What size doubles?

[Mr. Bubble]

I am in the market to get a set of twins, but I am not sure what sizt to get. I have seen several set ups. 95, 100,105, 120 and even 130's.

I know the first response will be..."it depends on what you want to do.".....

well, I want to wreck dive and cave dive...mostly within the recreational 130 ft range, but maybe some limited extended range.....

man...those twin 130's were heavy!

So, what do you recommend and why?

Thanks

Mr. B

[TSandM]

I recommend a set of tanks that will do what you want, and will balance easily for you.

For example . . . If you want to get two recreational dives out of a set of doubles, you need to sit down and calculate the likely depths and your necessary reserves, and figure out how big a tank you need to be able to do two dives.

If you are going to do one tech dive, you need to figure out your gas requirements and your necessary reserve, and see what size tank will do that for you.

Then, once you have a ballpark of the cubic feet you need, you need to figure out what will balance for you. Tall people often do better with longer tanks. I know I tried to dive doubled LP72s for months, and could never get them to balance well. The very first dive with my LP85s was like coming home :)

Ideal is to be able to borrow various sorts of tanks and try them, to see what feels right in the water.

[xiSkiGuy]

How tall are you? As TS&M alluded to, some people find that certain size tanks work well for them and some don't. I'm 6'2 and I find LP95s and X7-100s to be too short to trim out well. X8-130s work pretty well for me. AL80s and LP85s are the easiest I've tried. I haven't tried X7-80s or LP120s but I imagine they would be too short and too tall respectively. If possible, try some different tanks before you buy.

[Rick Inman]

Another thing to toss into the mix, depending of who/where you are getting your fills, it can be more difficult to...ah...maximize your fills in a HP set than a LP set. IOWs, when I show up to the dive site with my LP95's "full", I'll often have more CF of gas than my buddy with his "full" HP 100s (although I love how the 100's ride on me).

[Juno]

The "typical" doubles are LP95's/98's. I prefer the Fabers as they are a little lighter, but that size is a good all around tank. As the others have stated, from there you may want larger or smaller depending on your size, location etc. For most folks though, those tanks work out pretty well.

[nereas]

I recommend that you do the math first.

I have twin 130s which I use for boat diving, and twin 72s which I use for beach diving.

The 72s are really 65s that fill to 71 with a plus rating, which mine no longer have since they are so old. The 72s are the lightest twin tanks that I could find. However they are hard to find anymore. New 85s are now more common to be used for the lite end of twin tank diving.

The 130s often allow for 2 dives from a boat, although there is little hope of doing any beach diving with them since they are so heavy. But I designed them with the thought of my deepest dive in mind for 20 mins plus the rule of thirds. If you get yourself a copy of V-Planner and type-in all your data including RMV, then it will tell you how much gas you need of each mix on an extreme dive (TMX 10/70, TMX 20/40, TMX 30/30, EAN 50, and 100% O2) for a maximum dive (to 100 meters for 20 mins). This will then tell you how big your biggest tanks ever need to be, after you add on for the rule of thirds.

As far as trim is concerned, with long tanks (anything besides HP 80s) you should be able to move your bands up or down to create perfect trim. The myth that only a certain tank gives you good trim is foolishness.

And if your dive shop does not have a booster pump hooked up, so that it can pump to 3500 psi, then you need to find a new dive shop before you go tech.

If I lived in South Carolina, I would be diving U-Boats as much as possible, and forget about caves. A shipwreck has more sea life upon it than any reef (or cave) would ever have. In that case, your MOD would be your deepest local shipwreck. And the size of your largest doubles then calculated with V-Planner based on that deepest wreck.

V-Planner VPM & VPM-B dive decompression software (http://www.hhssoftware.com/v-planner/)

[Scared Silly]

The 72s are really 65s that fill to 71 with a plus rating, which mine no longer have since they are so old.

There should not be anything from preventing you from having the "+" rating put on the cylinders (other than them failing it but passing hydro).

There is often the myth that the "+" is good for only the first hydro. Or if it is missing on one hydro then it can not be done one the next. You just need to find a tester who is willing to take the time to find the right specs for it.

[nereas]

There should not be anything from preventing you from having the "+" rating put on the cylinders (other than them failing it but passing hydro).

There is often the myth that the "+" is good for only the first hydro. Or if it is missing on one hydro then it can not be done one the next. You just need to find a tester who is willing to take the time to find the right specs for it.

Thanks!:)

[xiSkiGuy]

If you get yourself a copy of V-Planner and type-in all your data including RMV, then it will tell you how much gas you need of each mix on an extreme dive (TMX 10/70, TMX 20/40, TMX 30/30, EAN 50, and 100% O2) for a maximum dive (to 100 meters for 20 mins). This will then tell you how big your biggest tanks ever need to be, after you add on for the rule of thirds.He's looking for his first set of doubles. It's probably better to find a manageable size and reasonable volume, not necessarily the largest tanks he'll ever need.


