jplacson
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Just wondering... what's the advantage of diving steels over AL tanks? Is that how much weight you really need to carry to dive dry?
weight integrated or not
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More gas in a smaller package, without the positive buoyancy shift from neutral, primarily.
An AL80 will go approximately +4 when empty. The PST HP80/100/120 will be approximately -1.5 empty. The HP100 is significantly SHORTER than an AL80, and yet holds 20% more gas.
If you dive air, you can outlast your NDL on most dives on the gas supply if you're a decent breather with AL80s, and the tanks are cheap. That's the good news.
The bad news is that if you dive Nitrox in the range of 60-80' or so, you will almost always hit the gas turn point first, not the NDL unless you are very "light" on your gas consumption. I average about 0.45 on my SAC when "loafing around" and thus the AL80s are enough for most no-deco dives above 100' for me as I run out of time and gas about the same time, but when spearfishing that consumption can get up to the 0.6-0.7 range - a major increase - due to the level of work involved. If I dive AL80s when spearing I will almost always hit my turn pressure long before I hit the NDL, and I have far less gas reserve to shoot a big fish with towards the end of the dive. This means many missed opportunities, as going OOA at 100' with a big AJ on the line is a good way to get bent or worse. Thus, I tend to dive steelies when I am spearing for the additional supply and safety factor they provide. If you hoover the gas (SACs much above 0.6 or so) then steelies are the "right" tank irrespective of your activity if you're diving Nitrox.
I have two HP100s and one HP120. There are times I like the HP120 and may even put an "H" valve on it, as an HP120 with an "H" valve would make a nearly-complete-redundant kit for light deco dives and eliminate the need for me to carry a pony for that purpose, yet have enough gas for me to make some significant deco incursions without running low on gas. This is unsafe without the "H" valve though as a first-stage reg failure (uncommon, but possible) or freeflow could really hose you.
I also like the HP120 a LOT if I intend to do two shallow (under 80' or so) dives with a short SI in a day, as I need to take only ONE tank. There I am limited by the NDL to ~70 minutes of total exposure across the two dives, and the single HP120 is enough gas for both.
Likewise, the HP100s, doubled, make an awesome kit for moderate deco dives, as they have enough gas for some pretty serious exposures and with the manifold carry enough safety to do so. If you lose your deco bottle for some reason there is enough backgas to deco out on the backgas (assuming Nitrox here) for most reasonable exposures, although the hang will get kinda long. They also permit two dives sequentially without changing things out - the first as a deco dive, the second with remaining gas as a NDL dive. That is also a very attractive option, and for many divers the latter can be done without ANY weight in a light to moderate wetsuit with an AL plate, or dry in a steel plate with only moderate weight on the belt.
An AL80 will go approximately +4 when empty. The PST HP80/100/120 will be approximately -1.5 empty. The HP100 is significantly SHORTER than an AL80, and yet holds 20% more gas.
If you dive air, you can outlast your NDL on most dives on the gas supply if you're a decent breather with AL80s, and the tanks are cheap. That's the good news.
The bad news is that if you dive Nitrox in the range of 60-80' or so, you will almost always hit the gas turn point first, not the NDL unless you are very "light" on your gas consumption. I average about 0.45 on my SAC when "loafing around" and thus the AL80s are enough for most no-deco dives above 100' for me as I run out of time and gas about the same time, but when spearfishing that consumption can get up to the 0.6-0.7 range - a major increase - due to the level of work involved. If I dive AL80s when spearing I will almost always hit my turn pressure long before I hit the NDL, and I have far less gas reserve to shoot a big fish with towards the end of the dive. This means many missed opportunities, as going OOA at 100' with a big AJ on the line is a good way to get bent or worse. Thus, I tend to dive steelies when I am spearing for the additional supply and safety factor they provide. If you hoover the gas (SACs much above 0.6 or so) then steelies are the "right" tank irrespective of your activity if you're diving Nitrox.
