+ Buoyancy of new light euro cylinders.

[Rydive]

Does anybody know, or know how to work out, the buoyancy of an empty set of twin 12 Euros. They weigh in at a very light 13.1kg each. I still seem to need quite a bit of weight to hold a stop.

I guess I just need what I need, but going from what I've seen on here I think I'm still waaay over weighted. Ta in advance.

[David G]

Originally Posted by Rydive

Does anybody know, or know how to work out, the buoyancy of an empty set of twin 12 Euros. They way in at a very light 13.1kg each. I still seem to need quite a bit of weight to hold a stop.

I guess I just need what I need, but going from what I've seen on here I think I'm still waaay over weighted. Ta in advance.

This page may help:

UK Scuba - Cylinder Buoyancy Calculation

Regards,

David.

[Rydive]

Thanks David,

I had seen another one of those type of calculators but it didn't let you enter the weight, it just gave calculations for one standard weight and displacement. Good stuff.

That gave me the following:

The cylinder is made of 13.1 kg of steel, (which has a density of 7.8 kg/litre).
The steel therefore has a volume of 13.1 / 7.8 = 1.68 litres, so the total volume is 12 + 1.68 = 13.68 litres.
The density of salt water is 1.03 kg/litre, giving 13.68 x 1.03 = 14.09 kg
Air has a density of 0.0012 kg/litre.
The air in a full cylinder weighs 0.0012 x 232 bar x 12 litres = 3.34 kg.
The cylinder when empty has a buoyancy of 14.09 kg - 13.1 kg = 0.99 kg
The cylinder when full has a buoyancy of 14.09 kg - 13.1 kg - 3.34 kg = -2.34 kg

So, I'll be 2kg positive with empty tanks minus the weight of the valves and manifold, SS back-plate, torch and 1st stages. I reckon that lot probably weighs in at about 4 kg or so in the water as a conservative guess. So, the rig should be at least about 2kg negative? Sound right?

I'm still needing about 15kg to hold a stop! Does that sound ridiculous?

I'm quite a big guy, about 6'4' and 15 1/2 stone. But I'm only using a 200gm under-suit, sometimes with a thin base layer underneath on the top half.

Should I be needing that much weight? Part of the attraction of moving to twins (apart from all the obvious benefits of gas and redundancy) was to loose a bit of lead from the waist. I've heard of people only needing a few kilos in the form of a V-weight. Not fair!

[mikecsmith]

Just out of interest Rydive how much weight do you normally need to sink on single steel tanks?

I'm 6'2 and about 17 stone so I'm a big bloke and when I went to do a weight check on wednesday I found I needed 35-38lbs of weight to sink which seems utterly OTT compared to what most people use - I do know that my wing is oversized for single tank diving which is where part of my problem is coming from but I honestly don't know if I'm doing something wrong, as once I've sunk past about 10m I feel overweighted, but if I don't have that much weight attached to me I can descend about a metre then I breathe in and float gently back to the surface...

[Rydive]

Originally Posted by mikecsmith

Just out of interest Rydive how much weight do you normally need to sink on single steel tanks?

About the same, or there abouts, maybe a touch less... +- 14KG. I thought I'd at least loose the weight of the backplate off my belt.

Mike, I wouldn't have thought the size of your wing will have any noticable effect, unless it's not fully empty, it shouldn't displace to much water. I've got a friend who uses about the same weight as you, it's alot. But, it sounds like you're a big fella.

[wreckferret]

Hi,
I am 6` 4" & 15 stone. With twin 12L`s and a weezle I need 35Lbs to feel comfortable.

I have tried to use less weight but I always end up too floaty. I have tried weighting myself with 50 bar in each tank but it always ends up @ 35Lbs.

I think you use what you need and thats it.

[Rydive]

Originally Posted by wreckferret

Hi,
I am 6` 4" & 15 stone. With twin 12L`s and a weezle I need 35Lbs to feel comfortable.

I have tried to use less weight but I always end up too floaty. I have tried weighting myself with 50 bar in each tank but it always ends up @ 35Lbs.

I think you use what you need and thats it.

Hmm, boo! At least it's not just me. Cheers.

[warmwaterdiver]

Originally Posted by Rydive

I'm still needing about 15kg to hold a stop!

Originally Posted by wreckferret

I need 35Lbs to feel comfortable.

[mikecsmith]

Least I'm not the only one, seems like I just need a lot of weight.

[eey_ore_9]

You need to look at your drysuit undersuit or wetsuit. POSITIVE BOUYANCY = Drysuit & undersuit approx 8kg
wing gas 3kg so 8+3 = 11 kgs positive, therefore your already 11 kilos positive before you start.
NEGATIVE BOUYANCY Twin 12s 2KGS X2 =4KGS
BACKPLATE 3KGS
BREATHING GAS 3KGS
WEIGHTBELT 3KGS SO 4+3+3+3=13KGS LEAVES YOU 13 -11 =2KGS NEGATIVE (AT START OF DIVE BEFORE YOU USE ANY GAS) This is the reason why most use a P weight or V weight (approx 3kgs) on twinset and 2 to 4kgs on belt.I found that trying when id got 35 bar on twins at 6 metre shelf, loaded up with weight then take weight off until i could fin to surface was best for me. I then divided weight between twinset and belt.Im overweighted at start but i can still dump weight to make it to surface. At end of dive im nicely negative but still like to drop a bit more weight off,I think that will come whem im more confident at holding stops to within 0.5 metres