double 104's

[Scuba_Vixen]

They require 3300# fills to get the 100cft, so usually you'll end up with 90 and short change.... Just too much weight and clumsyness for so little additional gas.

I'm still wondering what he needs so much gas for, as there's no indication of any deco dive certs. Most any experienced diver can dive a single 80 well into deco bottom times.

I believe I'm seeing some new diver excitement/adrenaline induced synaptic anomolys here.

Manifolded doubles, just like redundant bladders, can be either risk management tools, or just plain additional risks ...... It's the diver's training and experience that controls which......

I think some one is jumping the gun on doubles here.


Darlene


If you're really just an air hog on rec profile (ndl) dives, maybe a single E8-130 would be a good choice (less than 2# negative), but that much gas can get you in a world of hurt in a heartbeat if you don't know what you're doing.

 

[Don Burke]

FIXXERVI6 once bubbled... ok.... how about double aluminum 100's, just about the same bouancy as 80's.

would a 45# wing be good enough for double 100's and an aluminum back blate?

Those things are damned heavy on the surface. It's another 32 pounds or so to sling around.

They are designed to be neutral when empty, which means you lose 8 pounds of ditchable weight as compared to the 80s. I don't think you have it to lose.

If you get 3000psig fills, those 100 cuft tanks become 91 cuft tanks.

I don't see where you're going with the extra gas. The double 80s give you a reasonable safety factor for gas capacity at the no-stop limit for EAN32 at 100 feet and an outrageous amount of time shallower. Anything beyond that will require some extra measures for decompression, hydration, and thermal protection.

What is your dive buddy going to be wearing for tanks? With the 80s I can dive with people wearing single 131s and the mismatch isn't extreme.

Please don't nickel rocket yourself into a situation that gets you in trouble. You probably don't yet realize what 160 feet of gas really means. I know I didn't until I made a dive with it.

The nice thing about 80s is that they are always useful in some way, so the money is never wasted. I can't say that for 100s.

I wear a 45 pound wing with both 80s and 72s. I think a 40 pound wing would be enough.

 

[DA Aquamaster]

AL 100's weight nearly the same as LP 104's, are the same diameter and within an inch in terms of height. The significant differences are the square bottom on the AL tanks (which make the AL tanks appear to be more bulky), the better odds of getting a full fill on the LP 104's with their 2640psi service pressure and bouyancy as AL 100's are about 5 lbs less negative than LP 104's.

In my opinion both are bulky and heavy. A set of twin steel 72's are only about 12 pounds heavier than a single AL 100 or LP 104.

One of my regular dive buddies dives with a single AL 100 as he is a bit of an air hog and he has stated that if he had it to do over again, and did not already own several AL 100's he would have went with twin steel 72's instead. He has never even considered twin AL 100's (or LP 104's). It takes a good deal of strenght to get that amount of weight up the boarding ladder along with all your other gear at the end of a long cold dive.

From strictly a bouyancy standpoint the AL 100's make more sense if you are diving doubles in a wet suit as they would be 10 pounds less negative in the water.

I also agree the percieved need for doubles in this case may have more to do with ego or apprearance than operational neccessity.

 

[FIXXERVI6]

sorry to disappoint you guys but its not ego.

who am I to impress, my perminent dive buddy? She is a woman that sips air and is looking at getting doubles eventually too, albiet a lot smaller than what I would carry.

My air consumption is pretty good, but below 100 feet, 77 cubic feet of gas doesn't seem like much if you push the limits and get into an emergency situation, doubles would be nice for this, and I know that double 104's would be major overkill, but if later they served dual purpose? After reading and talking around chances are I'm just going to blow double the money into this eventually and have multiple rigs, I was hoping that 1 rig could do it all, since I have seen this done.

Do I NEED doubles? no, I can sling a pony, use a LP95 and do everything I need to do with it.

I would prefer doubles.

