Negative buoyancy and a steel tank--how much is too much?

[TNRonin]

I'm currently talking to a gent about buying his PST 104. I see that the full buoyancy is in the area of -11lbs. I'm trying to determine if this is an issue when diving wet. I currently use 6lbs to dive wet. Empty the 104 is only -3lb which means I would be light at the end, naturally I would not dive it this low.

You ladies and gents have way more dives and experience, how would I solve this problem?

Here are my possible solutions?

Should I calculate the PSI for neutral buoyancy and make that my "0" PSI?
Buy a thicker wetsuit?
Buy flotation devices to add buoyancy? LOL

[Bob DBF]

1. This would put you in a bad spot if you needed all the air.
2. Being overheated would cause it's own problems.
3. Unless the wing is too small, in which case replace it, carry a good high lift SMB and large spool for backup and know how too use it as a BC. It's a small chance you would need it if you take care of your gear, but it could avoid dumping your gear and a CSEA if Murphy showed up on your dive.


Bob
---------------------
I may be old, but I’m not dead yet.

[dumpsterDiver]

I'm currently talking to a gent about buying his PST 104. I see that the full buoyancy is in the area of -11lbs. I'm trying to determine if this is an issue when diving wet. I currently use 6lbs to dive wet. Empty the 104 is only -3lb which means I would be light at the end, naturally I would not dive it this low.

You ladies and gents have way more dives and experience, how would I solve this problem?

Here are my possible solutions?

Should I calculate the PSI for neutral buoyancy and make that my "0" PSI?
Buy a thicker wetsuit?
Buy flotation devices to add buoyancy? LOL



It is a concern for diving wet. If you now use an Al 80 and 6 lbs, you will probably be diving with no lead with this tank. Zero ditchable lead and you may start the dive a little heavier than before. The bigger tank will experience a bigger swing in bouyancy than an aluminum due to the capacity.

You should make sure you can swim the tank to the surface with no air in the BC when it is full. If that is not a problem, then the tank doesn't require any special accomodations... It will feel different than AL 80. It will be less stable and tend to roll you on your back... but it is all worth it for the extra capacity.

[awap]

What tank are you normally diving when you use 6 lb?

I would rather not be carrying excessive weight but it should not be a problem as long as you can swim your rig to the surface in the event of a BCD failure (or have alternate BCD). Assuming the LP 104 is leaving you over-weighted throughout the dive, you have another option for that gas volume in an HP100, but the difference is only a couple pounds. OTOH, I think you are saying you will still need some added weight when the tank gets low. If so, then this is quite normal. That is, a BCD failure early in a dive often leaves a diver somewhat negative but not to a degree that he can not swim his rig to the surface.

[TSandM]

The thing you need to worry about is a BC failure at depth at the beginning of the dive. You need to be able to arrest your descent and return to the surface (for example, if your corrugated hose fails at the junction with the BC, which can happen). To figure this out, you need to know how negative your tank is (-11) and how much buoyancy your exposure protection can lose (which depends on the thickness). A 3 mil suit isn't going to lose much (4 lbs makes me neutral in my 3 mil) but a 5 or 7 mil will lose a lot more. If you add the loss of buoyancy to the weight of the tank, can you swim up against that much? I know I can swim up 10 lbs, because I have done it. I'm not at all sure I could swim up 20.

[victor]

For me you need to add buoancy. If anyting goes wrong at the start of the dive you will descend. You will have no lead to release and once you are below 15ft your rate of descent will rapidly increase as your wetsuit is compressed.
It could be a freeflow, forgetting to attach your inflator hose, etc.
Stick to the ALU 80 or add buoyancy, not much just enough to keep you on the surface.

[AfterDark]

When I dive my 90's in double configuration I don't need any lead, I'm negative. I carry a 50lbs lift bag in case of a BCD failure. Maybe I need to make wooden "weights"!

[Ayisha]

TNRonin, you should wear 3 lbs in order to compensate for the difference between the ballast you require (6 lbs) and the empty buoyancy (3 lbs). You will be heavy throughout the dive and the others have told you how this will affect the comfort of your dive.

