50 replies to this topic

[gcbryan]

Assuming an ocean dive, if you are diving double 120 steels, you are over 21 pounds negative when first jumping in with full tanks. At the end of the dive, you are neutral. So, you will need less weight than with aluminum tanks to offset your positive buoyancy of the rest of your equipment.

With aluminum 80s, you are at about negative 12 or so at the start of the dive. You should be neutral at the end. You will need about 8 pounds or so of lead to offset the tanks' positive buoyancy at the end of the dive. Add to that to compensate for your remaining equipment.

Of course, both of these scenarios are based on empty tanks. So, you really should be a little more negative than this at the end of the dive if you have gas left in your tanks. However, the point is, if you have a wing and drysuit failure with double steels at the beginning of a dive, there is quite a bit of difference in the effort required to swim these up compared to aluminum 80s. Even if you ditch weight, you will still be pretty negative in the steels when compared to the aluminums.

I'm thinking that the major difference is in whether you are in warm or cold water, correct? First of all you are comparing steel 120's with aluminum 80's. If you compare steel 80's with aluminum 80's there is less difference of course. If you are in cold water you will have more weight on your weight belt to compensate for the additional undergarments. In cold weather I would think if you dropped your weight belt you would have no problem becoming positively bouyant. In warm water you probably aren't carrying enough ditchable weight to be significant when you drop it. Would you say this is correct?

[annasea]

If someone can show me how to do the multi-quotes it would make life easier.

I'll be creating a thread detailing the new features of the board as they're found, but in the meantime...

If you want to quote 2 or more people from different posts in your reply, hit the "Quote" button for the first post. You'll notice the + sign turns into a - and the button turns red.

Scroll down to your second post and hit the "Quote" button again. Once again, you'll see the + turn to a - and the button turning red.

Now, hit the "Add Reply" at the bottom of your screen. You'll now be taken to the page that allows you to enter your reply. Notice how both quotes appear in your reply box?

The nice thing about quoting this way, rather than cutting and pasting in a second quote as I used to do, is that when others are viewing your response with more than one quote, if they click on the red arrows seen in all quotes, they're taken back to the original thread.

Also, you can even add from other forums this way.

[PerroneFord]

Sorry everyone.

1. Saltwater = add weight. I apologize for the confusion

2. My desire to be positive at the end of the dive means removing ditchable weight. If I am trying to hold a stop, I will NOT be removing my belt. If I am at the surface trying not to drown, I will drop the belt. With Steel tanks, I would not be wearing a belt, and thus would have nothing to drop.

3. It was my understanding that a drysuit flood might cause one to become negative because of the undergarments. I apologize if this was in error.

Thank you.

[gcbryan]

Sorry everyone.

1. Saltwater = add weight. I apologize for the confusion

2. My desire to be positive at the end of the dive means removing ditchable weight. If I am trying to hold a stop, I will NOT be removing my belt. If I am at the surface trying not to drown, I will drop the belt. With Steel tanks, I would not be wearing a belt, and thus would have nothing to drop.

3. It was my understanding that a drysuit flood might cause one to become negative because of the undergarments. I apologize if this was in error.

Thank you.

Thanks Perrone. I'm trying to visualize diving doubles (which I don't do) in warm water (which I rarely do) and I'm seeing that having ditchable weight is not a given.

Edited by gcbryan, 26 January 2006 - 04:18 PM.

[intotheblue]

Sorry everyone.

1. Saltwater = add weight. I apologize for the confusion

2. My desire to be positive at the end of the dive means removing ditchable weight. If I am trying to hold a stop, I will NOT be removing my belt. If I am at the surface trying not to drown, I will drop the belt. With Steel tanks, I would not be wearing a belt, and thus would have nothing to drop.

3. It was my understanding that a drysuit flood might cause one to become negative because of the undergarments. I apologize if this was in error.

Thank you.

Ha... no problem... answering questions like these often creates more questions, and it is difficult to write everything down you might say in a conversation. (ha, ha... I almost wrote "difficult to writhe"... ) I'm glad nobody is attacking when we exchange these messages... and I certainly hope nothing I have written is taken that way.

One other thing to mention to clarify things; when talking aluminum versus steel, you also need to consider the difference between HP and LP steel. Their buoyancy characteristics vary greatly and even between different manufacturers within the same pressure/volume category they vary enough to make a difference.

So, the can of worms gets bigger.... <g>

ITB--

[finGrabber]

So, from what I'm reading (thanks for all the comments - they are great!)

if I decide to go with steel tanks, then I'd most likely need to dive dry to have any positive lift. Correct?

and if I decide to go with aluminum tanks, then I'd need to add more weight. Does anyone have a good calculator for how much extra?

and then, there's the question about HP vs LP. What are the differences between the 2? Why would I want one vs the other?

again Thanks!!

