I don't totally disagree with the above advice but there is a more moderate view point as well.
If you buy something well the first time you never have to buy it again, and from that perspective buying the right tank rather than the more or less standard, does nothing real well but everybody has one AL 80 makes sense.
There a few very good options other than an AL 80. For example:
1. The Worthington X7-100 3442 psi tank is excellent as is the PST E7-100 (same basic tank different manufacturer.) They weigh only a couple pounds more than an AL 80 (33 versus 31) , but are -2.5 lb bouyant when empty compared to +4.4 lbs for an AL 80, so if you are using lead weights, you can drop 7 pounds compared to what you currently use with an AL 80. That ends up being a net savings in weight of 5 lbs in total weight carried. It is a couple inches shorter than an AL 80 and the same diameter and holds an honest 100 cu ft as opposed ot the 77 cu ft in an AL 80. A lot more gas in a smaller package with better bouyancy traits. The lenght and trim characteristics work very well for all but the tallest divers.
2. The Worthington X8-130 is the same lenght as an AL 80 but slightly larger in diameter (8.0" compared to 7.25"). It is however substantially heavier at 43 lbs. But it again offers 130 cu ft at 3442 psi and its size and bouyancy traits make it ideal for user as either a single or as doubles for just about anyone able to carry the weight, but it is not as bad as it seems at first glance. They are also -2.5 lbs when empty so you are again saving 7 pounds of lead compared to what you carry with an AL 80 so the net increase in weight is only 5 lbs.
3. LP 95's are popular in places where you can get an overfill to 3600 psi (they are normally a 2400 psi tank with a plus rating fill of 2640 psi, where they hold 95 cu ft.) Faber LP 95's are significantly lighter than PST or worthington LP 95's 37 pounds versus 42 pounds, but all of them will hold 130 cu ft at 3600 psi and 95 cu ft at 2640 psi. They are very similar in lenght to a 3442 psi 100 cu ft tank but are larger in diameter, 8.0" rather than 7.25". They also trim out well for nearly everyone and they are -3.3 lbs bouyant when empty, so again if you use at least 8 pounds of weight, you can take 7.7 of it off and still save about a pound and a half in total weight compared to an AL 80.
4. LP 85's are popular as well. They are the same height and weight as an AL 80 but thinner at 7.0" in diameter. They are basically neutral when empty so you are again saving 4.4 lbs in total weight compared to an AL 80 if you need more than 4.4 lbs of lead weight to achieve neutral bouyancy. They hold 85 cu ft at 2640 psi and if you do not get the plus rating renewed at the first hydro test, they will hold only 77 cu ft at 2400 psi - the same as an AL 80.
There are other tanks available, but they are either very large, very heavy, very negatively bouyant, very tall, or have some other factor that limits their utility or desireability to a fairly limited number of divers.
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I am not opposed to technically inclined divers getting into doubles early on. It is not rocket science and they are different with more mass, but they are not overly difficult to dive - unless you have excessively large, tall or negatively bouyant doubles. If you stick with the ones listed above, they are not hard to dive at all.
It does make sense to get some instruction or mentoring to assist you in setting them up and helping you with a configuration that will be compatible with technical diving later on, but again it is not rocket science and is not hard to accomplish. As long as you start out right you will not develop bad habits and the experience will put you well ahead of the curve when you do start taking technical courses. Some will say you need to know procedures valve drills, etc, but in point of fact that can come later as you will essentially be diving them as a large single within the no deco limits and single tan procedures still work just fine if you use a set of doubles on what amounts to single tank dives.
In the vent you do go the AL 80 route, that is not all bad. Double AL 80's are exceptionally stable in the water and make good first doubles. And if you advance to deeper techncial double swith larger tanks, your old AL 80's will make great deco or stage bottles and the bands and manifold will work with any 7.25" diameter tanks.
The old steel 72's also make exceptional first doubles as they are comparatively lightweight, trim out well, have excellent bouyancy traits (about -1.5 lbs negative per tank when empty, but they vary a bit), and are fairly inexpensive to acquire.
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With a large single or set of doubles, there is a degree of increased diver responsibility as all that gas can get you into serious decompression if you do not mind your NDL's and that is the basis for most of the advice that divers not move to a larger single or doubles too soon. But I am big on personal responsibility and frankly, there are times when being really fat on gas is nice.
You also need to consider the swing weight of the gas. A large single like a 130 will have about 8 pounds of swing weight (the weight of the gas in the tank that you breath during the dive, making the tank that much more bouyant by the end of the dive) compared to only 5 for an AL 80. Double 100's have abnout 12.5 pounds of swing weight and double 130's have 16. Since you must be abel to be neutral with near empty tanks at the end of the dive, that will mean you woudl be 16 pounds negative at the start of the dive with double 130's. So you have to offset that with 16 pounds of lift in the wing (most wrap around jacket style BC's do not work real well with doubles) plus whatever bouyancy your wet suit loses at depth - perhaps another 15 pounds with a 7mm wet suit. That large an air volume can be harder to manage so your bouyancy skills have to be much better.
pd::scubadive:
