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scubadiver888
03-02-2009, 10:16
I've been reading some of the threads on tanks and realize there is a lot I don't know about tanks. Some of the stuff I've read:

- two tanks of a given capacity/material might weigh differently, i.e. two HP100 steels might not weigh the same.
- some tanks are not as easy to find a fill for, i.e. they need a certain compressor

What are all the things I have to consider when purchasing a tank?

If I buy my own tank I'd use it for wreck penetration. Most the wrecks are in the 90' to 110' range. I don't want something massively heavy if I don't have to have that. Right now I'm wearing 22lbs of lead with an AL80. So I have room to drop some weights if I go steel.

Anyone have sites for 'how to pick your tank'?

Rainer
03-02-2009, 10:34
So you don't know anything about cylinders, but you want them for wreck penetration?

Weird.


I've been reading some of the threads on tanks and realize there is a lot I don't know about tanks. Some of the stuff I've read:

- two tanks of a given capacity/material might weigh differently, i.e. two HP100 steels might not weigh the same.
- some tanks are not as easy to find a fill for, i.e. they need a certain compressor

What are all the things I have to consider when purchasing a tank?

If I buy my own tank I'd use it for wreck penetration. Most the wrecks are in the 90' to 110' range. I don't want something massively heavy if I don't have to have that. Right now I'm wearing 22lbs of lead with an AL80. So I have room to drop some weights if I go steel.

Anyone have sites for 'how to pick your tank'?

tc_rain
03-02-2009, 11:58
Here is a site with the specs on different tanks.

Scuba Cylinder Specifications from Tech Diving Limited - 928-855-9400 (http://www.tdl.divebiz.net/pub/tanks.html)

RoyN
03-02-2009, 12:00
I can't help you on the tanks, its pretty much what your comfortable with. You might want to go to your dive shop and ask them about it.

scubadiver888
03-02-2009, 12:06
No, I know some things about cylinders and I wonder if there is more information out there about them. Yes, my ULTIMATE goal is to use the cylinders for wreck penetration.

I know I have to start logging my SAC rate (approximately 0.77 cfm) and calculate my turning pressure, half enough air for if my buddy goes into free flow, etc. I know that were I want to be by the end of the summer, an AL80 is not going to cut it (unless I can GREATLY improve my SAC rate).

What I'm asking here is not what size cylinder is good for wreck penetration at 110' but are there things a novice wouldn't consider when purchasing a tank. Has someone put together a chart with all the differences for various cylinders? Are LP typically longer? larger in diameter? Do people use a certain cylinder because they know they can get a cave fill? Should I check local fill stations to see if that will be an issue?

Basically, is there something that pops to mind you think you'd like to share. Obviously this is going to be little bits of knowledge which will lead me to ask more questions and I do plan on asking my dive instructors similar questions.


So you don't know anything about cylinders, but you want them for wreck penetration?

Weird.


I've been reading some of the threads on tanks and realize there is a lot I don't know about tanks. Some of the stuff I've read:

- two tanks of a given capacity/material might weigh differently, i.e. two HP100 steels might not weigh the same.
- some tanks are not as easy to find a fill for, i.e. they need a certain compressor

What are all the things I have to consider when purchasing a tank?

If I buy my own tank I'd use it for wreck penetration. Most the wrecks are in the 90' to 110' range. I don't want something massively heavy if I don't have to have that. Right now I'm wearing 22lbs of lead with an AL80. So I have room to drop some weights if I go steel.

Anyone have sites for 'how to pick your tank'?

rustyshakelford
03-02-2009, 12:10
i dive with a LP108 and love it. if you can get it filled to 3000 you have tons of gas. double it up and you have a large set of doubles

it is a little heavier than the AL80 but i dont really notice it. the bouyancy caracterisitics are great with it also

brett

scubadiver888
03-02-2009, 12:11
Here is a site with the specs on different tanks.

Scuba Cylinder Specifications from Tech Diving Limited - 928-855-9400 (http://www.tdl.divebiz.net/pub/tanks.html)

Thank you. This is the sort of thing I was looking for.

I'm also wondering if there are other things which matter but usually doesn't get discussed? For example, with diamonds they talk about the 4C's, cut, clarity, colour and carat. What they don't talk about is that you can take two diamonds of exactly the same 4C's put them side by side and one diamond will look soapy and dirty. The reason being that the soapy diamond has a mild blue fluorescence. Most literature for the average consumer does not talk about fluorescence.

Is there something which makes one tank different from another even though the main specs are the same?

BSea
03-02-2009, 12:12
I personally like LP 85's. But I can get higher than normal fills. When I bought mine LP tanks were quite a bit less than HP tanks, but that's not the case the last time I looked. Probably the most popular tank around my LDS is the HP 100. Then comes the HP 120 for those that want more gas. One thing to consider is how much you are willing to carry, and how the tank trims out for you. Both the LP 85 & HP 100 are similar in size to an AL 80, with much better buoyancy (better=less in this case).

I have a 120, but it doesn't trim out to well compared to my 85's. I have to wear it up too high for perfect trim. YMMV.

scubadiver888
03-02-2009, 12:13
I can't help you on the tanks, its pretty much what your comfortable with. You might want to go to your dive shop and ask them about it.

The big problem in my area is that most places only rent AL80s. I'd like to try out different tanks. I do plan on asking my local dive shop. I just thought I'd ask here too.

BouzoukiJoe A.K.A. wrecker130 AKA Chuck Norris AKA joeforbroke (banned)
03-02-2009, 12:31
Do not penetrate wrecks without proper training and experience. There are countless ways to die doing this. I have never penetrated beyond the light zone, and even then one time we got blocked by a fallen panel while going up a stair way so we had to turn around. In the process of turning around my buddy (of course it was my buddy :D ) caused a complete silt-out that made his 24w HID completely useless. We had not run a line because we expected to be able to swim all the way through the wreck the way we had done before. Lots of bad things can happen down there.

By the time you are ready, you will likely have the answers to your tank questions. At a minimum you will have dive buddies or aquaintances who will be be more trustworthy and helpful than any anonymous poster on the internet. I don't see how you could get the experience and have it be otherwise.

That said- I understand you are ready to buy some tanks and don't want to have to re-buy down the road.

The answer is to buy 2 matched steel tanks of at least 100cf capacity. LP85 and LP95 tanks count if you can get overfills. These tanks need to be the same diameter, length, and capacity because you will want to double them later. If you get into wreck penetration you will want double tanks (backmount with isolation mannifold is most common). At a bare minimum I would want a large single with an H valve and a separate pony. Going in without two independent regulators is asking for trouble. If you go into any spaces in which side by side swimming with your buddy is not possible (almost all wreck penetration would qualify) then you will want to use a long hose configuration.

In pursuit of your goal, Cavern/Cave training would be very beneficial.

Byte Me
03-02-2009, 12:42
Nice link - great info! Tanks are on the list of things I need to get, appreciate the info. Leaning HP100 from LDS since they offer free lifetime fills. Like the better buoyancy and fill amount.

