Re: Tank Recommendations

Outer Bamnks diving on the Great Escape Southern California Live-Aboard Dive Boat

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Posted by Kendall Raine on February 06, 2007 at 08:13:33:

In Reply to: Tank Recommendations posted by Second Fiddle on February 05, 2007 at 12:33:18:

One way to think about it is to figure out what type of diving you do and go from there.

1. Are you diving wet or dry or both
2. What's your tolerance for cold
3. How many dives a day do you do
4. What are you breathing
5. How much deco do you want to do
6. How strong a swimmer are you
7. How much do you want to spend
8. Do you mind short fills

With a high capacity tank-95 or bigger-the weight of the gas (air or nitrox doesn't make a big difference) can become a buoyancy issue. If you're diving a high capacity tank wet, the compression of the wetsuit and the weight of a full tank need to be accounted for such that you can get up from, say 100, if your BC fails. Underweighting isn't the solution so having enough ditchable weight to recover from a deep BC failure needs to be accounted for. Are you more than 10 lbs negative at any point in the dive? If so, can you ditch enough weight to get up in a slow and controlled manner? I wouldn’t count on being able to swim up being more than 10 lbs negative. Maybe not even that. If you’re diving dry, maybe the weight of the steel means you can take weight off the belt. Wet or dry, you should be able to complete deco with an empty tank.

If you're diving wet, how long do you want to be in the water per dive and per day? Do you need all the gas of the high capacity tank offers. If you get cold after 30-40 minutes and you have a reasonable consumption rate, do you really need more than 80 cu. ft. (77)?

Are you breathing air or nitrox. If nitrox, the higher capacity tank means you don't need refills as often. Many boats don't pump nitrox so this could be an issue and an advantage to a higher capacity tank.

How long do you want to deco? The more gas you carry the longer you can stay and the more deco you need to do. If you're diving wet, how much deco should you be doing in California waters? Staying inside the NDL's sounds good, but you should be doing some deco on every dive, particularly if you're diving many times a day. Your computer can't get bent but you can.

The bigger the tank the more it tends to roll. The bigger the tank, the more weight you have full. It takes more effort to swim a big steel around than an AL 80. How hard to you want to work? Empty steels generally weigh more than empty aluminums.

Steels cost around 2.5x aluminums.

Most boats won't come close to giving you a 3500 psi fill. The time and wear on the compressor it takes to go the last 500 psi isn't cost/time effective for the boats. Forget what their capacity is or what they say they can do. The question is how high will they typically fill your tanks. On a busy day when they're filling 30 tanks in an hour, your fills will be fast and hot. Figure on 2800 to 3000 under those conditions.

Frankly, the right tank is the smallest that will let you do what you want to do safely and no smaller.

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