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This is a multi-part message in MIME format. ------=_NextPart_000_0000_01C06E91.D77ED260 Content-Type: text/plain; charset="iso-8859-1" Content-Transfer-Encoding: 7bit Thank you everyone who took the time to answer my questions by relating your experiences and knowledge regarding stage bottle selection. There are obviously considerations beyond mere specs, that can only be discovered through experience, and these are what I was hoping to discover by posting my question, and did learn through your stories and explanations. One of the reasons I posted my question was that I wasn't able to find the information I needed elsewhere. I was able to find conclusions and recommendations, but not the underlying information necessary to understand why the conclusions and recommendations were what they were. I don't like doing something without understanding how to figure out why. I appreciate your providing this foundation. Most of the responses I received were by private e-mail. This doesn't let others on the list who might be interested in following this thread benefit from the information. I myself have been frustrated by seeing other questions asked and then go unanswered -- at least publicly. So, for the benefit of others who might be interested in the Al vs. steel stage bottle question, I have copied all of the answers below. I left out the identities of the writers because these were private communications, and I assumed that those who did not post to the list did so because they for some reason wanted to maintain their privacy. I wish everyone the best with the New Year. Alex ----- Original Message ----- From: Alex Vasauskas To: techdiver@aquanaut.com Sent: Friday, December 22, 2000 8:24 PM Subject: Al vs. Steel Stages As far as I have been able to read, Al stage bottles are "good" and steel stage bottles are "bad" because steel bottles are supposedly relatively "too heavy for diving and comfort" and "unsafe". I checked the specs for the size of cylinder that would be appropriate for my open water diving. Here they are: Luxfer 48.4 cu.ft./3000 psi 21.15 lbs. empty -2.4 lbs. buoyancy full / +1.3 lbs. empty in salt water OMS 46 cu.ft. / 2640 psi 17.6 lbs. empty with valve -4.0 ...lbs. buoyancy full / 0.00 lbs. empty For approximately the same volume, the steel cylinder is lighter and neutral when empty, so I don't need extra weight to be balanced. The steel cylinder is lighter. So, is this just a unique example of the steel cylinder being the better choice, or am I missing something here? =============== >So, is this just a unique example of the steel cylinder being the better >choice, or am I missing something here? This is a unique example. Look at double steel 104s, or double steel 95s, vice double Al 80s. Also note that you are not allowing anything for the buoyancy of the regulator on that bottle. When you add 1 or 2 lbs negative for the reg, the balance shifts. The steel now becomes about 2 lbs negative when empty, and six lbs negative full, adding to your required lift capacity. =============== There's no good and bad about them. It's just a matter of personal preference. When we're cave diving, my partner prefers steel 95 CF stage bottles and I prefer aluminum 80 CF stage bottles. =============== You don't want to use the stage bottle as part of your weighting system. you need to be balanced without the stages. Sometimes you plan on taking them off (especially in cave diving). Maintaining buoyancy control while removing and replacing stages underwater is a big part of any training agency's course that involves using them, even in open water. If for some reason you cannot make your ascent with the stage bottles (like you clipped them off when entering a wreck and couldn't get back to them) you certainly don't want to be dependant on their weight to hold your deco stops. The aluminum tanks are used because they swing through neutral buoyancy, having minimal impact on the overall buoyancy when they are removed or replaced or breathed from, and because of the way that they behave in