Drysuit bouyancy question

[RichLockyer]

have a large amount of change in bouyancy and will be substantially negative at the start of the dive.
......
but are saddled with managing two air spaces and if taken to extreme defeats much of the insulating advantage of a dry suit if insufficient air is kept in the suit.

Everyone is at least 5 pounds overweighted at the start of the dive... those diving HP cylinders could be as much as 9 pounds heavy. That's between one and two gallons of water that needs to be displaced by either the suit or the BC. That's a big bubble in the suit, but it is manageable IF the diver is perfectly weighted. If the diver is overweighted, then it can quickly become a destabilizing bubble, leading to the notorious "feet first ascent" and other problems.

Now part 2, managing two airspaces need not be a problem.
Maintaining position as horizontally as practical, the shoulder dump can be left fully open for the entire dive. I've been using a drysuit for all non-tropical diving for well over 2 years now and have yet to even TOUCH my dump valve between the beginning of my initial descent and surfacing. On the surface, I'll add a little extra air and completely shut the valve.

If the suit is used as the primary means of buoyancy control, then the dump needs to be adjusted continually (opened) as the diver burns gas and gets lighter. Moving up in the water column is not a problem because the valve self-dumps (if adjusted properly), but if the diver flips to a head-up position then the suit will rapidly dump and the diver will lose buoyancy, leading to the imagined need to CLOSE the valve and add gas on ascent... while the legs are still suffering squeeze.

Maintaining any position OTHER than horizontal is going to create issues no matter how the suit is used, as the gas bubble will always be pushed to the highest point, but diving with MORE gas in the suit increases the dynamic instability and makes it even more important to remain prone.

As far as maintaining the same style for any type of dive.... why not? I can understand that one particular style may not work for every PERSON, but I believe that each individual is safest and most efficient when they are consistent. You don't have to dive my way, but don't confuse me by changing your way to something different every time I get buddied up with you

 

[RichLockyer]

I will closely look into your suggestion
I dive a 7mm Neoprene drysuit with a small steel tank and 10kg of lead.

The neoprene suit will compress at depth, which will require that you add more weight than a shell suit, but will leave you more negative on the bottom.

If it has neoprene seals, especially wrist seals that are not tuck-under, if you try to use the suit for primary buoyancy control and lift your arm, the bubble will likely simply blow out your wrist seal.

My first drysuit was a 7mm neoprene O'Neill, so I speak from experience.
I used that suit for two months and bought a Typhoon Trilam, used it for two months and bought a TLS350.
I just bought a second TLS350, as I have lost weight and need a custom fit.

 

[IndigoBlue]

Hi all.

I did the drysuit course last weekend. Went thru the texts and video myself then did the pool session and two OW sessions with the instructor. Not rocket science but takes some practise and there's always more than one way to skin a cat.

I know what the text says, but out there in the real world...how do you drysuit divers manage your bouyancy at depth...with your bc or your suit? And why do you do it the way you do.

My thinking is that inflating the suit just enough for insulation and reducing squeeze then using BC as normal is perfectly reasonable.

Thanks in advance.

During my descent, as long as my ears are clearing, I find that I can control the descent with the suit inflator alone. Once I get to the depth I want, then after I eliminate the suit squeeze, I start to inflate the wing to stop my descent and neutralize at the desired depth in order to compensate for the 5 to 10 lbs of air/mix that I will be using up during the open circuit dive.

If you keep the suit's dump valve turned all the way open, then you will always only have a minimum amount of air/argon in the suit to eliminate squeeze. If you monitor your breathing to keep your buoyancy neutral at all times, you will never over-inflate your wing.

A good dump valve on a suit will purge itself as you ascend, if you have opened the valve all the way and if you have a minimum volume in your suit.

A tug on your hose occasionally when needed will dump enough air/mix from the wing to keep you neutral as the dive progresses, since as the dive progresses the air/mix in your tank(s) will be consumed and exhaled during an open circuit dive, and then there will be less and less need for any air in your wing at all, if you have established good trim and weighting in the first place.

If you get to the end of your dive, and you still have a lot of air in your wing, then you are diving overweighted, and you should fix that, before you go diving again.

 

[aquaoren]

The neoprene suit will compress at depth, which will require that you add more weight than a shell suit, but will leave you more negative on the bottom.

If it has neoprene seals, especially wrist seals that are not tuck-under, if you try to use the suit for primary buoyancy control and lift your arm, the bubble will likely simply blow out your wrist seal.

My first drysuit was a 7mm neoprene O'Neill, so I speak from experience.
I used that suit for two months and bought a Typhoon Trilam, used it for two months and bought a TLS350.
I just bought a second TLS350, as I have lost weight and need a custom fit.

