iflyprops
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LOL! Thanks for straightening me out!Mo2vation:
What are the true advantages of steel tanks?
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someone posted:
This instructor pointed out that other than the size of the tank, there is not much advantage for a rec diver to dive steel. He mentioned that the idea of shedding weight is a myth because the weight is not being shed, it's being shifted (you're now carrying it on your back as opposed to your waist and steel tanks are heavier);
falconer replied:
hold on a minute, I was told but have never verified that a
steel tank is actually lighter than an aluminum in the same
rating..if this is true than you are in fact carrying less total weight. The steel tank walls are considerably thinner than
the thick aluminum walls making them lighter. I'm told the
decreased positive buoyancy characterisitic of a steel tank
is due to the smaller size of the container rather than the actual weight, as i said...not verified, but worth further
examination....
Kevin Falconer Fort Myers, FL
This instructor pointed out that other than the size of the tank, there is not much advantage for a rec diver to dive steel. He mentioned that the idea of shedding weight is a myth because the weight is not being shed, it's being shifted (you're now carrying it on your back as opposed to your waist and steel tanks are heavier);
falconer replied:
hold on a minute, I was told but have never verified that a
steel tank is actually lighter than an aluminum in the same
rating..if this is true than you are in fact carrying less total weight. The steel tank walls are considerably thinner than
the thick aluminum walls making them lighter. I'm told the
decreased positive buoyancy characterisitic of a steel tank
is due to the smaller size of the container rather than the actual weight, as i said...not verified, but worth further
examination....
Kevin Falconer Fort Myers, FL
When diving dry
For me, when I breathe a tank down toward the end of a dive, I have much better trim in the water with a larger steel tank. Aluminum 80s tend to make me "light" from the waist down once I get below 1000 pounds.
JAG
For me, when I breathe a tank down toward the end of a dive, I have much better trim in the water with a larger steel tank. Aluminum 80s tend to make me "light" from the waist down once I get below 1000 pounds.
JAG
Industry standard Catalina S80 AKA Genesis Aluminum 80 cylinder...
7.25 inch diameter
25.8 inches high
31.6 lbs empty dry weight
-1.8 lbs of buoyancy full and +4 empty
Closest physical sized steel cylinder from PST...The E7 100
7.2 inch diameter
24 inches high
32 lbs empty dry weight
-10.3 of buoyancy full and -1.3 empty
So there is your numbers. The 4 lbs of lead you wear to counteract the positive buoyancy of the aluminum cylinder near the end of the dive no longer have to be worn. The start of the dive is not the concern. It's the end. The tank is also around the same dry weight and holds 100 cf of gas at 3441 PSI, 90 cf at 3000 PSI and 80 cf at 2640 PSI. Bonus!
That's weight that serves no purpose until your cylinder empties out that now no longer has to be worn due to the reduced volume vs size of the steel cylinder.
Again you can do the math with whatever cylinder you want. It has nothing at all to do with dry weight. It has to do with buoyancy throughout and especially at the end of the dive.
For example the PST E7-80 is actually only 26 lbs dry but is negative 3.3 lbs in water empty! Less weight on the belt, way lighter tank out of the water. I would say that diving an 80 steel may be pointless for tall people since it is so short my might as well wear the tank on your head. (See concept of trim which I don't think is covered in the PADI EORD but that's not a surprise...)
If you are still having trouble with the concept check out the buoyancy section of the PADI Encyclopida of Recreational Diving or probably somewhere on the web.
Here are some links to tank specs:
Pressed Streel (PST) and Luxfer
Catalina Cylinders
OMS Cylinders
7.25 inch diameter
25.8 inches high
31.6 lbs empty dry weight
-1.8 lbs of buoyancy full and +4 empty
Closest physical sized steel cylinder from PST...The E7 100
7.2 inch diameter
24 inches high
32 lbs empty dry weight
-10.3 of buoyancy full and -1.3 empty
So there is your numbers. The 4 lbs of lead you wear to counteract the positive buoyancy of the aluminum cylinder near the end of the dive no longer have to be worn. The start of the dive is not the concern. It's the end. The tank is also around the same dry weight and holds 100 cf of gas at 3441 PSI, 90 cf at 3000 PSI and 80 cf at 2640 PSI. Bonus!