the water. They are buoyant on the ass end, so they're not dragging your waist down and screwing up your trim like steel bottles do. The favorites of OW divers are 30's and 40's because of their shape and balance, or 80's if you need that much gas or are using stages of bottom gas. The short fat aluminum tanks don't work so well. The aluminum tanks are much cheaper, too. You can buy 2 al 40's or even al 80's for what a steel 46 costs. =============== I use a Steel 72 for cave(freshwater) and Al50 for Ocean. they balance out nicely. The AL 50 is more of a back up gas(pony bottle) . I dive with Students(as recreational instructor) and the stage fits just fine. =============== for larger bottles there is a clear difference in bouyancy. agreed, for 40cuft size bottles, not much difference for bouyancy, EXCEPT you could buy TWO 40cuft AL bottles, & stage harnesses, & oxygen cleaning, etc for the price of 1 steel 40. =============== >For approximately the same volume, the steel cylinder is lighter >and neutral when empty, so I don't need extra weight to be balanced. This, exactly, is one of the flaws in your argument. Your weighting system has to be ditchable in the event of an emergency. You can't use parts of your life-support system as ditchable weight. If you need to take your stages off to enter a wreck (or you're diving a cave), you'll end up unbalanced and underweighted. If you use the stage to weight yourself, you won't be able to take it off. Yet another problem with steel stages is that their weight is distributed in all the wrong ways. The OMS 'drags' through the water laterally when clipped as a stage. The aluminum tanks tend to streamline longitudinally through the water or float butt-up in the lee of your shoulder so they generate very little drag. As for having the extra volume of the OMS 46, you don't (or shouldn't) need it. I don't know what kind of dives you do, but my buddies and I routinely dive past 300 feet for upwards of 25 minutes. We deco on an aluminum 30 and 40 with 50% and 100% oxygen and still have enough deco gas left to do a second dive in the 200 foot range for 40 minutes. If you need more gas than aluminum 30s and 40s can provide then there is another problem somewhere in your system. =============== PS, to answer your question, the OMS stages are 3-times more expensive and they are too negative. When diving with stages you want them nearly balanced neutral in the water. Slightly negative when full, slightly buoyant when empty. So that when you are swimming they just float back into the slipstream. When diving with steel stages, even the lighter OMS ones, they will hang on you like lead weights and cause a lot of drag rather than shifting naturally back into the slipstream and finding the most streamlined spot naturally. This is especially so if you are scootering. Stages should always be as neutral as possible so that adding or subtracting stages doesn't affect your basic weighting. This is the totally opposite logic from doubles on the back where you want them negative if you are drysuit diving. So, don't waste your money on the OMS stages. For ocean deco, get Luxfer or Catalina 40s. If you need more gas for deeper dives, use AL80s. They are 3-times cheaper and have better buoyancy. If you are talking about open water single tank diving then just get AL80s or if you want more gas and use a drysuit, get steel 95s or HP steel tanks (HP steel tanks are only good for single tank diving though). =============== When I started to dive in open water with deco bottles, I owned a steel 46 cu-ft bottle I used for oxygen in caves. That tank was placed near the cave entrance at 20'. I did not swim with it. I also owned an aluminum 30 I used to carry with me as a pony bottle (emergency use only) on deeper recreational dives. My trimix course had us using aluminum 40's. These were well balanced and comfortable to use, even for a newbie. I needed to have two deco bottles now for some of the diving I would do, so I experimented before buying more cylinders. I was also practicing to get used to diving with stage bottles