Weighting differences between AL80 Doubles and HP100 Doubles

[SeanW]

Greetings all,

TLDR:Searched around, but couldn't find a clear answer to this question. Assuming all else being equal (same wing, plate, exposure suit, water), how much of a weight difference is there between double AL80s and Double faber HP100s? Put another way, assuming all else equal, how much additional weight would I need going from HP100 doubles to AL80 doubles?

Background: I normally dive HP100 doubles and find my self overweighted at the end of the dive even with my thickest drysuit undergarments and aluminum backplate. I need to explore lighter tank options, so to start, I'm renting a pair of AL80 doubles to try. Just want to get a ballpark figure before I head out for a proper weight check.

Thanks in advance!

 

[Boarderguy]

Do you have any weights on you at all? Your wing should accommodate the doubles for the most part and your drysuit any extra lift that may be needed.

 

[SeanW]

I'm aware the wing and suit can hold the extra negative buoyancy, but I would like to find a better solution than accepting being overweighted at the end of the dive. For reference: HP100 doubles, aluminum backplate, thick drysuit undergarments, no additional ballast, fresh water and I'm still probably 6-8 pounds heavy at the end of dive with 500psi in the tanks.

 

[inquis]

10 lbs, all else being equal. That's based on the difference between empty buoyancies, assuming Luxfer/Metal Impact AL80s (+4.4 lb each) and Faber HP100s (-0.6 lb each).

 

[rx7diver]

@SeanW,

I'm trying to understand: You're diving both a BC and a drysuit, correct? At the end of your dive (at your 20 ft stop, say) will your functioning drysuit provide enough buoyancy for you to remain neutral if your double cylinders are at 500 psig (say) and your BC is empty?

(I am assuming that your functioning BC will provide enough buoyancy for you to remain neutral when your double cylinders are at 500 psig and your drysuit is flooded and providing no buoyancy beyond what your incompressible drysuit underwear is providing.)

Are you thinking of the situation where both your BC and your drysuit are unable to provide buoyancy?

rx7diver

 

[Boarderguy]

I'm aware the wing and suit can hold the extra negative buoyancy, but I would like to find a better solution than accepting being overweighted at the end of the dive. For reference: HP100 doubles, aluminum backplate, thick drysuit undergarments, no additional ballast, fresh water and I'm still probably 6-8 pounds heavy at the end of dive with 500psi in the tanks.

That's the nature of the beast with doubles. Part of why you go to a 40lb+ wing and a drysuit. 80s are rubbish in most cases unless you're in warm water and vacation diving. Puff up the suit to stay warm at your stop and add some to your wing. No longer negative and you can continue to enjoy your 200ft³ of air.

 

[SeanW]

@SeanW,

I'm trying to understand: You're diving both a BC and a drysuit, correct? At the end of your dive (at your 20 ft stop, say) will your functioning drysuit provide enough buoyancy for you to remain neutral if your double cylinders are at 500 psig (say) and your BC is empty?

(I am assuming that your functioning BC will provide enough buoyancy for you to remain neutral when your double cylinders are at 500 psig and your drysuit is flooded and providing no buoyancy beyond what your incompressible drysuit underwear is providing.)

Are you thinking of the situation where both your BC and your drysuit are unable to provide buoyancy?

rx7diver

Yes, I dive with a drysuit. I don't want to dive overweighted if I can avoid it. Just because my wing and suit can provide the necessary buoyancy if overweighted doesn't mean I'd like to

 

[SeanW]

That's the nature of the beast with doubles. Part of why you go to a 40lb+ wing and a drysuit. 80s are rubbish in most cases unless you're in warm water and vacation diving. Puff up the suit to stay warm at your stop and add some to your wing. No longer negative and you can continue to enjoy your 200ft³ of air.

I dive with a 50lb wing. I don't mind diving lighter tanks if that means I'm closer to being correctly weighted. I would prefer not to accept being overweighted just because that's what I have to do.

 

[SeanW]

10 lbs, all else being equal. That's based on the difference between empty buoyancies, assuming Luxfer/Metal Impact AL80s (+4.4 lb each) and Faber HP100s (-0.6 lb each).

Thank you for this! This was roughly the ballpark I was looking for.

 

[crofrog]

I dive with a 50lb wing. I don't mind diving lighter tanks if that means I'm closer to being correctly weighted. I would prefer not to accept being overweighted just because that's what I have to do.

If you’re planning on getting more into tech you’re going to end up, ending heavy. You're going to have multiple partial used stages. Your back gas is not going to be empty, canister lights, heater packs, etc.

That being said, trying to get close to neutral is obviously the goal and 160 vs 200cuft is not going to make a big difference in bottom time and you can always just bring a bottom stage