Dry Suit and Buoyancy Control

[abyss_scuba]

I was taught to use the dry suit for buoyancy, the thinking was in an uncontrolled ascent you only have to vent the suit not both. After many years I use the bc on the surface and suit below, which ever you choose it will become second nature after awhile.

 

[oum]

(for whatever reason,i tend to excel at deeper depths than shallow)

By the laws of physics: Pressure changes faster near the surface, so even a little extra air makes a large difference to buoyancy. The same amount of air at depth will make little difference (comparatively speaking). You may even be negatively buoyant at depth and compensate for it subconsciously, by swimming. Near the surface you can't compensate as easily, you have to consciously fight it, hence you notice it.

To make it short -- and forgive me for being so direct -- you don't 'excel' at depth, you just don't notice the problem. Just like I used to. The good news is, it only takes a bit of focused exercising to learn to control your buoyancy better. I had success by carefully tuning my weights (too much weight will force you to overcompensate with too much air), then trying to keep at the same depth while solving puzzles under water, so that my conscious mind would be occupied and buoyancy control could become a habit.

I remember finding very useful materials about correct weighting and buoyancy at Andy Davis' Sidemount Technical Wreck | Andy Davis Technical Diving Philippines

Have fun & all the best!

 

[billt4sf]

Consider the following (and someone tell me if I am mistaken):

After you descend you establish neutral buoyancy and also establish an appropriate level of quit squeeze using both the BCD and suit if necessary. If you descend further, you will need to add a little air to re-establish neutral buoyancy and to re-establish the same level of suit squeeze, so add a bit of air to the suit. If you ascend, just vent a little air. Done.

Seems to me that the only issue is to establish neutral buoyancy at the start of the dive after you descend. If you have to add much to the BC when you first descend, you are overweighted. If you are very squeezed after you descend, you are underweighted.

To quote that great sage Walter: "Am I wrong?"

- Bill

 

[Dhboner]

That's why I said I use my suit during descent for both since I need buoyancy control and loft at the same time. When I reach target depth any "corrections" or "tweaks" are done with my wing only. I don't want any more air in my suit than I actually need to stay warm since it is more difficult to vent on ascent.

 

[MXGratefulDiver]

I was taught to use the dry suit for buoyancy, the thinking was in an uncontrolled ascent you only have to vent the suit not both. After many years I use the bc on the surface and suit below, which ever you choose it will become second nature after awhile.

The thinking is in error ... drysuits are designed to vent more slowly than BCDs, so once you begin an uncontrolled ascent, it will be harder to get under control by venting the suit rather than the BCD. In fact, under certain conditions you'll reach a point where the air in your suit is expanding faster than you can possibly vent it ... in which case you aren't just going to the surface, you'll be accelerating the whole way there. Besides that, think for a moment about where the drysuit dump valve is located, and why they'd put it where they did ... in an uncontrolled ascent while dumping air from your BCD, you'll also be dumping it from your suit without any additional effort (assuming you've got your dump valve adjusted properly). By using the suit only for buoyancy control, you don't have that option.

The theory behind recommending suit for buoyancy control is for ease of air management. It's a nice theory, but in practice it tends to present more downsides than upsides. Sure, it's easier to learn that way ... but there's a reason why most experienced drysuit divers tend to only put sufficient gas in the suit for warmth and range of motion ...

... Bob (Grateful Diver)

 

[claymore]

I was taught to use the suit for bouyancy control because that is the PADI Line, because you have only one air bubble to deal with, but my instructor said that using the BC for buoyancy control was a better way. I started using the suit but later tried using the bc for buoyancy control and the suit for warmth. I found it much easier to control my trim and buoyancy when using the bc for buoyancy. With a smaller bubble in the suit it is a lot easier to control where the bubble is and keep it from getting away from you.
I DM a lot in my dry suit so i spend a lot of time hovering and moving around the students in about 20' of water. At that depth your buoyancy can get away from you fairly fast if you are not watching it so I prefer to keep my suit fairly empty and only have to worry about exhaling big time and bumping my bc a little if needed.

 

[BFRedrocks]

The theory behind recommending suit for buoyancy control is for ease of air management. It's a nice theory, but in practice it tends to present more downsides than upsides. Sure, it's easier to learn that way ... but there's a reason why most experienced drysuit divers tend to only put sufficient gas in the suit for warmth and range of motion ...

... Bob (Grateful Diver)

While some of us may disagree one way or the other, I think the key here is the bold text...it is the experienced drysuit diver who can (typically) manage two air bubbles better than a new drysuit diver. I agree that it's much easier to teach using your drysuit as the sole air bubble to control buoyancy at depth, but the ease at which this can be done is also predicated, in part, on suit type (neoprene vs shell) and proper weighting. I too was taught to only use my drysuit for controlling buoyancy at depth, and for my first 10-20 drysuit dives, that worked for me. However, as I've gotten more drysuit experience, I do see the other points about using just enough air in the suit to relieve squeeze and control buoyancy with the BCD. If done properly and with the proper experience, then the issue of managing two air bubbles upon ascent is not as difficult as first thought.

I think someone else said that you should go with whatever you're most comfortable with, but as you gain more and more experience, you may find that that method changes somewhat.

 

[bl6394]

I teach the PADI dry suit class - as it is designed - using the dry suit for primary buoyancy control underwater.

I then advise my students that if your lungs are a scalpel and your BCD is a hammer – your dry suit is a sledgehammer for controling buoyancy under water.

After they are certified- they can dive any way they want. I dive minimally weighted, with just enough air in the suit to relieve squeeze.

 

[Patoux01]

While some of us may disagree one way or the other, I think the key here is the bold text...it is the experienced drysuit diver who can (typically) manage two air bubbles better than a new drysuit diver.

Well, I dunno... Been told to use the drysuit during my OW class, decided to use the bcd instead once I was done with the class and got in a drysuit again (about 60 dives in between though), and "surprisingly", it's much easier to handle the bcd than a drysuit in terms of air in it. A BCD can dump air in any position, try that with a drysuit... There's no "second bubble" if you have (almost) no air in the suit. On ascent it will take ages before it'd even be able to take you for a ride (since there's little air in it, it won't expand a lot).

I think someone else said that you should go with whatever you're most comfortable with, but as you gain more and more experience, you may find that that method changes somewhat.

I believe that one should learn the way they should use it. No such thing as "this is very good for learning, but very bad once you're experienced". There's nothing complicated about diving a drysuit.

I teach the PADI dry suit class - as it is designed - using the dry suit for primary buoyancy control underwater.
I then advise my students that if your lungs are a scalpel and your BCD is a hammer – your dry suit is a sledgehammer for controling buoyancy under water.

Now this just makes me sad. I'd rather not teach a class than teach it against my beliefs...

 

[bl6394]

Now this just makes me sad. I'd rather not teach a class than teach it against my beliefs...

I understand your frustration. Consider that being an instructor involves more than just doing what you want, the way you want to do it. One has to consider (not necessarily in this order):

• the standards of the certifying agency
• risk mitigation
• business considerations
• delivering good value to the student

If you think carefully about my previous post - you'll see that each of these issues was considered in my response.