[Dive_buddy]

So, from what I'm reading (thanks for all the comments - they are great!)

if I decide to go with steel tanks, then I'd most likely need to dive dry to have any positive lift. Correct?

and if I decide to go with aluminum tanks, then I'd need to add more weight. Does anyone have a good calculator for how much extra?

That depends on how much lead you need to sink now. Off hand, I would say correct. But is possible that you would not. My Farmer John tunic and jeans had 26# of lift all by themselves (when new). I think we need to ask "How much weight do you need right now in order to sink? Are you wearing a 7mil F/J with that or a 3mil shorty?"

and then, there's the question about HP vs LP. What are the differences between the 2? Why would I want one vs the other?

again Thanks!!

In short HP vs. LP means same amount of air in a smaller package. You don't really get more air to breathe with a HP tank. It just take up less space. LP is more common and you should always be able to get it filled. HP tanks need a DIN valve (and makes all the BOW students og "ohhhh and ahhhhh" when they see you setting up). And not all fill stations can do DIN, and if they can, they may not be able to fill to the full pressure of your tank.

So, to give you a clearer answer, let's back up and find out what you are wearing now, how much lead you need and what tank you normally need. Then we can start this all over. (gee, whon't that be fun? )

Hope this helps.
Peter

[Dive_buddy]

I'm sorry if you felt I was nit picking your post as that is not what I had in mind.

I did not think you felt that the picture and the chart were related but was more concerned that others with less knowlage/experiance with tanks might draw a wrong conclusion.

Eric, I was just picking on everyone with that post. I saw where I did leave it open to a wrong interpretation. Gee, first you pick pick pic, now you nag nag nag.

The unfortunate downside to cyber space is that you do not get to see the facial expressions, hear the tone of voice, or any other "tells" of how the person speaking (typing) is intending the verse. And therefore some things said in a lite hearted manner are taken offensively. With me please use the following rule of thumb: most of what I say is meant in fun and/or serious conversation and, if I am offended, there will be little to no doubt that I am offend as I will clearly state that fact.

I apologize if I have offended anyone by offering my opinions here, maybe stronger than I should. I would simply HATE to see anyone get into real distress moving to doubles because they didn't consider the safety factors. It's clear that the divers here are thinking about what they are doing, so I'll shut up now on this thread.

Thanks,

-P

Perrone,
I don't think an apology is needed and the whole reason for this thread is the sharing of knowledge,ideas and opinions. Ultimately we decide for ourselves how we use the information but if it's not out there we don't have that option. As long as things do not become an attack on the person but a discussion on the pro/cons of the idea and most things have strengths and weaknesses so I look froward to your input on this and other threads.

Eric

I agree. No apology is needed and please keep adding your view point. I would liken it to music. Therefore we will differ in opinion as to the best music to listen to. That does not mean that your music or my music is wrong, it's just different. (This whole point goes out the window if he actually likes Celtic and Irish Folk music). As with your preferance for tanks, it is not wrong, just different. And your view point, as is everyone's, is important. For without different opinions, there would be no need of discussion.

You and I dive totally different ways. You are in the ocean and have to contend with surge, chop and such. I dive in a static lake, with little to no chop and no surge ever. You dive to depths I will never go, you enter places I will never venture. I dive places that would probably bore you to death. Not much need for a deco stop from 25'.

Is your equipment wrong, is your opinion wrong? NO! It is only different. Please continue with this, and other threads.

Peter.

[finGrabber]

So, from what I'm reading (thanks for all the comments - they are great!)

if I decide to go with steel tanks, then I'd most likely need to dive dry to have any positive lift. Correct?

and if I decide to go with aluminum tanks, then I'd need to add more weight. Does anyone have a good calculator for how much extra?

That depends on how much lead you need to sink now. Off hand, I would say correct. But is possible that you would not. My Farmer John tunic and jeans had 26# of lift all by themselves (when new). I think we need to ask "How much weight do you need right now in order to sink? Are you wearing a 7mil F/J with that or a 3mil shorty?"

and then, there's the question about HP vs LP. What are the differences between the 2? Why would I want one vs the other?

again Thanks!!

In short HP vs. LP means same amount of air in a smaller package. You don't really get more air to breathe with a HP tank. It just take up less space. LP is more common and you should always be able to get it filled. HP tanks need a DIN valve (and makes all the BOW students og "ohhhh and ahhhhh" when they see you setting up). And not all fill stations can do DIN, and if they can, they may not be able to fill to the full pressure of your tank.