After reading these posts, thank you all, its been helpfull, I won't be buying 104's, or probably even 95's. I talked to a local that will let me jump in the pool with 98's but suggested a double bladder wing.

so now I've changed my mind down to double standard 80's and a 45# wing.

 

[Big-t-2538]

Still doubles in a wetsuit involves a deal of risk...

Personally, I might dive a set of AL80s wet, but that would be it. I would not be slinging Steel anything as I just think that with a wetsuit, any un-necessary weight is a potential to make me an anchor on the bottom of whatever.

I am not a fan of double wings, but they are an option.

 

[Karl_in_Calif]

FIXXERVI6 once bubbled...
Do I NEED doubles? no, I can sling a pony, use a LP95 and do everything I need to do with it.

I would prefer doubles.

After reading these posts, thank you all, its been helpfull, I won't be buying 104's, or probably even 95's. I talked to a local that will let me jump in the pool with 98's but suggested a double bladder wing.

so now I've changed my mind down to double standard 80's and a 45# wing.

If we start with the assumption that doubles is the best way to go for scuba, which is indeed a feasible assumption, and we have discussed this before, feasible at least for those with backs strong enough to handle these out of the water, then you only need to decide what configuration is needed for the conditions of the dive.

For cave diving or shipwreck penitrations, the tank size will be a function of your RMV times the pressure at your MOD times your planned dive time, plus a 50% reserve for the rule of thirds computed with the greater of your or your buddy's RMV.

For non-penitrations, the size will be a function of your RMV times the pressure at your MOD times your planned dive time plus a reserve large enough to get you or your buddy directly back to the surface with safety stop(s).

Some divers may calculate this differently. Some divers always use the rule of thirds for all diving.

For a dive to 100 ft, for example, which is also the deepest that I recommend that non-tech divers go, the calculations are as follows:

Planned depth = 100 fsw = 100/33 + 1 ATAs = 4.0 ATAs
Planned mix = PO2/P = 1.4/4.0 = 0.35 = EAN35
EAD of EAN35 @ 100 fsw = (1 - 0.35)/0.79 x (100 + 33) - 33
= EAD of 76 fsw
Planned max time = 120 - 76 = 44 mins rounded down to 40 mins
CNS O2 limit of PO2 1.4 = 150 mins (per NOAA) therefore 40 mins at 100 fsw on EAN35 is safe.

My RMV for a working/swimming dive is 0.75

Vol of gas = 0.75 x 40 x 4 = 120 cu ft

Assuming my buddy also has a 0.75 RMV then with the rule of thirds, my total gas would be 120 x 150% = 180 cu ft

Tank size: TWIN 90s

Faber steel 95s are -1.2 lbs empty each (per the chart). Doubled, with a manifold and 2 regs, this comes to about -5 lbs. Adding 60 cu ft of reserve air weighing 5 lbs comes to -10 lbs.

OMS steel 98s are -0- lbs empty each (per the chart). Doubled, with a manifold and 2 regs, this comes to about -3 lbs. Adding 60 cu ft of reserve air weighing 5 lbs comes to -8 lbs.

Luxifer alum 78s are +2 lbs empty each (per the chart). Doubled, with a manifold and 2 regs, this comes to about +1 lbs. Adding 60 cu ft of reserve air weighing 5 lbs comes to -4 lbs.

An aluminum backplate is about -3 lbs and a steel backplate is about -6 lbs.

My natural ocean buoyancy without a suit is about +6 lbs.

With my shell drysuit, my ocean buoyancy is about +20 lbs.

I would presume that a semi-dry would run about the same +20 lbs, however I do not know. It could be more.

Now the task at hand is to configure all the above, so that I am as close to neutral at all times, with some ditchable weight to compensate for the weight of the gas when the tanks are full.

IF THE WATER IS WARM, defined as 82^F or more, then I will go with dive skins (natural buoyancy +6), aluminum tanks (-4), an aluminum backplate (-3), and 6 lbs ditchable weight (to make up for the reserve gas, if used). My fins should easily be able to kick against -1 lb negative buoyancy if I ditch my weights, even without a functioning B/C. Even so, I have my buddy's B/C to rely on to help me, if mine fails. NO DOUBLE WINGS.