You need to make sure you can swim up your rig without inflating the wing at the beginning of a dive if necessary.

Redundant buoyancy such as a lift bag and being able to ditch the 3 lbs if necessary would be good.
A drysuit would be better with a large steel tank, but I guess it would be too warm.

[TNRonin]

Thanks for all the replies! For reference I dive a 3/2 O'niel.

In my thought processes I'm thinking I'll need air in the wing from the get go. I'll be 5lbs negative (mathematically) at the start, if I add 3lbs to bring me to neutral I would theoretically be able to go to 0 psi with the tank. Adding the 3lbs will make me -8lbs at the onset of the dive. 500 psi will get me 1.77lbs so if I never drop below 500psi I would only need about 2lbs to stay neutral.

For the record I would be diving dry were it not that the DS has been sent off.

[spectrum]

Yea you are a little short for runway here. As noted you would probably need to swim the rig up and that could be tough sledding early in the dive with a (nearly) full cylinder.

The safest thing is to park this cylinder until the drysuit is back in service.

If you reallly want to dive it you first want to consider how you feel about not being able to make a buoyant ascent. It's very rare that you would want to do so but on a rare occasion it beats drowning. Other mitigations to a highly unlikely BC failure would be shooting a bag / buoy or buddy assist. All are compriomises but people do roll the dice.

Another trick that may or may not be an option is adding static buoyancy to your rig. Ideally solid hollow spheres that would be static buoyancy, like ping pong balls on steroids in BC pockets etc. For estimating a pint volume = a pound. It's a Red Green approach that I have used to make swimsuit dives with steel cylinders in fresh water with no BC. For shallow dives foam blocks in a pocketed soft weight belt worked slick.

Pete

[awap]

Thanks for all the replies! For reference I dive a 3/2 O'niel.

In my thought processes I'm thinking I'll need air in the wing from the get go. I'll be 5lbs negative (mathematically) at the start, if I add 3lbs to bring me to neutral I would theoretically be able to go to 0 psi with the tank. Adding the 3lbs will make me -8lbs at the onset of the dive. 500 psi will get me 1.77lbs so if I never drop below 500psi I would only need about 2lbs to stay neutral.

For the record I would be diving dry were it not that the DS has been sent off.

I plan my weight so I can empty my tank at 10 feet without having to work too hard to maintain depth. It would really to be forced to float to the surface if you still have gas just because you didn't have enough weight. You could even be working on a deco obligation.

[rx7diver]

I'm currently talking to a gent about buying his PST 104.


TNRonin,

This isn't what you asked about, but I thought I'd offer it anyway. (Reading a different thread just now brought this to mind.): Have you ever dove a large, extremely negatively buoyant, LP steel cylinder? I have, and I didn't like it one bit!

A while back, before I had my first daughter, I aspired to eventually become tri-mix trained and then make my first 300 fsw dive. With this in mind, I purchased a single LP OMS (Faber) 126, planning to purchase a second when funds became available. The daughter came first, though, then her twin sisters, and so I gave up that particular dream. But I still had the tank.

I tried the tank as a single with a singles wing (with an adapter and then without) on my BP. Exactly three times! Twice in a pool, and then in an Ohio diver's quarry. Absolutely hated this cylinder for single-tank diving using a BP/W. It sits to this day in my basement virtually new.

So my unsolicited advice is, try that PST 104 before you buy it!

Safe Diving,

rx7diver

P.S. On the other hand, one of my former dive buddies, a cave diver from the old days, owns a pair of the "original" PST 104's—the *really* negatively buoyant ones—which he thoroughly enjoys diving as singles in the Great Lakes.

[flots am]

I'm currently talking to a gent about buying his PST 104. I see that the full buoyancy is in the area of -11lbs. I'm trying to determine if this is an issue when diving wet. I currently use 6lbs to dive wet. Empty the 104 is only -3lb which means I would be light at the end, naturally I would not dive it this low.

What this would mean is that you'll be 5 pounds overweight when it's full, and the entire 11Lbs will be non-ditchable.