So, to give you a clearer answer, let's back up and find out what you are wearing now, how much lead you need and what tank you normally need. Then we can start this all over. (gee, whon't that be fun? )

Hope this helps.
Peter

Hey, I think it will be fun!

Ok, more information

I usually dive a 5mm full suit, in fresh or salt water. In salt water, I need 16lbs of weight for that suit. At the end of a week of diving, I usually add another 1mm under it and have to add another 2lbs. Actually, 1.5 would be best, but I just add 2lbs and call it a day!

I am interested in diving dry...I admit that I'm jealous of WW when she's dry during the surface interval, and I'm cold cuz I'm wet!

Other than that, I don't use any other suits

Kim

[PerroneFord]

Ok,

A couple of points:

1. I do mostly freshwater spring diving. HOWEVER, I bought the Al80 doubles mostly for ocean use, just haven't gotten there yet with them!

2. HP vs LP Steel. LP steel tanks, in the common sizes, tend to be fairly large tanks. LP85, 95s, 104s, 108s, 121s, are the most common sizes. HP tanks are the SAME SIZE generally, but because you can pressure them higher, they hold more gas, and are more negative because of that gas.

Tank 2640psi 3000psi 3442psi

E7 Steel 80 64 cu. ft. 72 cu. ft. 80 cu. ft.
E7 Steel 100 80 cu. ft. 89 cu. ft. 100 cu. ft.
E7 Steel 120 96 cu. ft. 107 cu. ft. 120 cu. ft.
E8 Steel 119 95 cu. ft. 107 cu. ft. 119 cu. ft.
E8 Steel 130 104 cu. ft. 117 cu. ft. 130 cu. ft.


Cylinder Pressure Diameter Height, Weight (dry) Buoyancy (full: empty)

E7 Steel 65 3442 7.25 16.75 23.2 - 6.4 : - 1.5
E7 Steel 80 3442 7.25 20.00 28.0 - 8.5 : - 2.5
E7 Steel 100 3442 7.25 24.12 33.0 - 8.5 : - 1.0
E7 Steel 120 3442 7.25 28.25 38.0 - 10.5 : - 0.0
E8 Steel 119 3442 8.00 24.00 41.0 - 10.5 : - 2.0
E8 Steel 130 3442 8.00 26.12 43.0 - 10.5 : - 1.0

Comparison Only

Aluminum 80 3000 7.25 26.10 31.4 - 1.4 : + 4.4

3. Consider your body shape. I am 6' tall. A set of HP 80s would come about halfway down my back. For a short woman, or man for that matter, the tanks would come much lower. They would make me EXTREMELY head heavy. Note that the HP130 is about the same height as an AL80. The HP120 is longer and would be more suitable for a taller diver. This all plays a role in determining trim. Since steel tanks to not float butt up when empty like AL tanks, they won't start to float your feet toward the end of a dive. This makes keeping them trim far easier.

4. Believe me when I tell you, Al80 tanks have a LOT of drawbacks as double tanks. The biggest advantages are that they are very light in the water, and they are cheap. You must select the correct tool for the job at hand.

5. Also not mentioned here are things like the weight of lights that technical divers use. The Jetfins or similar that we wear (mine are probably 3 pounds each), the fact that our BC's are not buoyant unlike recreational BCs, etc. Technical (deep, deco, cave, wreck, etc.) can end up being VERY negative at the beginning of a dive. A wing failure and the beginning of a dive, could see this diver be more than 30 pounds negative. That's like having a concrete block tied to your body. Pick up a 30 pound weight sometime at the gym and imagine swimming with it. Now imagine swimming with it with a few hundred feet of ocean below you, adreneline in your veins, and a very nervous buddy who may not know how to help you. It certainly bears thinking about.

Like the others, I think this thread has been marvelous. It is one of VERY few boards I belong to where these kinds of issues can be hashed out without it resorting to personal attacks. Kudos to you all, and it's an honor to be a part of a place like this.

[gcbryan]

If someone can show me how to do the multi-quotes it would make life easier.

I'll be creating a thread detailing the new features of the board as they're found, but in the meantime...

If you want to quote 2 or more people from different posts in your reply, hit the "Quote" button for the first post. You'll notice the + sign turns into a - and the button turns red.

Scroll down to your second post and hit the "Quote" button again. Once again, you'll see the + turn to a - and the button turning red.

Now, hit the "Add Reply" at the bottom of your screen. You'll now be taken to the page that allows you to enter your reply. Notice how both quotes appear in your reply box?