IF THE WATER IS COLD, defined as less than 82^F, then I will go with my shell suit (natural buoyancy +20), Faber steel 95s tanks (-10), a steel backplate (-6), and 10 lbs ditchable weight (to make up for the reserve gas, if used, and the buoyancy of the suit & thermals). If I ditch my weights, even without a functioning B/C, I should be positive. Even so, I have my buddy's B/C to rely on to help me, if mine fails. NO DOUBLE WINGS.

NO HIGH CAPACITY B/C EITHER, since I am neither a tech instructor nor carrying a heavy tool bag for a salvage op.

Thats how I would plan it.

 

[Karl_in_Calif]

The same calculations for a large single tank would be as follows:

For a dive to 100 ft, for example, which is also the deepest that I recommend that non-tech divers go, the calculations are the same as above.

Vol of gas = 0.75 x 40 x 4 = 120 cu ft

Assuming my buddy also has a 0.75 RMV then with the rule of thirds, my total gas would be 120 x 150% = 180 cu ft

Tank size: 120 is as big as it gets (although I have heard that the DOT recently approved LP 104s to be high pressurized to the equivalent of HP 130s, but I have not confirmed that yet.)

A PST LP 120 is -2 empty (according to my chart).

A PST HP 120 is +1 empty (according to my chart).

My natural ocean buoyancy without a suit is about +6 lbs.

With my shell drysuit, my ocean buoyancy is about +20 lbs.

IF THE WATER IS WARM, defined as 82^F or more, then I will go with dive skins (natural buoyancy +6), the steel LP 120 (-2), and 10 lbs ditchable weight (to make up for the reserve gas, if used, and the remaining natural buoyancy). If I ditch my weights I should be positive, in the event of a B/C failure.

IF THE WATER IS COLD, ... well thats easy. Just an ordinary day of diving, on the West Coast Best Coast.

Thats how I would plan it for a single tank with a stage backup.

Guess what the main difference is?

Answer:

1) A single tank is going to weight a whole lot less out of the water. That means, carrying it to and from the boat, on the shore, at the beach, etc.

2) You are going to spend a whole lot of money $$$ on twin tank bands, a manifold, backplate, harness, and most stores charge double to fill them.

 

[Dryglove]

FIXXERVI6 once bubbled...


My air consumption is pretty good, but below 100 feet, 77 cubic feet of gas doesn't seem like much if you push the limits and get into an emergency situation, doubles would be nice for this,

Also be careful as it is very easy to go beyond NDL limits and not even realize it when you are diving doubles. Be very aware and constantly monitor your gauges/computer to make sure that doesn't happen. I also advise against pushing the limits of NDL as you may find yourself in a deco dive or bent.

 

[Karl_in_Calif]

lal7176 once bubbled...


Also be careful as it is very easy to go beyond NDL limits and not even realize it when you are diving doubles. Be very aware and constantly monitor your gauges/computer to make sure that doesn't happen. I also advise against pushing the limits of NDL as you may find yourself in a deco dive or bent.

EANx solves that problem however. Burke pointed that out early on. Then he got mad because I did not have my references available to quickly agree or disagree with him. He was right.

 

[Spectre]

Karl_in_Calif once bubbled...
Planned max time = 120 - 76 = 44 mins rounded down to 40 mins

You want to explain where you got your NDL time?

Vol of gas = 0.75 x 40 x 4 = 120 cu ft

Assuming my buddy also has a 0.75 RMV then with the rule of thirds, my total gas would be 120 x 150% = 180 cu ft

Tank size: TWIN 90s

What about gas for the ascent? You have nothing about how much gas it will take to get from depth to the surface... Are you talking 40 minutes BT or 40 minutes run time? If 40 minutes run time, what time do you start your ascent? How much gas do you and your buddy need for that ascent?