why hate safety devices?

[Crush]

All your answers, and the solution to your over reliance on excerpting books and numbers mpetryk are contained here:goingdown:

Yeah, I learned LOTS about DCI while diving. Driving my car helped me to be a mechanic as well. Being a frequent flier, I am also well-prepared to pilot the aircraft in case the flight crew takes ill.

 

[aquaregia]

Dr. Wu,

Let's assume that you are diving with a 7mm suit in the Ocean without a BC and you had to use weight to be neutrally buoyant on the surface (or at 15ft) by using somewhere around 20 - 25 lbs. Now you go down to, let's say, 100ft. By definition your wetsuit compresses and loses at least half of its buoyancy at that dept. Now you are at least 10 lbs negative. How would you achieve neutral buoyancy then??

(Note: I am using "back of the envelop numbers for simplicity. I am making some approximation for ease of calculations. The suit also has its own "resistance" to compression in addition to other factors. The suit won't necessarily compress with 50%, it all depends on suit characteristics including material, gas used, etc.Even with 25%, the same question still holds, one still needs to compensate for wetsuit compression.).

My lungs have an FEV of 6.5L and a tidal volume of 0.5L. Lets assume that I use 5L of that for buoyancy control. 5L of displacement is around 11lb of lift. That means I can handle around 11lb of wetsuit compression and gas use.

If we imagine my 7mm has 18lb of lift on the surface and compresses linearly with pressure (pessimistic), we'll say that it has 12lb of lift at 15', 9lb of lift at 33', 6lb of lift at 66' and 5lb of lift at 100'. A pike dive to 15' against 10% of my body mass is not a problem, not even considering the weight of the gas I'm going to use. Assume I'm going to use around 50cf of gas (4lb), and that I want to be neutral at 15' with an empty tank. The end of the dive will have be with suit + gas loss=12+4=16lb. This means that suit+gas loss+lung needs to be the same, so the suit can compress down to 6lb using these numbers before I'd be uncomfortable. While neutral at 15' empty and at 100' full is a stretch with these numbers, it should show the method.

 

[DaleC]

Dr. Wu,

Let's assume that you are diving with a 7mm suit in the Ocean without a BC and you had to use weight to be neutrally buoyant on the surface (or at 15ft) by using somewhere around 20 - 25 lbs. Now you go down to, let's say, 100ft. By definition your wetsuit compresses and loses at least half of its buoyancy at that dept. Now you are at least 10 lbs negative. How would you achieve neutral buoyancy then??

(Note: I am using "back of the envelop numbers for simplicity. I am making some approximation for ease of calculations. The suit also has its own "resistance" to compression in addition to other factors. The suit won't necessarily compress with 50%, it all depends on suit characteristics including material, gas used, etc.Even with 25%, the same question still holds, one still needs to compensate for wetsuit compression.).

How about you're not neutral at the surface. That's new school thinking. If you use a pike dive you can be positive, swim down against bouyancy till your suit compresses and you are then neutral (actually better to be a bit negative). Use breath control and perhaps a rock to compensate for the bouyancy swing created by breathing down your air.

One has to also realise that when no BC diving was practiced the common tank was a St 72 which has excellant bouyancy characteristics. I can breath one down in the pool using no BC and no weightbelt and only my breath to compensate. In OW I often dive a DS only and just add enough air to the suit to take off the squeeze. At the end of the dive (< 300psi) I can just hold my safety stop.

 

[knowone]

Just put into practice dude, all that stuff you quote as gospel and you may gain a different perspective on the "apprenticeship of angst" that hopefully develops into a wary respect for all things water whilst maintaining some healthy apprehension, realising that many things occur despite what one knows, which will make DCS avoidance not as simple as 1,2,3.

 

[BoltSnap]

My lungs have an FEV of 6.5L and a tidal volume of 0.5L. Lets assume that I use 5L of that for buoyancy control. 5L of displacement is around 11lb of lift. That means I can handle around 11lb of wetsuit compression and gas use.

You are going to exhale all the way down to the bottom and then hold your breath or just do nothing but fiddle and fight for proper buoyancy?? Are you going to enjoy your dive or turn blue just to make a point. Please give me realistic scenarios that recreational divers encounter while enjoying their diving not trying to score points.

 

[BoltSnap]

How about you're not neutral at the surface. That's new school thinking. If you use a pike dive you can be positive, swim down against bouyancy till your suit compresses and you are then neutral (actually better to be a bit negative). Use breath control and perhaps a rock to compensate for the bouyancy swing created by breathing down your air.

One has to also realise that when no BC diving was practiced the common tank was a St 72 which has excellant bouyancy characteristics. I can breath one down in the pool using no BC and no weightbelt and only my breath to compensate. In OW I often dive a DS only and just add enough air to the suit to take off the squeeze. At the end of the dive (< 300psi) I can just hold my safety stop.