and double 80's. (I got a lot of funny looks on the dive boats on shallow reef dives where I was practicing.) I had hoped I could avoid spending more money on cylinders and find a way to make my exisiting ones work. That was not the case. I tried the alum. 30, the steel 46, and then both together. The alum 30 was fine, although a little small even for a 70' bottle. The steel tank was horrible on the dive, particularly when I did my first post-training tech dive and the only cylinder the dive operator could loan me for a second stage was also a steel 46. Four pounds each might not seem like much, but I was fighting to keep my trim during the whole dive, and most of the deco. I never used the steels for anything other than leaving in a cave entrance again. Maybe you can compensate for all of the weight pulling you down on the left side, but I hated it. When the tank empties, you start having the opposite problem if you have weighted the right side to compensate initially. One dive that way made it completely obvious that was not a good choice. Buy the right thing the first time: get aluminum 40's. The aluminum tanks are almost not noticable during the dive. The steels were a pain the whole time. =============== > Concerning the buoyancy considerations you mentioned: it sounds like you > are wanting a positively buoyant stage tank when it is getting empty. > Assuming that everything else is balanced without the stage, doesn't a > positive stage create a problem? Or, is it that the proper stage is only > positive enough so that the the whole stage rig with regulator, spg, etc. > is neutral when empty? What I really want to do is properly balance my rig with no stages, and then add stages that don't matter. The Luxfer aluminum tanks swing from a little negative to a little positive, having mimimal impact on your balance. > Which brands/models/sizes of Al cylinder are considered to be the best for > OW? From what you have said and just looking at the specs, the Luxfer 30s > and 39.9s appear to fill the bill. The Luxfer 40 is your best bet. I have a 30 and a 40, but if I were going to do it again I'd buy 2 40's. I use the 30 for O2 and the 40 for 70 ft gas, but I have acess to a Haskel and can fill my O2 bottle to its rated pressure while most others can only get maybe 2000 psi (that's why Mikey uses the 40 for O2 and the 30 for 70 ft gas). I do some diving that I fly to and borrow bottles, and there I use 2 40's. =============== END ------=_NextPart_000_0000_01C06E91.D77ED260 Content-Type: text/html; charset="iso-8859-1" Content-Transfer-Encoding: quoted-printable <!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.0 Transitional//EN"> <HTML><HEAD> <META http-equiv=3DContent-Type content=3D"text/html; = charset=3Diso-8859-1"> <META content=3D"MSHTML 5.50.4611.1300" name=3DGENERATOR></HEAD> <BODY> <DIV><FONT face=3DArial size=3D2>Thank you everyone who took the time to = answer my=20 questions by<BR>relating your experiences and knowledge regarding stage=20 bottle<BR>selection. There are obviously considerations beyond = mere=20 specs,<BR>that can only be discovered through experience, and these are=20 what<BR>I was hoping to discover by posting my question, and did=20 learn<BR>through your stories and explanations.</FONT></DIV> <DIV> </DIV> <DIV><FONT face=3DArial size=3D2>One of the reasons I posted my question = was that I=20 wasn't able<BR>to find the information I needed elsewhere. I was = able to=20 find<BR>conclusions and recommendations, but not the = underlying<BR>information=20 necessary to understand why the conclusions and<BR>recommendations were = what=20 they were. I don't like doing something<BR>without understanding = how to=20 figure out why. I appreciate your<BR>providing this=20 foundation.