Buoyancy with drysuit?

[Edward3c]

But the weight of the extra gas is the same whether contained in steel or aluminum, which is the issue at hand.

With a steel the extra weight (mass) is distributed evenly. With aluminum the extra weight sits in a lump upsetting trim. I much prefer steels over aluminium, they’re more comfortable.

 

[formernuke]

My answer is it depends.

Use the suit for comfort, sometimes this is the same as what is needed for bouyancy if not use the BC. This for me depends on which undergarment single vs double etc.

As for drysuit valve position it depends on the valve and takes some testing out. I do like my current valve full open, others I've had needed a couple clicks to the close.

 

[Divin'Papaw]

My answer is it depends.

This is key and is why a drysuit takes either some training or mentoring and a number of dives to master.

I learned initially to put just enough air into the suit to keep the squeeze at bay and use the BC for the rest. As I became more experienced I found that, at times, I liked more air in the suit and less in the BC. It all depended upon the water temps and what I was diving (doubles vs singles).

As with most things in diving, you start with a fairly simplistic view and then add nuance and situational differences over time.

Just relax, get in a dumber of dives and slowly expand your drysuit skillset from there.

As an aside, eventually muscle memory will take over and you will begin doing things second nature. I no longer dive a drysuit (moved to FL in 2016) but for the longest time when diving wet, on descent I always reached for the inflator and on ascent I raised my left arm to vent. Now if I were to get out my drysuit, I would need a few shakedown dives to get things sorted out again.

 

[tbone1004]

@tbone1004

I would never dive an aluminium cylinder on a standard rig unless I was on holiday somewhere tropical and (ideally) in a wetsuit. Horrible cylinders to dive on a traditional rig with a drysuit because they 'pop' - they go positive. Lovely things to dive as stages, because they are neutral when full, and go positive when empty.

Aluminium cylinders have been traditionally rare (as main cylinders), in the UK. The saga over them cracking and requiring extra testing killed off the few that where in circulation.
There are a lot of ALi80's in the UK - used as stages, where the way they behave is a benefit.
It's also noticeable, that they are Ali80's. If you want an European spec aluminium cylinder, it would normally be a 7 litre, or smaller.

We tend to dive steel cylinders, even the rentals are steel. The only time we see aluminium cylinders normally is as stages, or when on holiday, where you are likely to be diving in a wetsuit.

One nice thing about a steel 12, on a standard rig or wing, with a drysuit, is the buoyancy control is really easy. Once the CVD is set, you don't need to do anything, other than add gas as you get deeper. The CVD does all the work, all you need to do is roll right a fraction if you do feel too positive.

mass of the gas is what the bcd is compensating for, buoyancy swing from gas consumption is a function of the volume of gas carried regardless of whether the vessel changes from negative to positive, stays negative, or stays positive. You weight yourself to be neutrally buoyant with an empty tank and then use the bcd to compensate for the mass of the gas that you've added. Your argument is completely irrelevant in the scheme of using a drysuit to compensate for buoyancy instead of a buoyancy compensator.

 

[Outbound]

One nice thing about a steel 12, on a standard rig or wing, with a drysuit, is the buoyancy control is really easy. Once the CVD is set, you don't need to do anything, other than add gas as you get deeper. The CVD does all the work, all you need to do is roll right a fraction if you do feel too positive.

But what does that have to do with the material of the cylinder? That's how everyone dives a drysuit.

 

[pauldw]

My biggest fear is shooting up to the surface feet first.

I wear spurs with my drysuit. Makes it easy to vent air in that kind of an emergency. But I do have to duct tape the suit afterward.

But seriously, I'm probably odd in that I've taken two drysuit diver courses from two different agencies, to try to better know how to use my drysuit. It's making more sense now that I've dove it more out in the real world, but neither course really explained the exhaust valve to me. So I just leave it open.

 

[Edward3c]

I wear spurs with my drysuit. Makes it easy to vent air in that kind of an emergency. But I do have to duct tape the suit afterward.

But seriously, I'm probably odd in that I've taken two drysuit diver courses from two different agencies, to try to better know how to use my drysuit. It's making more sense now that I've dove it more out in the real world, but neither course really explained the exhaust valve to me. So I just leave it open.

The idea behind the ‘constant volume valve’ is that you set it so the spring pressure holds the correct volume of air for you to be neutrally buoyant. If you then go deeper you need to add more air as the volume of air will have reduced. When you go shallower, the volume of air in the suit increases, The valve should let the excess air out, bringing the volume back to what you set it at.

It takes a number of dives to find the sweet spot. If your hiring suits the spring‘s properties are different on every suit. My last suit the sweet stop was 6 clicks Bach from fully closed. On my current one it’s 5 clicks from fully open.

 

[Leon_2020]

For me it's the BC that is used as primary bouyancy regulator. The suit is only for isolation and to negate squeeze.
I dive steel double 12 liters.

If you want to see if you can swim up with you set-up, I suggest to go down to 21 meters (63 feet), dump all the air out of your suit and see if you can swim up to the surface. If you can, keep it as it is, if you can't, get a BC.