Questions for the drysuit divers

[TrimixToo]

The reason to dive dry is to stay warm. Staying warm requires air in the suit, which means adding it as you descend. How much air to add depends on you, the suit, and the undergarments, but there needs to be enough air to let the undergarments loft and provide insulation against the cold. You will likely need to play with weighting to make the buoyancy work out.

 

[broncobowsher]

My exhaust valve I run full open or a click or two in. Different brands react different.
On descent, add air to the suit first. Wing second.
You can only control the suit (vent it on ascent) if there is enough gas to vent. If you have too much squeeze at depth, the wing will be over inflated to make up for it, and you will be cold from the insulation being compressed. On ascent what little gas you have in the suit will expand to where it should be. The overfilled wing will be dumping like mad to make up for it.
If you start with more gas in the suit, and the auto dump is dumping like it should. During ascent it is almost like magic as the suit auto dumps and takes care of itself.

 

[TravisD]

Have you done a proper end-of-dive weight check recently? Diving dry, "weight is warmth", and if you're under weighted, you're going to end up compensating for that by running less air in the suit.

I'm *not* saying that you should overweight - but rather that at end of dive/minimal gas in your cylinder, that you should have enough weight to both say neutral at depth, while still having enough gas in the suit to stay warm and remove the squeeze - enough weight to be comfortable. And don't forget that different undergarments will need different weighting to be right.

Trim also matters. Not being horizontal is going to result in more squeeze on whatever parts are lower in the water column at any given time. At the other end, you're going to have a bubble that's now larger, and if you're head-up/feet-down, that bubble is going to also try and escape thru your dump valve if it's open, or worse, thru a neck or wrist seal.

 

[Divingblueberry]

Thank you all for your advice. It is greatly appreciated.

I think I got the weighting ok : I went to the pool this winter and spent some time figuring out how much lead I need. 26 pounds brings me at eye level (without my gear on). But based on what I read, maybe a couple of pounds more could help... At this point, I prefer using the BCD for buoyancy as it is faster to dump air than the suit. I just add a bit of air as I go down and add more for comfort and leave the valve is fully open.

What is new is to "plan" the ascend phase and dump air ahead to avoid rising too fast and causing problems. I guess it'll come with time, but it is not the case at this point.

I'll keep your advice in mind when I dive at the quarry next week-end.

Thanks !

 

[TravisD]

26 pounds brings me at eye level (without my gear on). But based on what I read

Knowing how much lead it takes to sink the suit is a good data point, but doesn't give you an accurate picture of what you need to actually dive with. Some cylinders, for example, end up positively buoyant when they're (nearly) empty), while others are negative.

Do a weight check at the end of your next dive, when you're down to ~500 PSI.

As far as suit vs. BCD, I tend to use the BCD more at first due to needing to offset more weight (weight of the gas in the cylinder), then rely more on the suit near the end when I've mostly drained the BCD due to losing the weight of gas used.

 

[Gareth J]

For me, suit gas and BCD gas are handled differently. Short-term buoyancy swings caused by ascending or descending are compensated by adding to or venting the suit. That keeps my suit volume more or less constant regardless of depth. The slow, gradual increase in buoyancy due to breathing down my tank is compensated by venting my wing.

A valid approach.

I tend to teach use the suit at the start. That simplifies things, one single buoyancy volume to manage. Later, when carrying more equipment, it is easy to adapt to using both wing and suit.

I dive a CCR with an aluminium 80 stage almost all the time, I can comfortably dive on the suit in this configuration.

I watched someone at the weekend fighting to stay down at 6m at the weekend, they had added gas to the wing and not taken account of it during the ascent - and they where supposedly experienced!

 

[AJ]

Having done 500 plus drysuit dives I noticed recently I tend to use both wing and drysuit. It takes time to master it, but when you do it does not matter anymore where you put your gas because it's part of your buoyancy system. I must admit I tend to carry just as much lead as I need to to stay down with 30 bar left. This means I almost have no gas in my wing and litle in my drysuit while under water. This makes controlling the bubble relatively easy while ascending.

 

[dewdropsonrosa]

For my initial descent to depth, I split the difference. From the surface to roughly 10-15ft (3-5m) from my target depth, I add air to my drysuit until I am comfortable with the temperature and the amount of squeeze.

If that's not enough air to establish neutral buoyancy, then I begin adding air to my wing to finish compensating.

 

[Gareth J]

As I said, generally I can manage on the suit. There have been occasions when carrying multiple stage cylinders when I have used the wing. Similarly, on occasion I have done the same when on the rebreather, with multiple stage cylinders.

I am however, very conscious, that in the event of an emergency, who ever is lifting me will need to manage two (or in the case of the rebreather, three), buoyancy volumes. Personally, when lifting a diver from depth, I have found significantly easier to fully open the CVD first, and then lift the diver using the wing. This is significantly easier to manage.

 

[JMBL]

that DVD might help

https://www.amazon.com/Diving-Depth...rysuit+diving&qid=1558437002&s=gateway&sr=8-1