Weighting differences between AL80 Doubles and HP100 Doubles

[VsubT]

LP85 steel tanks might be a good option if the AL80’s are light on you. Nice for cave fills if you can get them too.

Lance

 

[halocline]

There’s nothing wrong with double 80s, actually I kind of like them. They trim way better than single 80s. I wouldn’t add 10 lbs, maybe start with 6 and do a nice easy dive and blow them down to 300 on your safety stop. I would try to keep the weight fairly low and see how your trim goes. Heavy fins like jets can help too.

 

[mdwalter]

There’s nothing wrong with double 80s, actually I kind of like them. They trim way better than single 80s. I wouldn’t add 10 lbs, maybe start with 6 and do a nice easy dive and blow them down to 300 on your safety stop. I would try to keep the weight fairly low and see how your trim goes. Heavy fins like jets can help too.

Yeah, that's the point. the OP says he's 6-8 lb too heavy at the need of the dive in HP100s, so he wants the 10 lb lighter AL80s to be close to neutral at the ned of the dive. Obviously he would not add 10 lb of lead, because then he'd be 6-8 lb overweighted again. The whole point is to not add any weight if possible, or a max of 2-4 lb if needed.

 

[crofrog]

Yeah, that's the point. the OP says he's 6-8 lb too heavy at the need of the dive in HP100s, so he wants the 10 lb lighter AL80s to be close to neutral at the ned of the dive. Obviously he would not add 10 lb of lead, because then he'd be 6-8 lb overweighted again. The whole point is to not add any weight if possible, or a max of 2-4 lb if needed.

I see you marked my post as confusing and it sort of is because it’s a bit of a contradiction.

There are 3 assertions I have;

1) you are going to end up diving “over weighted” in tech diving. If you’re carrying around double 130s because you need the gas for a lot of people you’re going to end up overweighted, and your finishing the dive with 1/3 of the gas still in the tank you’re going to be heavy. So learn to be comfortable being heavy.

2) you should still strive to be as close to neutral as possible at your lightest possible gas weight. I.e. back gas at or below 500psi

3) In a typical entry level tech dive. You’re limited by decompression time more than bottom gas. So the difference from the extra 40 cuft gas between double 100s and double 80s doesn’t matter.

 

[Scared Silly]

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.

Though the answer was given, I have to ask the OP what was your search process? Finding the buoyancy of cylinders is pretty easy for AL80 and HP100s. Further, calculating the difference is pretty fundamental. Anyone diving doubles should be able to do both without resorting to asking others. Not being able to so is rather large red flag.

 

[SeanW]

Though the answer was given, I have to ask the OP what was your search process? Finding the buoyancy of cylinders is pretty easy for AL80 and HP100s. Further, calculating the difference is pretty fundamental. Anyone diving doubles should be able to do both without resorting to asking others. Not being able to so is rather large red flag.

I searched on here for peoples experiences. Pretty certain my dive abilities have no correlation to research skills. What a useless comment

 

[rjack321]

I want to know who needs basically no lead in a drysuit, hp100s are barely negative (-2lbs total for both plus -2 for the crossbar and ali plate combined = maybe -4lbs total) when empty so *something* is offsetting the inherent buoyancy of the OP's drysuit. 4lbs seems minimal. Are you diving in warm freshwater with a Tshirt for insulation?

 

[SeanW]

I want to know who needs basically no lead in a drysuit, hp100s are barely negative (-2lbs total for both plus -2 for the crossbar and ali plate combined = maybe -4lbs total) when empty so *something* is offsetting the inherent buoyancy of the OP's drysuit. 4lbs seems minimal. Are you diving in warm freshwater with a Tshirt for insulation?

I sink like a stone. As mentioned before, double hp100s with an aluminum backplate and drysuit w/ thick undergarments leaves me heavy by about 6lbs at the end of the dive. When I jump in the water (fresh water) without any gear on except my drysuit, fins, mask, it takes about 12lbs of lead to sink me with my thickest undergarments. My rig mentioned previously is 17lbs negative with 500psi in the doubles (measured this by suspending the rig in the water with a luggage scale). Ended up needing 4lbs of weight on the crotch strap in al80s to be correctly weighted when I tried them, so the estimate of being 10lbs lighter was pretty close. I'm diving in low 50s water so my "thick" undergarments may not be as thick as some other people. I do wish I could wear just a tshirt though

 

[boulderjohn]

I want to know who needs basically no lead in a drysuit, hp100s are barely negative (-2lbs total for both plus -2 for the crossbar and ali plate combined = maybe -4lbs total) when empty so *something* is offsetting the inherent buoyancy of the OP's drysuit. 4lbs seems minimal. Are you diving in warm freshwater with a Tshirt for insulation?

When I dive with doubles, either Faber HP 120's or XS (Worthington) LP 108's, I am heavy at the end of the dive while wearing a drysuit and carrying no weight with an AL backplate. Those are both less buoyant than 100's, but I would guess I could still dive 100s without weight. I do not wear my steel BP with those doubles because of the weight. If I were to take those tanks down to near empty rather than ending the dives with my reserves, though, it would be closer to neutral.

I don't fight the weight because I want to be sure that if an emergency put me well into my reserve, I could still stay down.

 

[crofrog]

I don't fight the weight because I want to be sure that if an emergency put me well into my reserve, I could still stay down.

Lots of options available to solve being a bit to heavy. Not so many for too light.