Which tank is best?

Even though 95% of my diving is resort diving, I am considering getting a pair of tanks for my occasional Gulf dives. I always just assumed I would go out and get AL80s but now after a little research I find several options.
What is the difference in LP and HP steel tanks? What are the advantages and disadvantages? PSI/BAR is one measuring stick but really the important thing is volume of gas in the tank so what difference is there in the LP and HP?
Also, knowing that steel is going to be negative start and finish makes them appealing but I also know that AL is popular for a reason and it isnt just price of the tank, or is it?
I like the size of the LP77 steel tanks, shorter than the AL80s, and can have as much cubic feet of gas. But to hold that, doesnt the steel have to be juiced up some, meaning overfilled?
And that leads to the question that if everyone says just go ahead and overfill your steel tank to get that little extra gas, what is the purpose of calling it a 77 when the consumer will make it something more?
I realize this rattles on but what I am asking is, if I can get worthington LP77s for slightly more than I would pay for Luxfer AL80s, should I do it?
Oh, in the event it is relevant, I pretty much only do warm water, mostly carribean, Bahamas, Gulf of Mexico off the Florida coast. Rare, rare dip in a Florida spring that I consider chilly but as things go, is probably not very cold. (68-70F) I generally wear a 1/2mm or 1 mm full suit. With those chilly dips, I dig out the heavy suits, either a full 3/2 or 4/3.

Hello Cdiver:
We named the LP77 for the reason that it has a capacity of 77 cubic feet at the maximum working pressure (2640 psi - 2400 psi + 10%) as allowed by DOT.

Though the external dimensions of a standard aluminum 80 is greater, it is the LP77 that has a greater internal volume. The difference is because the AL80 has a much greater wall thickness. An AL80 holds 678 cubic inches of water volume and the LP77 is 798 cubic inches. If both cylinders were filled to an equal pressure the LP77 will always have greater volume of gas. When the AL80 is filled to 3000 psi it essentially has the same volume of gas as the LP77 filled to 2640 psi.

With the skyrocketing cost of aluminum, we are close to the day when you'll find both cylinders at your local dive store for nearly the same cost. Take into account that the LP77 has a round bottom and will generally include a boot with an added value of $10.00. The AL80 has a flat bottom and rarely includes a boot.

As posted by many divers on this forum, the LP77 in many cases is a better cylinder for the average recreational diver.

You can find much more information at this thread:http://scubaboard.com/showthread.php?t=180070&highlight=LP77

Carribeandiver:

I like the size of the LP77 steel tanks, shorter than the AL80s, and can have as much cubic feet of gas. But to hold that, doesnt the steel have to be juiced up some, meaning overfilled?
And that leads to the question that if everyone says just go ahead and overfill your steel tank to get that little extra gas, what is the purpose of calling it a 77 when the consumer will make it something more?

Click to expand...

The only reason the AL80 is popular is price. Steel will last longer and has better buoyancy characteristics.

The difference between LP and HP steel is nothing more than the rated pressure. A LP108 is pretty much the same tank in size and weight as an HP130 (the 108 is slightly bigger but not much).

As far as the overfill stuff, every new steel tank should have the + rating which means it can be filled to 2640 (or 4000 in some parts of the country ) which will give it its rated capacity. When you do your first hydro, request the + testing and it will continue to be rated to 2640.

I wouldnt let coming with a boot or not decide if you get steel or AL, but I would recommend the Steel....The prices are becoming so close and the benefits of the steel are worth the price difference.

My question is you talk about diving the bahamas and carribean, Are you planning on taking the tanks with you?

When I was first certified a then friend suggested we do a remote dive trip where we would dive over two or three days. Not knowing any better at the time I bought enough AL80s to give me enough gas for the trip. After all that is what I certified with and was familiar with and that he recommended.

(Side note: Just before the trip he told me he decided to play golf instead of scuba that summer so the trip was never made.)

Had I to do it all over again I'd have followed this process:
-Figured out how much gas I needed for each dive in my occasional local diving. That would have given me the capacity of each tank.
-Added the number of tanks I needed to carry me over between refills.
-Considered how much weight I wanted to add over my basic rig.

In my case that would have resulted in a pair of steel tanks in the 100 - 120 cf range.
I've dived aluminium tanks in various sizes and steels from 85 - 120 cf. I like steel 100s best. But, that is just me. Others may be different.

So, my recommendation is to do the same. Figure out what your gas needs are for your dives, how often you want to, or can, refill the tanks and buy steel tanks to match.

Edited to add ditchable weight comment:
If the resulting tank(s) don't give you any ditchable weight I'd consider going to something lighter to mount it on. Something like an aluminium bp or a transpacII, or somesuch.

If you don't do much local diving, why not just rent? In my area (SF bay area),
I can rent a tank for $9-$10 for a week. If I go back to the shop, some will fill it
for free while rented.

Since you are wearing almost no suit, you probably shouldn't get a tank that is
too negatively buoyant. Something like a modern LP85 or LP77 or LP80 would be nice. My Worthington HP80 starts at 10.5# negative when full (11.5# in fresh water), which means I would sink without any lead, if diving in no suit and if had a BC failure. I haven't personally had the opportunity to dive steel in warm water. I don't really have any problem with aluminum in warm water, except that it would be nice to have a somewhat shorter (steel) tank.

It is nice to have your own tanks, because you can keep them filled and ready to go all the time.

What size tank is best for you depends on several factors:

1) your typical depth (assume 75 ft)
2) your typical comfortable dive time (assume 30 mins)
3) your surface consumption rate (assume SCR = 0.6 cu ft per min)
4) your desired reserve (assume rule of thirds)

Now do the math:

[ (75 ft / 33 ft ) + 1 ] x 0.6 x 30 x 3 / 2 = 88 cu ft

Next you would need to look at the buoyancy characteristics of the various tanks in that size, aluminum or steel, and decide which best fits your needs. The general rule is steel with drysuits, or aluminum with wetsuits.

If you want a longer dive time (remembering your NDL limits), you would need to re-do the calculation and compute a larger tank.

Or you can try out several types and sizes of tanks, and see from experience which works best for you. Most people probably have used this latter approach.

Dive Right In Scuba:

I wouldnt let coming with a boot or not decide if you get steel or AL, but I would recommend the Steel....The prices are becoming so close and the benefits of the steel are worth the price difference.

My question is you talk about diving the bahamas and carribean, Are you planning on taking the tanks with you?

Click to expand...

NO, the tanks are for my occasional trips to the Florida panhandle or springs. I realize my travel will still mean I get AL80s from the liveaboard or resort.