CWSWine
03-02-2009, 12:52
I just purchased two HP100ís with the plans of using them as doubles in the future and one HP119 for my single tank after doubling my HP100ís. I choose the HP 100 because weight out the water was about the lightest that gave me good amount of air for diving. I choose the X8 HP100 since it was really close the HP100 in buoyancy so I donít have to mess with extreme weighting problems switching between tanks. Switching from AL80 to steel is quite a change to your buoyancy and you can loose quite a bit weight from you belt. Slow down and enjoy the hobby - there no hurry!!

CompuDude
03-02-2009, 13:10
It's hard to go wrong with matched HP100s (or matched LP85s if you can be sure overfills will be readily available to you). Eventually, you may outgrow them, but only if you progress really far, and at that point, a couple more tanks will seem like nothing. They're lighter than anything else out there, and give you the most gas, pound for pound (dry weight). Very versatile for singles or doubles.

I prefer Worthington's galvanized finish to Faber's paint, for salt water diving. Be sure you have a convertible DIN/Yoke valve, because if you end up diving doubles, you'll end up with DIN regs anyway... this way you have both options covered. (Also handy to have both options if you ever lend a tank to a friend.) Thermo valves are the best (for singles).

When I say "matched" I mean tell the shop you're planning to double the tanks so they can special request two tanks with identical characteristics on their order... there is a lot of small manufacturing variation that's no issue at all for single tank, but you don't want one tank 1/2" longer than the other for doubles.

Rainer
03-02-2009, 13:15
This topic has been covered a number of times, so you might want to do a search.

That said, what are your expectations for the cylinders? Will you be trying to do two recreational dives off one set? For a single T1 dive, even AL80s are just fine.

Start by determining how much gas you need. Run some typical profiles and post up gas requirements. Include RB calculations.

What's your ability to get fills? Can your shop's compressor hit 3500 psi? Can you get overfills (say to 3000) on LPs?

Is your SCR really nearly 0.8? That's pretty darn high. Might want to just concentrate on some simple dives while you get more comfortable. Hitting the gym will also bring that number down. If it comes down, smaller cylinders are going to come back into consideration.

Do some homework and post back.

Flatliner
03-02-2009, 13:20
I personally like LP 85's. But I can get higher than normal fills. When I bought mine LP tanks were quite a bit less than HP tanks, but that's not the case the last time I looked. Probably the most popular tank around my LDS is the HP 100. Then comes the HP 120 for those that want more gas. One thing to consider is how much you are willing to carry, and how the tank trims out for you. Both the LP 85 & HP 100 are similar in size to an AL 80, with much better buoyancy (better=less in this case).

I have a 120, but it doesn't trim out to well compared to my 85's. I have to wear it up too high for perfect trim. YMMV.

BSea, How tall are you. I am looking at tanks and leaning tword the HP120s (singles now, doubled later in the year or early next year at the latest. I am 6'5" and was told by a taller tech diver that the HP100s suck as doubles tanks as far as trim goes. He said they push you nose over when you are tall.

Rainer
03-02-2009, 13:28
HP100s *are* a bit short for taller divers. I'm 6'0" and wouldn't want anything shorter. You'd be better off in AL80s or HP130s. I think the 120s are ridiculously long, and it's nice to have doubles that teammates can dive (if everyone you dive with is at least 6'5", rock on with the 120s). Gear really does become a team resource when you start diving a lot. At a minimum, standardizing cylinder choices can help improve logistical issues, from gas planning, to filling, to swapping cylinders amongst your group.

CompuDude
03-02-2009, 13:29
I personally like LP 85's. But I can get higher than normal fills. When I bought mine LP tanks were quite a bit less than HP tanks, but that's not the case the last time I looked. Probably the most popular tank around my LDS is the HP 100. Then comes the HP 120 for those that want more gas. One thing to consider is how much you are willing to carry, and how the tank trims out for you. Both the LP 85 & HP 100 are similar in size to an AL 80, with much better buoyancy (better=less in this case).

I have a 120, but it doesn't trim out to well compared to my 85's. I have to wear it up too high for perfect trim. YMMV.

BSea, How tall are you. I am looking at tanks and leaning tword the HP120s (singles now, doubled later in the year or early next year at the latest. I am 6'5" and was told by a taller tech diver that the HP100s suck as doubles tanks as far as trim goes. He said they push you nose over when you are tall.

I can't speak to 6'5", but at 6'3" I adore my HP100s. They're just not massive enough to cause issues... doubled HP119s (or LP95s), however, I have heard some of those complaints about. I've never heard anyone complain about HP100s, though, including some taller friends that I have who diver them (I think at least one is 6'5"). Whoever told you HP100s suck for trim, well, apparently sucks. ;) IMO, someone diving at technical levels should be able to trim out quite a large variety of tanks.

BSea
03-02-2009, 13:30
I personally like LP 85's. But I can get higher than normal fills. When I bought mine LP tanks were quite a bit less than HP tanks, but that's not the case the last time I looked. Probably the most popular tank around my LDS is the HP 100. Then comes the HP 120 for those that want more gas. One thing to consider is how much you are willing to carry, and how the tank trims out for you. Both the LP 85 & HP 100 are similar in size to an AL 80, with much better buoyancy (better=less in this case).

I have a 120, but it doesn't trim out to well compared to my 85's. I have to wear it up too high for perfect trim. YMMV.

BSea, How tall are you. I am looking at tanks and leaning tword the HP120s (singles now, doubled later in the year or early next year at the latest. I am 6'5" and was told by a taller tech diver that the HP100s suck as doubles tanks as far as trim goes. He said they push you nose over when you are tall.I'm 5'11". I think 120's are really perfect for the 6'2" or taller diver. I've seen some guys that were several inches shorter than me using them, but for me, a 120 will push my head up unless I wear it really high. Then the reg will hit my head. Not a huge issue, but not the best option for me. I'm thinking of selling it, and getting a HP119 or LP 108 or LP 95, all 8" diameter tank so I can get the gas with a shorter tank.

Rainer
03-02-2009, 13:31
I personally like LP 85's. But I can get higher than normal fills. When I bought mine LP tanks were quite a bit less than HP tanks, but that's not the case the last time I looked. Probably the most popular tank around my LDS is the HP 100. Then comes the HP 120 for those that want more gas. One thing to consider is how much you are willing to carry, and how the tank trims out for you. Both the LP 85 & HP 100 are similar in size to an AL 80, with much better buoyancy (better=less in this case).

I have a 120, but it doesn't trim out to well compared to my 85's. I have to wear it up too high for perfect trim. YMMV.

BSea, How tall are you. I am looking at tanks and leaning tword the HP120s (singles now, doubled later in the year or early next year at the latest. I am 6'5" and was told by a taller tech diver that the HP100s suck as doubles tanks as far as trim goes. He said they push you nose over when you are tall.

I can't speak to 6'5", but at 6'3" I adore my HP100s. I've never heard anyone complain about them, including some taller friends that I have who diver them (I think at least one is 6'5"). Whoever told you HP100s suck for trim, well, apparently sucks. ;)

You haven't talked to a lot of taller divers then. The 100s ARE short and I know of many tallish divers who complain about them. For someone 6'5", 100s are like me trying to dive HP80s (at 6'0"). Just a stupid amount of mass up high. Pretty doable for more experienced doubles divers, but I wouldn't want to learn in them.