As far as trim is concerned, with long tanks (anything besides HP 80s) you should be able to move your bands up or down to create perfect trim. The myth that only a certain tank gives you good trim is foolishness.Again, he's looking for his first set of doubles. A skilled doubles diver can dive any tanks and make it look easy. But picking a tank that is best suited to your individual build will ease the transition. And moving tanks too far in the bands can make valve manipulation difficult.


If I lived in South Carolina, I would be diving U-Boats as much as possible, and forget about caves.Which U-boats would you be diving off South Carolina?

A shipwreck has more sea life upon it than any reef (or cave) would ever have.Sealife isn't usually why people dive caves. And from Upstate South Carolina, North Florida cave country is about the same drive as the region's best wreck diving (Morehead City).

[texdiveguy]

IMO..... get what 'works' best for your body size and your diving physical conditioning,,,then look at the type of diving you intend to do, this part of the formula will include a 'number' of factors. In the end or down the road you may just end up with several different sets.

Know one can tell you whats best....try out several combo's.....visit with local divers in your area whom are diving doubles and get a feel from them regarding their kits. We all have such differing needs and opinions when it comes to cylinder selection.

Having said that....I persl. prefer a smaller set....I really like the Worthington st. lp85's as a 'general fit' for many of my dive profiles/sites and my physical size and comfort zone of fit....a larger set does at times come into the factoring of certain dives so you must remain flexible and comfortable with change.

;)

[nereas]

He's looking for his first set of doubles. It's probably better to find a manageable size and reasonable volume, not necessarily the largest tanks he'll ever need.

Again, he's looking for his first set of doubles. A skilled doubles diver can dive any tanks and make it look easy. But picking a tank that is best suited to your individual build will ease the transition. And moving tanks too far in the bands can make valve manipulation difficult.

Which U-boats would you be diving off South Carolina?
Sealife isn't usually why people dive caves. And from Upstate South Carolina, North Florida cave country is about the same drive as the region's best wreck diving (Morehead City).

I would bet that you would be a great mentor for this fellow!

I believe you are right about the "first set" issue. LP85s therefore come to mind.

[xiSkiGuy]

I would bet that you would be a great mentor for this fellow!I'd be happy to help out if he ever dives Lake Jocassee.


I believe you are right about the "first set" issue. LP85s therefore come to mind.I agree. I think they make a great first set for most people.

[Mr. Bubble]

Thanks everyone....WHy do some of youadvocate the LP rather than the HP ?? I can't imagine an LP having more CF of air than a HP filled to 3442.

Yes, both the NC coast (U352 fyi) and the North Florida springs are about the same distance. I went on a NC dive this past summer and the DM had HP95's.

Yeah I dive Jocassee on occassion, just to fill the void every now and then.

So, why LP and not HP...I think I can handle the HP95's........

I dive single HP120's now.


Mr. B

[Rainer]

Reasons I dive LP85 doubles:

Trim (no HP equivalent cylinder)
Cheaper (*much* less than similar capacity HP cylinders)
Capacity (I also have HP100s, but with short fills on those, and "good" fills on the LP, I get the same capacity on my LP85s as my HP100s, if not better on the LPs)
Transfilling (much easier to fill my LP cylinders from spare HP cylinders, than the other way around!)

[texdiveguy]

Rainer, you might just define a 'good fill' for the OP....I know were you are with this,,,but he may not...... :-)

[Dive-aholic]

Mr. B, your height may or may not eliminate some tanks. LP95s are usually a little shorter than the other usual tanks. If you are 5'8" or shorter, they may be the tank for you. If you're 5'8" or taller, then you may want to go with a taller tank for better trim. Eventually you should be able to dive any tank so that won't matter much. I'm 6' and can dive pretty much whatever tank I'm given, but the taller tanks do trim out a little better on me. As for LP v. HP. An LP95 holds 95cf of gas when filled to 2400psi. An HP100 holds 100cf of gas when filled to 3442psi. Fill an LP95 to 3600psi and the tank is now holding a lot more than 95cf. Fill an HP100 to 3000psi and it's holding a lot less than 100cf. Some shops can only fill to 3000psi. Some places will fill LP tanks to 3600 regularly. Also, I haven't heard of an HP95. Who is making that?

[Mr. Bubble]

Also, I haven't heard of an HP95. Who is making that?

Good point! I'm pretty sure thats what he told me. Maybe he ment Lp filled to 3600= HP...??? I looked up available tanks and you are right...no HP95's only LP.

I did not realize filling up to capacity was that difficult. I have not run into that problem yet. So, LDS' will top off an LP to 2600 if they have the ability? So with temp. variation it may go back to 2400 which is about 100psi below the rating right? And a set of HP 100's filled to 3800 (if they can fill it that fare) would settle to 3500 give or take.
so were are talking only 10-12 cf of air........thats a pretty good bit to get you out of a jam if you needed it.....

But task loading is another point as well........it may take up that extra air just to haul those big puppies around.

B

[cool_hardware52]

Some shops can only fill to 300psi.

