buoyancy, dry suit vs wet suit

[Ayisha]

Hi!

I am a super new diver - I got my certification just last week. I live in a cold country and I did it with a dry suit. Buoyancy was achieved with the dry suit, the BCD was only ever inflated on the surface, and stayed completely deflated during descent, ascent, and diving.

My next dive will be - for sure! - in a warmer sea, but I did not really practice buoyancy with a wet suit. For those who use both, what do you find easier? Is it very difficult to achieve neutral buoyancy with a BCD?

Thanks!

A wetsuit is easier than a drysuit. A thinner wetsuit is easier than a thicker 2-piece wetsuit.
Like with any new gear, you should do an easy, check-out type (shallower) dive with it first, to do a weight check, learn the new gear, and get comfortable with it.

With the drysuit, it sounds like you had a bit too much gas in it, likely as you went shallower, which migrated to the feet, and caused you to go feet up. You should just have enough gas in the drysuit to relieve the squeeze.

 

[MaxTorque]

stupid (maybe) question regarding drysuit and Neutral Buoyancy:

With a Trilam drysuit, the material of the suit is broadly incompressable, therefore, if i adjust my overall weighting so as to have just the right amount of air in my suit to get the right squeeze/insulation, then i won't need to use my BCD because that volume is constant (with a variable mass of air in it ie increasing with depth)?

This means my overal weighting when drysuit-ing is more to do with comfort than it is buoyancy? ie the right amount of ballast is that that enables you, with an empty bcd, to have just the goldilocks amount of air in your suit to ensure there is not excessive squeeze and to ensure i am warm enough for the water temp i am diving in. By extension,t hat means more weight the colder the water gets?


The only other significant change is the slow reduction of the mass of my breathing gas as the dive progresses, which as per diving wet, means starting a bit "heavy" as the 2 to 3kg of air in my cylinder bleeds off.

In effect the choice between BCD and Drysuit for buoyancy is automatically found in favour of the drysuit, because being comfortable at any depth is also being neutrally buoyant at that depth?

Is this right??

 

[Bowers]

stupid (maybe) question regarding drysuit and Neutral Buoyancy:

With a Trilam drysuit, the material of the suit is broadly incompressable, therefore, if i adjust my overall weighting so as to have just the right amount of air in my suit to get the right squeeze/insulation, then i won't need to use my BCD because that volume is constant (with a variable mass of air in it ie increasing with depth)?

This means my overal weighting when drysuit-ing is more to do with comfort than it is buoyancy? ie the right amount of ballast is that that enables you, with an empty bcd, to have just the goldilocks amount of air in your suit to ensure there is not excessive squeeze and to ensure i am warm enough for the water temp i am diving in. By extension,t hat means more weight the colder the water gets?


The only other significant change is the slow reduction of the mass of my breathing gas as the dive progresses, which as per diving wet, means starting a bit "heavy" as the 2 to 3kg of air in my cylinder bleeds off.

In effect the choice between BCD and Drysuit for buoyancy is automatically found in favour of the drysuit, because being comfortable at any depth is also being neutrally buoyant at that depth?

Is this right??

you will be a touch heavy at start of dive do to full tanks. This extra weight is what needs to be compensated for by either bcd or more air in suit. But yes, near end of dive you won’t need to use bcd because comfort equals neutral buoyancy.
I personally have no problem with a few lbs worth of extra air in my suit so I don’t have to bother with bcd. But if im diving with lots of air and my weight shift will be several lbs, then i use the bcd at start of dive and then less and less as the dive progresses.

 

[BlueTrin]

stupid (maybe) question regarding drysuit and Neutral Buoyancy:

With a Trilam drysuit, the material of the suit is broadly incompressable, therefore, if i adjust my overall weighting so as to have just the right amount of air in my suit to get the right squeeze/insulation, then i won't need to use my BCD because that volume is constant (with a variable mass of air in it ie increasing with depth)?

This means my overal weighting when drysuit-ing is more to do with comfort than it is buoyancy? ie the right amount of ballast is that that enables you, with an empty bcd, to have just the goldilocks amount of air in your suit to ensure there is not excessive squeeze and to ensure i am warm enough for the water temp i am diving in. By extension,t hat means more weight the colder the water gets?


