Dry suit conflict

[john cootes]

Have just completed my PADI Dry Suit specialty, but have come across some conflicting advice. The PADI "Adventure Dive" manual says I should control buoyancy underwater with my Dry suit and use my BCD only at the surface. However, the instruction manual from Prestige Dry Suits says I should NEVER use my suit as a buoyancy control, and that the BCD should always be used underwater.

Personally I find it a lot easier to use the BCD - I am used to its configuration and it seems a lot easier to control buoyancy during my safety stop - I assume I will feel comfortable with both options after a few more dry suit dives - but I would like some feedback on how other divers control their buoyancy with this type of suit.

 

[Diver0001]

PADI teaches to use the drysuit for controlling buoyancy because they believe it's less task loading for newbie drysuit divers if they don't have any air in their BCD's.

In practice people use both the suit and the BCD to varing degrees. Many cyber-divers will tell you to use the suit to eliminate squeeze and the use the BCD to control buoyancy. In reality you have to just try it and see what works for you.

I think the message your drysuit manual was trying to give you is that your BCD is a *required* bit of gear for your safety.

R..

 

[S. starfish]

What you'll find most people telling you on this board is to use the BC for primary bouyancy and only to put enough air in the suit to aleviate squeeze - I agree with them. Why exactly the PADI manual says that I'm not sure, you can use the drysuit for bouyancy but it's a lot less stable in the water and harder/slower to vent. Quite often however, when new divers are taught to use a dry suit (e.x. in an open water course) they will be told to use the drysuit only to avoid task loading.
Bottom line If you're just learning the drysuit it may be a good idea to try using it for bouyancy just to get used to manipulating the air bubble and so that dumping air from the suit becomes second nature to you, after that I'd only use the BC for bouyancy and the suit for comfort, with less air in your suit you are more stable in the water, you can move around a bit more without if affecting your bouyancy too much and there is less chance of a foot first ascent.

 

[do it easy]

When I first started diving dry, I used the suit exclusively, but quickly found it was easier to use the BCD and add just enough air to relieve squeeze.

Lately, I've found that I add more and more air to the suit and less to the BCD. The air in the suit vents automatically, which makes ascents easier and keeps me warmer. I also use the air in my drysuit to trim myself out since it tends to lift the feet.

 

[Jim Baldwin]

Have just completed my PADI Dry Suit specialty, but have come across some conflicting advice. The PADI "Adventure Dive" manual says I should control buoyancy underwater with my Dry suit and use my BCD only at the surface. However, the instruction manual from Prestige Dry Suits says I should NEVER use my suit as a buoyancy control, and that the BCD should always be used underwater.

Personally I find it a lot easier to use the BCD - I am used to its configuration and it seems a lot easier to control buoyancy during my safety stop - I assume I will feel comfortable with both options after a few more dry suit dives - but I would like some feedback on how other divers control their buoyancy with this type of suit.

I worked with two veteran divers this past weekend at Vortex Springs in Florida. They were experienced divers and were doing their drysuit specialty. They had reviewed the manual, watched the video and done dives in the pool. PADI teaches to use the drysuit for buoyancy control and your BCD on the surface and that was what they were doing.

I had them use their BCD as they had been doing and simply use enough air to get rid of the squeeze. On ascent I had them use their OPV on their drysuit and dump air from their BCD as they had already been doing. They were able to control their buoyancy much easier, faster and better than using their drysuit for primary buoyancy.
It really requires minimum task loading.

 

[oly5050user]

What you'll find most people telling you on this board is to use the BC for primary bouyancy and only to put enough air in the suit to aleviate squeeze - I agree with them. Why exactly the PADI manual says that I'm not sure, you can use the drysuit for bouyancy but it's a lot less stable in the water and harder/slower to vent. Quite often however, when new divers are taught to use a dry suit (e.x. in an open water course) they will be told to use the drysuit only to avoid task loading.
Bottom line If you're just learning the drysuit it may be a good idea to try using it for bouyancy just to get used to manipulating the air bubble and so that dumping air from the suit becomes second nature to you, after that I'd only use the BC for bouyancy and the suit for comfort, with less air in your suit you are more stable in the water, you can move around a bit more without if affecting your bouyancy too much and there is less chance of a foot first ascent.