I'd suggest not buying it.

If you get a tank that's only slightly negative when full and positive when empty, you can compensate for the positive buoyancy with weights, which are ditch-able.

flots.

[elan]

I'm currently talking to a gent about buying his PST 104. I see that the full buoyancy is in the area of -11lbs. I'm trying to determine if this is an issue when diving wet. I currently use 6lbs to dive wet. Empty the 104 is only -3lb which means I would be light at the end, naturally I would not dive it this low.

You ladies and gents have way more dives and experience, how would I solve this problem?

Here are my possible solutions?

Should I calculate the PSI for neutral buoyancy and make that my "0" PSI?
Buy a thicker wetsuit?
Buy flotation devices to add buoyancy? LOL



If you use an AL80 now then while using this tank you will be about 2-3 lb overweight when the tank is at a 500psi. When the tank is full you will be 8-9 lb overweight.

while it might be doable to swim it up in case of the failure - I was able to swim up about 16lbs from about 60ft, it might not be worth the trouble at all.

Check LP85s - they are more positive and still give you a lot of gas for a dive. If you need more gas I would just either move to doubles (BM or SM) or just sling a stage.

A stage will be less comfortable though...

I would stick to aluminum with a wet suit as they give you more freedom in terms of trimming (you can add trim weights)

[dumpsterDiver]

I dive all the time with a single LP steel and a negative 13 cu-ft pony and a thin, worn out 3 mm wetsuit. I can wear no lead and I am fine (but kinda fat). I have 149, 125's, 112-108's, 98's and smaller steels.

If you can swim the tank up from the bottom at the start of the dive with zero air in your BC, then it should not be a problem. I see people making all kinds of silly comments recently .. I do this every weekend for over 10 years now (for 6 months out of the year). You aren't GONNA DIE!

In all honesty, it is safer to dive with a less negative tank and carry a 5-6 lb belt that you can ditch, but this is not that big of a deal. ARE you strong enough to swim the tank up?

[DivemasterDennis]

I want to comment on the "lift bag as emergency buoyancy provider" comment earlier in the thread. Has anyone noted that a safety sausage ( smaller and easier to carry than a lift bag, can provide such additional buoyancy if there is a wing or bcd failure? It's another reason to carry a sausage. Just a thought.
DivemasterDennis

[tomfcrist]

I want to comment on the "lift bag as emergency buoyancy provider" comment earlier in the thread. Has anyone noted that a safety sausage ( smaller and easier to carry than a lift bag, can provide such additional buoyancy if there is a wing or bcd failure? It's another reason to carry a sausage. Just a thought.
DivemasterDennis

Yes, and i teach it to all of my advanced students. Probably never have to go that route, but if they need to do it just one time in their life, they will know how to explore their options.

[AfterDark]

I want to comment on the "lift bag as emergency buoyancy provider" comment earlier in the thread. Has anyone noted that a safety sausage ( smaller and easier to carry than a lift bag, can provide such additional buoyancy if there is a wing or bcd failure? It's another reason to carry a sausage. Just a thought.
DivemasterDennis

That was my post. I carry both, in the same pouch with a finger spool. The right tool for the job works the best. If I'm in 100+ FSW with those double 90's I want the right tool for the job which is saving my butt.

[TNRonin]

Coincidentally, I have a guy that is going to loan my his PST 104 this w/e, it will be his first dive on them as well from what I understand, but he is diving dry. I do need the air, how would a HP 120 or 130 differ? I'm not versed on the buoyancy of these tanks. Thanks.

---------- Post added May 9th, 2012 at 01:07 PM ----------

I'm going to try swimming it up from about 40fsw this week end to see if it is an issue.

[spectrum]

I'm going to try swimming it up from about 40fsw this week end to see if it is an issue.

Suit properties are very hard to come by and vary with make, model, age and usage. That being said 40 FSW is probably not worst case in evaluating the minimum wetsiut contribution to buoyancy. I realize were talking about contingencies for improbable situations but sometimes the devil is in the details.