CompuDude
03-02-2009, 13:39
I personally like LP 85's. But I can get higher than normal fills. When I bought mine LP tanks were quite a bit less than HP tanks, but that's not the case the last time I looked. Probably the most popular tank around my LDS is the HP 100. Then comes the HP 120 for those that want more gas. One thing to consider is how much you are willing to carry, and how the tank trims out for you. Both the LP 85 & HP 100 are similar in size to an AL 80, with much better buoyancy (better=less in this case).

I have a 120, but it doesn't trim out to well compared to my 85's. I have to wear it up too high for perfect trim. YMMV.

BSea, How tall are you. I am looking at tanks and leaning tword the HP120s (singles now, doubled later in the year or early next year at the latest. I am 6'5" and was told by a taller tech diver that the HP100s suck as doubles tanks as far as trim goes. He said they push you nose over when you are tall.

I can't speak to 6'5", but at 6'3" I adore my HP100s. I've never heard anyone complain about them, including some taller friends that I have who diver them (I think at least one is 6'5"). Whoever told you HP100s suck for trim, well, apparently sucks. ;)

You haven't talked to a lot of taller divers then. The 100s ARE short and I know of many tallish divers who complain about them. For someone 6'5", 100s are like me trying to dive HP80s (at 6'0"). Just a stupid amount of mass up high. Pretty doable for more experienced doubles divers, but I wouldn't want to learn in them.

I've spoken to a decent number.

Irrelevant, however, if the OP is 5'11". 100s or 85s should be fine.

Rainer
03-02-2009, 13:45
I personally like LP 85's. But I can get higher than normal fills. When I bought mine LP tanks were quite a bit less than HP tanks, but that's not the case the last time I looked. Probably the most popular tank around my LDS is the HP 100. Then comes the HP 120 for those that want more gas. One thing to consider is how much you are willing to carry, and how the tank trims out for you. Both the LP 85 & HP 100 are similar in size to an AL 80, with much better buoyancy (better=less in this case).

I have a 120, but it doesn't trim out to well compared to my 85's. I have to wear it up too high for perfect trim. YMMV.

BSea, How tall are you. I am looking at tanks and leaning tword the HP120s (singles now, doubled later in the year or early next year at the latest. I am 6'5" and was told by a taller tech diver that the HP100s suck as doubles tanks as far as trim goes. He said they push you nose over when you are tall.

I can't speak to 6'5", but at 6'3" I adore my HP100s. I've never heard anyone complain about them, including some taller friends that I have who diver them (I think at least one is 6'5"). Whoever told you HP100s suck for trim, well, apparently sucks. ;)

You haven't talked to a lot of taller divers then. The 100s ARE short and I know of many tallish divers who complain about them. For someone 6'5", 100s are like me trying to dive HP80s (at 6'0"). Just a stupid amount of mass up high. Pretty doable for more experienced doubles divers, but I wouldn't want to learn in them.

I've spoken to a decent number.

Irrelevant, however, if the OP is 5'11". 100s or 85s should be fine.

Agree, at around 6'0" almost anything would work. Again, though, no point making recommendations till the OP actually does his HW: compressor, ability to get overfills on LPs, use as doubles, and team standard issues should all be determined first.

scubadiver888
03-02-2009, 13:56
I personally like LP 85's. But I can get higher than normal fills. When I bought mine LP tanks were quite a bit less than HP tanks, but that's not the case the last time I looked. Probably the most popular tank around my LDS is the HP 100. Then comes the HP 120 for those that want more gas. One thing to consider is how much you are willing to carry, and how the tank trims out for you. Both the LP 85 & HP 100 are similar in size to an AL 80, with much better buoyancy (better=less in this case).

I have a 120, but it doesn't trim out to well compared to my 85's. I have to wear it up too high for perfect trim. YMMV.

I have a fairly long torso so I think I can handle something longer than an AL80 without banging my legs or head. I figure I can get a tank with a bigger circumference and keep the length the same as say an AL80. Is there any disadvantage to that? I know the straps on my gear could handle something bigger than an AL80 without trouble.

BSea
03-02-2009, 14:00
I personally like LP 85's. But I can get higher than normal fills. When I bought mine LP tanks were quite a bit less than HP tanks, but that's not the case the last time I looked. Probably the most popular tank around my LDS is the HP 100. Then comes the HP 120 for those that want more gas. One thing to consider is how much you are willing to carry, and how the tank trims out for you. Both the LP 85 & HP 100 are similar in size to an AL 80, with much better buoyancy (better=less in this case).

I have a 120, but it doesn't trim out to well compared to my 85's. I have to wear it up too high for perfect trim. YMMV.

I have a fairly long torso so I think I can handle something longer than an AL80 without banging my legs or head. I figure I can get a tank with a bigger circumference and keep the length the same as say an AL80. Is there any disadvantage to that? I know the straps on my gear could handle something bigger than an AL80 without trouble.About the only disadvantage I know of is that some charters won't let you bring 8" diameter tanks because their tank holders won't hold them.

scubadiver888
03-02-2009, 14:40
Do not penetrate wrecks without proper training and experience. There are countless ways to die doing this. I have never penetrated beyond the light zone, and even then one time we got blocked by a fallen panel while going up a stair way so we had to turn around. In the process of turning around my buddy (of course it was my buddy :D ) caused a complete silt-out that made his 24w HID completely useless. We had not run a line because we expected to be able to swim all the way through the wreck the way we had done before. Lots of bad things can happen down there.


Thanks for the concern Joe. I've taken the PADI course on wreck penetration and I am CONSTANTLY asking anyone and everyone about things like this. I definitely take everything from the Internet with a grain of salt. I use this information more for something to get me thinking/investigating rather than the final answer.

Basically, if I didn't have people like you warning me, I'd think the PADI course was enough and I'd be putting myself at greater risk. I read a lot and post occasionally. Only after months (years) of poking, probing, asking, reading do I usually feel comfortable.

Just as a point of background, I took a 'discovery' scuba before it was standardized. I survived without serious injury because of dumb luck. A couple of other people were not so lucky. It took me years to even consider trying scuba again.

I'd NEVER enter a wreck without running a line. I'd get a full briefing from the boat crew on each wreck before penetrating it.

If I was diving a wreck with a swim through I'd probably dive it twice. Once to run a line and make sure I can get all the way through and the second time to recover the line. I'd talk to people about that first though in case they had reasons why that is a bad idea. :smiley2:



By the time you are ready, you will likely have the answers to your tank questions. At a minimum you will have dive buddies or aquaintances who will be be more trustworthy and helpful than any anonymous poster on the internet. I don't see how you could get the experience and have it be otherwise.

That said- I understand you are ready to buy some tanks and don't want to have to re-buy down the road.

The answer is to buy 2 matched steel tanks of at least 100cf capacity. LP85 and LP95 tanks count if you can get overfills. These tanks need to be the same diameter, length, and capacity because you will want to double them later. If you get into wreck penetration you will want double tanks (backmount with isolation mannifold is most common). At a bare minimum I would want a large single with an H valve and a separate pony. Going in without two independent regulators is asking for trouble. If you go into any spaces in which side by side swimming with your buddy is not possible (almost all wreck penetration would qualify) then you will want to use a long hose configuration.