The nice thing about quoting this way, rather than cutting and pasting in a second quote as I used to do, is that when others are viewing your response with more than one quote, if they click on the red arrows seen in all quotes, they're taken back to the original thread.

Also, you can even add from other forums this way.

Thanks Caetlonn, for all your hard work. I think I've got it now.

[captsteve]

as gcbryan pointed out, all tanks have a broad range of bouyancy throughout a dive. if i remember correctly, each 12.5 cubic foot of air weights about 1 pound......so the larger the tanks capacity, the larger the bouyancy range during the dive.
i believe if you work through the combinations of tanks and backplates availiable, you can find what you are looking for. personally, i envision finding a combination that allows me to carry a few lbs of lead in salt water......
here is a chart i found on the internet to help....i havent tried it though....... http://dive.scubadiv...calc_chart.html

oh.....and i do think i made a mistake on the steel 72 volume.....sorry

[6Gill]

Well, I guess I had to read the entire thread after all. Is someone making "new" stl 72's??? Stl 72's for the longest time that were rated at 2250 lbs (plus a 10% overfill) and were actually about 64.7(or something close to that) cu ft cylinders. They were only 71.2 cu ft. when overfilled. They were called 72 cu ft.
Most of the steel 72's around are older and many will not pass hydro... and I'm not sure if they actually fail or if testing facilities are going out of their way to remove them from service. I have had several that looked great (in and out), never had significant overfills, and were "failed" by local testers. Nobody I have talked with in the cave community would think of "cave-filling" a stl. 72. Most are used as cave deco cyls. that are left clipped off at 20 ft in the cave where their negative buoyancy holds them in place on the floor somewhere... and they are usually only filled with about 2200 psi of O2.

To the best of my knowlage noone is making the classic '72 but Scubapro did offer a 71.4cuft/3300psi /6.84in dia./20.47in high no valve/29.0lbs manufactured by Faber but you'll have to check with your local Scubapro dealer if it's still avalible

2. My desire to be positive at the end of the dive means removing ditchable weight. If I am trying to hold a stop, I will NOT be removing my belt. If I am at the surface trying not to drown, I will drop the belt. With Steel tanks, I would not be wearing a belt, and thus would have nothing to drop.

Thats the advantage of diving with SLA batteries in the canister...

and then, there's the question about HP vs LP. What are the differences between the 2? Why would I want one vs the other?

Well for mixing it's much easier for the blender,your also able to get more out of your Cascade system,less stress on your first stage,more choices in tank valves are a couple reasons I prefer LP over HP

Eric, I was just picking on everyone with that post. I saw where I did leave it open to a wrong interpretation. Gee, first you pick pick pic, now you nag nag nag.

and you point?

The unfortunate downside to cyber space is that you do not get to see the facial expressions, hear the tone of voice, or any other "tells" of how the person speaking (typing) is intending the verse. And therefore some things said in a lite hearted manner are taken offensively. With me please use the following rule of thumb: most of what I say is meant in fun and/or serious conversation and, if I am offended, there will be little to no doubt that I am offend as I will clearly state that fact.

Ain't that the truth...
Yet this is why this group is intresting to discuss with unlike other site were peoples ability to tie their shoes let alone give dive advice is questioned when some just wants the weather report.

Eric
ps this muti-quote thing is pretty cool

[Dive_buddy]

I usually dive a 5mm full suit, in fresh or salt water. In salt water, I need 16lbs of weight for that suit. At the end of a week of diving, I usually add another 1mm under it and have to add another 2lbs. Actually, 1.5 would be best, but I just add 2lbs and call it a day!

I am interested in diving dry...I admit that I'm jealous of WW when she's dry during the surface interval, and I'm cold cuz I'm wet!

Other than that, I don't use any other suits

Kim

Okay, I am going to assume that you are using an AL-80, else you probably would not have even started this topic. When I went from An AL-80 to an HP-100 I took 6# off my belt. It would more than likely be closer to 5# needed to be taken off. So for a wild ballpark guestamate I would say that one steel tank would require about 11 or 12 pounds for you. Keep in mind, this is just a starting suggestion. Try it in the shallows first.

Also, depending on how many dives you have, or more specifically, how far along you are with fine tuning your trim, you may be able to remove a few more pounds. If you do that, then you could be close to the point where you might need the extra lift of a dry suit with steel doubles. But that is just my opnion and there could be an error in my guess work.

[normblitch]

Not necessarily...

Most River Caver's here are diving Sidemount steelie dubs WET, not dry...supposedly no issues...

nhb

So, from what I'm reading (thanks for all the comments - they are great!)

if I decide to go with steel tanks, then I'd most likely need to dive dry to have any positive lift. Correct?

again Thanks!!