Guy Alcala
Contributor
I was a bit unsure whether I should post this here, in the DIR or Hogarthian forums, or in the Tanks, bands and valves forum. But I figure most of our local tech divers follow one or all of these, so decided to try it here.
As many of you know, I plan to go tech so I can dive deep wrecks. I'll be taking Fundies in the not too distant future in a borrowed set of doubles and wing (thanks to Dan Bermingham), but as soon after that as money allows I'll want to buy a set of tanks that are more suitable for doubling than my Asahi 100s. From talking to numerous people and researching, I've narrowed down my choices for my first set of doubles to either HP100s or LP85s. Having perused spec sheets and figured out where I think my diving is likely to go, I've narrowed down my options to 4 different tanks from three manufacturers. In no particular order, they are: Faber LP85; Worthington LP85; PST E7-100; Worthington X7-100.
My only doubles experience to date consists of about 45 minutes spent in a pool with a pair of Faber LP85s, which seemed to trim perfectly, but given my total lack of experience and the lack of weight needed that doesn't necessarily mean much. So, I'd like to hear from those of you who have experience with using one or (preferably) more than one of these tanks doubled, as far as trim, whether you use an Al or S/S BP, and any other good/bad points you've found. For LP tanks, if you know of an East/South Bay (Hayward south, off 880 or 101) or Monterey shop that will routinely do overfills for Nitrox and/or tri-mix, please give that info (via PM if you think they'd prefer not to say so publicly). I only know of two shops in the SF Bay and Monterey areas that do tri-mix: AWS and Bamboo Reef, and AWS isn't convenient for me owing to their hours and location.
Just so you understand where I'm coming from, I plan to use these tanks for local shore and boat diving in Monterey, and probably in SoCal, with the option of diving them wet there if reasonable. I'm 6', 180 lb., and expect to eventually progress to the Tech 2/2+ level or thereabouts, but these tanks only have to be suitable for Tech 1/1+ dives or the non-GUE equivalent, although if they're okay beyond that, terrific. I'm currently +18 lb. buoyancy in my drysuit and single-layer fleece, but for prolonged deco I expect that warmer insulation will increase that to +22 to +24 lb. So I need to have a balanced rig that's -22 to -24 lb. negative at the end of the dive (500 PSI), preferably with some margin to allow me to shift weight for trim. I own a S/S BP, and not having to buy an Al BP at the same time as the tanks would be an advantage, albeit not a requirement.
For the sake of argument, all the above tanks can be assumed to be used with the following nominal equipment and buoyancy:
S/S BP @ -6 lb.; 2 regs, hoses etc. @ -4 lb; bands, bolts and crossbar @ -4 lb.; and can light & 2 back-up lights @ -3 lb.
Total -17 lb.
or
Al BP @ -2 lb.; 2 regs @ hoses @ -4 lb; bands, bolts and crossbar @ -4 lb.; and can light & 2 back-up lights @ -3 lb.
Total -13 lb.
Thanks,
Guy
P.S. For those who're interested, here's the relevant specs, empty weight/tank, and approximate buoyancy (air @ 500 PSI) doubled, and what I think are the relative advantages and disadvantages of the tanks:
Faber LP85 (85 cu. ft. actual), 25.98" x 7.01", 31.2 lb, +2.2 lb.. Total negative buoyancy with standard gear: S/S BP -14.8; Al BP -10.8 lb.
Advantages. Lightest tanks; could be used locally with S/S backplate with lots of weight left over for trim; easy to get full fill; could be used in SoCal with Al BP for wetsuit diving; taller than others so allows more trim shift; less expensive than X7s.
Disadvantages. Odd diameter so bands can only be used for these tanks; likely more subject to external corrosion than hot-dipped glavanized tanks; require overfill to ~3100 PSI to get 100 cu. ft./tank, which many LDS may not be willing to do.
Worthington LP85 (82.9 cu.ft. actual), 24.7" x 7.25", 34.3 lb., -3.8 lb. Total negative buoyancy with standard gear: S/S BP, -20.8 lb. Al BP, -16.8 lb.
