Al to Steel conversion

[surfsidedav]

After reading several posts about weighting I came to the following conclusion. Does this sound about right?

I'm currently using 12 lbs with an Al 80. I'm pretty sure I'm switching to E8 130's. So, empty the Al 80 is +4.4 and the 130 is -1, for a swing of 5.4, say 6 lbs. So If I drop 6lbs I should be at the same place, buoyancy wise, at the end of the dive. Right, wrong?

I keep getting thrown off by the weight at the beginning of the dive, where as the 80 is -1.4 full and the 130 is -10.5. I know the 130 has more air, but if you adjust it down to 80 capacity, it would still be -7. It seems I'll be way over weighted at the beginning.

 

[Mo2vation]

After reading several posts about weighting I came to the following conclusion. Does this sound about right?

I'm currently using 12 lbs with an Al 80. I'm pretty sure I'm switching to E8 130's. So, empty the Al 80 is +4.4 and the 130 is -1, for a swing of 5.4, say 6 lbs. So If I drop 6lbs I should be at the same place, buoyancy wise, at the end of the dive. Right, wrong?

I keep getting thrown off by the weight at the beginning of the dive, where as the 80 is -1.4 full and the 130 is -10.5. I know the 130 has more air, but if you adjust it down to 80 capacity, it would still be -7. It seems I'll be way over weighted at the beginning.

What are your buddies diving?

This is important, as if they're all still diving AL80s, HP-100's, e8-119's or whatever - you are never (and I do mean never) gonna drain the thing. So on every dive you're gonna be there wondering why you're so over-weighted.

I moved to the 130 about 3 years ago (better - 3 seasons ago) and its one of the best things I've ever done. But I'm telling you, all my buddies dive 100's or 119's and some Al80's.... and I consistently come up with 1600, 1300, 1100, etc. Its the rare dive when I break 1000 with my tank. Even lobstering with a buddy who also has a 130, I'm coming up after 88 minutes with about 800 - 900 left.

Chew on that for a bit. I'd rather be over weighted than under, of course. But not THAT over weighted. I started backing down the weights a bit when I dive with certain people.

I really don't need any weight until I get below about 1000 with this silo.

---

Ken

 

[spectrum]

After reading several posts about weighting I came to the following conclusion. Does this sound about right?

I'm currently using 12 lbs with an Al 80. I'm pretty sure I'm switching to E8 130's. So, empty the Al 80 is +4.4 and the 130 is -1, for a swing of 5.4, say 6 lbs. So If I drop 6lbs I should be at the same place, buoyancy wise, at the end of the dive. Right, wrong?

I keep getting thrown off by the weight at the beginning of the dive, where as the 80 is -1.4 full and the 130 is -10.5. I know the 130 has more air, but if you adjust it down to 80 capacity, it would still be -7. It seems I'll be way over weighted at the beginning.

You have the right idea on dropping 5.4 (6) pounds of lead.

Remember that coreect weigting is achieved at the end of the dive when your tank is neariong empty like at 500 PSI. This is the minimum weight you need to make a stop and a controled final ascent.

Forget about the beginning of the dive it's irrelevant. By definition you will be less buoyant than you need to be at that point in the dive but that is an inescapable fact due to the mass of air at your cylinder. A mega cylinder will exagerate this swing. This is one more reason to consider such a cylinder only when you have a real need for all that gas.

The E8-130 as an empty cylinder will be 9.4 pounds heavier than an AL80 as an empty cylinder. The extra air will weigh 4.2 additional pounds. This will be partially offset by the lead you get to eliminate.

Pete

 

[Dive1Dennis]

After reading several posts about weighting I came to the following conclusion. Does this sound about right?

I'm currently using 12 lbs with an Al 80. I'm pretty sure I'm switching to E8 130's. So, empty the Al 80 is +4.4 and the 130 is -1, for a swing of 5.4, say 6 lbs. So If I drop 6lbs I should be at the same place, buoyancy wise, at the end of the dive. Right, wrong?

I keep getting thrown off by the weight at the beginning of the dive, where as the 80 is -1.4 full and the 130 is -10.5. I know the 130 has more air, but if you adjust it down to 80 capacity, it would still be -7. It seems I'll be way over weighted at the beginning.

Surfsidedav, You are on the right track. I am making a similar conversion. I currently dive an AL80 and last year dove a borrowed E7120. I dropped 5lb. off of my belt and could not notice a difference between the 80 and the 120, at least not until I glanced at the SPG. :59: As Ken said, you will have a had time breathing the waterheater down when you are diving with buddies on lowly AL80s. Per PST's spec. sheet the E8130 is 1 lb. more negative when empty than the E7120 I dove so you will be very close if you drop 6 lb.