Pete

[TNRonin]

Suit properties are very hard to come by and vary with make, model, age and usage. That being said 40 FSW is probably not worst case in evaluating the minimum wetsuit contribution to buoyancy. I realize were talking about contingencies for improbable situations but sometimes the devil is in the details.

Pete

Errr ok. If we are talking about worst case scenarios, I guess I'll never be able to create a truly worst case scenario. I'll just do the best I can, I could take it to the bottom trench of the quarry at 78/80 fsw and give it a shot.

Seriously, I may try to find a 5mm suit as these seem to be a pretty common thickness for a wider range of diving conditions. I'm going to be using lavacore under the 3/2 this w/e, and I know that is is supposed to be neutral so that is a non-issue.

[flots am]

I'm currently talking to a gent about buying his PST 104. I see that the full buoyancy is in the area of -11lbs. I'm trying to determine if this is an issue when diving wet. I currently use 6lbs to dive wet. Empty the 104 is only -3lb which means I would be light at the end, naturally I would not dive it this low.

I'm not sure if it's been said plainly anywhere in the thread yet, so I'll leave it hear "just in case".

The issue is that as you descend, your suit loses buoyancy and compresses.

If you were to do something such as forget to inflate your BC and jump in with your air off or an empty tank, with all your weight as a non-ditchable, significantly negative tank, you would find yourself rocketing towards the bottom with nothing to breathe and no way to inflate your BC and not enough strength or air to swim it back to the surface.

It's one thing to be able to swim a negative rig up. It's quite another to do it without breathing.

Having enough ditchable weight to make yourself close to neutral (or even positive) would make handling the above incident much easier.

flots.

[TNRonin]

I'm not sure if it's been said plainly anywhere in the thread yet, so I'll leave it hear "just in case".

The issue is that as you descend, your suit loses buoyancy and compresses.

If you were to do something such as forget to inflate your BC and jump in with your air off or an empty tank, with all your weight as a non-ditchable, significantly negative tank, you would find yourself rocketing towards the bottom with nothing to breathe and no way to inflate your BC and not enough strength or air to swim it back to the surface.

It's one thing to be able to swim a negative rig up. It's quite another to do it without breathing.

Having enough ditchable weight to make yourself close to neutral (or even positive) would make handling the above incident much easier.

flots.

Gotcha, I think we've been bouncing between the absolute worst case scenario like you have listed.
no air in bcd
no air to breath
negative buoyancy
negatively buoyant

I'm currently looking at 5mm suits to see what is going on with their buoyancy. I know from diving a 7mm that there is significant buoyancy swings at various depths. There is a lot going on here. I'm just taking it slow and making sure I'm not jumping into the deep end prematurely.

[flots am]

Gotcha, I think we've been bouncing between the absolute worst case scenario like you have listed.


Jumping off the boat with the air off is actually relatively common. On some BCs, getting the dump valve string caught on something is also pretty common, so ending up in the water with an empty BC and no air isn't a isn't all that far-fetched.

I probably see it once a summer, but it ends up not being a big problem because the wetsuit divers tend to not have significantly negative tanks.

flots.

[tomfcrist]

Suit properties are very hard to come by and vary with make, model, age and usage. That being said 40 FSW is probably not worst case in evaluating the minimum wetsuit contribution to buoyancy. I realize were talking about contingencies for improbable situations but sometimes the devil is in the details.

Pete

Errr ok. If we are talking about worst case scenarios, I guess I'll never be able to create a truly worst case scenario. I'll just do the best I can, I could take it to the bottom trench of the quarry at 78/80 fsw and give it a shot.

Seriously, I may try to find a 5mm suit as these seem to be a pretty common thickness for a wider range of diving conditions. I'm going to be using lavacore under the 3/2 this w/e, and I know that is is supposed to be neutral so that is a non-issue.

You have a quarry that is 80 FSW? I thought the only place with sea water was the sea?

[katepnatl]

At the end of the day, it's about what can be managed in practice vs. in theory. So far there have been a couple people who have spoken to what they know they are capable of doing - they've tried it out and they know what they can and can't do. THAT is what I would suggest for anyone.

