Drysuit use and buoyancy

[HKGuns]

It helps to keep the volume of air down in the suit. This could be a critical issue if the diver gets inverted or the suit dump has a problem. Certain types of undergarments have been known to get sucked into the valve and cause it to not work as well or at all.
Or if the diver is using doubles or diving sidemount with steels, it makes managing the bubble harder because it's larger. I've personally seen divers add too much air to the suit and not be able to dump it quick enough and, as a result, pop up to the surface, get inverted and end up on the surface hanging upside down, have gas escape out of the neck seal allowing 40 degree water in, and struggle with trim because the suit doesn't fit like it should in some areas and the gas gets into those.
You already manage two areas with a wet suit. BC and lungs. Adding a drysuit, with proper training, is not a big deal. Managing two spaces is often easier than managing one big one.

I am properly weighted and diving a single HP80, so I'm not putting a lot of air into the suit at all.

 

[grf88]

(For info, what pressure are LP 95s & 120s normally blown to? Want to convert that to litres)

15 and 19 litres water capacity respectively 182 bar for rated capacity..

 

[Wibble]

15 and 19 litres water capacity respectively 182 bar for rated capacity..

(sorry for OT -- Are they quite "light weight" compared with 12 litre 232 bar cylinders?)

 

[grf88]

Faber Cylinders | Scuba Center | Faber Steel Scuba Cylinders

 

[kelemvor]

Nowadays I use just enough air to take care of the squeeze, which is also enough for insulation. More air eventually just ends up in my feet which makes it hard to maintain a decent trim.

Ankle gaiters will solve that problem. Get them sewn onto your drysuit if you can, this way you'll never forget them. Even if you forget to cinch them down as long as they're on your leg you can fix it underwater. They're really just a piece of 1inch/25mm webbing with velcro on the ends. They slow the air flow into your feet making it trivial to manage. Luckily for me, my suit came from the factory with gaiters so I've never not used them.

 

[REP]

Ankle gaiters will solve that problem. Get them sewn onto your drysuit if you can, this way you'll never forget them. Even if you forget to cinch them down as long as they're on your leg you can fix it underwater. They're really just a piece of 1inch/25mm webbing with velcro on the ends. They slow the air flow into your feet making it trivial to manage. Luckily for me, my suit came from the factory with gaiters so I've never not used them.

I use rock boots, which have velcro ankle straps. I can’t say I thought about them for slowing air flow, but more importantly they prevent the risk of having your fins pop off when inverted

 

[REP]

Another point to be made is that as much as you can and I have managed buoyancy with my drysuit, air moves slower through the suit’s undergarments and my DS’s only have a vent on the left shoulder, which faces down while I swim. Not the best for purging air as u swim. As a general practice I will typically float vertically as I pass the 30 ft point when coming up from a deep dive. Then I’ll wiggle and purge most of the air out of my DS with my left shoulder pivoted up. This gets any extra air out of my feet and legs. The reasoning is that buoyancy adjustment is 2 to 3 times easier at 75 or 100 ft compared to at 15 ft. E.g. the air in your DS or BCD will expand 2 to 3 times (approx) more over a 5 ft depth change from 15 ft to 10 ft than it will from say from 80 ft to 75ft or 105 to 100ft. …Boyle’s law and all
Occasionally I spend 4 to 6 hours diving in <15 ft water inspecting invasive water plants etc. Buoyancy control in the shallows with many depth changes is definitely more effort in the shallows. It is definitely easier with a WS, but I wear the DS for the warmth in the summer, if I need to be in the water for long periods of time.

 

[ATJ]

I dive with a 3.5mm neoprene suit.

If I dive with a 12.2L 232bar tank, my suit is all I need for comfort and buoyancy.

I most often dive with a 12L 300bar tank and I put air in both my wing and my drysuit at the start of the dive because the 300bar when full is more dense than the 232bar tank. As I go through the dive I vent the wing and by around halfway through the dive I'm only using the drysuit for my buoyancy and comfort.

If I dive with twin10.5L 232bar tanks, I also have to use both wing and drysuit for similar reasons to the 300bar tank.

In the 9 years I have been diving in drysuits (and the last 4 years in the neoprene suit), I've had no issues with using both wing and suit as required. I actually find my drysuit much easier to add and vent air.