</FONT></DIV> <DIV> </DIV> <DIV><FONT face=3DArial size=3D2>Most of the responses I received were = by private=20 e-mail. This<BR>doesn't let others on the list who might be = interested=20 in<BR>following this thread benefit from the information. I = myself<BR>have=20 been frustrated by seeing other questions asked and then = go<BR>unanswered -- at=20 least publicly. So, for the benefit of others<BR>who might be = interested=20 in the Al vs. steel stage bottle question,<BR>I have copied all of the = answers=20 below. I left out the identities<BR>of the writers because these = were=20 private communications, and I<BR>assumed that those who did not post to = the list=20 did so because<BR>they for some reason wanted to maintain their=20 privacy.</FONT></DIV> <DIV> </DIV> <DIV><FONT face=3DArial size=3D2>I wish everyone the best with the New=20 Year.</FONT></DIV> <DIV> </DIV> <DIV><FONT face=3DArial size=3D2>Alex</FONT></DIV> <DIV> </DIV> <DIV><FONT face=3DArial size=3D2></FONT> </DIV> <DIV> </DIV> <DIV><FONT face=3DArial size=3D2>----- Original Message ----- <BR>From: = Alex=20 Vasauskas <BR>To: <A=20 href=3D"mailto:techdiver@aquanaut.com">techdiver@aquanaut.com</A> = <BR>Sent:=20 Friday, December 22, 2000 8:24 PM<BR>Subject: Al vs. Steel = Stages</FONT></DIV> <DIV> </DIV><FONT face=3DArial size=3D2> <DIV><BR>As far as I have been able to read, Al stage bottles are = "good"<BR>and=20 steel stage bottles are "bad" because steel bottles are<BR>supposedly = relatively=20 "too heavy for diving and comfort" and<BR>"unsafe". I checked the = specs=20 for the size of cylinder that<BR>would be appropriate for my open water=20 diving. Here they are:<BR> <BR>Luxfer 48.4 cu.ft./3000 = psi<BR>21.15=20 lbs. empty<BR>-2.4 lbs. buoyancy full / +1.3 lbs. empty in salt=20 water<BR> <BR>OMS 46 cu.ft. / 2640 psi<BR>17.6 lbs. empty with=20 valve<BR>-4.0 ...lbs. buoyancy full / 0.00 lbs. empty<BR> <BR>For=20 approximately the same volume, the steel cylinder is<BR>lighter and = neutral when=20 empty, so I don't need extra weight<BR>to be balanced. The steel = cylinder=20 is lighter.<BR> <BR>So, is this just a unique example of the steel = cylinder=20 being<BR>the better choice, or am I missing something here?</DIV> <DIV> </DIV> <DIV>=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D</DIV> <DIV> </DIV> <DIV>>So, is this just a unique example of the steel cylinder being = the=20 better<BR>>choice, or am I missing something here?</DIV> <DIV> </DIV> <DIV>This is a unique example.</DIV> <DIV> </DIV> <DIV>Look at double steel 104s, or double steel 95s, vice double Al = 80s.</DIV> <DIV> </DIV> <DIV>Also note that you are not allowing anything for the buoyancy of=20 the<BR>regulator on that bottle. When you add 1 or 2 lbs negative = for the=20 reg,<BR>the balance shifts. The steel now becomes about 2 lbs = negative=20 when empty,<BR>and six lbs negative full, adding to your required lift=20 capacity.</DIV> <DIV> </DIV> <DIV>=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D</DIV> <DIV> </DIV> <DIV>There's no good and bad about them. It's just a matter = of<BR>personal=20 preference. When we're cave diving, my partner prefers<BR>steel 95 = CF=20 stage bottles and I prefer aluminum 80 CF stage bottles.</DIV> <DIV> </DIV> <DIV>=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D</DIV> <DIV> </DIV> <DIV>You don't want to use the stage bottle as part of your weighting = system.=20 you<BR>need to be balanced without the stages. Sometimes you plan on = taking=20 them<BR>off (especially in cave diving). Maintaining buoyancy control = while=20 removing<BR>and replacing stages underwater is a big part of any = training=20 agency's<BR>course that involves using them, even in open water. If for = some=20 reason you<BR>cannot make your ascent with the stage bottles (like you = clipped=20 them off<BR>when entering a wreck and couldn't get back to them) you = certainly=20 don't<BR>want to be dependant on their weight to hold your deco stops. = The=20 aluminum<BR>tanks are used because they swing through neutral buoyancy, = having=20 minimal<BR>impact on the overall buoyancy when they are removed or = replaced or=20 breathed<BR>from, and because of the way that they behave in the water. = They are=20 buoyant<BR>on the ass end, so they're not dragging your waist down and = screwing=20 up your<BR>trim like steel bottles do. The favorites of OW divers are = 30's and=20 40's<BR>because of their shape and balance, or 80's if you need that = much gas or=20 are<BR>using stages of bottom gas. The short fat aluminum tanks don't = work so=20 well.