use drysuit or BC for buoyancy?

[Teamcasa]

great i will try using my bcd instead. I have the whites nexus 3 and i was using it to do bouyancy with and it was causing me to go in to rapid assents thanks for the info

Your rapid ascents were due to your not purging the air from your suit and/or your BC.

As you learn, open the purge valve all the way at first. When you decide to ascend, start by inhaling a nice deep breath and purging your BC and suit. Ascent control and speed will come with practice.

Here is a good thread as well.
A question about buoyancy control at shallow depth

 

[TSandM]

I don't know that there is a consensus.

I do believe that, for a new drysuit diver, using the minimum amount of gas in the suit that's necessary to be comfortable is an easier strategy. I was originally taught to use the suit for buoyancy, and I got into trouble doing that. For Fundies, I went to the "20 foot squeeze", which made managing buoyancy MUCH easier (but also left me cold). For two years, I minimized gas in the suit and used the wing for buoyancy, and then I took a Helitrox class from another instructor, who encouraged us to use the suit far more. By this time, my grasp on my buoyancy was much better, and I found that more air in the suit meant a number of things: Easier buoyancy control on ascent when your hands are tied up (with a bag, or a reel, for example), a much warmer dive, and a greater ability to position air to balance myself in the water.

Nowadays, for a simple dive, I put as much air in the suit as I think is manageable, and only add to the wing if that's not enough (like with two extra bottles the other day). But I do it differently if conditions require it -- for example, the entrance to one of the Mexican caves is a very steep passage that isn't very tall, so you have to swim very much head-down, and having all the gas in the suit doesn't work well there. So I use the wing in that place, and when I get to the bottom and level out, I transfer the gas from the wing to the suit, so that I'm beautifully set up for a hands-free venting on exit.

So maybe start out with the suit pretty tight, and as you gain facility with it, experiment with how you like to manage things. The only extent to which there is a "right" answer is that, whatever you do, you have to be able to manage your buoyancy accurately that way.

 

[Rick Inman]

... Easier buoyancy control on ascent when your hands are tied up (with a bag, or a reel, for example)...

Yeah, it's true that the almost self-dumping properties of the Fusion makes it tempting to dive the easy (lazy?) way...

 

[DA Aquamaster]

There are specialty situations that develop. If I am colder or in colder water, more gas goes in the suit. If I have to pee, more air goes in the suit as less squeeze seems to promote better flow. If I am ascending soemthing like the Ear at Ginnie, or in Little River or some place with lots of flow like Manatee where I also need to not exceed a deco stop, I'll dump an excess from the suit before I start up to reduce the gas management.

I am also one of those who will use the adjustable valve and close it a few clicks when I want to maintain more volume in the suit and close it a few more if I want to do barrel rolls with the scooter, roll over on my back in a cave to view the ceiling, or anything else where I do not want to autmoatically or unintentionally vent air from the suit and lose perfect buoyancy.

 

[Anti-Hero]

My suit + Undergarments don't vent fast enough, or reliably enough to have a lot of additional gas in the suit. I prefer enough gas in the suit to stay comfortable, and the rest is controlled through the wing.

 

[dave4868]

I am new to a drysuit and i use a trilame with a heavy undergarment. I use about 36lbs of weight in it and was wondering if it is better to use the suit for buoyancy or use the BCD and just put enuff air in the suit for the squizz
thanks for your help

great i will try using my bcd instead. I have the whites nexus 3 and i was using it to do bouyancy with and it was causing me to go in to rapid assents thanks for the info

For the most part, this thread has been very informative in offering the rationales and circumstances for using different methods to control bouyancy when diving in a drysuit. It's probably true that more people use the bcd as the primary control and the drysuit only for adjusting the squeeze. Then again, here in the Northeast, I know many people who use only the drysuit for bouyancy control.

I agree completely that you should practice using both methods and then you'll be able to have the advantages of either method, depending on the situation.

Personally, I use only my drysuit for buoyancy control, mainly for the improved warmth and simplicity. I prefer that method, even if it seems radical to use something not officially called a "buoyancy device".

Here are some things to consider as you figure out what works best for you.

Compared to your situation, I wear significantly more insulation and weight, but issues of air shifting and slow venting are completely managable in my suit. That might not be the case with your suit.

Most likely, in my case, the air shifting is managable because my drysuit fits pretty snugly over my insulation.

How loosely does your suit fit over your thick insulation? With my suit, the snug fit makes most of the shifting air travel through the undergarment material. That slows it down compared to traveling above it. Perhaps your suit fits a little more loosely and lets the bubble shift too quickly.

My suit's snug fit, especially in the legs, also reduces the ballooning effect seen in baggier drysuits, so my overall air shift is limited nicely. Perhaps your suit legs are a little baggy. Gaiters might help.