In pursuit of your goal, Cavern/Cave training would be very beneficial.
Hmm, good planning. I would have done this by luck. I typically dive two tanks a day. I would buy two of the same tanks just because that is me.

I have a few hundred wrecks to pick from so I'll be sticking to the roomier ones at first. I'm okay with confined spaces though. I've been in situations were my gear got hooked on a swim through. Insta-buddy just stopped and watched me so I took all my gear off, swam through, retrieved my gear, re-donned and called the end to the dive. Certainly wasn't going to keep going with the guy who didn't help me.

Trouble with overfilling is I sometimes go as far as 600 kms (400 miles) from home to go diving. Even if I can find fills at home I might not be able to at other locations.

I've seen some guys diving with double HP100s and few diving with Nitrox with HP119 and a 19cf pony.

scubadiver888
03-02-2009, 14:59
It's hard to go wrong with matched HP100s (or matched LP85s if you can be sure overfills will be readily available to you). Eventually, you may outgrow them, but only if you progress really far, and at that point, a couple more tanks will seem like nothing. They're lighter than anything else out there, and give you the most gas, pound for pound (dry weight). Very versatile for singles or doubles.


I have no way of knowing whether I can get overfills for LP85s. I might be able to find some locally but my dive area is so big (400 miles to the north [Lake Superior or Tobermory], 400 miles to the east [St. Lawrence River], 200 miles to the south-west [Lake Erie], 200 yard to the south [Lake Ontario]) that I might be able to get overfill some places but not all of them. I will probably fill at home, dive the first dive then get refills at the dive site for the rest of the weekend.



I prefer Worthington's galvanized finish to Faber's paint, for salt water diving. Be sure you have a convertible DIN/Yoke valve, because if you end up diving doubles, you'll end up with DIN regs anyway... this way you have both options covered. (Also handy to have both options if you ever lend a tank to a friend.) Thermo valves are the best (for singles).

I'll probably only use my tanks in fresh water. Hadn't thought about using DIN for doubles. I'll keep that in mind.



When I say "matched" I mean tell the shop you're planning to double the tanks so they can special request two tanks with identical characteristics on their order... there is a lot of small manufacturing variation that's no issue at all for single tank, but you don't want one tank 1/2" longer than the other for doubles.

This is the sort of stuff I wouldn't have thought of. I can see me picking up a tank, using it and renting AL80 for the first few months then picking up another tank later. I guess it would be best to buy both at once.

scubadiver888
03-02-2009, 15:21
This topic has been covered a number of times, so you might want to do a search.

That said, what are your expectations for the cylinders? Will you be trying to do two recreational dives off one set? For a single T1 dive, even AL80s are just fine.

Start by determining how much gas you need. Run some typical profiles and post up gas requirements. Include RB calculations.

What's your ability to get fills? Can your shop's compressor hit 3500 psi? Can you get overfills (say to 3000) on LPs?

Is your SCR really nearly 0.8? That's pretty darn high. Might want to just concentrate on some simple dives while you get more comfortable. Hitting the gym will also bring that number down. If it comes down, smaller cylinders are going to come back into consideration.

Do some homework and post back.

Sorry, I guess I'm still not clear on what I'm asking. I'm not trying to figure out what size tanks I should be looking at. I'm more interest in why you might buy one brand over another or the finer criteria for deciding.

I mentioned that I'd read the messages on here as a way of saying, I know enough to figure out how many cf I need for various dives.

Things like CompuDude posted he prefers Worthington over Faber because the coating is better for salt water.

I want something so I can do one dive to 110' with an appropriate safety margin. I'd buy two tanks but I'd dive one tank at a time. If my SAC rate is too high to dive 110' on an HP100 but the HP100 looks good for all other intends and purpose, I'll spend the summer working on my SAC rate.

I was just about to explain how I calculated my SAC rate when I realized, I did it wrong. Doh. I don't know how wrong it is but you are right. That number is way too high.

As a review, what I've read is take the current PSI in the tank, take the current time. Do your dive at a fixed depth (99', 66' or 33' makes the math a little easier). After a period of time (e.g. 10 min at 99' or 15 min at 66') note the PSI and elapsed time. With these numbers I should be able to figure out my SAC rate (start cf/ end cf) / elapsed time / ATA. Right?

I also need to find something to convert the PSI for that size tank to cf.

BSea
03-02-2009, 15:29
I also need to find something to convert the PSI for that size tank to cf.Here's a little excel file I made for tank volume calculations.

EDIT: Just don't change the formulas in the blue areas

scubadiver888
03-02-2009, 15:31
HP100s *are* a bit short for taller divers. I'm 6'0" and wouldn't want anything shorter. You'd be better off in AL80s or HP130s. I think the 120s are ridiculously long, and it's nice to have doubles that teammates can dive (if everyone you dive with is at least 6'5", rock on with the 120s). Gear really does become a team resource when you start diving a lot. At a minimum, standardizing cylinder choices can help improve logistical issues, from gas planning, to filling, to swapping cylinders amongst your group.
This is the sort of 'extra' information I was looking for. I never noticed that the HP120s are a lot longer. I would have assumed HP130s were longer.

I'm also 6'0" so it is good to know that HP100s are probably the shortest I'd want to go. When you are talking about HP100, HP120, HP130 are you typically talking about Faber? Worthington?

I noticed that an AL80 doesn't actually hold 80cf. Do all the steel cylinders hold what you would expect? e.g. HP119 is 119cf.

scubadiver888
03-02-2009, 15:37
I personally like LP 85's. But I can get higher than normal fills. When I bought mine LP tanks were quite a bit less than HP tanks, but that's not the case the last time I looked. Probably the most popular tank around my LDS is the HP 100. Then comes the HP 120 for those that want more gas. One thing to consider is how much you are willing to carry, and how the tank trims out for you. Both the LP 85 & HP 100 are similar in size to an AL 80, with much better buoyancy (better=less in this case).

I have a 120, but it doesn't trim out to well compared to my 85's. I have to wear it up too high for perfect trim. YMMV.

I have a fairly long torso so I think I can handle something longer than an AL80 without banging my legs or head. I figure I can get a tank with a bigger circumference and keep the length the same as say an AL80. Is there any disadvantage to that? I know the straps on my gear could handle something bigger than an AL80 without trouble.About the only disadvantage I know of is that some charters won't let you bring 8" diameter tanks because their tank holders won't hold them.

Not an issue were I dive so far. All the boats use rubber straps to hold the tank to the wall and let it sit on the deck. I think this is because we have recreational divers using AL80s and some SERIOUS technical divers using everything under the sun.

Rainer
03-02-2009, 15:39
You're starting to ask some good question. Hope this is proving useful.

Personally, all of my steels (eight, soon to be ten) are either PSTs (no longer made new, but they rock), Worthingtons or Asahis (older cylinders). I also prefer HDG over painted. That said, the HDG ones are a bit crappy when doubled up in SW (noticeable corrosion between the SS bands and cylinders; it washes up ok, but does take work). That said, I'd stick with HDG myself. If you're doing FW as you said, don't worry about it.