I'd avoid them;)

Tobin

[fweber]

As you've specified that these are your first set, and likely to be used to around 130' and it sounds like in open ocean or overhead wreck diving. You might want to really consider the lp85's that others have mentioned. I have 4 sets of old 72's(rougly the same dimensions as 85's) only because they were around and available. If I were going to go out and purchase new steel for open ocean diving it would be 85's or the hp equivilent in physical size. They usually provide sufficient gas for dives with run times in the 45-60 minute range and contingencies of upto around 90 minutes. However, there are plenty of other things to consider. One, what are your buddies diving? While any decent deco class is going to teach you enough to make gas matching with your buddies easy, identical tanks make it a non-issue. Second, if you're diving from charter boats, you may find it's easier to bring one large set of doubles that you can get 2 dives from. It can save on space requirements and elimanates the need to change tanks between dives.

There are alot of variables that can lead to one setup being preferable to another. You really have to weigh out your particular circumstances to come up with the ideal solution. I would however suggest talking to your instructor/mentor, who will probably have reasonably strong reasons why they dive the way they do. And, talk or coordinate with your likely buddies or teammates.

[Mr. Bubble]

Great info everyone...thanks

I''ll see what the crew says and keep this info to decide.

Thanks again

Mr.B

ps. just from my enternet research

HP100 = 7x24 33lbs
lp 85 = 7x25 35lbs
lp 95 = 8x23 41lbs
HP 100's are one inch shorter, a double set would be 4 lbs lighter and have 30 cf more gas ( a whole pony bottle). Something to concider. WIth good fills of coarse.

[Rainer]

Great info everyone...thanks
HP100 = 7x24 33lbs
lp 85 = 7x25 35lbs
lp 95 = 8x23 41lbs
HP 100's are one inch shorter, a double set would be 4 lbs lighter and have 30 cf more gas ( a whole pony bottle). Something to concider. WIth good fills of coarse.

A few things to consider.

This assumes 3442 fills on the HP100s and only 2640 on the LP85s (service pressure is NOT 2400). If you can't get 3400 in the HP cylinders, *and* can get around 3000 in the LP85s, the "85s" will be holding more gas than the "100s". If you do get fills only to service pressure (i.e. can't get any overfill in the LPs), then the HP100s will still be only about TWO pounds lighter, since you'll be hauling around extra gas in the bigger cylinders. The HP100s are also going to set you back an extra $200-300.

[xiSkiGuy]

Just clear a few things up: LP tanks are rated to 2400psi plus 10% (or 2640psi). When the volume of a LP tank is given (LP85, LP95, LP104, etc) it includes the 10%. So, LP tanks are at their rated volume when they are at 2640psi. A single LP95 that is only filled to 2400psi has a little over 86cf of gas in it.

On any tank to determine volume at any given pressure (to find out how much gas in cubic feet X tank has at Y psi): Divide the rated volume by the rated pressure and then multiply by the actual pressure (or desired pressure or whatever).

For example, a LP85 holds 85cf of gas when filled to 2640psi.
85cf divided by 2640psi = 0.0322cf/psi
0.0322cf/psi multiplied by 3600psi = 115.92cf
So a LP85 that has been filled to 3600psi has almost 116cf in it.

For example, an X8-130 holds 130cf of gas when filled to 3442psi.
130cf divided by 3442psi = 0.0378cf/psi
0.0378cf/psi multiplied by 3000psi = 113.4cf
So a X8-130 that has only been filled to 3000psi has 113.4cf in it.

[xiSkiGuy]

Thanks everyone....WHy do some of youadvocate the LP rather than the HP ?? I can't imagine an LP having more CF of air than a HP filled to 3442.A HP100 filled to 3442 has 100cf in it. A LP108 filled to 2640 has 108cf in it.


Yes, both the NC coast (U352 fyi) and the North Florida springs are about the same distance. I went on a NC dive this past summer and the DM had HP95's. If the DM was Kenny on Diverdown, they were LP95s (and I was on the trip).

[Mr. Bubble]

So, yeah...Hp100's at 3000psi is only 87cf and the lp85's would be 96cf. with doubles that would be 38cf less with the twin Hp100's.

Gives the argument to get good fills does'nt it? How much of a problem is it getting 3442 fills? I have not had that much trouble thus fare. Is this a rampant problem, or something you only run ito occasionally? I definately have to get them topped off, but have never had anyone say they could'nt do it, although I have heard people mention it. Then you also have to be with a shop that will over fill 5-600 lbs over rating for the lp tanks.

[xiSkiGuy]

Gives the argument to get good fills does'nt it? How much of a problem is it getting 3442 fills? I have not had that much trouble thus fare. Is this a rampant problem, or something you only run ito occasionally? I definately have to get them topped off, but have never had anyone say they could'nt do it, although I have heard people mention it. Then you also have to be with a shop that will over fill 5-600 lbs over rating for the lp tanks.It depends on where you dive. You mentioned cave diving. Shops in cave country pretty much fill all steel doubles to 3600psi (or more), regardless of rated pressure. Some shops in other places will fill to rated pressure only. The occasional shop will put whatever you want in the tank once you've developed a good relationship with them. Getting fills off of a boat compressor will probably limit you to 3000psi (or less).

IMO if LP85s had an exemption equivalent, they would be just about the perfect all around doubles.

