Living the US for two years - what should my strategy for tanks be?

[inquis]

The HP100:s buoyancy profile seems to be very negative, almost 8 pounds per tank at full and slightly negative even at empty, which I'm not sure I like.

What matters is the empty buoyancy minus perhaps a pound for reserve air. Contrast this, for example, to an AL tank, with a positive empty buoyancy -- you have to then carry something else (e.g., lead or steel backplate) to compensate back to at least neutral. This is one reason steel tanks are loved by many. The additional gas is another (when compared to the very common AL80). Not a problem for single-tank diving in a wetsuit.

ETA: For double-tank diving in a wetsuit, the issue you face with a wing failure is the same regardless of steel or AL tank. It's just a question of whether you can swim up to compensate the full buoyancy and buoyancy lost to wetsuit compression. If not, then you'll need to be able to drop enough lead to get off the bottom to where the suit regains buoyancy. It is for the redundant buoyancy that drysuits are preferred for doubles (and warmth, of course).

 

[inquis]

You may not realize it, but the LP85s are 13.0L cylinders and HP100s are 12.9L. Approximately the same amount of gas at the same pressure, but the latter is more likely to be filled to a higher pressure in your area.

 

[IrenePanik]

There are no aluminum LP tanks for SCUBA. Those are a steel tank of probably 18L.
You want to be looking for some HP100s, they are common.

There are no aluminum LP tanks for SCUBA. Those are a steel tank of probably 18L.
You want to be looking for some HP100s, they are common.

That's probably what it was. I know of some mine divers back home who used those sizes before they took the jump over to rebreathers.

 

[IrenePanik]

What matters is the empty buoyancy minus perhaps a pound for reserve air. Contrast this, for example, to an AL tank, with a positive empty buoyancy -- you have to then carry something else (e.g., lead or steel backplate) to compensate back to at least neutral. This is one reason steel tanks are loved by many. The additional gas is another (when compared to the very common AL80). Not a problem for single-tank diving in a wetsuit.

ETA: For double-tank diving in a wetsuit, the issue you face with a wing failure is the same regardless of steel or AL tank. It's just a question of whether you can swim up to compensate the full buoyancy and buoyancy lost to wetsuit compression. If not, then you'll need to be able to drop enough lead to get off the bottom to where the suit regains buoyancy. It is for the redundant buoyancy that drysuits are preferred for doubles (and warmth, of course).

If you have the drysuit as a compensation, I fully agree! In a theoretical case of a wetsuit, if you were diving doubles that are as heavy in the water as HP100:s I think you wouldn't be able to be weighted correctly to handle a bcd failure.

 

[IrenePanik]

You may not realize it, but the LP85s are 13.0L cylinders and HP100s are 12.9L. Approximately the same amount of gas at the same pressure, but the latter is more likely to be filled to a higher pressure in your area.

Since I already have butt and v-weight on my setup for 2x12, this would make a lot of sense then. Might just as well have heavier tanks and forgo those weight.

 

[Jim Lapenta]

Since I already have butt and v-weight on my setup for 2x12, this would make a lot of sense then. Might just as well have heavier tanks and forgo those weight.

Given your current location, there is only one place I would consider for used cylinders.
Tracy at Below the Grade Scuba in Livonia, Michigan, which, all said and done, isn't that far from you.
Tracy is a member on here and I used to send all my students to him for steel cylinders.
I'm not sure about now but I know he used to have more sets of used doubles and single cylinders for sale than all but the biggest dive shops. And for sure a better selection of sizes.

Below the Grade Scuba

belowthegrade.com

@Tracy

 

[inquis]

If you have the drysuit as a compensation, I fully agree! In a theoretical case of a wetsuit, if you were diving doubles that are as heavy in the water as HP100:s I think you wouldn't be able to be weighted correctly to handle a bcd failure.

Yes, thick wetsuit+AL doubles is more common. The feasibility of steel doubles will greatly depend on your other equipment choices. Double AL80s, for instance, require about 10 lbs more ballast (negatively buoyant "stuff") than HP100s to be neutral. Typically, much of that ballast is in the form of lead, which can be ditched if the wing completely died. (Ditching a little less than the remaining non-reserve gas makes you neutral at the safety stop again.) HP100s, in contrast, don't need that 10 lbs of ballast, so there may be a less than ideal amount of ditchable ballast (i.e., lead) available in such a scenario.

It's an open question whether your kicking strength can make up for that deficiency. Other options are to deploy a DSMB, rely on a buddy, or orient the damaged portion of the wing down low to restore partial buoyancy.

It sounds like you're going to run doubles, so you've got some choices to make. [ETA: including perhaps using an AL backplate] One tool that may be of use is the calculator at buoyancy.cc or the more comprehensive spreadsheet that inspired that web tool.

 

[IrenePanik]

Yes, thick wetsuit+AL doubles is more common. The feasibility of steel doubles will greatly depend on your other equipment choices. Double AL80s, for instance, require about 10 lbs more ballast (negatively buoyant "stuff") than HP100s to be neutral. Typically, much of that ballast is in the form of lead, which can be ditched if the wing completely died. (Ditching a little less than the remaining non-reserve gas makes you neutral at the safety stop again.) HP100s, in contrast, don't need that 10 lbs of ballast, so there may be a less than ideal amount of ditchable ballast (i.e., lead) available in such a scenario.

It's an open question whether your kicking strength can make up for that deficiency. Other options are to deploy a DSMB, rely on a buddy, or orient the damaged portion of the wing down low to restore partial buoyancy.

It sounds like you're going to run doubles, so you've got some choices to make. [ETA: including perhaps using an AL backplate] One tool that may be of use is the calculator at buoyancy.cc or the more comprehensive spreadsheet that inspired that web tool.

Thanks so much for the link! Right now I have a more rudimentary document for different water temperatures, salt/fresh water and stage-bottles, but not different tank sizes.

 

[inquis]

Adjustment for salt is easy: ¼ lb for every 10 lbs of diver+gear weight.