I'm well aware of the compression of neoprene in depth and loss of positive buoyancy and I still don't think I'm awfully overweighted with 10kg of lead and a 7mm Drysuit.
Using your seals for buoyancy wouldn't work with gauntlet style gloves And I don't see a reason not to use the exhaust valve on my left arm if I need it. As previously said, I'm using my BC for Buoyancy and inflate my suit so much to make comfortable and warm

 

[alemaozinho]

if you are properly weighted then there is no reason to use your bcd in addition.It,s much safer this way because you would struggle if an emergency arises (freeflowing regulator(freeze up) , a frozen drysuit valve ,or a stuck low pressure inflator button will do it,for example)could lead to a major struggle,because of the additional time needed to undue the increased buoyancy which could lead to panic=accident/injuries/death.Keep it simple!Peace

 

[ScubaDadMiami]

Put just enough gas in the drysuit to avoid squeeze, nothing more. Use the BC for what the "B and C" stand for.

You will have to multitask if you have to start dealing with adjusting/pushing the exhaust, venting the suit and venting the BC during the ascent. Imagine trying to do all this and then also having to deal with something else at the same time. Doesn't that sound like juggling?

As I ascend, I have little gas in my suit to start with. So just lifting my left arm a bit (occasionally, I have to perhaps SLIGHTLY adjust my angle of attack for a second to make sure that suit gas moves to the exhaust), I vent any expanded gas in a split second. I can pretty much just keep my arm in the right place, asending properly and venting gas as necessary. Coincidentally (not really) this is the same arm as used for the BC inflate/deflate. You can do everything at the same time.

 

[AtomicWalrus]

I find that after adding air to my drysuit to counteract squeeze, I usually don't need much air in my BCD. However, I do like using my BCD for some of my buoyancy control because the BCD dump valve is MUCH faster than a drysuit dump valve. If I have to make a quick adjustment to my buoyancy (as in catching a runaway student), being able to dump air fast is important.

 

[RichLockyer]

I find that after adding air to my drysuit to counteract squeeze, I usually don't need much air in my BCD.

That's the idea, and happens when you are properly weighted. You need only enough to offset the gas in your tank, which in the case of an 80 is only about 5 pounds. That's just a touch over a gallon of air in the BC.

If the suit is just offsetting squeeze and it is consistent, then it's buoyancy is not changing during the dive. This is a concept... and advantage of shell suits... that people sometimes have a hard time realizing. The properly fitted and properly inflted shell suit will change buoyancy with depth no differently than your buoyancy will change when you're diving in a T-shirt and shorts in Cozumel.

 

[Phish-phood]

As String said this is personal preference!

Personally when I dive I like to be in a slightly head down feet up position. Putting just enough air in my Drysuit to alleviate the suit squeeze will generally be enough to get me neutrally bouyant anyay and I just allow the air to migrate to my legs and keep my feet up for most of the dive. I find it easier to move around in the water and change position if I am using my drysuit.

That said I am thoroughly comfortable using either my BC or drysuit diving. As I said before in a previous thread, I don't wear my drysuit abroad and *have* to switch to using my BC and it causes me no problems whatsoever.

My advice would be use whatever you are most comfortable with but make sure you can use the other just as well

 

[DA Aquamaster]

Everyone is at least 5 pounds overweighted at the start of the dive... those diving HP cylinders could be as much as 9 pounds heavy. That's between one and two gallons of water that needs to be displaced by either the suit or the BC. That's a big bubble in the suit, but it is manageable IF the diver is perfectly weighted. If the diver is overweighted, then it can quickly become a destabilizing bubble, leading to the notorious "feet first ascent" and other problems.

I don't think we disagree here. If the diver is properly weighted and is diving with a single tank with a "normal" capacity and swing weight, then the air in the suit is going to be manageable.

If the diver switches back and forth from singles to doubles or is for some other reason greatly over weighted at the start of the dive, then augmenting lift with the BC may be the way to go.

But believe it or not some divers actually dive single tank all the time and do not carry lots of stuff like reels, lights, stage bottles etc, and in fact can benefit from just using the suit to manage bouyancy.

I find that after adding air to my drysuit to counteract squeeze, I usually don't need much air in my BCD.

That's the idea, and happens when you are properly weighted. You need only enough to offset the gas in your tank, which in the case of an 80 is only about 5 pounds. That's just a touch over a gallon of air in the BC.

If the suit is just offsetting squeeze and it is consistent, then it's buoyancy is not changing during the dive. This is a concept... and advantage of shell suits... that people sometimes have a hard time realizing. The properly fitted and properly inflted shell suit will change buoyancy with depth no differently than your buoyancy will change when you're diving in a T-shirt and shorts in Cozumel.

Not much air is needed - my point exactly - whether it is in the BC or the suit. So if 5 pounds of air in the suit (which is in fact 5/8 of a gallon and is slighly over two quarts, not a "touch over a gallon") is not excessive, then why would the diver necessarily have to use the BC at all?

Again, a diver needs to try both ways and go with the one that works best for them and should not feel pressured to use both the BC and suit to maintain bouyancy just because doing it that way is a current trend that happens to popular with many members of scuba board.