Doubles etc.

[NJScubaDoc]

Agreed, that's the way we do it here. BUT, a couple of years back I had an OOA diver, from the same boat, that I needed to donate to and I'm guessing he was glad that I had the backgas to oblige.

Absolutely, I'm sure he was. That's also why I'd sling the 30, just in case a situation like that arose.

 

[dsteding]

Absolutely, I'm sure he was. That's also why I'd sling the 30, just in case a situation like that arose.

Okay, if your inventory is currently two regs and you'll need a new wing anyways, here is another way to look at it.

A slung 30 will cost you ~$400 in gear (new reg, $250 minimum, add an SPG ($100) for that one, and $40 for the sling). You'll need a new SPG for your independant doubles ($100 with hose).

This is actually more expensive than buying bands ($100) and a 'fold ($165). Heck, you'll be into things for close to $350 more doing it the way you plan. Take that $350, buy an HP 130, build a simple transfill whip ($100) and you'll have the following:

A set of doubles.

Two single 95s.

One HP 130.

If you do boat dives with the 95s, you can get a nice, long dive off of them on dive one (say 100 cf of gas). Assuming they are at 3000 psi, you end dive 1 at 1500 psi. Transfill from the 130, if nicely filled you'll be at 2300 psi for dive 2. That gives you another 1700 psi or over 100 cf of gas for the second dive. If you want even more gas, bring a 95 and a 130 for transfilling, you can probably get to 2000 psi off of the 95 and then up to 2700 psi using the 130.

 

[AquaW]

Onto some questions posed, and my feelings...

If there is one key point that I take from all the posts thus far is that decompression diving requires proper training, equipment, and a certain mentality. When the time comes that I want to get into decompression diving I certainly have a good sense of what to expect and how to go about it. Thanks.

In the meantime (read while I amass more funding) I need to increase my gas volume allow me to reach the maximum limits of my NDLs as provided by the Nitrox I'm diving ($15 a fill). The best way I can figure to do that is to take my four tanks and dive them as 3 sets of independent doubles (for potentially 3 boat dives). In practice, I would take 2 full 95s on my first dive, breathe them down in increments of 500 psi. At the end of dive number one I would have one tank with 1500 psi and one with 500 psi (i'd breathe the last 1000 psi off a single 95). For dive two I would take a fresh tank and the 1500 psi tank from dive one and breathe the full tank down to 1500, then switch off to the half full (always an optimist) tank from the first dive, and breathe the final 1000 off that. For dive numero tre I would simply repeat the same procedure as with dive #1.

The first thought is probably, my that's an awfully complicated amount of gas management. I don't think it is though, and I think the same level of competency in gas management and ability would be required for decompression/technical diving anyway. I think I'd also sling my 30cft which I'm currently using as a pony. Aside from it offering me another redundant air source, I think it'll get me used to diving with bottles in that configuration.

Any thoughts, are as always, welcome.

If I read your gas management plan correctly it doesn't have enough reserve planned into it. Look up the rule of thirds: Third of your supply for the descent & ascent, a third for your dive and third for reserve/problems/ other diver. Even though you are slinging a bottle that's not enough in my opinion. It’s also not as quick to get in an emergency, especially if you aren't used to it. And what about another diver? Notice I didn’t even say buddy. Sometimes perfect strangers come up to you in an emergency and they don’t know anything about your gear. So the idea of telling them to use the bungeed reg that someone suggested won’t work. I just read the other posts and saw that someone mentioned this happening to them. Francousteau said,
BUT, a couple of years back I had an OOA diver, from the same boat, that I needed to donate to and I'm guessing he was glad that I had the backgas to oblige. Your reply “Absolutely, I'm sure he was. That's also why I'd sling the 30, just in case a situation like that arose.” The 30 is not big enough. It isn’t fast enough to access especially with some stranger hanging on to you in northeast waters. Instead of just him dying he’ll take you out too.


I don’t like that you are planning to breath one tank down to 500 psi so you can use the 1500 in the other and then breathe most of that. While you are slinging a bottle, which is good, I'm still not comfortable with that. I've seen too much s##t happen. And with your plan your sling bottle is not an extra redundancy. It is your only redundancy and not enough gas at that. How about this for a plan:
Buy a single 80 cf tank for beach diving. New it should be less than $160 and you should be able to find one used. If you just don't do one wreck dive you'll have the money for it. And you'll like it too. This way, you don't have to use your 95's for the beach, wasting nitrox fills. But you will have to add weight. Other than that it'll be a lot easier. Someday, you'll probably want a complete beach set up so you don't have to mess with your doubles.
I wouldn’t do the third dive until you can get more tanks. Or decide if you’ll do a third dive by the amount of gas you have left. If you have a lot of gas left in some tanks plan it but if not, dive another day. If you have say 1200 in 2 tanks plan a dive. Double up the 2 tanks with the most in them but always, always, always keep plenty in reserve. Better yet, if you have enough $, buy 1 more steel tank and then you can have a full tank and a ½ filled one for the 3rd dive. Last thing on reserves; many feel they don’t need THAT much in reserve. Yeah, you do. Years of experience and accident analysis have proven it.
That’s my idea anyway. I like that you are thinking of things, asking questions, saving up and wanting to get trained. I know it’s frustrating to be so excited and limited by time and money. It takes time to buy what you need, time for training and experience. I liked what another diver said to you too:
“Patience! At age 22, you have an entire lifetime of diving ahead of you. This sport is dependent on equipment, training, knowledge, and skill. To go deeper and stay longer you need a lot of it. Take your time, make the right investments and you can enjoy this sport for your entire life. Take short cuts and make compromises and go to fast and sooner or later it will catch up to you.”