Also - for me - I do not choose to overly count on an SMB or lift bag for buoyancy. I've thought to myself a couple times, "pretend you just lost all the gas in your wing and get your SMB inflated really quick so you don't drop to the ocean floor at 400 feet"... and I would say that it is not as easy as one might think to quickly get the SMB out, get it inflated, launched, and usable, while trying to maintain buoyancy physically (by swimming). i do know I can swim up steel 95's from 30 feet and hold (well, swim) a stop for 3 minutes at about 15 feet in a drysuit with a base layer only. I also know it was NOT easy.

[TNRonin]

At the end of the day, it's about what can be managed in practice vs. in theory. So far there have been a couple people who have spoken to what they know they are capable of doing - they've tried it out and they know what they can and can't do. THAT is what I would suggest for anyone.

Also - for me - I do not choose to overly count on an SMB or lift bag for buoyancy. I've thought to myself a couple times, "pretend you just lost all the gas in your wing and get your SMB inflated really quick so you don't drop to the ocean floor at 400 feet"... and I would say that it is not as easy as one might think to quickly get the SMB out, get it inflated, launched, and usable, while trying to maintain buoyancy physically (by swimming). i do know I can swim up steel 95's from 30 feet and hold (well, swim) a stop for 3 minutes at about 15 feet in a drysuit with a base layer only. I also know it was NOT easy.

I have no clue if I can do it. I'm going to give it a shot. I had not even thought about the pesky safety stop.

Sent from my DROID X2

[Bob DBF]

"pretend you just lost all the gas in your wing and get your SMB inflated really quick so you don't drop to the ocean floor at 400 feet"

In that scenario, should I not make the recovery I was anticipating, I would shortly opt for littering.



Bob
----------------------
I may be old, but I’m not dead yet.

[katepnatl]

In that scenario, should I not make the recovery I was anticipating, I would shortly opt for littering.


Not sure if I'm reading that correctly... do you mean littering the ocean floor with the SMB if it took too long to get it deployed, or something else?

I wasn't talking about dropping the SMB - I was talking about using the SMB to prevent ME from dropping "400 feet to the ocean floor." Point being, I'm just not sure how quickly I can count on pulling out a lift bag/SMB in order to slow a descent due to catastrophic BC failure. Well - not exactly true - I DO in fact have a decent idea - only bc I have practiced it. But I've heard a lot of people say they would use SMBs/lift bags for alternate lift, who have never "done the math" so to speak. But was that what you meant, even? :confused:

[PfcAJ]

Using an SMB as some sort of "redundant buoyancy" is fantasy land stuff. Dive a balanced rig and be done with it.

[dumpsterDiver]

I'm not sure if it's been said plainly anywhere in the thread yet, so I'll leave it hear "just in case".

The issue is that as you descend, your suit loses buoyancy and compresses.

If you were to do something such as forget to inflate your BC and jump in with your air off or an empty tank, with all your weight as a non-ditchable, significantly negative tank, you would find yourself rocketing towards the bottom with nothing to breathe and no way to inflate your BC and not enough strength or air to swim it back to the surface.

It's one thing to be able to swim a negative rig up. It's quite another to do it without breathing.

Having enough ditchable weight to make yourself close to neutral (or even positive) would make handling the above incident much easier.

flots.

What the heck are you talking about? If the tank is empty (and off) it will not be heavy and he will float.

If the tank is full (and off) he will float on the surface (or nearly so) because his wetsuit will be uncompressed...

Where do we come up with the idea that this tank is going to send him plummeting to the depths?

[flots am]

Where do we come up with the idea that this tank is going to send him plummeting to the depths?

The OP was considering a tank that would make him negatively buoyant with non-ditchable weight.

Jumping in with the air off and/or the pull dump string trapped would be a problem.

flots.

[Bob DBF]

[QUOTE=katepnatl;6337733]Not sure if I'm reading that correctly... do you mean littering the ocean floor with the SMB if it took too long to get it deployed, or something else?
QUOTE]

If you are truly screwed, you dump your rig and swim to the surface, Old School 101.

