Drysuit Buoyancy ????????????????????

[Newbie100]

I recently purchased a Waterproof crushed (3.5) neopreme drysuit and have had one pool cession with it. Accourding to the PADI Text & My instructor my BCD is only to be used at the surface and not during the dive: buoyancy to be controlled by adding and venting air from the drysuit. The text further states that the only exceptions to this are 1) when using a neopreme drysuit--not crushed, and for technical divers that use a combination of air in the bcd and drysuit. At our world underwater this weekend I talked to a Technical diver and instructor that told me just to add enough air to avoid suit squeeze and to use the BCD for buoyancy ( I have a rear inflation bcd). My guess that it is easier to control a smaller BCD air space. Is is possible that both situations are correct depending on circumstances? Is there a reason that one method is preferred to the other, could someone give me some reasoning. What do other non PADI agencies teach? Also the neck seal seems a bit tight. I tried to stetch it out around a kitchen canister for a week about 1 & 1/2" smaller than my neck. After abouty an hour and 15 minutes I thought that I wasd going to pop. I was told by my instructor not to trim the neck seal because if there is a small nick perpindicular to neck seal it will conmtinue to tear and I will have to replace it. I was further told to stretch and spray the neck with food grade silicone spray. I would really appreciate a good explination from anyone who has the time.

 

[ScubaRich]

This is one of those questions that is answered, what ever is more comfortable for you. Most people I know (me included) Add just enough air to the drysuit to take away the squeeze and control the rest with the BC or wing. As far as the neck seal, I don't know about the stretch it out methode since i'm guessing it's latex and is just going to snap back. If you are careful trimming tearing shouldn't be an issue. Don't dive a neck seal too tight! I'd rather replace a neck seal the end up dead.

 

[BettyRubble]

Well this should prove an interesting thread.

 

[kjvander]

I recently purchased a Waterproof crushed (3.5) neopreme drysuit and have had one pool cession with it. Accourding to the PADI Text & My instructor my BCD is only to be used at the surface and not during the dive: buoyancy to be controlled by adding and venting air from the drysuit. The text further states that the only exceptions to this are 1) when using a neopreme drysuit--not crushed, and for technical divers that use a combination of air in the bcd and drysuit. At our world underwater this weekend I talked to a Technical diver and instructor that told me just to add enough air to avoid suit squeeze and to use the BCD for buoyancy ( I have a rear inflation bcd). My guess that it is easier to control a smaller BCD air space. Is is possible that both situations are correct depending on circumstances? Is there a reason that one method is preferred to the other, could someone give me some reasoning. What do other non PADI agencies teach? Also the neck seal seems a bit tight. I tried to stetch it out around a kitchen canister for a week about 1 & 1/2" smaller than my neck. After abouty an hour and 15 minutes I thought that I wasd going to pop. I was told by my instructor not to trim the neck seal because if there is a small nick perpindicular to neck seal it will conmtinue to tear and I will have to replace it. I was further told to stretch and spray the neck with food grade silicone spray. I would really appreciate a good explination from anyone who has the time.

For this I’ll try my best to answer your questions in two parts, buoyancy and then trimming seals.

Part 1
For the buoyancy… Most instructors and texts start out by telling you to use the drysuit during the dive for buoyancy as to decrease the amount of task loading that is present while learning to dive a drysuit. By using the drysuit only during the dive you only have to worry about one air pocket just as if you were diving a wetsuit and a BC. With the drysuit method you move the air bubble from on your back to around your body. This is a good method if you have your weight right and aren’t too over weighted. The problem with this theory and method is that if you need to add to much air to the drysuit you will have too large of a bubble to control easily and can run into some problems during the dive. Moving along in your diving and comfort with the drysuit most people will migrate to the use of both airspaces. Just taking the squeeze off in the drysuit and then adjusting with the BC reduces the air pocket in the drysuit and minimizes the chance of getting too much air in your feet and other undesirable circumstances. This does add to the task loading during the dive as you now have to deal with two different air pockets but once practiced becomes easy. Hopefully that kind of gives you an idea of the two different methods. Both are perfectly acceptable to use….just depends on what you are comfortable with and what you practice.

Part 2
For the neck seal issue. With how you stated this I am going to assume that you have a latex seal on your neck. The following applies to latex seals. There are rings on your seal both on your wrists as well as your neck. These are templates for trimming your seals for a better fit. Depending on where you got your drysuit from, if you got it from a dive shop then they should have taken the time to trim your seals when you picked it up. If not you should find someone that is trained in drysuit repairs for this kind of thing at first. It is your neck seal so if you want to take a shot at it with out knowing what is going on…by all means….it’s not that hard. However, for the sake of learning take it to someone that knows what they are doing and watch and learn. But yes the seal should be trimmed so that it fits snug but does not cut off circulation. The method that you used to stretch out the seal is that once you get it close you can do that to add a little bit of a stretch to the seal….but it is not a cure all.

Hope this helps.

 

[sschlesi]

I'd say do what works. For me the BCD is only used on the surface.

Undergarments play a big role in the decision.

Those who wear few undergarments because they are:
a) in relatively warm water
b) have a thick neoprene suit
c) are tolerant of colder temperatures

will probably find that the volume of air required for buoyancy substantially exceeds the volume of air required to alleviate squeeze/loft their undergarments. And many of them prefer to manage that additional air in their BCD.

Those who wear thick undergarments because they are:
a) in relatively cold water
b) have a thin tri-lam suit
c) are afraid of the cold

will probably find that the volume of air required to alleviate squeeze/loft their undergarments is very close to that required for buoyancy control, and their is little benefit in adding any air to their BCD.

 

[Newbie100]

I appreciate the reply concise and helpful

 

[chaOs85]

About the buoyancy question I personally find that the air required to relieve squeeze is enough to gain natrual buoyancy. This is with a single steel cylinder though. With doubble 12L steels I need to add air to the wing because I am very heavy with full tanks and if all the air was put in the suit it would be a problem. The most important thing is to do a good weightcheck. Good luck!

 

[muddiver]

As a commercial diver I learned to use the dry suit for buoyancy. We don't wear BCDs when diving for work, unless on scuba, which is not done very often.

But, there are some folks here on the board with a lot more scuba and tech experience than myself that will tell you that is wrong and you could have serious buoyancy issues, therefore control buoyancy with the BCD and add air to the suit for comfort.

Your choice.

 

[a22shady]

During my Drysuit Class I was told the same thing through the PADI Book. The instructor and the dive shop stated that the best way to properly work the system is to use the suit for squeeze only and BC for buoyancy. Through the course the like you do it the reverse simply because at first it is easier. But from what I see can cause some troubles later. 1st problem I see if your using the suit for buoyancy and start ascending too quickly it could be a lot more difficult to get the air out fast enough to stop. Whereas the BC lets the air out quicker again depending on how you have the suit vent set. Personally It is a lot easier to control your buoyancy and ascent/descent by your BC. it's easier to maintain your rate by venting most from your BC and only needing a minuscule amount from the Drysuit.

 

[Gerbs]

I use the suit only up to 10m depth while descending, then I keep the suit volume constant and use the BCD. When surfacing, I try to have an empty BCD by the time I get back to 10m, and do the rest with the suit.

Seems to work well for me with a crushed neoprene dry suit with thinsulate undergarments. Your milage may vary, but generally you want the amount of air in the suit and BCD such that the depth changes during your breathing cycle don't exceed your vital capacity's ability to compensate.

How you split the air is a bone of contention - if you are diving a Weezle undersuit, which compresses easily, under a tri-lam dry suit, your balance of air distribution might be different to a fleece undersuit in a neo dry suit.

Gerbs