.

Most common reason given: "I need it to feel comfortable since I'm draining out the 80s."
Most commonly seen underwater for those who request or insist on larger tanks: averaging 15 breathing cycles a minute with outliers at 25.

Should divers learn to relax while underwater and breathe slowly or be encouraged/allowed to continue (by supplying larger and larger tanks) to come close to hyper-ventilation and 'still have enough air left?'

For the more educated on the topic of DCS (not me) will breathing that much more gas at depth, say 50% more by comparing 80s to 120s will there be an adverse impact on the diver using the larger tank? Easier chance of DCS or same? Two assumptions. First being same size/height/weight approximately and second differing stats.

Thanks in advance for the constructive inputs!

It probably has to do with the increasing girth and decreasing fitness level of people these days. People just get bigger and bigger. So naturally they want a bigger thank to match their bigger waist.

N

 

[MSDT476614]

Thanks TSandM, Searcaigh, Bonairetrip and Nemrod!

Will take all your observations in mind. I'll probably cater for 10% of tanks to be 15Ls though the twins will remain as 12L twins. Hope its a good ratio as we'll be handling somewhere in the vicinity of 120 tanks a day for filling excluding tec and CCR fills.

On new divers, perhaps its a toss between having them on 12s vs 15s when they try to get bouyancy under control first. I'd rather spare/give the OW diver 1 more tank/dive during training dives to get buoyancy right (includes breathing, finning etc). Could be that much harder to kick off with 15s.

 

[Mustard Dave]

the fear is that 120's would allow you to exceed ndl and still get onboard with the designated psi. some boats want to use one model for gas consumption. the standard 80. sea and surface makes little difference when the model is that an s80 at 80 ft will produce a 20 min dive for everyone except the 2 guys that have 120's. messes up SI's for the group also as they model s80 dive 2 hour si and another s80 dive. It would appear that you are using the psi for something usefull. if you dont exceed ndl and deco dives are not allowed because it is a recreational based, milti dive, group based, dive plan then the 120's are a problem to the boat operators. Finally , to newer divers, larger tanks are the answer to bottom time, they indicate you can go deeper and longer before hitting accent psi. It goes along with boats not allowing other than single tank rigs. I dont have problems with them cause i call first and ask what the tank limits are, so all is well. ITS THIER BOAT. A slight overfill on an lp95 is a lot of air. compared to an s80.. many times i have surfaced with 15-1800 on a lp95 and the insta-buddy with s80 is at 500 so its no biggy. Still plenty of air to share if needed. The greatest latitude in tanks was when one group (club) did a trip. we had doubles you name it. Normally a mixed group is more stringent to the s80's. Besides you dont fnd to many boats that can hold 8" tanks. Sand dollar out of coz would only allow thier s80's, Another place would allow the 120 but charged double for a fill whether it had 1800 in it or 300 so they advised to not bring them for that reason and they could not stage that large of tank with the group size.



---------- Post added December 14th, 2012 at 11:59 PM ----------

You just reinforced my above post. The only difference is that you opinion is usually the opinion onf the boat. Many of the boats I have been out on do not provide a DM in the water, Our group I guess you would say goes without a waterborn DM and the boat is just for transportation and body counting and dive plan management.

Jesus Christ! Do people put up with that? I've never heard of a skipper insisting on a maximum tank size and if somebody told the club I dive with we couldn't bring a particular size tank, they'd very quickly and less than politely be told where to go. You're right to say it's their boat, but it's the customer's money. If I was that customer, they would not be getting a penny off me and I'd use another boat.

The only bit of dive planning the skipper needs to get involved in is telling me what time we are diving. If he wants us out of the water at a particular time because we need to be ready to steam away to the next site, that is fine, but I'm a trained diver - I do not need somebody to tell me how to plan my dives or calculate NDLs for me.

I'm not sure why they want to enforce the no deco rule. Why does it matter to the recreational divers? I've been on boats where technical divers and recreational divers are free to do what they are comfortable / qualified to do without one group ruining the others' plans.

The single tank only rule is ridiculous unless it is a small RIB. I dive twins because it is safer. If I get a freeflow or my reg fails, I can shut down the offending reg and switch to my backup.