As has been pointed out, you should be able to swim your rig to the surface, but if you are looking at your imminent demise, explore your options and act. I won't own any peice of dive gear thats worth my life.



Bob
------------------------
I may be old, but I’m not dead yet.

[JamesK]

The OP was considering a tank that would make him negatively buoyant with non-ditchable weight.

Jumping in with the air off and/or the pull dump string trapped would be a problem.

flots.

Why the hell would you do that?

[TSandM]

Why the hell would you do that?

You skipped the buddy check?

[TNRonin]

You skipped the buddy check?

That's ok, we'll check each other on the way down as he will be diving a 104 also this w/e. LOL

[jamiep3]

Just to throw out an alternative scenario.

If you really feel the need for the larger tank, you might look at the Blue Steel / Faber Line. They have LP 95s and 108s that are very close in overall buoyancy to an AL80, although you would probably find the trim a little different.

[TNRonin]

Jamie thanks! If I can find them used I will certainly look.

Just to throw out an alternative scenario.

If you really feel the need for the larger tank, you might look at the Blue Steel / Faber Line. They have LP 95s and 108s that are very close in overall buoyancy to an AL80, although you would probably find the trim a little different.

[flots am]

You skipped the buddy check?

That's usually how it happens.

Buddy checks are so rare that when I actually see one in a rec diver, it's an "unusual event".

Being dumb shouldn't be fatal, especially if there's an easy way to prevent it.

flots.

---------- Post added May 10th, 2012 at 04:43 PM ----------


Why the hell would you do that?

Because some people make mistakes, some are lazy, some grow complacent. The reason is irrelevant.

And assuming your tagline of "Undercover DIR Agent" means you somehow follow DIR, you should already be aware of the advantages of engineering out possible failures.

flots.

[SkimFisher]

The OP was considering a tank that would make him negatively buoyant with non-ditchable weight.

Jumping in with the air off and/or the pull dump string trapped would be a problem.

flots.

Probably the 4th or 5th problem he's got if it gets to that point.

[dumpsterDiver]

The OP was considering a tank that would make him negatively buoyant with non-ditchable weight.

Jumping in with the air off and/or the pull dump string trapped would be a problem.

flots.


I said about 5 freaking times.. make sure you can swim the full tank up from depth with zero air in BC.. Have you ever used one of these tanks... it is not gonna make a normal person in a wetsuit sink uncontrollably from the surface......

[Sleepdr]

If you are truly screwed, you dump your rig and swim to the surface, Old School 101.

As has been pointed out, you should be able to swim your rig to the surface, but if you are looking at your imminent demise, explore your options and act. I won't own any peice of dive gear thats worth my life.

That was my thought as well. If the descent rate needle was pegged at "Patent Pending" in blue water and I couldn't swim up or get positive, I would be unfastening or cutting away my rig with quickness. At least as much quickness as I could muster whilst out of breath, deep, and in a state of uneasiness. My current experience level dictates ditching, as I'm not yet facile with quick drawing & deploying an SMB.

An uncontrolled buoyant ascent vs uncontrolled descent - I'll choose what might kill me over what will absolutely kill me. Being morbid, it would also make recovery of my body easier if it's on the surface. Most compatible with life, though, is trying to avoid this situation altogether.

[TNRonin]

Well the deal fell through. It seems my candid email offended him. He stated he was going to lower the price but not now. Wow I guess I really missed the privilege of buying from him. I'm scheming on a Faber 121 now. I think it is even in hydro and viz. $150

Sent from my DROID X2

[elan]

The OP was considering a tank that would make him negatively buoyant with non-ditchable weight.

Jumping in with the air off and/or the pull dump string trapped would be a problem.

flots.

In this case the tank being negative is probably the least of these problems :)

[halocline]

I'm currently talking to a gent about buying his PST 104. I see that the full buoyancy is in the area of -11lbs. I'm trying to determine if this is an issue when diving wet. I currently use 6lbs to dive wet. Empty the 104 is only -3lb which means I would be light at the end, naturally I would not dive it this low.





