DIR- Generic Weight considerations with Al80 twin set

[MaxE]

I’m sure this has been asked before, i tried to search but did not really find anything.
I‘m beginning to incorporate diving with a twin set. So far it has been with steel tanks and a drysuit. This time of year on a boat that just seems too hot and no fun. I have a set of AL 80’s I’ll use diving wet. I’m trying to wrap my head around weighting. I know what I need with a single AL80. If I’m going to keep the same weight for two dives same tanks no fill in between I’ll be a little heavy dive 1 to be properly weighted at the end of dive 2. One one hand full the 2nd tank is like 2lbs negative but empty another 5lbs positive. Do the bands, manifold and additional 1st stage off set that? Do I dive the same weight as a single 80? Drop a few lbs?
Thanks

 

[inquis]

If I’m going to keep the same weight for two dives same tanks no fill in between I’ll be a little heavy dive 1 to be properly weighted at the end of dive 2.

Beats the alternative of being underweighted if you have to use some of Dive 2's air on Dive 1. Weight yourself for nearly empty tanks. The wing easily compensates for the negative buoyancy until then.

 

[inquis]

I would drop 9 lb as a first cut going from a single AL80 to manifolded AL80s.

ETA: that's -10.5 lb for my bands (Highland) and manifold (Thermo); +1.5 for another AL80 and reg in freshwater. If this is saltwater, drop 8 lb.

If you have a hot tub (or even a large trashcan), you can measure the buoyancy of both configurations with a luggage scale and drop the difference.

 

[Matan]

If I’m going to keep the same weight for two dives same tanks no fill in between I’ll be a little heavy dive 1 to be properly weighted at the end of dive 2. One one hand full the 2nd tank is like 2lbs negative but empty another 5lbs positive. Do the bands, manifold and additional 1st stage off set that? Do I dive the same weight as a single 80? Drop a few lbs?
Thanks

1. I haven't seen an al80 cylinder that's 5lbs positive when empty - which brand are these?
2. Bands + manifold + another 1st stage add weight.
3. Same weight as single al80? no - go ahead and do a weight check
   1. it saves you guessing weights and being unsure if you're properly weighted.
   2. Empty cylinders (~400psi?) - make sure you can stay at 6m with empty wing.
   3. Full cylinders - make sure you can dump enough weight and swim up with empty wing.

I agree drysuit in the summer is a nightmare - you need to have fun


Matan.

 

[MaxE]

1. I haven't seen an al80 cylinder that's 5lbs positive when empty - which brand are these?
2. Bands + manifold + another 1st stage add weight.
3. Same weight as single al80? no - go ahead and do a weight check
   1. it saves you guessing weights and being unsure if you're properly weighted.
   2. Empty cylinders (~400psi?) - make sure you can stay at 6m with empty wing.
   3. Full cylinders - make sure you can dump enough weight and swim up with empty wing.

I agree drysuit in the summer is a nightmare - you need to have fun


Matan.

Toda raba Matan. The tank is like 2lbs negative full and 3lbs positive empty so the swing is 5lbs. A weight check empty tanks is ideal but not always practical/possible

 

[MaxE]

I would drop 9 lb as a first cut going from a single AL80 to manifolded AL80s.

ETA: that's -10.5 lb for my bands (Highland) and manifold (Thermo); +1.5 for another AL80 and reg in freshwater. If this is saltwater, drop 8 lb.

If you have a hot tub (or even a large trashcan), you can measure the buoyancy of both configurations with a luggage scale and drop the difference.

This is very helpful. I was severely underestimating the weight of the bands.

 

[inquis]

A weight check empty tanks is ideal but not always practical/possible

There is a way to check weight with full tanks at the surface: use less lead to simulate having breathed the non-reserve air (5 lb in an AL80). If you can ascend and descend with breath alone (empty BC/wing), that's approximately what you need for full tanks. Then add lead to match the non-reserve air that will be gone at the end of the dive.

This isn't always feasible either (e.g., anchored in current), but it's occasionally useful. Do a proper weight check at the end of the dive and adjust from there.

 

[jeffmg]

The best way to find out how much weight you need is to get in at the beach in your full setup with a weight bag full of 1 or 2 lb weights and your tanks around 500psi

get to 10-15 feet of water, empty your bc completely and start dropping weights 1 or 2 lbs at a time. while motionless if you start to drift up, put a couple pounds back in the bag and make sure you can hold a 10 foot stop comfortably, sometimes it takes an extra pound or two to feel comfortable

Al80 doubles still need alot of lead in a wetsuit, they get really floaty at the tail end so I put a couple of 5lb tail weights on the lower bolt with a webbing extension to get them close to the bottom of the tanks

then the rest can be a v-weight, I like these, V-Weights

or you can wedge some soft weights in between the two tanks, then put your wing and backplate on top and squeeze them in place

If you still need more it can go on a weight belt or harness

Next step if you're wetsuit diving is to get to a site at 100 foot depth with full tanks, get that bc fully deflated and start kicking your way up, if you can make progress towards the surface you're good to go, if not then the buoyancy swing of your exposure gear is too much and you should look at other options, e.g. drysuit or thinner wetsuit

trying to estimate and flub around without going through these motions takes more time and is more frustrating than just getting it done

proper weighting keeps a minimum amount of air in your wing, makes you more streamline and keeps your rig as light as possible