For someone at 6'0", you're going to likely find LP85s/HP100s (almost the same size) to be just long enough (note, ALL of my recommendations so far consider going to doubles with these cylinders; for singles, just about anything will work!). Would be great if they were actually just slightly longer. I find my double AL80s and HP130s to trim out better than my LP85s/HP100s. For *singles* only, if you're going to dive to 110' (which is deep for a single cylinder), I personally would want to be in a HP130. I use my single HP100s for stuff shallower than 80' typically (usually in the 40-60' range).

CompuDude
03-02-2009, 16:11
HP100s *are* a bit short for taller divers. I'm 6'0" and wouldn't want anything shorter. You'd be better off in AL80s or HP130s. I think the 120s are ridiculously long, and it's nice to have doubles that teammates can dive (if everyone you dive with is at least 6'5", rock on with the 120s). Gear really does become a team resource when you start diving a lot. At a minimum, standardizing cylinder choices can help improve logistical issues, from gas planning, to filling, to swapping cylinders amongst your group.
This is the sort of 'extra' information I was looking for. I never noticed that the HP120s are a lot longer. I would have assumed HP130s were longer.

I'm also 6'0" so it is good to know that HP100s are probably the shortest I'd want to go. When you are talking about HP100, HP120, HP130 are you typically talking about Faber? Worthington?

I noticed that an AL80 doesn't actually hold 80cf. Do all the steel cylinders hold what you would expect? e.g. HP119 is 119cf.

HP120s are really long and skinny. (7.25", same as hp100 and Al80s, but but so much taller it just looks impossibly long and skinny). HP130's are a similar height (not exactly), but 8" diameter makes it seem more natural. HP119s are the exact same height as HP100s (usually), but 8" diameter instead of 7.25".

Al.80s are indeed odd ducks, given that they actually hold 77.4cf of gas but are called "80". Steel tanks generally hold the amount they're rated for, but watch out for low pressure tanks. LP tanks are referred to at their rated volume WITH a 10% overfill, which is permitted only if you tank has a + rating. An LP85 has a working pressure of 2400psi, but a + rated fill of 2640. You need to fill it to 2640 to get the full 85cf. Fairly irrelevant if you're getting overfills, where you'll be over 85 anyway, but pretty important to know if you're at a shop that's a stickler, because if you actually need 85cf and they'll only fill to 2400psi because you didn't get a + stamp at the last hydro, you're going to have issues. At 2400psi that "LP85" only holds 77cf.

scubadiver888
03-02-2009, 16:22
You're starting to ask some good question. Hope this is proving useful.

Personally, all of my steels (eight, soon to be ten) are either PSTs (no longer made new, but they rock), Worthingtons or Asahis (older cylinders). I also prefer HDG over painted. That said, the HDG ones are a bit crappy when doubled up in SW (noticeable corrosion between the SS bands and cylinders; it washes up ok, but does take work). That said, I'd stick with HDG myself. If you're doing FW as you said, don't worry about it.

For someone at 6'0", you're going to likely find LP85s/HP100s (almost the same size) to be just long enough (note, ALL of my recommendations so far consider going to doubles with these cylinders; for singles, just about anything will work!). Would be great if they were actually just slightly longer. I find my double AL80s and HP130s to trim out better than my LP85s/HP100s. For *singles* only, if you're going to dive to 110' (which is deep for a single cylinder), I personally would want to be in a HP130. I use my single HP100s for stuff shallower than 80' typically (usually in the 40-60' range).

My plan before posting was to do two HP100 for now. I'd dive singles because the boats typically go out for two dives in the morning, back for fills then two tanks in the afternoon. Once I start doing penetration throw a pony on the main tank or sling something.

When I start going deeper or longer penetration, switch to doubles.

I'm now thinking two HP130, as singles, then throw in a pony when I need it. Put off serious penetration until next year and buy two HP100s at that time.

I was originally thinking HP130s would be too big but the reality is anything smaller than an HP100 might be too small for my body.

I'm assuming the cylinder size, regardless of valve, is what matters for trim. Adding a valve which is 1" higher than some other valve is not going to have as significant effect as adding 1" of tank.

For anyone reading this without reading other threads:

HDG = Hot Dipped Galvanized
SW = Salt Water
SS = Stainless Steel
FW = Fresh Water

in_cavediver
03-02-2009, 16:51
On tanks - for your size, its hard to go wrong with either LP85/HP100 or LP104/HP130's. The LP and HP tank combinations I gave are pretty close to the same size/buoyancy characteristics but with different fill pressures. I'm 5'10" and use either doubled 85's, doubles 104's or double Al80's (wetsuit) for backmounts. All trim nicely and swim well. I also cave fill when needed so capacity isn't a concern to me. If you were really short or quite tall, the HP80's or HP120's might be other options. To me, they are too short or too tall.

I'll also warn you if you aren't diving dry now, you should look at that soon. Steel doubles are not something to do in a wetsuit in most cases.

Last point. You mentioned a lot about wreck penetration. No offense intended but PADI's wreck specialy is not good penetration training. Its OPTIONAL for the instructor to do on the last dive. If you are serious about wreck penetration, do it right and get technical training in it, even if you really don't want to go 'outside rec limits'. I personally feel every overhead is a tec dive, be it cavern, cave, deco or wreck. TDI and IANTD offer tec wreck classes. (I am sure there are otheragencies as well but htose two came to mind instantly). A cavern class is also a good choice. Fundies might also help you get ready. The proper training is far more important that minor nuances in gear.

Flatliner
03-02-2009, 17:55
BSea, if you are interested in swapping that HP120 for an LP98 PM me.

scubadiver888
03-02-2009, 18:35
I'll also warn you if you aren't diving dry now, you should look at that soon. Steel doubles are not something to do in a wetsuit in most cases.

Why? Is it a buoyancy issue? I know for people diving 3mm or 5mm wetsuit, steel doubles will add more weight that you can afford to drop off your weight belt. I'm diving with 7mm and 14mm on the core plus hood, gloves, etc. Right now I'm down to 22lbs with an AL80. I tried going to 20lbs but had a hard time at the safety stop. I'm looking to double my time in the water this summer but I doubt I'm going to get below 18lbs.



Last point. You mentioned a lot about wreck penetration. No offense intended but PADI's wreck specialy is not good penetration training. Its OPTIONAL for the instructor to do on the last dive. If you are serious about wreck penetration, do it right and get technical training in it, even if you really don't want to go 'outside rec limits'. I personally feel every overhead is a tec dive, be it cavern, cave, deco or wreck. TDI and IANTD offer tec wreck classes. (I am sure there are otheragencies as well but htose two came to mind instantly). A cavern class is also a good choice. Fundies might also help you get ready. The proper training is far more important that minor nuances in gear.I've read enough here and other boards to realize the PADI wreck specialty is not good penetration training. The people who took me out to the wreck were actually TDI and IANTD instructors. We definitely went beyond what was in the PADI documentation.

I actually went out to do my AOW. We were all staying together at a dive cottage so we spent evenings doing class work and days doing diving. On the four day my instructor told me I was qualified for a PADI wreck specialty. I think I was probably overqualified but still not at the level of the people I was diving with.

Right now I'd only do wreck penetration with my instructor. I trust her with my life. She knows my limits and that I don't like to push them. I think she likes the fact that I never panic.