I don't think your numbers quite add up if you're saying that you use 6 lbs of ballast with an AL80, and if you're properly weighted. (neutral w/empty tank) The AL80 is +4lbs empty, the 104 is -3. That's a difference of 7; you're only using 6, so theoretically you could use no lead and still be -1 at the end of the dive.

Honestly though, I have to wonder about being neutral with an empty AL80 and wearing a wetsuit and only 6 lbs of ballast. The wetsuit is going to be at least +4, the tank +4 (4.4 for luxfer) and I suspect your BC is at least +2, unless you're using a BP/W. That's 10 lbs of buoyancy right there, offset by only 6 lbs lead plus the negative buoyancy of other gear like a regulator (maybe -2?). If you're a fatless muscle-man that sinks like a stone, congratulations and my apologies for doubting you! If you have another source of ballast like a steel plate, you might find that using an AL plate works well with a steel tank in warm water.

I realize you already passed on this deal, but assuming you keep looking for a steel tank this issue will still be relevant.

[TNRonin]

I wish I were fatless, though I am pretty dense. LOL
I dive the following when I have dove a AL80

3/2 wetsuit
2.5mm beanie
Hog 32 wing
standard harness
accessories totaling about 1lb
Hollis Plate 6lbs
Hog tech fins 2-3lbs
Conshelf 21 reg set (now Hog 2nds) 3lbs??
6lbs on back trim pockets


I try to surface with at least 500psi. I have no problem staying down with this config. I will dive my steel 72 this w/e and probably drop some more weight off the set up. I'm sorry if this doesn't make sense, but it is what I dive, and I sink quite well.

[diverrex]

I wish I were fatless, though I am pretty dense. LOL
I dive the following when I have dove a AL80

3/2 wetsuit
2.5mm beanie
Hog 32 wing
standard harness
accessories totaling about 1lb
Hollis Plate 6lbs
Hog tech fins 2-3lbs
Conshelf 21 reg set (now Hog 2nds) 3lbs??
6lbs on back trim pockets


I try to surface with at least 500psi. I have no problem staying down with this config. I will dive my steel 72 this w/e and probably drop some more weight off the set up. I'm sorry if this doesn't make sense, but it is what I dive, and I sink quite well.

Now it all makes sense. A steel plate and steel tank with a 3mm suit generally doesn't work. When I know I'm diving steel tanks in warm water I switch my BP/W to my old BC. You need to move to an AL plate (as Halocline says) to dive steel tanks with a 3 mm. I've started to look at the new Halcyon travel BP for that reason.

When using my steel plate I always think of that as diving with 6 lb weights, so if I was also using 6 lb in pouches I'd look at it as I was using 12 lbs, just so happens 6 lbs is on the plate.

[TNRonin]

Now it all makes sense. A steel plate and steel tank with a 3mm suit generally doesn't work. When I know I'm diving steel tanks in the tropics I switch my BP/W to my old BC. You need to move to an AL plate (as Halocline says) to dive steel tanks with a 3 mm. I've started to look at the new Halcyon travel BP for that reason.

When using my steel plate I always think of that as diving with 6 lb weights, so if I was also using 6 lb in pouches I'd look at it as I was using 12 lbs, just so happens 6 lbs is on the plate.

Based on the specs I'm reading (-5lbs full, -1-2lbs at 500PSI) I should be able to drop down in my weights.

[beaverdivers]

Now it makes sense - SS backplate. Before you clarified this neg. fact, I was going to suggest adding a SS backplate, find a ripping down current and enjoy the ride.

Go Deep or Go Home!

Just kidding.

Why not use a 19, 30 or 40 cuft Al. pony?

[halocline]

I wish I were fatless, though I am pretty dense. LOL
I dive the following when I have dove a AL80

3/2 wetsuit
2.5mm beanie
Hog 32 wing
standard harness
accessories totaling about 1lb
Hollis Plate 6lbs
Hog tech fins 2-3lbs
Conshelf 21 reg set (now Hog 2nds) 3lbs??
6lbs on back trim pockets


I try to surface with at least 500psi. I have no problem staying down with this config. I will dive my steel 72 this w/e and probably drop some more weight off the set up. I'm sorry if this doesn't make sense, but it is what I dive, and I sink quite well.