[Mr. Bubble]

What size wing would be best? 45,60, 85,90? Remember, I may have some stage bottles as well.

Thanks

[Rainer]

What size wing would be best? 45,60, 85,90? Remember, I may have some stage bottles as well.

Thanks

Add up those bits of kit that are negative and those that are positive. Your wing needs to float your rig (with you out of it) and you in the rig with maximum compression/drysuit flood. People on the internet can only guess about your rig. Do the math yourself. Stage bottles don't factor into the calcs for wing selection.

[xiSkiGuy]

What size wing would be best? 45,60, 85,90? Remember, I may have some stage bottles as well.

ThanksWe would need to know which tanks you would be using and what exposure protection. But you can definitely rule out anything with more than 70lbs of lift.

Most people recommend aluminum stages/deco bottles and they don't change your wing needs very much.

[rjack321]

Mr. Bubble are you in a wetsuit or dry?

[Mr. Bubble]

Well, the weight and displacement should be nominal between the two tanks +/- 4 lbs. and one inch. Exposures would include full recreational to 130 with possible advanced nitrox to 150. I don't see myself going much deeper than that any time soon.

[xiSkiGuy]

Well, the weight and displacement should be nominal between the two tanks +/- 4 lbs. and one inch. Exposures would include full recreational to 130 with possible advanced nitrox to 150. I don't see myself going much deeper than that any time soon.Between which two tanks? Don't forget gas has a weight, too. In double 130s the 260cf of air weighs 20lbs. 170cf in 85s weighs about 13lbs.

By exposure protection we mean wetsuit or drysuit and what kind?

[Doc Intrepid]

With respect to who makes a high-pressure example of a LP95, the answer is PST with their E8-119. Unless I'm mistaken, Worthington also makes such a tank, but the dimensions are different.

You may be missing one of the more important criteria -

Steel tanks should be purchased such that the diver can balance out wearing them. They have to work for the individual body type, weight, size, etc. of the diver.
All other considerations are secondary.

I first purchased a set of E8-119s (HP95s). I could not get them to work for me - they put too much weight above my COG. I exchanged them for a set of E8-130s. Perfect balance.

Whatever you buy needs to work FOR you, not against you.

This is why it's optimal to borrow a set of tanks from several of your buddies, and dive them in confined water ~20 fsw or so. At these depths all your errors will compound and be instantly noticeable. Once you find a set of steel tanks that works for you here - allows you to position yourself perfectly, no matter how large or small they are - buy a set of those, whatever they are.

Learning doubles is hard enough without getting a set of tanks for reasons of cost, size, brand, length, or whatever else - but with complete disregard for how you dive wearing those specific tanks.

Learn what fits you first. Buy those.

Everything else is less important than what works well for you underwater.

Here are the specs for PST tanks, including the "HP 95s" (E8-119):
http://www.lloydbaileysscuba.com/PST%20E%20Series%20Tanks.htm

Good luck...

[nereas]

With respect to who makes a high-pressure example of a LP95, the answer is PST with their E8-119. Unless I'm mistaken, Worthington also makes such a tank, but the dimensions are different.

You may be missing one of the more important criteria -

Steel tanks should be purchased such that the diver can balance out wearing them. They have to work for the individual body type, weight, size, etc. of the diver.
All other considerations are secondary.

I first purchased a set of E8-119s (HP95s). I could not get them to work for me - they put too much weight above my COG. I exchanged them for a set of E8-130s. Perfect balance.

Whatever you buy needs to work FOR you, not against you.

This is why it's optimal to borrow a set of tanks from several of your buddies, and dive them in confined water ~20 fsw or so. At these depths all your errors will compound and be instantly noticeable. Once you find a set of steel tanks that works for you here - allows you to position yourself perfectly, no matter how large or small they are - buy a set of those, whatever they are.

Learning doubles is hard enough without getting a set of tanks for reasons of cost, size, brand, length, or whatever else - but with complete disregard for how you dive wearing those specific tanks.

Learn what fits you first. Buy those.

Everything else is less important than what works well for you underwater.

Here are the specs for PST tanks, including the "HP 95s" (E8-119):
http://www.lloydbaileysscuba.com/PST%20E%20Series%20Tanks.htm

Good luck...

Doc, I have heard from everyone that PST is temporarily out of business while they relocate their manufacturing facilities overseas to Asia. In the meantime it is virtually impossible to get tanks from them. It may be all urban legend, but so far that is what everyone has been saying.

[xiSkiGuy]

Doc, I have heard from everyone that PST is temporarily out of business while they relocate their manufacturing facilities overseas to Asia. In the meantime it is virtually impossible to get tanks from them. It may be all urban legend, but so far that is what everyone has been saying.


With respect to who makes a high-pressure example of a LP95, the answer is PST with their E8-119. Unless I'm mistaken, Worthington also makes such a tank, but the dimensions are different.Worthington makes the X8-119 and Faber makes the FX-117. Similar to LP95s/LP98s.

I'm pretty sure no one has PST stock right now.

[nereas]

What size wing would be best? 45,60, 85,90? Remember, I may have some stage bottles as well.