Advantages. Can probably be used locally with S/S BP with enough weight left over for trim; standard diameter so bands could also be used on Al 80, HP80, HP100 or HP120 tanks; marginally acceptable for SoCal wetsuit diving with Al BP; easy to get full fills, second tallest tank so can be moved for trim; Hot-dipped galvanized with lifetime warranty against external corrosion; less expensive than Fabers or X7s.
Disadvantages. Heaviest of the four tanks; smallest capacity at working pressure; need overfill to approx. 3200 PSI to get 100 cu.ft., which many LDS won't do.
PST E7-100 (100? cu. ft. actual), 24" x 7.25", 33 lb. (one source claims that includes the valve), -4.2 lb. Total negative buoyancy with S/S BP, -21.2 lb. Al BP, -17.2 lb.
Advantages. Maybe lighter than X7s; can probably be used locally with S/S BP, with enough weight left over for trim; standard bands can be used on variety of tanks; marginally acceptable for SoCal wetsuit diving with Al BP; tied for shortest tank, easy to carry and store; Hot-dipped galvanised; no issues with + ratings or overfills; Used, so may be less expensive.
Disadvantages. Company out of business so only available used; may be more likely to fail hydro than other tanks; may be too short to alter trim much by moving tanks in bands; May have trouble getting full fill.
Worthington X7-100 (99.5 actual), 24" x 7.25", 33 lb., -7.2 lb. Total negative buoyancy with S/S BP -24.2 lb. Al BP -20.2 lb.
Advantages. Hot-dipped galvanised with excellent warranty; standard diameter, so bands can be used with variety of tanks; make good single tanks; no issues with + ratings or overfills; tied for shortest tanks, so easy to store and carry.
Disadvantages. Marginal for using locally with S/S BP, will almost certainly need Al BP; unacceptable for SoCal wetsuit diving; most expensive; May be too short to alter trim much by moving tanks in bands; may have trouble getting full fill.
As many of you know, I plan to go tech so I can dive deep wrecks. I'll be taking Fundies in the not too distant future in a borrowed set of doubles and wing (thanks to Dan Bermingham), but as soon after that as money allows I'll want to buy a set of tanks that are more suitable for doubling than my Asahi 100s. From talking to numerous people and researching, I've narrowed down my choices for my first set of doubles to either HP100s or LP85s. Having perused spec sheets and figured out where I think my diving is likely to go, I've narrowed down my options to 4 different tanks from three manufacturers. In no particular order, they are: Faber LP85; Worthington LP85; PST E7-100; Worthington X7-100.
My only doubles experience to date consists of about 45 minutes spent in a pool with a pair of Faber LP85s, which seemed to trim perfectly, but given my total lack of experience and the lack of weight needed that doesn't necessarily mean much. So, I'd like to hear from those of you who have experience with using one or (preferably) more than one of these tanks doubled, as far as trim, whether you use an Al or S/S BP, and any other good/bad points you've found. For LP tanks, if you know of an East/South Bay (Hayward south, off 880 or 101) or Monterey shop that will routinely do overfills for Nitrox and/or tri-mix, please give that info (via PM if you think they'd prefer not to say so publicly). I only know of two shops in the SF Bay and Monterey areas that do tri-mix: AWS and Bamboo Reef, and AWS isn't convenient for me owing to their hours and location.
Just so you understand where I'm coming from, I plan to use these tanks for local shore and boat diving in Monterey, and probably in SoCal, with the option of diving them wet there if reasonable. I'm 6', 180 lb., and expect to eventually progress to the Tech 2/2+ level or thereabouts, but these tanks only have to be suitable for Tech 1/1+ dives or the non-GUE equivalent, although if they're okay beyond that, terrific. I'm currently +18 lb. buoyancy in my drysuit and single-layer fleece, but for prolonged deco I expect that warmer insulation will increase that to +22 to +24 lb. So I need to have a balanced rig that's -22 to -24 lb. negative at the end of the dive (500 PSI), preferably with some margin to allow me to shift weight for trim. I own a S/S BP, and not having to buy an Al BP at the same time as the tanks would be an advantage, albeit not a requirement.
