Weighting Going From Single To Double Steels

[Bigeclipse]

All,
Just trying to get a rough idea of what to expect going from single steel to double (yes I know the whole story of doing a weight check...etc. just looking for a place to start). Currently in fresh water cold diving with drysuit I wear 15lbs lead, steel backplate (6lbs) with steel cambands(not plastic...add probably 1lb negative), and a STA (2lbs) along with a Faber FX 100 (which is about -.5lbs empty). I will be going to double tank Worthington x7-100 which are a bit more negative compared to the Faber FX100s. How negative are a typical manifold and tank bands? I know I will add another reg set so that may be another say 2-4lbs negative as well. Any thoughts and considerations to get me a ballpark. I will be doing the proper weight check when I get to the water, just want an idea of where I might end up. Thanks!

 

[tbone1004]

so you are going from negative buoyancy of about 1.5, to 7 for the tanks alone. Add in another 4lbs for the crossbars and bands, another 2lbs for the extra first stage, and you are adding about 12lbs to the rig. With that setup, you shouldn't need any lead unless you are putting a lot of air in the drysuit.

 

[Bigeclipse]

so you are going from negative buoyancy of about 1.5, to 7 for the tanks alone. Add in another 4lbs for the crossbars and bands, another 2lbs for the extra first stage, and you are adding about 12lbs to the rig. With that setup, you shouldn't need any lead unless you are putting a lot of air in the drysuit.

Thanks Tbone. Just seeing if being able to use a steel backplate is still an option as I already own 2 and one just sits at home. If not...I'll have to buy an aluminum plate

 

[Stoo]

Like tbone said... I wear 14 pounds with twin 80s, but with 108s, I wear no lead at all. I also carry a camera that's about 5 pounds negative in fresh water. A bit will depend on your undies and stuff, but you won't need much that's for sure.

Regarding the backplate, I use an old "plastic" thing of some sort. I don't think it has any "weight" at all in the water, so if you are using a SS plate, you won't need any weight at all, pretty much guaranteed...

 

[tbone1004]

it all depends on how much underwear you are wearing and how inflated that suit is. If I was diving that rig in the caves, I would need an aluminum plate and still be way too heavy. If I was diving under the ice, I'd probably want 10lbs on top of the plate if I was under there for a while. That is the problem with estimating with drysuits. Wetsuits are easy because they only have so much inherent buoyancy. Drysuits have a theoretical max buoyancy when they're full, but even that is dependent on the diver and a bunch of other variables like how tight the harness is. Even then, there is no rule for how much weight you need and it is very annoying to try to do weight checks. One thing you can fairly easily do is to get a luggage scale, and hang your single tank rig from it *without any extra lead on there* and write that weight down. Normalize for an empty tank, so subtract however much air is in the bottles. Then assemble the doubles rig and do the same normalization for empty tanks and write that down. The delta is how much lead you need to remove from the belt assuming exposure protection is the same. That may change depending on your bottom times. With doubles you'll be extending your bottom time tremendously and that may dictate a larger thermal protection requirement which changes things again.

 

[Aquavelvet]

I usually still need at least a 5 lb tail weight on my doubles (with steel backplate), but I dive in cold salt water. Balance and trim might be a little different from what you are used to. The manifold and twin regulators will add more weight up by your head. You will want to set the tanks as low as practical in the bands to compensate. Most of us like to have the top of the upper band at or just below where the tanks start to curve.
You will also need a doubles wing with about 45 lbs lift. Don't go too big or the wing will wrap around your tanks and trap air, making it difficult to dump when you need to.

 

[Compressor]

Great advice above. The rig will get heavy so keep that in mind. Be aware that if you are too negative, you will/should be able to make a safe ascent to the surface without struggling and the answer is not to have a wing full of air.

 

[REVAN]

All,
Just trying to get a rough idea of what to expect going from single steel to double (yes I know the whole story of doing a weight check...etc. just looking for a place to start). Currently in fresh water cold diving with drysuit I wear 15lbs lead, steel backplate (6lbs) with steel cambands(not plastic...add probably 1lb negative), and a STA (2lbs) along with a Faber FX 100 (which is about -.5lbs empty). I will be going to double tank Worthington x7-100 which are a bit more negative compared to the Faber FX100s. How negative are a typical manifold and tank bands? I know I will add another reg set so that may be another say 2-4lbs negative as well. Any thoughts and considerations to get me a ballpark. I will be doing the proper weight check when I get to the water, just want an idea of where I might end up. Thanks!

You are on the right track. Just add up the deltas in buoyancy from the equipment you are using to the equipment you are switching to. No need to ask others, unless you can't get data on some piece of equipment. If you do the math, your estimates will have more meaning than any numbers said by anyone here. Their situation is their situation; yours is unique to you. Tank manufacturers will have published buoyancy information for the tanks. A manifold is small and dense enough that you can neglect its displacement for a first cut estimation. Just consider it a point mass for now.

 

[eelnoraa]

I was bored at some point and weighted a lot of dive gears. Here is what I can share. Photos can be post upon request:
1. brass din first stage, MK25 and Atomic M1 in this case, ~1.35lb.
2. Thermo single pro valve: 1.5lb each
3. Thermo 230bar manifold: 4.9b total. => Cross bar along is 1.9lb only
4. Highland 2.5" wide, 7.25" diameter band set: 3.9lb
5. Most stainless steel plate quoted for 6lb is actually just above 5lb. DR SS plate: 5.06lb.

So adding a x-7 HP100, that is -2lb. Adding a 1st stage: -1.35lb. Added cross bar: -1.9lb. Adding bands: -3.9lb. Total is just a bit over 8lb. Assuming you are not changing your plate, you can subtract 8lb from your weight belt. It is inline with my own experience.

 

[eelnoraa]

Here are some picture on kitchen scale