Reason could also be that if you are weighed correctly where if all air out of bcd and suit on surface you just barely float and sink when you exhale,by adding air to suit at depth you are only replacing volume you lost as descending so buoyancy will be same at depth as it was on surface.I use this method and works fine usually..May use a little air in bc to trim out but mosly the suit ..Time to surface you can leave the dump valve open and let it self vent for the most part..

 

[ClayJar]

I trim myself out by playing suit inflation against BC inflation. If my feet are sinky, shuffle a little air from the BC to the suit. For floaty feet, move air the other way. Of course, most of the finer work I do with breathing, but manipulating lungs, BC, and suit at the same time is hardly difficult, and it makes the diving, oh, so easy.

(Of course, the key is to be properly trimmed to begin, but if you are, little adjustments like this are great.)

 

[Thalassamania]

I have trouble understanding why this topic always gets so complex. Everyone agrees that you should use add gas to your drysuit to alleviate squeeze, that means maintain constant volume in the suit. Now, if you maintain constant volume is the suit, what else has an effect on your buoyancy? There is just compression of your neoprene gloves and hood (if so equipped), which is negligible, and compression of gas in your BC that you may have added to buoy up the gas that you will consume during the dive.

If you’re diving a single that’s perhaps 5 lbs. and if you can comfortably swing that shift by moving your breathing cycle, well all that’s left is adding and subtracting to your suit to maintain constant volume. If you have small lungs or are carrying a heavier gas load you will be adding some air to your BC at that start of the dive to float your gas and you will be venting off that buoyancy, bit by bit throughout the dive, as you use up your gas, while you maintain near constant volume in your drysuit.

Bottom line: Constant volume in your suit, diminishing volume in your BC through the dive. So on your descent you need first to add to your suit so that it “feels” the same (and set your OPV) and if (and only if) you are using your BC to float your gas you will need to add to that also. So you arrive at your planned depth, adjust your suit (again) and then trim out with your BC (again). If you remain at that depth for the duration of the dive all you will have to do is trim out by dumping a bit from your BC every now and again to stay neutral. If you are going to continue to descend you need to continue to adjust your suit and then trim your BC every now and again. If you ascend, your OPV should take care of your suit, but you will need to dump some gas from your BC.

Were it can get tricky is close to the surface, especially if you’ve got two pockets of gas, one in the suit and one in the BC, both of which are rapidly changing with respect to changes in depth. But what you’ve got going for you is that, with proper planning, your BC in now empty (you’ve used up all that gas and don’t have to float it any more) and you can completely dump your BC and just work on maintaining constant volume in your suit on the way up and at your stops.

 

[The Horn]

As you can see it is personal preference. I use BC and remove squeeze with suit only. Lots of commercial divers just use the suit as they don't bother with a BC. What ever works for you. Practice your style.

 

[MikeFerrara]

Reason could also be that if you are weighed correctly where if all air out of bcd and suit on surface you just barely float and sink when you exhale,by adding air to suit at depth you are only replacing volume you lost as descending so buoyancy will be same at depth as it was on surface.I use this method and works fine usually..May use a little air in bc to trim out but mosly the suit ..Time to surface you can leave the dump valve open and let it self vent for the most part..

Sort of...
A correctly weighted diver will be heavy by the weight of the breathing gas they carry. About 6 pounds for an 80 cu ft tank? If more breathing gas is being carried, the diver will be that much heavier. Letting all the air out of the bc at the start of the descent should get you sinking pretty good with a full tank. Probably too fast for a lot of divers. A nice controled descent will be started by just letting enough air out of the bc to get neutral and exhaling to become slightly negative. This is where PADI's method starts to fall apart and I don't think they could get away with it at all if they taught descents correctly in the first place. Certainly any diver who has been taught to descend would have to comment in class..."But...I didn't completely empty my bc to start the descent in the first place" LOL

It continues to fall apart as the diver carries more breathing gas (or other ditcheable gear) and gets heavier. Try it when carrying 16 pounds of breathing gas and you'll have such an air bubble in the suit that if you raise an arm or get slightly head up, all that air will burp out through a seal and you'll be dropping like a rock. Talk about task loading!

By contrast, using the bc for...you guessed it...buoyancy control, works all the time regardless of configuration while using the suit for buoyancy control only even comes close to working under special conditions.

The best approach, IMO, is to learn it right to start with and use an exposure suit for what it was designed for and a bc for what it was designed for. A screw driver can sometimes be made to work as a pry bar but sometimes you just end up with a job done poorly and a bent screw driver...though it does reduce task loading by eliminating the need to know the difference. LOL