Steel Tank Confusion/Weighting Advice needed

[Jason Craig]

I know weighting is covered a lot here and I have read many posts on the subject and think I am pretty close. I am looking for some confirmation in my guess on an upcoming weight change. On a upcoming trip I will be switching from Fresh to Salt and from an AL80 to a Steel 100 (not positive of the brand but I think they use FABER).

I have just started diving with a BP&W in the last 2 months (Dive Rite XT steel (5.6lbs) backplate and DGX Singles wing (30lb)). I primarily dive fresh water and with my 7mm wetsuit I use 10lbs of lead with the BP&W and standard gear config w/ the AL80. I might be able to drop 2lb more but not sure yet (will be checking it out in the next two weekends with some more local dives on my BP&W). Switching from Fresh to Salt I should need to add about 6-7lbs (assuming I was diving a AL80). However, for the switch to the HPsteel 100, assuming its a Faber HP100 its about -1lbish empty, therefore I should only use about 3-4lbs of additional lead to account for the buoyancy from the AL80 for a total of 14lbs. Am I thinking about that correctly?

As it’s opening day for lobster season, I won’t have the luxury of doing a weight check before the first jump and if I am too light and have to return for weight I will get nothing but silt and antenna on the first dive. However, I don’t want to be overweighed either. My plan is to add the 4lb of lead to accommodate for the salt and steel change, does this sound reasonable or should it be more or less?


From a Scubaboard post

Manufacturer & Model

Service pressure (PSI, spec)

Full air capacity (ft3, spec)

Water volume (l, spec)

Full air capacity (ft3, calc from volume)

Difference (% of spec)

EAN32 capacity @ 3600 PSI (ft3, calc)

EAN32 Tank Factor (ft3 / 100 psi)

Spec Air Tank Factor (ft3 / 100 psi)

Difference (% of EAN32)

Outer diameter (in)

Length without valve (in)

Empty weight (lbs, w/o valve*)

Empty Weight per Tank Factor

Buoyancy Empty (lbs, w/valve)

Buoyancy Full (lbs, w/valve)

Worthington X7-100

3442​

99.50​

12.20​

95.78​

-3.73​

100.57​

2.79​

2.89​

-3.36​

7.25​

22.70​

33.10​

0.33​

-2.50​

-10​

Faber M100DVB

3498​

100.00​

12.00​

95.75​

-4.25​

98.92​

2.75​

2.86​

-3.88​

7.24​

24.21​

38.70​

0.39​

-6.69​

-14.11​

PST E7-100

3442​

100.00​

12.73​

99.95​

-0.05​

104.94​

2.92​

2.91​

0.34​

7.25​

24.00​

32.00​

0.30​

-1.30​

-8.8​

Faber HP100-HDG

3442​

100.00​

12.90​

101.28​

1.28​

106.34​

2.95​

2.91​

1.68​

7.25​

25.30​

34.00​

0.32​

-0.59​

-8.41​

 

[Brett Hatch]

Hi Jason, I think you are very much on the right track here. The key thing missing from your table is that a typical AL80 is about 4 lbs positive (when empty). Steel tanks vary a lot, but the two 3442 psi Faber and PST tanks you mentioned are both very common, and both are about 1 lb negative (again, when empty). This means that all else being equal, you'll need 5lbs less ballast with a Faber HP100 HDG versus, say, a Luxfer AL80.

Not sure how you got to the 6-7 lbs figure, sounds pretty close to me. The steel tank will count for 5 of that, so, yeah if the 6-7 lb estimate is right, you will need 1-2 lbs to meet it. But for your first dive, 4 or 6 lbs is a better starting place, since you really do not want to be underweight. At the end of that first lobster dive, in say 10-15 feet of water, see if you can hand off your catch bag and couple pounds of lead to your buddy, or clip it off to a drop line if you're diving off a boat. If you can do that, then you can shave that lead off for your second dive.

Cheers

Edit to add: as one point of reference, I am 6'0", 185lbs, and dive a steel backplate with a 32lb wing and a wingle-piece harness. My wetsuit is an 8mm/7mm AquaLung SolAfx wetsuit with integrated hood, and I dive with 5mm gloves and booties and neutral fins (Deep6 Eddys). When I dive in the ocean with a single Faber HP100 HDG tank, I need 12 lbs of lead. In the same setup with an AL80, I need 5 more lbs, so I add 6 and dive with 18 lbs. If you are a similar size and build, you'll probably need a similar amount of lead, which is pretty close to what you posted.

 

[inquis]

Weight will be about the same. Drop about 5 lbs moving to the steel tank. Add about 5-6 moving to salt water. (Add 2.4% the dry weight of you and rig, assuming average salinity.)

 

[Jason Craig]

Hi Jason, I think you are very much on the right track here. The key thing missing from your table is that a typical AL80 is about 4 lbs positive (when empty). Steel tanks vary a lot, but the two 3442 psi Faber and PST tanks you mentioned are both very common, and both are about 1 lb negative (again, when empty). This means that all else being equal, you'll need 5lbs less ballast with a Faber HP100 HDG versus, say, a Luxfer AL80.

Not sure how you got to the 6-7 lbs figure, sounds pretty close to me. The steel tank will count for 5 of that, so, yeah if the 6-7 lb estimate is right, you will need 1-2 lbs to meet it. But for your first dive, 4 or 6 lbs is a better starting place, since you really do not want to be underweight. At the end of that first lobster dive, in say 10-15 feet of water, see if you can hand off your catch bag and couple pounds of lead to your buddy, or clip it off to a drop line if you're diving off a boat. If you can do that, then you can shave that lead off for your second dive.

Cheers

Edit to add: as one point of reference, I am 6'0", 185lbs, and dive a steel backplate with a 32lb wing and a wingle-piece harness. My wetsuit is an 8mm/7mm AquaLung SolAfx wetsuit with integrated hood, and I dive with 5mm gloves and booties and neutral fins (Deep6 Eddys). When I dive in the ocean with a single Faber HP100 HDG tank, I need 12 lbs of lead. In the same setup with an AL80, I need 5 more lbs, so I add 6 and dive with 18 lbs. If you are a similar size and build, you'll probably need a similar amount of lead, which is pretty close to what you posted.

Thanks, 5'10" 180lbs so pretty close, thanks for the description.