I'd also like to know what the pizza stained shirt thing meant. I didn't get it.

 

[NJScubaDoc]

I wouldn’t do the third dive until you can get more tanks. Or decide if you’ll do a third dive by the amount of gas you have left. If you have a lot of gas left in some tanks plan it but if not, dive another day. If you have say 1200 in 2 tanks plan a dive. Double up the 2 tanks with the most in them but always, always, always keep plenty in reserve. Better yet, if you have enough $, buy 1 more steel tank and then you can have a full tank and a ½ filled one for the 3rd dive. Last thing on reserves; many feel they don’t need THAT much in reserve. Yeah, you do. Years of experience and accident analysis have proven it.

Can you clarify on this a bit? Are you suggesting independent doubles, but utilizing 5 tanks?

 

[jim T.]

Bob, for clarification for the o.p., are you really saying that there will be twice the 1200 p.s.i. in the transfer whipped doubles? (1200psi being the single spg reading off of one post) but in reality there will be 2400p.s.i. to complete an additional recreational dive?

Bob and anyone else: When you read your spg do you always "double" the reading in your mind for gas reserve? For example's sake only, not as the commonly used erroronius minimum.... IF you always exit with a fixed shore dive, p.s.i. minimum i.e. for example: 500psi spg reading or 1000p.s.i. (actual/ mentally doubled/contents?) What is the most common way that agencies or tech divers think of/state the reamining gas?

As a new doubles diver, I'm seeing and hearing different "philosophies" and methods being used on local shore dives, without further explanation from other doubles divers.

If I tell another diver that I'm "mentally doubling" my spg reading to keep track, they sometimes respond, "That's the way you think of it." (ex. 500psi_1000 actual psi) "I" just think of it as 500 p.s.i.". No further explanation as to whether or not "their 500 p.s.i. spg reading REALLY meant to them that they had DOUBLE that amount of gas remaining. Or that they would wait until their doubles spg read 250p.s.i. before exciting.

For the o.p. and my own edification, do you meet divers with different ways of stating (and thinking of) their remaining gas supply in doubles? Is their variance from agency to agency or in general practice? It's little scarey that more doubles divers aren't using a universal method. Or maybe it's still an apples to apples comparison just stated differently and no problem?

This has been bugging me and it I believe the question is in line with the inquiries the o.p. has been making.
What's the most common or even "proper" way of stating one's gas reserves on doubles using one spg.

I've also seen divers arguing whether or not using two spgs (one on each post) will give independent tank readings even with the isolator open! They were only using one spg so I guess they're ripe for a "science experiment" to prove/disprove their "hypothesis"!

Thanks everyone.

 

[crpntr133]

Bob, for clarification for the o.p., are you really saying that there will be twice the 1200 p.s.i. in the transfer whipped doubles? (1200psi being the single spg reading off of one post) but in reality there will be 2400p.s.i. to complete an additional recreational dive?

When you read your spg do you always "double" the reading in your mind for gas reserve? For example's sake only, not as the commonly used erroronius minimum.... IF you always exit with a fixed shore dive, p.s.i. minimum i.e. for example: 500psi spg reading or 1000p.s.i. (actual/ mentally doubled/contents?) What is the most common way that agencies or tech divers think of/state the reamining gas?

As a new doubles diver, I'm seeing and hearing different "philosophies" and methods being used on local shore dives, without further explanation from other doubles divers.

If I tell another diver that I'm "mentally doubling" my spg reading to keep track, they sometimes respond, "That's the way you think of it." (ex. 500psi_1000 actual psi) "I" just think of it as 500 p.s.i.". No further explanation as to whether or not "their 500 p.s.i. spg reading REALLY meant to them that they had DOUBLE that amount of gas remaining.

Thanks!

A third is a third is a third no matter how many tanks, using the PSI. It just takes you longer to get there assuming you are using a manifold. The only difference I can think of is if you use LP and your buddy uses HP. Then 1000psi for him isn't the same as for you.

 

[MXGratefulDiver]

Bob, for clarification for the o.p., are you really saying that there will be twice the 1200 p.s.i. in the transfer whipped doubles? (1200psi being the single spg reading off of one post) but in reality there will be 2400p.s.i. to complete an additional recreational dive?