The issue of slow venting is also managable in my suit, even when ascending in shallow water with lots of rapidly expanding air in my suit. Perhaps your exhaust vent is too slow. Perhaps your undergarment insulation is blocking the vent to some extent. Some people fix that issue by stiffening the undergarment material with duct tape where it contacts the vent.

There's also the slow venting issue that results from having one's weighting adjusted to the so-called "correct" minimum. Near the end of the dive, getting neutral with such "correct" weighting is significantly delayed while waiting for the air to get squeezed out of the suit.

I don't have that problem, probably because I use a little more weight than the so-called "correct" weighting, hence, I can get negative or neutral quicker when needed. Man, am I a rebel!

You mentioned "rapid ascents" occuring because you were using your suit for buoyancy. You may be right and the suit may be a limiting factor, but you might still find it managable with practice.

I'd suggest you practice both methods, experiment and learn what's really happening. If you stay open-minded, you'll be more likely to find what works best for you and why.

Dave C

 

[Thalassamania]

This seems to be a confusing and reoccurring problem.

There are only three things that change your buoyancy situation:

1. The quantity of air in your lungs, that is to say where the mid point in your breathing cycle is. You will need to learn to control this and keep it fairly constant.
2. The weight of gas in your tank. Most divers can ignore this when using a single 80, with other tank arrangements the BC is inflated at the start of the dive to offset the weight of gas, and air is either vented as the gas is used up or when the diver ascends or added when the diver descends.
3. The quantity of air in your drysuit. This should be kept as constant as possible, just on the comfortable side of being "shrink wrapped." Add air so that you keep the squeeze away and set your shoulder valve (but don't trust it) so that proper volume is maintained during ascent.

 

[dave4868]

This seems to be a confusing and reoccurring problem.

There are only three things that change your buoyancy situation:

1. The quantity of air in your lungs, that is to say where the mid point in your breathing cycle is. You will need to learn to control this and keep it fairly constant.
2. The weight of gas in your tank. Most divers can ignore this when using a single 80, with other tank arrangements the BC is inflated at the start of the dive to offset the weight of gas, and air is either vented as the gas is used up or when the diver ascends or added when the diver descends.
3. The quantity of air in your drysuit. This should be kept as constant as possible, just on the comfortable side of being "shrink wrapped." Add air so that you keep the squeeze away and set your shoulder valve (but don't trust it) so that proper volume is maintained during ascent.

There clearly are problems and advantages of both of the methods of buoyancy control being discussed. It appears more a matter of opinion and preference than of confusion.

When I use only the drysuit for buoyancy control, the increase in warmth is significant and indispensable for me on long, cold dives.

It's not for everybody, however.

Dave C

 

[Thalassamania]

If you need more warmth, plan for that and weight accordingly, you still should try and keep your suit at a constant volume. Keep in mind that no matter how much more air you will not help the situation on your chest where everyting gets compressed. It is possible to stay warmer by (gasp) going vertical.

 

[dave4868]

If you need more warmth, plan for that and weight accordingly, you still should try and keep your suit at a constant volume. Keep in mind that no matter how much more air you will not help the situation on your chest where everyting gets compressed. It is possible to stay warmer by (gasp) going vertical.

My favorite topic.... how to stay warm under water! I love to be toasty warm!

I agree that maintaining a constant small volume of air in the drysuit will have some advantages, if you're talking about the amount of air needed to make the squeeze comfortable. The problem is it's just not as warm as having a larger amount of air, such as when using only the drysuit for bouyancy and/or adding "excess" weight.

The improved warmth doesn't result just from better loft (primarily in the areas of the "bubble"), but also from the undergarments being kept drier, IMHO.

I believe there's substantial drying of the undergarments as the greater volume of air moves around in the drysuit. Also, sawtooth depth changes will increase the drying effect because the suit air is partially vented and replenished with dry air periodically.

As for your suggestion to achieve the desired warmth by adding more insulation and weight, I've done that. My insulation even includes a homemade 4-layer fleece chest pad to better resist undergarment compression in that area. Still, it's substantially warmer with more air in the suit.

The insulation I wear for 60 to 90 minute dives in sub-40F water temps requires about 48 lbs of lead, absolute minimum. On top of that, I'll add about 6 lbs extra, which makes a big difference at the end of the dive when the tank is less negative and there is correspondingly less air in the suit.

Right now, my thermal protection has been good enough to allow fully functional, low activity dives of almost 2 hours in 34F degree water. Very comfortable for the first 60 to 90 minutes and ending with no shivering, no chills, just a little coldness of the hands and feet. Those dives were usually followed by a second dive after an hour SI.

I'm convinced that maintaining more air in the drysuit is warmer....

As was discussed, there are drawbacks to maintaining more air in the drysuit, but if they can be managed, the warmth and simplicity are well worth it.

Dave C