What are your buddies diving?

This is important, as if they're all still diving AL80s, HP-100's, e8-119's or whatever - you are never (and I do mean never) gonna drain the thing. So on every dive you're gonna be there wondering why you're so over-weighted.

Ken, I completely understand where you are coming from. But anyone diving a big tank carries the extra air because we might need it someday. I would hate to be in a situation where I had to breath the big tank down and could not hold a safety or decompression stop due to being underweighted. Just food for thought, I think we all do this to an extent. I have never done a weight check with a truly empty tank, well except for once, on an 80, by mistake :icon10:

 

[mark99]

Ken makes an excellent point really worth thinking about, even though Pete's position is "by the book". If you are diving with a buddy with the same air consumption rate as your own, but he has an AL-80, and you will break the surface when he hits 500 lbs, then: He has (500/3000)* 80= 12.8 cu ft of air left, he used (80-12.8) = 67.2 cu ft, then you will have (130-67.2)= 62.8 cu ft of air left in your tank. If you weight for 500 cu ft then you will be weighting for (500/3442)* 130 = 18.9 cu ft, and you will be "overweighted" at the end of the dive by (67.2-18.9) = 48.3 cu ft. In other words, you will be carrying the weight to counter the loss of 48 cu ft. of air you will not actually consume. You could drop that weight from your belt because you won't "drop it" out of your tank. Air being 12.5 cu ft per pound, you could drop (48/12.5)=3.84# (more than the 5.4 # you already dropped switching to the steel tank from the AL)

 

[spectrum]

Mark99,

I agree that the larger cylinder (or easy breather) diver could rig for the dive considering a portion of their air as static mass but I can't say I like the idea because:

* If the dive results in more air consumption than planned ( a freeflow, a significant entanglement, who knows) the large tank diver will be challenged to end the dive in propper form.

* It just perpetuates a bad set-up. If someone is going to dive often with divers of a certain configuration (capacity/consumption) adding or renting the appropriate cylinders is ideal.

* The more consistent you keep your configuration the better.

Pete

 

[mark99]

I do not disagree. As an example I was on a night lobster dive last fall with a buddy who had an AL-80, we ended up at about 90 ft and he signaled me with 700#. And if I was underweighted, then we both could have had a problem.

On the other hand, I have been shore diving with buddys who had 80 cu ft where the max depth was 30 ft. and in that situation, buoyancy control would be easier dropping 4# from the usual configuration. But you're right, I personally have always dived with the same weight. And when I switch from an Al-80 to my E7-120, I drop 6#. It was just interesting doing the calculations.

 

[KMD]

I do not disagree. As an example I was on a night lobster dive last fall with a buddy who had an AL-80, we ended up at about 90 ft and he signaled me with 700#. And if I was underweighted, then we both could have had a problem.

On the other hand, I have been shore diving with buddys who had 80 cu ft where the max depth was 30 ft. and in that situation, buoyancy control would be easier dropping 4# from the usual configuration. But you're right, I personally have always dived with the same weight. And when I switch from an Al-80 to my E7-120, I drop 6#. It was just interesting doing the calculations.

A better solution might be to let some air out of your tank before the dive. Having the tank filled to 2600 or 3000 psi will reduce the negative buoyancy at the begining of the dive while allowing you to dive with the normal amount of lead.

A fill when you have only 600psi left and a fill where you have 1800psi will cost you the same.

 

[spectrum]

A better solution might be to let some air out of your tank before the dive. Having the tank filled to 2600 or 3000 psi will reduce the negative buoyancy at the begining of the dive while allowing you to dive with the normal amount of lead.

A fill when you have only 600psi left and a fill where you have 1800psi will cost you the same.

That would work too but if I'm going to lug a bigger cylinder around I want the safety margin that a full fill provides. Being my own devils advocate I have and would again make a second dive on the same fill under the right conditions.

Just dive a good fill. This notion that we are overweighted at the start of the dive is nonsense. You are over weighted if you have more weight than you need to END the dive safely. By definition you are going to be heavy at the start of the dive. That is why we wear a Buopyancy Compensatore, to compensate for inadequate inherent buoyancy due to fluctuatons in cylinder content mass and neoprene compression. There is no shame in diving with air in a BC bladder, lung volume will only go so far especially with heavy exposire protection and with cylinders that have high capacity, meaning great mass fluctuations. The only time it should pose any challenge is when diving a roller coaster profile along the bottom and that's easilly controlled with a little practice.

Pete