Thanks

The stage bottles are virtually neutral so those do not normally need to factor into the wing equation. I recently did the math on this, and here is what I got for double tanks:

-6.0 lbs backplate
-4.0 lbs 2 regs
-2.0 lbs tank bands
-4.0 lbs manifold
-2.0 lbs tanks (empty)

-18 lbs gross neg buoyancy without backgas

Onto this -18 lbs you then need to compute the weight of your backgas mix at roughly 0.08 lbs per cu ft.

Twin 85s = 170 cu ft = -13.6 lbs

So for you that equals a minimum of 32 lbs lift capacity for your wing.

The next highest available Oxycheq wing is 40 lbs. Their prices and quality are pretty good.

[nereas]

Worthington makes the X8-119 and Faber makes the FX-117. Similar to LP95s/LP98s.

I'm pretty sure no one has PST stock right now.

Glad I bought my PSTs when I did.:D

[cool_hardware52]

The stage bottles are virtually neutral so those do not normally need to factor into the wing equation. I recently did the math on this, and here is what I got for double tanks:

-6.0 lbs backplate
-4.0 lbs 2 regs
-2.0 lbs tank bands
-4.0 lbs manifold
-2.0 lbs tanks (empty)

-18 lbs gross neg buoyancy without backgas

Onto this -18 lbs you then need to compute the weight of your backgas mix at roughly 0.08 lbs per cu ft.

Twin 85s = 170 cu ft = -13.6 lbs

So for you that equals a minimum of 32 lbs lift capacity for your wing.

This is only 1/2 the answer. Without knowing the buoyancy of the divers suit you cannot size a wing.

Tobin

[nereas]

This is only 1/2 the answer. Without knowing the buoyancy of the divers suit you cannot size a wing.

Tobin

I gave the drysuit answer, yes. And with a drysuit, he would be able to keep his suit neutral at all depths, of course.

With double steel tanks he should not be diving in a wetsuit. That is probably a different thread. Or else someone can take up that gauntlet here.

Thanks, Tobin. Good point.

[cool_hardware52]

I gave the drysuit answer, yes. And with a drysuit, he would be able to keep his suit neutral at all depths, of course.

With double steel tanks he should not be diving in a wetsuit. That is probably a different thread. Or else someone can take up that gauntlet here.

Thanks, Tobin. Good point.

Are you suggesting that the initial buoyancy of the diver's drysuit will not impact the required wing size?


Tobin

[Mr. Bubble]

I think I have opened up Pandora's box......:11doh: This is much more complicated than my DPV scooter specialty coarse :rofl3: Maybe they need a coarse just for doubles.

Please continue......:popcorn:



Mr.B

[cool_hardware52]

I think I have opened up Pandora's box......:11doh: This is much more complicated than my DPV scooter specialty coarse :rofl3: Maybe they need a coarse just for doubles.

Please continue......:popcorn:



Mr.B

I'll run an example for you of how I would size a wing for doubles.

First a few assumptions:

1. Your Drysuit cannot loose more buoyancy than it starts with. Put on your undies and suit and stand up in neck deep water. Vent all the gas you can from your suit, Now add lead until you sink when you pick up your feet. The amount of lead represents the buoyancy of your suit when with minimum gas in it. For this example lets say it takes 25 lbs of lead to get neutral in your suit at the surface. While it is very unlikely, it is possible that a total failure of your suit, i.e. ripped neck seal, torn suit etc. a suit that cannot trap gas can loose all of it's initial buoyancy, but no more.

2. You may need to use all of your back gas. This means you could be lighter at the end of the dive by 100% of your gas.

3. If you have an extended stay at a shallow stop you will want to inflate your suit a bit, for warmth. That makes your suit a bit more buoyant than what was determined in #1, say 3 lbs of extra inflation gas.

Lets say you are using 130's

Your gas will weigh ~21 lbs, that means you need to be negative at the start of the by 21 (gas) + 3 (extra inflation for suit) or 24 lbs. To stay at the surface you need to use 24 lbs of your wings capacity.

Now what happens if your suit fails? You could need another 25 lbs of wing capacity.

24 + 25 = 49 lbs.

What might your rig require to float it at the surface?

Plate and harness 6 lbs. Regs 5 lbs., Manifold and bands 5 lbs. Can light 2. Full 130's -22 lbs. Total - 40 lbs with full tanks, around -20 with empty tanks. You will also need about 4 lbs of ballast i.e. in a belt.

Remember this is just an example. What if your suit is only +18 lbs and you are using LP85's?

Tobin

[DeepSeaExplorer]

You can't go wrong with AL 80s as your first set of doubles. They're cheap and well suited for all types of diving, especially in the beginning. Later, if you want to get into big dives or cave diving, you'll want to get a big set of steels. Either way, you'll eventually want several sets anyway. But, what you don't want, is to have to use big set of steel tanks for a smallish dives because that's all you have.

[fweber]

You can't go wrong with AL 80s as your first set of doubles. They're cheap and well suited for all types of diving, especially in the beginning. Later, if you want to get into big dives or cave diving, you'll want to get a big set of steels. Either way, you'll eventually want several sets anyway. But, what you don't want, is to have to use big set of steel tanks for a smallish dives because that's all you have.