Yes and no. Nothing bad has ever happened from surfacing with too much air. But carrying more gas imposes additional costs of one sort or another. Larger tanks tend to cost more. Larger tank are more unwieldy on the boat -- even more so for a shore dive. Smaller tanks are simply easier and that difference is noticeable -- above and below the water. Otherwise we would all be diving doubles with an iso bar -- or surface supplied.

I am a big guy (with a decent SAC) and can easily handle the weight of HP 100 -- yet on some tropical dives I use an AL 63. Why? It is enough air (including a reserve) to do the job and it is a tad bit easier to handle in or out of the water. I know some very small females who do well with (I think) a 40. On the other hand, for a cold water dry suit dive, I would likely go with either an al 80 or (if available) a HP 100.

In other words, the right tank for the unique combination of diver and dive. (And, when in doubt, got to a larger tank).

As a customer, I appreciate it it if the operator offers me (as a customer) some choices -- IMHO there is no good reason to make the air hog use a small tank nor to make the 4'11" gill breather fight with an 80 or 100. For your pros, I would upsize the tanks from what they might use as a customer (the margin to chase a wayward diver who unexpectedly went deeper).

Larger tanks do cost more but the person buying the cylinder gets to make that decision. A dive operator can supply what they want but a successful business gives the customer what he wants. If they want, they can always charge a little bit extra if a customer wants a bigger tank.

A 12 litre 232 bar cylinder (roughly the same as a 100) seems to be the popular choice for UK divers. Very few people have problems carrying a one, including the extra lead a cold water diver needs in a drysuit. I have two of these on my back normally and yes, they are f**king heavy but I put up with it as it is the best tool for the job for what I want to do. Yes, of course smaller tanks are easier to handle, but if the choice of cylinder size is there, the diver can decide what he wants.

I agree with what you say but other than bigger cylinders being harder to handle, there is no valid safety reason to limit the size of a cylinder.

 

[tyesai]

I dive in a tourist location with most of the dives being "guided" and the dive shop that I use has both 12L, 15L, and even a few 18L whoppers! When I was really new I was appreciative that they had the 15L tanks so those of us with higher air consumption could have more bottom time. I personally would rather dive a 12L as it feels much better in and out of the water and I do so unless the dive plan calls for something else now that I've settled down a bit. However I've watched people burn through an 18L tank in about 30 minutes at depths no greater than 60 feet so I'm thankful they have the big tanks when my dive buddies can't go with me and I'm diving with the group. Long story longer different people have different needs and it is nice when the shops can make things much more accommodating for everyone by simply having different sized cylinders.

 

[Bob DBF]

I look at it another way -- a new diver, enthralled with his new sport, may be much more tempted to push his air supply to the limit, if he has to do it to get a long enough dive to feel satisfied with.

I have seen issues with newbes and it has not involved trying to push the air supply, but not paying enough attention to the air supply by being enthralled with his new sport, narked, or just not having a real feel for the difference in gas useage between the 25' training and the 60'+ dive being made. The "Oh S**t" moment comes from suddenly seeing the gas is way lower than expected, or gone, rather than the attention you need to pay when nurseing the bottle to the bottom.

I dive 72's a lot, since I have many, and because they lend themselves to shallow, cold dives on the North Coast in a wetsuit for dive #2 and/or 3. I recomend them to new divers because they are small and they lend themselves to paying close attention to ones gas supply, which is a very good habit to have when diving. Minimizing the gas supply minimizes a lot of other issues, untill one gets good. Also, the tanks are cheap and only slightly buoyant empty.

When diving with more experienced divers, match the tanks for the dive but put a more experienced diver with the newbe to minimize supprises.



Bob
-----------------------------
I may be old, but I’m not dead yet.

 

[Billy Poore]

I usually dive an 80 and always come up with more air than my fellow divers despite being the only one diving a full face mask. It's never been a problem *however* I wouldn't mind diving a 100 just for the reason that sometimes I catch myself concentrating more on my breathing rate than the actual dive. It would be nice to relax a little bit and not be so constantly obsessed with my air consumption rate.