Bob and anyone else: When you read your spg do you always "double" the reading in your mind for gas reserve? For example's sake only, not as the commonly used erroronius minimum.... IF you always exit with a fixed shore dive, p.s.i. minimum i.e. for example: 500psi spg reading or 1000p.s.i. (actual/ mentally doubled/contents?) What is the most common way that agencies or tech divers think of/state the reamining gas?

As a new doubles diver, I'm seeing and hearing different "philosophies" and methods being used on local shore dives, without further explanation from other doubles divers.

If I tell another diver that I'm "mentally doubling" my spg reading to keep track, they sometimes respond, "That's the way you think of it." (ex. 500psi_1000 actual psi) "I" just think of it as 500 p.s.i.". No further explanation as to whether or not "their 500 p.s.i. spg reading REALLY meant to them that they had DOUBLE that amount of gas remaining. Or that they would wait until their doubles spg read 250p.s.i. before exciting.

For the o.p. and my own edification, do you meet divers with different ways of stating (and thinking of) their remaining gas supply in doubles? Is their variance from agency to agency or in general practice? It's little scarey that more doubles divers aren't using a universal method. Or maybe it's still an apples to apples comparison just stated differently and no problem?

This has been bugging me and it I believe the question is in line with the inquiries the o.p. has been making.
What's the most common or even "proper" way of stating one's gas reserves on doubles using one spg.

I've also seen divers arguing whether or not using two spgs (one on each post) will give independent tank readings even with the isolator open! They were only using one spg so I guess they're ripe for a "science experiment" to prove/disprove their "hypothesis"!

Thanks everyone.

Roughly, yes ... but it depends on how you want to calculate your reserves. If you're going to be using the 500 psi reserve rule, then you'll have less usable gas in the doubles.

Look at it this way ... (using rounded-off numbers) in an LP95 for every 100 psi your gauge reads you get about 3.6 cubic feet of breathing gas. So if you've got 2,400 psi in your cylinder, you've got about 68.5 cubic feet of gas to breathe (1,900 psi usable). That leaves you with a reserve of about 18 cubic feet. In a set of doubles at 1,200 psi you'd have the same amount of gas, but if you're still going to set your reserves at 500 psi you're going to be dedicating about 36 cubic feet of gas to reserves ... rather than the 18 cubic feet you'd be dedicating on a single. That'll only leave you about 50.5 cubic feet of gas for the dive.

I don't think there's any real "standard" way of looking at it.

... Bob (Grateful Diver)

 

[dsteding]

What's the most common or even "proper" way of stating one's gas reserves on doubles using one spg.

I'd say in PSI, and if you are using different tanks than others on the team, follow it with the size of the tanks.

Of course, the real answer in terms of "reserve" or rock bottom is to think in cubic feet and then convert to PSI based on your tank factor.

I'm not sure I track you here Jim, but I'll try and play this out:

If you start "doubling" your PSI (because you are used to single tanks?!?!?!? a little confused here), imho, you are adding more confusion than utility to your readings. If someone started a dive by telling me they had 7000 psi (but meant 3500 in doubles), for instance, I'd run away. Fast.

Likewise, if someone said they had a "reserve" of 1000 psi (they had "doubled" it because they were used to single tanks) we'd probably have issues. Especially because I'd take that number and convert it to cubic feet and compare it to rock bottom. That gives you 70 cf in double 119s at a SPG reading of 1000, but only 35 if the actual reading is 500. One is enough to get back to the surface safely from 100 feet, the other isn't.

All of this goes to the utility of knowing how many cubic feet per 100 psi your tank(s) hold.

Double 100s: 6 (actually 5.7).
Double 95/119s 7.
Double 104/130s 7.5.

 

[jim T.]

Thanks very much guys. (Bob and Doug). The conversion to cf makes all the difference and that definitely clarifies what I was asking.
Next time I run into these guys I'll see if they are considering the cf capacity remaining when they made their "partial" statements as to what they were actually saying/thinking.

Edited: Math question. Saw my " duh " error for initial fill amount I'd punched in. Never mind. Must be the tropical vacation I just returned from. Thanks again.

 

[AquaW]

Can you clarify on this a bit? Are you suggesting independent doubles, but utilizing 5 tanks?

I didn't really explain it well sorry
Personally, I'd like him to get enough manifolded doubles but he wants to start out with independents.
He wants to do 3 dives a day with doubles. His first set would be full obviously. His 2nd and third dive would have 1 full and 1 used tank. So he's pushing it I think on 2 dives. By getting a 5th tank he can have 2 full sets for 2 dives and use the best of the 4 as his second tank. I was recommending the 5th tank because he also does beach diving and it was a different option than getting an alum 80 for that. He's trying to get the most out of the money he has to spend so that's what I was thinking.