Why would you say that al80's would make a better first set, than say steel lp85's?Pressuming that if you are diving doubles you are considering going into deco and wouldn't want to be dumping weight and finding yourself to be a cork. The 85's will lead to a lighter overall rig, with equal or better gas volume.

[DeepSeaExplorer]

Most tech divers in my area wear Al80s, they work for probably 80% of non-cave tech dives. There's absolutely nothing wrong with the buoyancy of 80s. It's just different and easily compensated for. I have four sets of doubles: 2 are AL 80s, and 2 are steels. I have a lot more dives on the 80s than any of the others. Why spend 3 times as much for steels if you don't have to. Then, there's also the issue of steels in the ocean without a drysuit. But, I won't go there...

[cool_hardware52]

Why would you say that al80's would make a better first set, than say steel lp85's?Pressuming that if you are diving doubles you are considering going into deco and wouldn't want to be dumping weight and finding yourself to be a cork. The 85's will lead to a lighter overall rig, with equal or better gas volume.

I prefer to dive my LP 85's vs AL80's. A pair of 80's + the required ballast makes for a heavier rig out of the water.

OTOH, a pair of AL80's can often be had fairly inexpensively, and if you get Luxfers you have stage bottles in waiting if you progress to that point.

Tobin

[fweber]

I prefer to dive my LP 85's vs AL80's. A pair of 80's + the required ballast makes for a heavier rig out of the water.

OTOH, a pair of AL80's can often be had fairly inexpensively, and if you get Luxfers you have stage bottles in waiting if you progress to that point.

Tobin
Tobin, I agree. While I don't have any lp85's I do have several sets of old 72's which have fairly similar characteristics. I was questioning DeepSeaX's whole hearted endorsement of the al80's as a first set. I've had a couple sets of just those, and the only two positives that I think they really have is the low cost and their adaptability to stages.

With the cost of everything else that is involved in a transition to doubles and presumably deco or tech diving, the lower initial cost of the al80's may or may not represent a meaningful savings in the long run.

[nereas]

I'll run an example for you of how I would size a wing for doubles.

First a few assumptions:

1. Your Drysuit cannot loose more buoyancy than it starts with. Put on your undies and suit and stand up in neck deep water. Vent all the gas you can from your suit, Now add lead until you sink when you pick up your feet. The amount of lead represents the buoyancy of your suit when with minimum gas in it. For this example lets say it takes 25 lbs of lead to get neutral in your suit at the surface. While it is very unlikely, it is possible that a total failure of your suit, i.e. ripped neck seal, torn suit etc. a suit that cannot trap gas can loose all of it's initial buoyancy, but no more.

2. You may need to use all of your back gas. This means you could be lighter at the end of the dive by 100% of your gas.

3. If you have an extended stay at a shallow stop you will want to inflate your suit a bit, for warmth. That makes your suit a bit more buoyant than what was determined in #1, say 3 lbs of extra inflation gas.

Lets say you are using 130's

Your gas will weigh ~21 lbs, that means you need to be negative at the start of the by 21 (gas) + 3 (extra inflation for suit) or 24 lbs. To stay at the surface you need to use 24 lbs of your wings capacity.

Now what happens if your suit fails? You could need another 25 lbs of wing capacity.

24 + 25 = 49 lbs.

What might your rig require to float it at the surface?

Plate and harness 6 lbs. Regs 5 lbs., Manifold and bands 5 lbs. Can light 2. Full 130's -22 lbs. Total - 40 lbs with full tanks, around -20 with empty tanks. You will also need about 4 lbs of ballast i.e. in a belt.

Remember this is just an example. What if your suit is only +18 lbs and you are using LP85's?

Tobin

When I do the math for my twin 130s, I get 40 lbs also. So I have opted for a 50 lbs Oxycheq doubles wing. These run about $350 each. A good price.

If you get a 50 lbs doubles wing, it will serve you for any sized doubles, not just for your smaller initial steel 85s or alum 80s.

Tobin himself offers the best backplates, if you don't already have one. He can even rig it for you Hogarthian, with 4 D rings and a metal buckle. His backplates are variable sized (small, med, and large) and variable weighted, however for twin tanks you would likely only need the traditional 6 lb backplate. You can adjust the straps yourself to be tight or loose, when you get it.

[Mr. Bubble]

"Then, there's also the issue of steels in the ocean without a drysuit. But, I won't go there.."

Please expand. I am using single steel 120's with a wet suit now.

Heres the deal. I want to get full cave certified, but I don't want to go down there and take my certification using doubles for the first time. I also want to get advanced nitrox and advanced wreck training. I would like to have a dry suit, but I would also rather go on a few dive trips this year too, so a wet suit 5/7 is all I can muster for exposure suits for the forseeable near future. I wish I could buy all the gear AND go an all the trips, but I have to do half and half for a while.