<BR>The aluminum tanks are much cheaper, too. You can buy 2 al 40's = or even=20 al<BR>80's for what a steel 46 costs.</DIV> <DIV> </DIV> <DIV>=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D</DIV> <DIV> </DIV> <DIV>I use a Steel 72 for cave(freshwater) and Al50 for = Ocean.<BR> <BR>they=20 balance out nicely.<BR> <BR>The AL 50 is more of a back up gas(pony = bottle)=20 ..<BR>I dive with Students(as recreational instructor) and the = stage<BR>fits just=20 fine.</DIV> <DIV> </DIV> <DIV>=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D</DIV> <DIV> </DIV> <DIV>for larger bottles there is a clear difference in = bouyancy.<BR>agreed, for=20 40cuft size bottles, not much difference for bouyancy,<BR>EXCEPT<BR>you = could=20 buy TWO 40cuft AL bottles, & stage harnesses, & oxygen = cleaning,<BR>etc=20 for the price of 1 steel 40.</DIV> <DIV> </DIV> <DIV>=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D</DIV> <DIV> </DIV> <DIV>>For approximately the same volume, the steel cylinder is=20 lighter<BR>>and neutral when empty, so I don't need extra weight to = be=20 balanced.</DIV> <DIV> </DIV> <DIV>This, exactly, is one of the flaws in your argument. Your=20 weighting<BR>system has to be ditchable in the event of an = emergency. You=20 can't use<BR>parts of your life-support system as ditchable = weight. If you=20 need to<BR>take your stages off to enter a wreck (or you're diving a = cave),=20 you'll<BR>end up unbalanced and underweighted. If you use the = stage to=20 weight<BR>yourself, you won't be able to take it off.</DIV> <DIV> </DIV> <DIV>Yet another problem with steel stages is that their weight=20 is<BR>distributed in all the wrong ways. The OMS 'drags' through=20 the<BR>water laterally when clipped as a stage. The aluminum tanks = tend<BR>to streamline longitudinally through the water or float = butt-up<BR>in=20 the lee of your shoulder so they generate very little drag.</DIV> <DIV> </DIV> <DIV>As for having the extra volume of the OMS 46, you don't (or=20 shouldn't)<BR>need it. I don't know what kind of dives you do, but = my=20 buddies and<BR>I routinely dive past 300 feet for upwards of 25 = minutes. =20 We deco<BR>on an aluminum 30 and 40 with 50% and 100% oxygen and still = have=20 enough<BR>deco gas left to do a second dive in the 200 foot range for 40 = minutes.<BR>If you need more gas than aluminum 30s and 40s can provide = then=20 there is<BR>another problem somewhere in your system.</DIV> <DIV> </DIV> <DIV>=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D</DIV> <DIV> </DIV> <DIV>PS, to answer your question, the OMS stages are 3-times = more<BR>expensive=20 and they are too negative. When diving with stages<BR>you want = them nearly=20 balanced neutral in the water. Slightly<BR>negative when full, = slightly=20 buoyant when empty. So that when<BR>you are swimming they = just float=20 back into the slipstream. When<BR>diving with steel stages, even = the=20 lighter OMS ones, they will<BR>hang on you like lead weights and cause a = lot of=20 drag rather than<BR>shifting naturally back into the slipstream and = finding the=20 most<BR>streamlined spot naturally. This is especially so if you=20 are<BR>scootering. Stages should always be as neutral as possible=20 so<BR>that adding or subtracting stages doesn't affect your=20 basic<BR>weighting. This is the totally opposite logic from = doubles=20 on<BR>the back where you want them negative if you are drysuit=20 diving.<BR> <BR>So, don't waste your money on the OMS stages. = For=20 ocean deco,<BR>get Luxfer or Catalina 40s. If you need more gas = for=20 deeper<BR>dives, use AL80s. They are 3-times cheaper and have=20 better<BR>buoyancy.<BR> <BR>If you are talking about open water = single tank=20 diving then<BR>just get AL80s or if you want more gas and use a drysuit, = get<BR>steel 95s or HP steel tanks (HP steel tanks are only good = for<BR>single=20 tank diving though).