That's weight that serves no purpose until your cylinder empties out that now no longer has to be worn due to the reduced volume vs size of the steel cylinder.
Again you can do the math with whatever cylinder you want. It has nothing at all to do with dry weight. It has to do with buoyancy throughout and especially at the end of the dive.
For example the PST E7-80 is actually only 26 lbs dry but is negative 3.3 lbs in water empty! Less weight on the belt, way lighter tank out of the water. I would say that diving an 80 steel may be pointless for tall people since it is so short my might as well wear the tank on your head. (See concept of trim which I don't think is covered in the PADI EORD but that's not a surprise...)
If you are still having trouble with the concept check out the buoyancy section of the PADI Encyclopida of Recreational Diving or probably somewhere on the web.
Here are some links to tank specs:
Pressed Streel (PST) and Luxfer
Catalina Cylinders
OMS Cylinders
The most important difference between PST and Fabers is the color. After a couple of years the PSTs will be a dull gray, not the shiny gray they were before two dives. The Fabers will be a rusty brown, no matter how many times you paint them.Mo2vation:
Billseamon posted:
Hieght Weight Empty Buoyancy Full Buoyancy Empty Tank
20.0" 30.9 lbs -10.9 lbs -4 lbs HP 80
24" 39 lbs -14 lbs -7 lbs HP 100
26" 31.7 lbs -1.9 lbs +4 lbs AL 80
Kevin Falconer responded:
Bill, these numbers seem to dispell the myth that the steel
tanks are "heavier" they are sometimes even lighter in the
same cf rating than the aluminum. It's the smaller size of
the tank that makes the steel tanks less positively buoyant.
The tank is smaller because it can be filled to a higher pressure to achieve its' rating.....
Hieght Weight Empty Buoyancy Full Buoyancy Empty Tank
20.0" 30.9 lbs -10.9 lbs -4 lbs HP 80
24" 39 lbs -14 lbs -7 lbs HP 100
26" 31.7 lbs -1.9 lbs +4 lbs AL 80
Kevin Falconer responded:
Bill, these numbers seem to dispell the myth that the steel
tanks are "heavier" they are sometimes even lighter in the
same cf rating than the aluminum. It's the smaller size of
the tank that makes the steel tanks less positively buoyant.
The tank is smaller because it can be filled to a higher pressure to achieve its' rating.....
"Heavier" would typically be in reference to it's buoyancy in water (which is what is important). In this way, steel tanks are heavier. I don't think there are any comparable sized AL tanks that are less buoyant.Falconer:
You may want to take another look at the specs for Al 80 vs the PST 100s. I believe (and I could be wrong) that when I compared them (prior to purchase) I noted that the out of water weight specs for the PST E7 100 includes the weight of the Thermo DIN/Yoke valve. The specs for the AL 80 is for the tank only. When you add the valve it comes out dead even. I have 4 E7 100s (2 for air & 2 EANx) and 2 E7 80s (for the wife and son) and love them. The only problem is sometimes the LDS gives me short fills on them, but even at 3000 PSI I have more gas in the 100s than the other guys in our group (they are still diving Al 80s). I can be a "gas hog" if I want and still be the last to call the dive. It's also nice to lose 6 lbs of dead lead off of my belt.
The only information on Catalina's site says "Buoyancy calculated with a K valve in Seawater. Who knows about dryweight but I have a Genesis valve or two around here. How much weight would you guess it accounts for? About a pound.
Regardless if the Catalina doesn't factor the valve then the steel 100 is even lighter. Which would further the argument for not against.
Regardless if the Catalina doesn't factor the valve then the steel 100 is even lighter. Which would further the argument for not against.
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