The only other significant change is the slow reduction of the mass of my breathing gas as the dive progresses, which as per diving wet, means starting a bit "heavy" as the 2 to 3kg of air in my cylinder bleeds off.

In effect the choice between BCD and Drysuit for buoyancy is automatically found in favour of the drysuit, because being comfortable at any depth is also being neutrally buoyant at that depth?

Is this right??

1. With a trilam drysuit, the suit is incompressible but you will have an undersuit, the undersuit role is to give a bit of bulk and it will have some volume.
   
   So the volume is not constant, the drysuit is itself incompressible but the air inside is not. Picture a balloon, the balloon membrane is not so compressible but the air inside is. It is similar for the drysuit.
   
   Typically you need to top up a bit of air when you go down.
   
   
2. You are correct when you say that if you are perfectly weighted, you should have an empty BCD at the end of the dive. Personally, I prefer to be a tiny bit heavier rather than exactly perfectly weighted, so I have a bit more room in case some air is trapped somewhere.
   
   
3. Normally you use a thicker undersuit when it's cold rather than adding more weight and overinflating your drysuit.
   
   With a thicker undersuit you will have more bulk under your drysuit and that will keep you warmer.
   
   
4. You can use your drysuit for buoyancy but I don't think you should do it mostly because it feels warmer.
   
   Using the drysuit has one advantage: it is that you have only one source of buoyancy to manage.
   
   Using the BCD for buoyancy gives you more stability:

• because the air is in your wing, it is not moving in your drysuit. Because it is smaller, it will migrate less.
  
  
• you can dive with your drysuit valve always open, you will top up air only when you feel a squeeze in your drysuit and lift your shoulder when you want to release from your drysuit. This requires you to be fairly flattish or you will release air accidentally.
  
  
• however this means that for example during an ascent, you need to be releasing air from two sources at once. This can require a bit of practice

 

[inquis]

The suit exhaust valve is typically far slower than that of the wing. Diving an AL80 requires you put more than 2 liters of extra volume in either the suit or the wing at the beginning of the dive. (This compensates for the weight of the air you haven't yet breathed, and larger tanks require even more volume.) The suit may not be able to vent fast enough if you get "behind" for whatever reason when ascending (e.g., up current, task loading, or equipment malfunction). You also cannot vent most suits while swimming head-down to reduce that ascent rate, but that is easy when the extra air is in the wing. (I guess I am assuming proficiency at using the hip dump.)

Perhaps I'm weird, but the bubble of extra air tickles me as it moves around the suit. If I put it in the wing, it doesn't.

 

[Rukkian]

I am still fairly new to my drysuit, but I personally do not use my drysuit for buoyancy. My wing does much better for that. I like a little air in my wing, as it really helps keep me horizontal while under water. I can also dump air from different positions, say I get inverted, and am struggling (hasn't happened yet), I could dump from the bottom dump pretty easily. I also normally leave the shoulder dump on my drysuit full open during the dive.

 

[boulderjohn]

A comparison of drysuit to wetsuit depends very much on the thickness of the wetsuit.

If you are diving with a lot of neoprene in cold water, diving with a wetsuit is harder than a drysuit because of the compression of the suit. With a drysuit, the volume of air in the suit required to be neutrally buoyant at 10m of depth will be the same at 30m of depth. You will need to add air as you descend to maintain that volume, but it will be the same volume. That means your weighting needs will be the same at any depth, changing only by the weight of the air breathed during the dive. If you are properly weighted at 10m, you are properly weighted at 30m.

In contrast, as a thick wetsuit descends, it compresses, and it compresses a lot. That changes your volume, which changes your weighting needs. You need more weight in shallow water than you do in deep water, but there is nothing you can do about it. You will be overweighted on the deepest part of your dive, and as you ascend, you will suddenly get more buoyant in the shallow water. You can;t vent air from the wetsuit as you ascend the way you can with a drysuit. (When I ascend with a drysuit, I barely notice that air leaving.)

The same thing will technically be true while diving a thin (3mm) suit in warm water, but the difference will not be significant, and you will barely notice it.