</DIV> <DIV> </DIV> <DIV>=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D</DIV> <DIV> </DIV> <DIV>When I started to dive in open water with deco bottles, I = owned<BR>a steel=20 46 cu-ft bottle I used for oxygen in caves. That tank<BR>was = placed near=20 the cave entrance at 20'. I did not swim with it.<BR>I also owned = an=20 aluminum 30 I used to carry with me as a pony<BR>bottle (emergency use = only) on=20 deeper recreational dives. </DIV> <DIV> </DIV> <DIV>My trimix course had us using aluminum 40's. These were=20 well<BR>balanced and comfortable to use, even for a newbie. = </DIV> <DIV> </DIV> <DIV>I needed to have two deco bottles now for some of the diving = I<BR>would do,=20 so I experimented before buying more cylinders. I<BR>was also = practicing=20 to get used to diving with stage bottles and<BR>double 80's. (I = got a lot=20 of funny looks on the dive boats on<BR>shallow reef dives where I was=20 practicing.) I had hoped I <BR>could avoid spending more money on=20 cylinders and find a way to<BR>make my exisiting ones work. That = was not=20 the case. </DIV> <DIV> </DIV> <DIV>I tried the alum. 30, the steel 46, and then both together. =20 The<BR>alum 30 was fine, although a little small even for a 70' = bottle.<BR>The=20 steel tank was horrible on the dive, particularly when I did<BR>my first = post-training tech dive and the only cylinder the dive<BR>operator could = loan me=20 for a second stage was also a steel 46. </DIV> <DIV> </DIV> <DIV>Four pounds each might not seem like much, but I was fighting = to<BR>keep my=20 trim during the whole dive, and most of the deco. I<BR>never used = the=20 steels for anything other than leaving in a cave<BR>entrance = again. =20 </DIV> <DIV> </DIV> <DIV>Maybe you can compensate for all of the weight pulling you = down<BR>on the=20 left side, but I hated it. When the tank empties, you<BR>start = having the=20 opposite problem if you have weighted the right<BR>side to compensate=20 initially.</DIV> <DIV> </DIV> <DIV>One dive that way made it completely obvious that was not a=20 good<BR>choice. Buy the right thing the first time: get aluminum=20 40's.<BR>The aluminum tanks are almost not noticable during the = dive. =20 The<BR>steels were a pain the whole time.</DIV> <DIV> </DIV> <DIV>=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D</DIV> <DIV> </DIV> <DIV>> Concerning the buoyancy considerations you mentioned: it = sounds=20 like you<BR>> are wanting a positively buoyant stage tank when it is = getting=20 empty.<BR>> Assuming that everything else is balanced without the = stage,=20 doesn't a<BR>> positive stage create a problem? Or, is it that = the=20 proper stage is only<BR>> positive enough so that the the whole stage = rig=20 with regulator, spg, etc.<BR>> is neutral when empty?</DIV> <DIV> </DIV> <DIV>What I really want to do is properly balance my rig with no stages, = and=20 then<BR>add stages that don't matter. The Luxfer aluminum tanks swing = from a=20 little<BR>negative to a little positive, having mimimal impact on your=20 balance.</DIV> <DIV> </DIV> <DIV>> Which brands/models/sizes of Al cylinder are considered to be = the best=20 for<BR>> OW? From what you have said and just looking at the = specs, the=20 Luxfer 30s<BR>> and 39.9s appear to fill the bill.</DIV> <DIV> </DIV> <DIV>The Luxfer 40 is your best bet. I have a 30 and a 40, but if I were = going=20 to<BR>do it again I'd buy 2 40's. I use the 30 for O2 and the 40 for 70 = ft=20 gas,<BR>but I have acess to a Haskel and can fill my O2 bottle to its = rated=20 pressure<BR>while most others can only get maybe 2000 psi (that's why = Mikey uses=20 the 40<BR>for O2 and the 30 for 70 ft gas). I do some diving that I fly = to and=20 borrow<BR>bottles, and there I use 2 40's.</DIV> <DIV> </DIV> <DIV>=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D</DIV> <DIV> </DIV> <DIV>END</FONT></DIV></BODY></HTML> ------=_NextPart_000_0000_01C06E91.D77ED260-- -- Send mail for the `techdiver' mailing list to `techdiver@aquanaut.com'. Send subscribe/unsubscribe requests to `techdiver-request@aquanaut.com'.
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