Thanks for all the great info...lots of good points....lots of things to think about....and yes, my dive instructor recommended the multiple route as well.....so there goes another dive trip I could have taken. :(

I am real surprised to learn that there is not a magic set, or something that works for the majority. Like, I am x ft tall and wear a wet suit and want to do this...so get that,

or I am x feet tall and wear a dry suit and want to do this, so get that...it just seems odd that I have to try out everyone in the store to get what I need. Then theres the Wing it's self. Would'nt different twins perform differently using different wings? IMO, yes they would. So, now I have to try out 4-5 sets of doubles with 4-5 sets of wings...oh yeah, and don't forget your exposure suit, wet and dry.......Ughh....

Well, maybe this time next year I will have it figured out.

[xiSkiGuy]

"Then, there's also the issue of steels in the ocean without a drysuit. But, I won't go there.."

Please expand. I am using single steel 120's with a wet suit now. This gets brought up once every two weeks. Here's a recent thread: http://www.scubaboard.com/forums/basic-scuba-discussions/196082-diving-steel-tank-wetsuit-dangerous-idea.html

The readers digest version: single steels and a wetsuit are fine. Double steel tanks are probably negative enough you will need the redundant lift of a drysuit in case of a wing failure.


Heres the deal. I want to get full cave certified, but I don't want to go down there and take my certification using doubles for the first time. Yeah, that wouldn't work real well.


I am real surprised to learn that there is not a magic set, or something that works for the majority. Like, I am x ft tall and wear a wet suit and want to do this...so get that,:rofl3: You know what they say about opinions. . .

[cool_hardware52]

"Then, there's also the issue of steels in the ocean without a drysuit. But, I won't go there.."

Please expand. I am using single steel 120's with a wet suit now.

Heres the deal. I want to get full cave certified, but I don't want to go down there and take my certification using doubles for the first time. I also want to get advanced nitrox and advanced wreck training. I would like to have a dry suit, but I would also rather go on a few dive trips this year too, so a wet suit 5/7 is all I can muster for exposure suits for the forseeable near future. I wish I could buy all the gear AND go an all the trips, but I have to do half and half for a while.

Thanks for all the great info...lots of good points....lots of things to think about....and yes, my dive instructor recommended the multiple route as well.....so there goes another dive trip I could have taken. :(

I am real surprised to learn that there is not a magic set, or something that works for the majority. Like, I am x ft tall and wear a wet suit and want to do this...so get that,

or I am x feet tall and wear a dry suit and want to do this, so get that...it just seems odd that I have to try out everyone in the store to get what I need. Then theres the Wing it's self. Would'nt different twins perform differently using different wings? IMO, yes they would. So, now I have to try out 4-5 sets of doubles with 4-5 sets of wings...oh yeah, and don't forget your exposure suit, wet and dry.......Ughh....

Well, maybe this time next year I will have it figured out.

The admonition against steel doubles in a wetsuit in the ocean is based on the impacts of a buoyancy failure. Steel doubles, in particular steels that are quite negative, PST 104 for example, will leave the diver with no ditchable weight. With a drysuit for redundant buoyancy you have another means to returning the surface in a controlled manner.

Al80's are about +4 each vs ~4 each for 104's and as such will typically require the dive add ballast. If this ballast is ditchable then a diver in a wetsuit that suffers a wing failure can drop weight.

Doubles, and all the associated equipment is expensive, no way around that.

What I suggest to the diver considering doubles is first determine what you will be using for an exposure suit and tanks.

Once this is a "known" you can determine how much lift you will need. That alone will reduce the number of possible wings to just a few.

Now take a look at whether or not you will need a substantial weight belt, and also take a look at the length of the tanks. This provides a clue about what wing shape will be helpful. Short tanks, 95's 119's etc. and no weight belt usually means head heavy.

Longer tanks and a weight belt, for example al80's often works pretty well, long tanks, smaller person and weight belt can be butt heavy.

There's still a bit of guess work, but it's not as unpredictable as it seems to you right now.

Good luck,

Tobin

[fweber]

"Then, there's also the issue of steels in the ocean without a drysuit. But, I won't go there.."

Please expand. I am using single steel 120's with a wet suit now.

I am real surprised to learn that there is not a magic set, or something that works for the majority. Like, I am x ft tall and wear a wet suit and want to do this...so get that,

or I am x feet tall and wear a dry suit and want to do this, so get that...it just seems odd that I have to try out everyone in the store to get what I need. Then theres the Wing it's self. Would'nt different twins perform differently using different wings? IMO, yes they would. So, now I have to try out 4-5 sets of doubles with 4-5 sets of wings...oh yeah, and don't forget your exposure suit, wet and dry.......Ughh....

Well, maybe this time next year I will have it figured out.

Diving double steels wet= Some steel tank combinations can result in being extremely negative. A drysuit can help offset this negativity. A wetsuit that compresses at depth can magnify the issue. If going into deco(a soft overhead) some form of redundant bouyancy is generally required. A drysuit is consider to fulfill this requirement. A wetsuit needs to be dived with either a dual bladder wing, 2 wings, or a combination of a wing and some other lift device like a large smb or small lift bag. There are many threads on these optioin both here and on thedecostop. Use the search function and enjoy the reading.