I'm a cautious diver so I'll probably take the TDI course and the IANTD course as well. Everyone who dives the wrecks in my area are TDI or IANTD trained. A few got trained by cave divers in Florida. They were a little too intense for me so I didn't get the details from them. Maybe once I'm IANTD I can hold a conversation with them. :smiley36:

Fundies? Why does this sound familar? What is Fundies?

UCFKnightDiver
03-02-2009, 20:27
Fundies is GUE Fundamentals. A class that prepares you for tech training, by allowing you to become proficient at some of the basic core skills of tech training in a more benign open water environ.

I would suggest that you dive alot more, and get more expirience, tag along with a group of divers that are doing the type of diving you would like to do (of course dive to your level of training) having a mentor to help you with things is immensley helpful.

In relation to tanks if getting hp130s now I think those would be a great tank to double up also, you get alot of gas dont need to worry about overfills, and are just a nice all around tank. Compareable to LP 104s/108s in size buoyancy, and weight. I am 5'11 also and trim out nicely in 108's/104s which are like HP130s. I would also second the recommendation to get Worthington tanks, Fabers tend to rust quite a bit more, and PST tanks are tending to fail hydro quite a bit more than the others.

As to your buoyancy question people tend to shy away from diving heavy steel doubles in the ocean with a wetsuit/without a drysuit because if your wing fails its not all that easy to kick to the surface especially at the start of the dive when your doubles are really negative, and having a drysuit gives you a redundant means of buoyancy in order to get you to the surface.

Also keep in mind that there is a fairly big buoyancy swing in steel tanks from quite a bit negative when full to almost neutral sometimes when empty so you may not be able to drop as much weight as you think. So do a proper 500 psi buoyancy check to get dialed in so you dont have problems when it could really count like air sharing on an ascent and sucking your tanks down more than you normally do.

But most of all go out and dive all of this info will come with time!!!

RoyN
03-02-2009, 23:29
Yep, Fundies is DIR-F also. I took that last year, a wonderful class which helps the divers from everything to buoyancy and trouble.

in_cavediver
03-03-2009, 05:14
Why? Is it a buoyancy issue? I know for people diving 3mm or 5mm wetsuit, steel doubles will add more weight that you can afford to drop off your weight belt. I'm diving with 7mm and 14mm on the core plus hood, gloves, etc. Right now I'm down to 22lbs with an AL80. I tried going to 20lbs but had a hard time at the safety stop. I'm looking to double my time in the water this summer but I doubt I'm going to get below 18lbs.

To answer why steel doubles are potentially an issue, lets look at pure numbers for my LP104's (my preferred tec tanks).

These are PST made and they are -11.3lbs full, and -3.3lbs empty. For doubles, the tanks are -7lbs + another -3lbs or -4lbs for the bands manifold when empty. I give them -11lbs, dead empty. This is a lot of negative weight. If you add in gas weight, that's another -16lbs if full. So, you could be anywhere from -11lbs to -27lbs in just tanks/bands with a DOT fill. (Cave fill adds another -8lbs or so for air to make them -35lbs or so). This does not even take into account the weight of your BP/Wing or BC or any other gear. That's another -7lbs to -9lbs for me with with my SS plate and can light.

Why this is important, assume you have a wing failure early in the dive. You now have a LOT of negative weight in your scuba unit and no way to offset it and no way to ditch it. Wetsuits compress with depth so you lose that inherent buoyancy to offset it.

Each set of tanks will provide unique numbers and you should do the math on it. Al 80's are acceptable as doubles in a wetsuit. LP85's are marginal and the 104's simply aren't. Do the math for your rig and see what you get.

scubadiver888
03-03-2009, 11:10
rox@ucf11 and in_cavediver,

Thanks for the information. Cannot afford a drysuit this season but I also won't be diving doubles yet either. Makes me wonder, how can I be sure I can handle BC failure? I know all the wrecks I'm diving right now have a mooring line attached to a HUGE buoy and/or the boat. Worst case scenario I could pull myself up the rope.

Plan right now... ask my instructor. Suggestion... see if I can swim my gear up the line without using any air and without using the line on the last dive of the day.

Do you consider handling buddy loses lift that you will have to have enough lift for you and him? Or would you drop his tanks and have him switch to your octo?

Rainer
03-03-2009, 11:13
Um, we use dry suits as back up.

Dropping your buddy's cylinders is an almost guarantee of disaster.

If you can't swim up your rig with a failed wing in a wet suit, you're over-weighted and need to make changes. For me, that's just not an acceptable setup.

Flatliner
03-03-2009, 11:57
If you can't swim up your rig with a failed wing in a wet suit, you're over-weighted and need to make changes. For me, that's just not an acceptable setup.

I understand what you are saying for a recreational diver BUT is this realistic for a tech diver. I am not one yet, but I understood that you carry a lift bag or large SMB as a 3rd back up in case of a total failure of drysuit and wing. I know in many tech setups you can be VERY negative at the begining of a dive?

I am not trying to stir the pot, I really want some of the experienced tech guys to chime in.

Rainer
03-03-2009, 12:14
If my wing fails, I have a dry suit and a 50# bag. I'm getting up just fine. I also have a teammate or two to assist. For bigger dives, I have He in my cylinders, which is noticeably less negative than nitrox. I'm not worried. Good luck getting up, though, in steel doubles with a failed wing in a wet suit. Isn't going to happen if you have any stops to maintain.

Flatliner
03-03-2009, 12:20
I must have misunderstood your previous post. That was the point I was asking about.

Rainer
03-03-2009, 12:21
I must have misunderstood your previous post. That was the point I was asking about.

Sorry, what are you asking?

Flatliner
03-03-2009, 13:06
I must have misunderstood your previous post. That was the point I was asking about.

Sorry, what are you asking?

It sounded to me as if you were saying that you wouldn't dive any rig you couldn't swim to the surface in a wetsuit. I was asking if that was a realistic requirement in tech diving. As I stated, I must have misunderstood because in your next post you clarified.

Thanks

Rainer
03-03-2009, 13:08
For any 'tech dive' I'd be in a dry suit. Wet suits and steel doubles don't mix.

UCFKnightDiver
03-03-2009, 14:21
First off I wouldnt recommend this to anyone but....

have shot a lift bag from depth using double lp120's and climbed up the cave line attached to the reel... its not easy and I did it from 30 ft in a 5mil wetsuit so.... etc

2nd option is you could ride your buddy up acctually havent tried this one yet, but it seems like it would be doable.

3rd option is you can kick your way to the surface have tried this from 30ft using double lp85s overfilled to 3000, and a 5mil wetsuit, and I did it with one fin. A saftey stop and/or deco is not really an option in this case.

That being said I will not dive steel doubles, or doubles for that matter in the Ocean or a deep Lake without a drysuit and since I dont have a drysuit I dont. I might and I say again might consider diving lp85s in the ocean, but that would be risking it big time. I have tried all these things in a spring, and if worse comes to worse I could always climb my way out.

in_cavediver
03-03-2009, 19:07
There is another option - double wings. Some circles frown upon them others don't. Lots of issues to sort out but very doable. I count a lift bag as a distant third on my list. Its doable but it won't be fun.