For the sake of argument, all the above tanks can be assumed to be used with the following nominal equipment and buoyancy:
S/S BP @ -6 lb.; 2 regs, hoses etc. @ -4 lb; bands, bolts and crossbar @ -4 lb.; and can light & 2 back-up lights @ -3 lb.
Total -17 lb.
or
Al BP @ -2 lb.; 2 regs @ hoses @ -4 lb; bands, bolts and crossbar @ -4 lb.; and can light & 2 back-up lights @ -3 lb.
Total -13 lb.
Thanks,
Guy
P.S. For those who're interested, here's the relevant specs, empty weight/tank, and approximate buoyancy (air @ 500 PSI) doubled, and what I think are the relative advantages and disadvantages of the tanks:
Faber LP85 (85 cu. ft. actual), 25.98" x 7.01", 31.2 lb, +2.2 lb.. Total negative buoyancy with standard gear: S/S BP -14.8; Al BP -10.8 lb.
Advantages. Lightest tanks; could be used locally with S/S backplate with lots of weight left over for trim; easy to get full fill; could be used in SoCal with Al BP for wetsuit diving; taller than others so allows more trim shift; less expensive than X7s.
Disadvantages. Odd diameter so bands can only be used for these tanks; likely more subject to external corrosion than hot-dipped glavanized tanks; require overfill to ~3100 PSI to get 100 cu. ft./tank, which many LDS may not be willing to do.
Worthington LP85 (82.9 cu.ft. actual), 24.7" x 7.25", 34.3 lb., -3.8 lb. Total negative buoyancy with standard gear: S/S BP, -20.8 lb. Al BP, -16.8 lb.
Advantages. Can probably be used locally with S/S BP with enough weight left over for trim; standard diameter so bands could also be used on Al 80, HP80, HP100 or HP120 tanks; marginally acceptable for SoCal wetsuit diving with Al BP; easy to get full fills, second tallest tank so can be moved for trim; Hot-dipped galvanized with lifetime warranty against external corrosion; less expensive than Fabers or X7s.
Disadvantages. Heaviest of the four tanks; smallest capacity at working pressure; need overfill to approx. 3200 PSI to get 100 cu.ft., which many LDS won't do.
PST E7-100 (100? cu. ft. actual), 24" x 7.25", 33 lb. (one source claims that includes the valve), -4.2 lb. Total negative buoyancy with S/S BP, -21.2 lb. Al BP, -17.2 lb.
Advantages. Maybe lighter than X7s; can probably be used locally with S/S BP, with enough weight left over for trim; standard bands can be used on variety of tanks; marginally acceptable for SoCal wetsuit diving with Al BP; tied for shortest tank, easy to carry and store; Hot-dipped galvanised; no issues with + ratings or overfills; Used, so may be less expensive.
Disadvantages. Company out of business so only available used; may be more likely to fail hydro than other tanks; may be too short to alter trim much by moving tanks in bands; May have trouble getting full fill.
Worthington X7-100 (99.5 actual), 24" x 7.25", 33 lb., -7.2 lb. Total negative buoyancy with S/S BP -24.2 lb. Al BP -20.2 lb.
Advantages. Hot-dipped galvanised with excellent warranty; standard diameter, so bands can be used with variety of tanks; make good single tanks; no issues with + ratings or overfills; tied for shortest tanks, so easy to store and carry.
Disadvantages. Marginal for using locally with S/S BP, will almost certainly need Al BP; unacceptable for SoCal wetsuit diving; most expensive; May be too short to alter trim much by moving tanks in bands; may have trouble getting full fill.
Do you own your own compressor or does one of your friends? I do not know a single dive shop around that will overfill that much. 
If I need MORE gas I pump them up to 4200 psi, giving me roughly 240 CF...oh wait that is a standard fill. FWIW I am 5'11 and about 165lbs.