Okay, so you use 12 lbs of ballast with an AL80 and your wetsuit. You could easily and comfortably dive the 104 (or many different steel tanks) by getting an AL or kydex (deep sea supply) backplate. If hammerhead is still in business, they make a nice AL plate for under $50.

I find with my LP72s that they're neutral or just a bit positive empty, so you might try diving this weekend with 2 lbs instead of 6 in the pockets, that'll probably be pretty close.

[Ayisha]

The Faber 120 is 16.22 lbs negative when full, so you will be extremely overweighted throughout the dive. The empty buoyancy is 7.22 lbs negative, so you would be 5 lbs overweighted at the end of the dive without any weights. This tank would not be adviseable with a wetsuit, especially a thin one.

Again, the question would be, can you swim this rig up with your wing empty and a full tank?

[TNRonin]

The Faber 120 is 16.22 lbs negative when full, so you will be extremely overweighted throughout the dive. The empty buoyancy is 7.22 lbs negative, so you would not require any extra weight. This tank would not be adviseable with a wetsuit, especially a thin one.

Again, the question would be, can you swim this rig up with your wing empty and a full tank?

wow I looked it up and I didn't see that amount. I thought it was less than the 104.

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[Ayisha]

It's a lot. Here's one chart:Scuba Cylinder Specification Chart from Huron Scuba, Ann Arbor Michigan (http://www.huronscuba.com/equipment/scubaCylinderSpecification.html)

[halocline]

Those are not the 120s that everyone gets. You would get the special permit (3442PSI) tanks, not the old 3AA 3180+10% tanks. I honestly don't know if faber sells a special permit 120; I have one of the 100s and I like it alot.

[irishsquid]

Hey TNRonin, When I first got my SS BP/W and steel tanks, I did what most suggested here and did it in the quarry I believe you are talking about. I was in my 5mm wetsuit, made sure my wing was empty and dropped to the trench with a FULL tank. Then I proceeded to swim it up to the surface. I didn't find it difficult at all. At that quarry, you always have the option of walking/crawling it up and out. ;) Whatever tank you use, be sure you can reach the valve and turn it on if you decide to enter with it off.:eyebrow: You're still welcome to try my AL40 pony anytime (nice redundancy for these tests). I'll probably be diving SM most of the time this summer at the quarry just to familiarize myself more with the setup and can bring the pony for you. I actually did the same "swim my rig up" with my SM at the quarry the first time I dove it. That wasn't a problem either. Of course I'm using LP77s.

[dumpsterDiver]

The Faber 120 is 16.22 lbs negative when full, so you will be extremely overweighted throughout the dive. The empty buoyancy is 7.22 lbs negative, so you would be 5 lbs overweighted at the end of the dive without any weights. This tank would not be adviseable with a wetsuit, especially a thin one.

Again, the question would be, can you swim this rig up with your wing empty and a full tank?


Yeah that is not a tank people seem to use.. I would not use it.... Other faber 120's (I have two) which are rated to 2400 psi and like -12 lbs full or something.... that is reasonable for most people.

On the other hand a steel plate and a big steel with a thin wetsuit.... Not gonna work unless you are a HFS...Huge Fat "scuba-diver".

[TNRonin]

I'll need to look for an aluminum plate from the sounds of it. Squid I picked up and set up a 19cf pony bottle. I dove it last weekend and it worked great. I'm about to head out now.

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[TNRonin]

Dove my 72 today. I was about -2 lbs. I'll need an aluminum plate for sure.

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[TNRonin]

Dove my friend's pst 104 today. Pretty good dive. Got pretty floaty at about 1k psi but in general not bad. I offered to store it for him but no joy. LOL

I just need to be patient one will show up. Hopefully this seller won't think he its doing me a favor. My dive buddy got both tanks for $200 total.:(

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