If it was me, and I had the choice of 2 wings and a wetsuit or no dive, I'd dive the double wings. Its not likely as I have 2 drysuits. (I like to actually dive when I take the time to setup a trip).

The real moral is, if you want to tec dive, you better have a big checkbook because it ain't cheap.

Grin
03-04-2009, 09:16
The good old "what tank?" debate. personally I'm glad to see you lean toward 130s. I have HP120s and I'm 6 ft tall and they are great tanks. I have 4 HP120s 7.25 diameter models. And a couple LP85s. I never notice a difference in the water. I'm sure there is a little dofference, but it's not notworthy. I had some HP 100s a few years back and they are nice tanks, but for the money your spending I like to get some serious gas. The difference between a 80 and 100 is not much. Unless your completely happy wiht the capacity of your good old reliabel AL 80s, I would go bigger than 100s for single diving. A 65 year old dive buddy of mine (not a tall man either) uses Hp 130s. He does two dives a day and can stay down a hour + in 70-80 ft for each dive and not be in deco. After diving AL 80s and the HP100s and even my LP85s, those are all sufficient tanks. But it sure is nice to have excess sized tanks and virtually eliminate the entire need to even have to think about gas supply. I do my 130 ft dives with a 120 and surface with something like 1500-1700 lbs regularly. But a few times I have chased a fish around down there, and used almost the entire tank on a single 130 ft dive. Still didn't go into deco, still had enough gas to make it a zero factor. Moral of the story, steel tanks cost alot, get the biggest tanks you think you can handle. And remember 1500-1700lbs in a Hp 120 is good for another dive, we do it all the time. I'm 6 ft and 165 lbs is all. Unused air is not a waste, because the next planned 30 minute dive can effortlessly turn into a 50 minute dive at your disposal. Why dive constricted on purpose. I remember the days of hitting the bottom and 5 minutes later your thinking "Damn that tank is going fast", then your entire dive revolves around how long your tank will last. Now your checking pressure, and double checking, and calculating your dive over the damn tank capacity. Screw that! Get big tanks and use your computer/Nitrogen loading to calc your bottom time. That's the real limiting factor, unless you want to throw the tank size factor into your dive profile for some reason.
A 7.25 inch diameter HP 120 is about 3 inches taller than a AL 80. You remove about 5-6 lbs of lead, when going to the HP 120 from a AL 80 tank. Remove the same 5-6 lbs when going from the AL 80 to the LP85.
The only way AL 80s and HP 100 singles are plenty of gas, is if your diving straight air. If your on Nitrox, you'll wish you had the big tanks. They cost close to the same when comparing a HP 100/120/130.
That's my opinion! Screw those 100s :smilie39:

BouzoukiJoe A.K.A. wrecker130 AKA Chuck Norris AKA joeforbroke (banned)
03-04-2009, 10:09
At least the Faber lp85s can work wet in the ocean depending on rest of gear (thickness of wetsuit, type of plate, etc.)

For bigger tanks, some people I know use dual bladder wings (with the second inflator disconnected). Other people I know frown on this and dive dry in 78 degree water. Both camps tease each other relentlessly. Neither camp seems to die in measurable numbers.

I fall in the drysuit category but I'm not a zealot about it. I prefer the drysuit not so much for backup buoyancy, but because I can survive longer before succumbing to hypothermia.

CompuDude
03-04-2009, 12:15
The good old "what tank?" debate. personally I'm glad to see you lean toward 130s. I have HP120s and I'm 6 ft tall and they are great tanks. I have 4 HP120s 7.25 diameter models. And a couple LP85s. I never notice a difference in the water. I'm sure there is a little dofference, but it's not notworthy. I had some HP 100s a few years back and they are nice tanks, but for the money your spending I like to get some serious gas. The difference between a 80 and 100 is not much. Unless your completely happy wiht the capacity of your good old reliabel AL 80s, I would go bigger than 100s for single diving. A 65 year old dive buddy of mine (not a tall man either) uses Hp 130s. He does two dives a day and can stay down a hour + in 70-80 ft for each dive and not be in deco. After diving AL 80s and the HP100s and even my LP85s, those are all sufficient tanks. But it sure is nice to have excess sized tanks and virtually eliminate the entire need to even have to think about gas supply. I do my 130 ft dives with a 120 and surface with something like 1500-1700 lbs regularly. But a few times I have chased a fish around down there, and used almost the entire tank on a single 130 ft dive. Still didn't go into deco, still had enough gas to make it a zero factor. Moral of the story, steel tanks cost alot, get the biggest tanks you think you can handle. And remember 1500-1700lbs in a Hp 120 is good for another dive, we do it all the time. I'm 6 ft and 165 lbs is all. Unused air is not a waste, because the next planned 30 minute dive can effortlessly turn into a 50 minute dive at your disposal. Why dive constricted on purpose. I remember the days of hitting the bottom and 5 minutes later your thinking "Damn that tank is going fast", then your entire dive revolves around how long your tank will last. Now your checking pressure, and double checking, and calculating your dive over the damn tank capacity. Screw that! Get big tanks and use your computer/Nitrogen loading to calc your bottom time. That's the real limiting factor, unless you want to throw the tank size factor into your dive profile for some reason.
A 7.25 inch diameter HP 120 is about 3 inches taller than a AL 80. You remove about 5-6 lbs of lead, when going to the HP 120 from a AL 80 tank. Remove the same 5-6 lbs when going from the AL 80 to the LP85.
The only way AL 80s and HP 100 singles are plenty of gas, is if your diving straight air. If your on Nitrox, you'll wish you had the big tanks. They cost close to the same when comparing a HP 100/120/130.
That's my opinion! Screw those 100s :smilie39:

I don't disagree with a general leaning towards nice big tanks, but there are certainly times that a nice light tank like an HP100/LP85 are nice to have, as the weight difference between the HP100/LP85 is significant compared to HP119/120/130 and larger tanks (and their similarly-sized LP versions). I also disagree that "The difference between a 80 and 100 is not much.", when in fact, you get over 20% more gas with the HP100 (or overfilled LP80) compared to an Al.80. Anytime you're looking at 20% more, that's significant, in my book, especially given almost zero weight difference between the tanks. (and a net reduction in overall weight carried when going from aluminum to steel tanks)

Grin
03-04-2009, 15:06
One might look at it that way as that is correct (on paper :smiley36:). But if a AL 80 doesn't make you happy why go a mere 20% more. Look at it that way and it's alot of money for not much more time. Say the typical newby gets 25 minutes at 75 ft on his AL 80. His new Steel HP 100 should get him like 31 minutes for a mere $325, for 6 minutes extra. His new HP 130 would get him a easy 40 plus minutes for what? $50 more than the HP100! Now your talking! 40 minutes is alot when your used to 25. 31 minutes is, well!, better than nothing! Seems like alot of money to get 6 lbs off your belt and 6 extra minutes to me.
Lets also look at the other common factors. If a person using AL80s is buying new tanks, highly likely for more bottom time, he probably is already surfacing with little left in the AL 80. If done per the book he surfaces with what? 500-1000lbs. So now that 20% extra really starts to look like not much. Or, this diver is in the common club of using all the air routine. Where he surfaces with 100lbs. A HP 100 would do nothing but get him the same bottom time with 500lbs at the surface, or extend bottom time by about 5 mins and still surface with 100lbs. It would be nice to at least get rid of the bad habit and get the extra bottom time over just one of those.
20% is ok, 40% now your talking! With 40% you really eliminate just about all scenarios, and bad habits, and possibly still have excess. It's just too nice.
In 25 ft of water I did 1.5 hours a few weeks ago on a HP120. In 75 ft I can do a hour and I'm really ready to come up when the tank gets low. 130 I am more worried about Nitrogen loading than tank size by far. But if my loading gets me into deco, I have plenty of gas to cover it.
My Lp85s are Ok! But I only throw them on he boat if all my 120s are empty. There is just no point! And when I do use them it seems I always am surfacing with 100lbs.
I think a full sized male is doing himself a diservice by going HP100. It's a nice tank but if buying new get the real deal. Get your girlfriend a HP100.