There is no magic setup because people are all so different and so can be their goals or requirements. Some people are bouyant, others sink like a stone. Some people are comfortable diving to 130' on a cylinder of air, others need doubles with some helium to feel safe below 100'. Your set up is going to possibly be unique to your needs. Even within a regiment approach like DIR, there are going to be areas that you have to sort through. Like the lift distribution of different wings and finding the one that works for you, as you pointed out.

If you have it "all sorted" by this time next year, you are doing extremely well and ahead of many folks who take that long or longer to reach the point they feel "sorted" with all aspects of their tech rig. Try to find an excellent mentor, they should be able to help shorten the learning curve.

Patience, and a lot of reading, will both be very useful to you. Start with the archives here and at thedecostop, use the search functions. You'll learn tons.

Good Luck,

[Mr. Bubble]

Would'nt the dual bladder wing eliminate that problem?

[fweber]

A whole 'nother discussion for a different thread in a different forum. But, a discussiobn that's been had many times before. So, please, use the search feature. You can read the several archived threads that go over the various sides, again, and again, and again, ..............

again................

and again...................

did I say again?..............

or again?..........

[Rainer]

Even a modicum amount of searching yourself would help answer a lot of your questions. Seriously.

[nereas]

Would'nt the dual bladder wing eliminate that problem?

Yet another can of worms opened ... .

[Mr. Bubble]

Thanks for the great advice........I did'nt realise this was a MOC (mighty old conversation) issue!


Mr. B

[b1gcountry]

How tall are you? As TS&M alluded to, some people find that certain size tanks work well for them and some don't. I'm 6'2 and I find LP95s and X7-100s to be too short to trim out well. X8-130s work pretty well for me. AL80s and LP85s are the easiest I've tried. I haven't tried X7-80s or LP120s but I imagine they would be too short and too tall respectively. If possible, try some different tanks before you buy.

SkiGuy-
I thought the X8-130s were the same height as the X7-100s? with just about the same buoyancy empty?

Tom

PS, I'm 6'6" and dive the X7-100. Diving dry, I trim fine. Diving wet, it depends what depth I'm at.

[b1gcountry]

I'm in the same boat as the OP, although I might be a tad farther away from my first purchase. Living in the middle of country, though, I'll be diving mostly freshwater. Looking back through my dive logs, I've only worn 12 lbs with a single AL80 plus AL BP; and 6lbs with a single HP100 plus AL BP diving freshwater. From what I've read about double AL80s, they weight out about the same as a single AL80 (when empty, the extra weight from the manifold, and extra first stage offset the buoyancy of the tanks). So I would guess I would still need about 12 lbs with the double AL80s.

With Double Steels, I'm already only wearing 6lbs. If I doubled the tanks up, I would probably be close to neutral with no extra balast. Wearing anything other than the drysuit, I would probably be heavy.

One of the reasons I'm looking at doubles is to check out some of the caves/mines in the area. The most interesting one I've found is only 70' deep or so, so huge tanks would not be necessary in my mind. The other interest would be in Great Lakes wrecks, and 160cf should be fine for most of that stuff as well, and would get me two dives at most recreational depths.

I've got two HP100s right now. Doubling them up is not an option (wife dives them). I was considering getting some HP130s, or just going ahead and setting up some doubles with AL80s.

[rookers]

My first set were X7-120s, they trim really well for me (6'3"), but of course its sometimes hard to get them filled to rated. I also own LP108s which don't trim quite as well, but filled to 3k give a lot of gas. I like them both, and have dove numerous other sets, none of which I really found objectionable, other than some LP80s and only because I had to wear some lead with them and a drysuit.

[xiSkiGuy]

SkiGuy-
I thought the X8-130s were the same height as the X7-100s? with just about the same buoyancy empty?No. The X8-130s are at least an inch and 1/2 taller, if not 2". Seen side by side, the difference is obvious. Empty buoyancy is probably similar, but I've never known someone who has used both (doubles) to describe them overall as "similar".


PS, I'm 6'6" and dive the X7-100. Diving dry, I trim fine. Diving wet, it depends what depth I'm at.Are you diving a single or doubles? I can make a HP80 trim out fine with singles. Doubles are a bit tougher.

[b1gcountry]

I'm diving singles only. Haven't doubled anything up yet.

I own two X7-100s, and I borrowed NWGratefulDiver's X8-130 while I was diving up in the PS area last month. My feet dropped a little with the 130 whenever I was below 40', and they were floaty at the safety stop. I was wearing a lot of neoprene though.

I never had the two side by side, so I couldn't tell relative height. They felt about the same as my 100s, but there were a lot of other things different about that dive that might have just been more obvious. (first time with a can light, no stage bottle, wearing more neoprene than usual, etc.)

Theoretically, though, if I were to double up some large steels, being 6'6" tall, it sounds like you would expect the taller tanks to trim out better. The X8-130, or even the X7-120, instead of the X7-100?

Tom

[xiSkiGuy]

Theoretically, though, if I were to double up some large steels, being 6'6" tall, it sounds like you would expect the taller tanks to trim out better. The X8-130, or even the X7-120, instead of the X7-100?Yes. Theoretically, the X7-120s would work really well for you.