I have two HP100s and one HP120. There are times I like the HP120 and may even put an "H" valve on it, as an HP120 with an "H" valve would make a nearly-complete-redundant kit for light deco dives and eliminate the need for me to carry a pony for that purpose, yet have enough gas for me to make some significant deco incursions without running low on gas. This is unsafe without the "H" valve though as a first-stage reg failure (uncommon, but possible) or freeflow could really hose you.
I also like the HP120 a LOT if I intend to do two shallow (under 80' or so) dives with a short SI in a day, as I need to take only ONE tank. There I am limited by the NDL to ~70 minutes of total exposure across the two dives, and the single HP120 is enough gas for both.
Likewise, the HP100s, doubled, make an awesome kit for moderate deco dives, as they have enough gas for some pretty serious exposures and with the manifold carry enough safety to do so. If you lose your deco bottle for some reason there is enough backgas to deco out on the backgas (assuming Nitrox here) for most reasonable exposures, although the hang will get kinda long. They also permit two dives sequentially without changing things out - the first as a deco dive, the second with remaining gas as a NDL dive. That is also a very attractive option, and for many divers the latter can be done without ANY weight in a light to moderate wetsuit with an AL plate, or dry in a steel plate with only moderate weight on the belt.
I normally dive steel 72's and sold off the Al 80's years ago. I found I could remove about 4 lbs of weight moving from a AL80 to a Steel 72 and this added up to 8 lbs less weight with doubles.
With twin 72's and a stainless steel backplate I can dive with 12 lbs of weight in the weight pocktes and still be neutral at 15 ft with near empty tanks, a 7mm semi-dry, a 5/7mm cheater hood, 7mm boots and 5mm gloves. The same weight works with my dry suit and dry gloves as well and I can get by with 4-5 lbs less weight in warmer water with lighter underwear.
This is an improvement over the 20 lbs of weight required with twin AL 80's in my semi-dry or drysuit. The AL 80's are also larger and heavier than the steel 72's the total weight of the rig was about 12-15 lbs heavier with twin 80's as opposed to twin 72's.
On the plus side, the positive bouyancy of the AL 80's give you a bit more stablity and it is much like swimming around under a blimp. On the other hand, with a backplate I have never had a stability problem swimming around under negatively bouyant tanks.
Weight integration does mean that you have a lot of weight on your shoulders on the boat, but it also means none of it is on your back during the dive. I have never actually weighed my rig, but I would estimate that with Steel 72's two regs, weights and backplate that it weighs 85-90 lbs with full tanks. However, this is a lot but better than the 100 or so pounds that the same rig with twin 80's would weigh.
The total weight is one reason I use a cross over tech BC (a Genesis Recon with the Stainless steel plate kit.) The wide straps and general design carries the weight more comfortably than a backplate and web harness. I liked back inflation when I first started diving in the late 70's but never liked the web harness used on back inflates at the time. And being older, I still don't like the web harness.
One thing with interagred weight pockets is that they can be hard to insert properly even on the boat. I have found a piece of stiff plastic cut to the shape of the pocket helps. You insert it into the pocket in the BC before the weight pouch and it allows the weight pouch to slide past the velcro inside the pocket that utimately retains the pouch. You pull the plastic out and then the fully inserted pocket can engage the velcro.
Otherwise the velcro engages before the pouch is fully inserted preventing it from fully seating and making it more likely to come loose. This places nearly all of the burden of retention on the flap over the front of the pouch.
This really becomes an issue with fairly full and bulky weight pouches that are harder to insert and at the same time are the ones that will place the most strain on the retaining system.
They require some care and the velcro needs to be kept clean, but I would not call them inherently unsafe.
The most likely place for an inadvertant ditch with velcro retained weight pocket is at the surface if you trip over your fins on the giant stride entry and do a face plant. But then you are still on the surface so it is just an economic rather than saftey issue.
Velcro retaining systems are much like diving in general, it's unsafe only if you do it wrong.
The most likely place for an inadvertant ditch with velcro retained weight pocket is at the surface if you trip over your fins on the giant stride entry and do a face plant. But then you are still on the surface so it is just an economic rather than saftey issue.
Velcro retaining systems are much like diving in general, it's unsafe only if you do it wrong.
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