Rainer
03-04-2009, 15:16
Ignoring the mathematical challenges above (80->100cf is not a 20% increase), the bigger issue is whether or not you *need* more capacity than 100cf (or even 80cf). If you're somewhere where dives are no deeper than 50' (e.g. nearly all the shore sites where I used to be in MA), then who cares. I used to get multiple dives off a single HP100. If you're doing square profiles, I know I could nearly max NLDs at 100' on nitrox while maintaining RB. A bigger cylinder wouldn't really help. Shoot, I could use my double LP85s to get two recreational dives, while almost always hitting max NDLs in the 80-100' range.

That said, I did pick up some single HP130s when I came to CA. For the deeper shore dives, they give enough gas to both max deep NDLs, while still providing gas for coming shallow and extending the dive. Also allow a bit more RB padding. They're a great cylinder, but seriously, most divers do not need them. And seeing as I've had two sets of double HP130s, they aren't the most practical cylinders to pair up. Double HP100s/LP85s are a lot nicer out of the water, so that's something to consider if you're buying singles now with the future idea of manifolding them later.

When considering new cylinders, first determine your gas needs. If you don't need 130cf for any of the singles dives you're currently doing or will likely be doing, don't bother. After you determine how much gas you need, figure out how you're going to get it. Go LP if you can get reliable over-fills, can't get HP fills, get a good price break over HP, plan to do your own PP blending, or plan to top off the cylinders with a transfill whip from HP cylinders you already own. Otherwise, get HP.

BSea
03-04-2009, 15:17
The good old "what tank?" debate. personally I'm glad to see you lean toward 130s. I have HP120s and I'm 6 ft tall and they are great tanks. I have 4 HP120s 7.25 diameter models. And a couple LP85s. I never notice a difference in the water. I'm sure there is a little dofference, but it's not notworthy. I had some HP 100s a few years back and they are nice tanks, but for the money your spending I like to get some serious gas. The difference between a 80 and 100 is not much. Unless your completely happy wiht the capacity of your good old reliabel AL 80s, I would go bigger than 100s for single diving. A 65 year old dive buddy of mine (not a tall man either) uses Hp 130s. He does two dives a day and can stay down a hour + in 70-80 ft for each dive and not be in deco. After diving AL 80s and the HP100s and even my LP85s, those are all sufficient tanks. But it sure is nice to have excess sized tanks and virtually eliminate the entire need to even have to think about gas supply. I do my 130 ft dives with a 120 and surface with something like 1500-1700 lbs regularly. But a few times I have chased a fish around down there, and used almost the entire tank on a single 130 ft dive. Still didn't go into deco, still had enough gas to make it a zero factor. Moral of the story, steel tanks cost alot, get the biggest tanks you think you can handle. And remember 1500-1700lbs in a Hp 120 is good for another dive, we do it all the time. I'm 6 ft and 165 lbs is all. Unused air is not a waste, because the next planned 30 minute dive can effortlessly turn into a 50 minute dive at your disposal. Why dive constricted on purpose. I remember the days of hitting the bottom and 5 minutes later your thinking "Damn that tank is going fast", then your entire dive revolves around how long your tank will last. Now your checking pressure, and double checking, and calculating your dive over the damn tank capacity. Screw that! Get big tanks and use your computer/Nitrogen loading to calc your bottom time. That's the real limiting factor, unless you want to throw the tank size factor into your dive profile for some reason.
A 7.25 inch diameter HP 120 is about 3 inches taller than a AL 80. You remove about 5-6 lbs of lead, when going to the HP 120 from a AL 80 tank. Remove the same 5-6 lbs when going from the AL 80 to the LP85.
The only way AL 80s and HP 100 singles are plenty of gas, is if your diving straight air. If your on Nitrox, you'll wish you had the big tanks. They cost close to the same when comparing a HP 100/120/130.
That's my opinion! Screw those 100s :smilie39:

I don't disagree with a general leaning towards nice big tanks, but there are certainly times that a nice light tank like an HP100/LP85 are nice to have, as the weight difference between the HP100/LP85 is significant compared to HP119/120/130 and larger tanks (and their similarly-sized LP versions). I also disagree that "The difference between a 80 and 100 is not much.", when in fact, you get over 20% more gas with the HP100 (or overfilled LP80) compared to an Al.80. Anytime you're looking at 20% more, that's significant, in my book, especially given almost zero weight difference between the tanks. (and a net reduction in overall weight carried when going from aluminum to steel tanks)I agree, there are times when an old steel 72 is plenty of air. Not every dive has to be deep. In the lakes around here, I'll usually only do the 1st dive deep, and even then it's so cold that they don't usually last so long that I'd feel cheated if I only had a 100. Now, If I had a boat in the ocean, then yeah, I'd want big tanks all the time. But when I have to haul them, or when the dives are shallow, there's nothing wrong with a smaller tank.

CompuDude
03-04-2009, 16:10
Ignoring the mathematical challenges above (80->100cf is not a 20% increase)

For the record, I said over 20%. ;) I didn't feel like being overly precise since the Al.80 is 77.4cf, not a round # like 80cf. I suppose technically I should have said over 25%, which is still lower than the actual number. You're welcome to do the actual division if you want, but the precise figure wasn't the point of my post. :smiley9:

Rainer
03-04-2009, 16:19
Ha, I was responding to Grin's post (where the error is carried out repeatedly). Didn't see you also fell victim!

BSea
03-04-2009, 16:24
Ignoring the mathematical challenges above (80->100cf is not a 20% increase)

For the record, I said over 20%. ;) I didn't feel like being overly precise since the Al.80 is 77.4cf, not a round # like 80cf. I suppose technically I should have said over 25%, which is still lower than the actual number. You're welcome to do the actual division if you want, but the precise figure wasn't the point of my post. :smiley9:Actually, this supports your position (and mine) even more.:smiley20:

CompuDude
03-04-2009, 16:27
Ha, I was responding to Grin's post (where the error is carried out repeatedly). Didn't see you also fell victim!

No, the 20% figure came from me. I was being lazy. Just pointing out that in the original post where 20% came from, I did say OVER 20%. :smiley9:

Grin
03-05-2009, 09:05
I was going to mention that also, but refrained! :smiley20:
Nothing gets by you techies!
My 5 minutes on this site today is up! See you all tomorrow.