Weighting question when changing cylinder size

[BcunningPDX]

I'm a tall diver (6'5") working on gear configuration. In the quest for better trim, I'm altering my set up from a Worthington HP100 to a Faber HP120. My question is how much weight should I plan on adjusting to for my first dive with this new tank?

I'd like to get as close as possible before my first weight check. Current configuration is: Salt water, Trilam drysuit, 4th Element Halo undergarment, Halcyon Long SS BackPlate (5.57lb), Halcyon Weighted STA (7.55lb), (12 lbs) ditchable weight (2x4lb waist pockets, 2x2lb trim pouch on top cam band)

From what I have found, the Worthington HP100 specs are: -10.2 lbs (full), -2.5lbs (empty) 33.1lbs (base weight empty). The Faber HP120 specs are: -8.82 lbs (full), +.65lbs (empty), 39.2 lbs (base weight empty)

Thanks in advance and I appreciate the input! (I have tried to crunch the numbers, but can't seem to get to a number that makes sense to me...maths is hard some times!)

 

[happy-diver]

Nice regs BcunningPDX, leave your gear how it is and feel the difference

 

[inquis]

If the only thing changing is the tank, your overall minimum buoyancy changes by the difference in the empty tank buoyancies:
New - Old = +0.65 - (-2.5) = +3.15 lb
You would need to add 3.15 lbs of additional ballast to compensate.

Personally, I'd put on 3 more lb of lead and evaluate at the safety stop on the next dive. Adjust as needed for the following dive.

As a follow on, it's typical to target being neutral with a minimal amount of gas in the tank and an empty wing. You'll need less pressure in the bigger tank to get that same amount. It's common to use 1 lb of air which equals 12.5 cubic ft. This requires 500 psi in an AL80 tank, 430 psi in the HP100, and 360 psi in the HP120. Call it 400 psi. (Get these numbers by using the rated volume and pressure: 12.5 cf / 120 cf * 3442 psi = 360)

Just be aware that minimum isn't sufficient reserve in many cases and should be adjusted for each dive. However, don't consider the increased amount for the purpose of weighting.

 

[JoeTPhilly]

I'm a tall diver (6'5") working on gear configuration. In the quest for better trim, I'm altering my set up from a Worthington HP100 to a Faber HP120. My question is how much weight should I plan on adjusting to for my first dive with this new tank?

I'd like to get as close as possible before my first weight check. Current configuration is: Salt water, Trilam drysuit, 4th Element Halo undergarment, Halcyon Long SS BackPlate (5.57lb), Halcyon Weighted STA (7.55lb), (12 lbs) ditchable weight (2x4lb waist pockets, 2x2lb trim pouch on top cam band)

From what I have found, the Worthington HP100 specs are: -10.2 lbs (full), -2.5lbs (empty) 33.1lbs (base weight empty). The Faber HP120 specs are: -8.82 lbs (full), +.65lbs (empty), 39.2 lbs (base weight empty)

Thanks in advance and I appreciate the input! (I have tried to crunch the numbers, but can't seem to get to a number that makes sense to me...maths is hard some times!)

Out of curiosity, what size wing do you use? Also, are you using the Halcyon ACB pockets? If so, how do you like using them? Thanks!

 

[BcunningPDX]

Nice regs BcunningPDX, leave your gear how it is and feel the difference

Thanks happy-diver! I love my regs too.... sadly it is getting harder and harder to find someone that will service the mk5. At the end of the day, I'm sure it will certainly all come down to "feel", but I started looking at the numbers/ variables and wanted to find a better starting point.

 

[BcunningPDX]

Out of curiosity, what size wing do you use? Also, are you using the Halcyon ACB pockets? If so, how do you like using them? Thanks!

I have a 40# Eclipse wing as well as the ACB pockets. I love them both... and having the "long" back plate has made quite a bit of difference for me as far as comfort goes.

 

[BcunningPDX]

If the only thing changing is the tank, your overall minimum buoyancy changes by the difference in the empty tank buoyancies:
New - Old = +0.65 - (-2.5) = +3.15 lb
You would need to add 3.15 lbs of additional ballast to compensate.

Personally, I'd put on 3 more lb of lead and evaluate at the safety stop on the next dive. Adjust as needed for the following dive.

As a follow on, it's typical to target being neutral with a minimal amount of gas in the tank and an empty wing. You'll need less pressure in the bigger tank to get that same amount. It's common to use 1 lb of air which equals 12.5 cubic ft. This requires 500 psi in an AL80 tank, 430 psi in the HP100, and 360 psi in the HP120. Call it 400 psi. (Get these numbers by using the rated volume and pressure: 12.5 cf / 120 cf * 3442 psi = 360)

Just be aware that minimum isn't sufficient reserve in many cases and should be adjusted for each dive. However, don't consider the increased amount for the purpose of weighting.

Thanks so much... This is incredibly helpful andI appreciate the info!