DaleC,

I am sure that you can "manage" to get down to the bottom some how but it won't be easy or convenient. I don't think that collecting rocks or anything else U/W is a way to spend your precious U/W time. Why spend your energy and your precious air kicking like mad to get the desired depth (if you stop kicking, you'd lose ground and float up to the surface)?? Are diving to enjoy the diving or to just score points??

What about if you are involved in some sort of an U/W activity such as spearfishing, photography, U/W survey, etc.? How many tasks are you going to be able to handle? What about an instructor who is handling a class with students going up and down? The list goes on and on.

If you are worried about losing a skill, so what? I am gaining another skill that makes it much more convenient, safer, more comfortable, more enjoyable while losing nothing.

 

[kanonfodr]

DaleC,

I am sure that you can "manage" to get down to the bottom some how but it won't be easy or convenient. I don't think that collecting rocks or anything else U/W is a way to spend your precious U/W time. Why spend your energy and your precious air kicking like mad to get the desired depth (if you stop kicking, you'd lose ground and float up to the surface)?? Are diving to enjoy the diving or to just score points??

What about if you are involved in some sort of an U/W activity such as spearfishing, photography, U/W survey, etc.? How many tasks are you going to be able to handle? What about an instructor who is handling a class with students going up and down? The list goes on and on.

If you are worried about losing a skill, so what? I am gaining another skill that makes it much more convenient, safer, more comfortable, more enjoyable while losing nothing.

Have you ever even considered that MANY people dive without a BC, and in the early days there was no such thing as a Bouyancy Compensator? It's mostly about proper weighting, but you will be positive on the surface, a tad bit negative on the bottom, and neutral when your tank is around half-full. This is a very simplified explanation of course.

With the tanks I use, when they are down to about 1000 psi I can dump every ounce of gas in my BCD and swing the tank with my breath alone. And I can stay in horizontal trim and be neutrally bouyant until the barest end of the tank (2-300 psi). And I'm truly happiest when I've reached that point, because it's one less task to handle, especially on the uppsy-downsy reefs here around Oahu. Oh yeah, and I'm still shooting video, keeping track of my buddy, and occasionally navigating back to the exit, too.

Peace,
Greg

 

[aquaregia]

My lungs have an FEV of 6.5L and a tidal volume of 0.5L. Lets assume that I use 5L of that for buoyancy control. 5L of displacement is around 11lb of lift. That means I can handle around 11lb of wetsuit compression and gas use.

You are going to exhale all the way down to the bottom and then hold your breath or just do nothing but fiddle and fight for proper buoyancy?? Are you going to enjoy your dive or turn blue just to make a point. Please give me realistic scenarios that recreational divers encounter while enjoying their diving not trying to score points.

I think you misunderstand. The difference between my lungs completely full and completely empty is 6.8L. When taking a normal breath, about 0.5L moves through my lungs. This means that I can breathe with my lung volume changing from 2.0L to 2.5L or 4.0L to 4.5L, with no change in comfort but a 4.5lb lift difference. I imagine there is some risk of hypercapnia if you're breathing all the way at the top of your lungs for an extended time, which is one reason I only dive fairly shallow wingless.

I've done dives for 30-45 minutes at 10-35' in a 7mm wetsuit using tanks ranging from 65cuft to 108cuft. I actually find it more enjoyable than with a wing, and the lung control happens sort of automatically. I strongly recommend that you give it a shot in a swimming pool at some point. After I first did it, I really started noticing the flapping of an empty wing.

 

[BoltSnap]

Have you ever even considered that MANY people dive without a BC, and in the early days there was no such thing as a Bouyancy Compensator? It's mostly about proper weighting, but you will be positive on the surface, a tad bit negative on the bottom, and neutral when your tank is around half-full. This is a very simplified explanation of course.

With the tanks I use, when they are down to about 1000 psi I can dump every ounce of gas in my BCD and swing the tank with my breath alone. And I can stay in horizontal trim and be neutrally bouyant until the barest end of the tank (2-300 psi). And I'm truly happiest when I've reached that point, because it's one less task to handle, especially on the uppsy-downsy reefs here around Oahu. Oh yeah, and I'm still shooting video, keeping track of my buddy, and occasionally navigating back to the exit, too.

Peace,
Greg

First, I was one of these folks that didn't use a BC for about 10 years. Did you ever consider that these folks who didn't use the BC way back then, didn't use it because there was no such thing as BC's and if there were, they would have used them?

BTW, I am not arguing against your right to not use a BC for whatever rationalization you have, I am only saying that using a BC is the most convenient, more enjoyable and safer way of diving for the greater majority of "recreational" divers. I am also saying that it is not a "cop out" to us the BC.

 

[Crush]

Just put into practice dude, all that stuff you quote as gospel and you may gain a different perspective on the "apprenticeship of angst" that hopefully develops into a wary respect for all things water whilst maintaining some healthy apprehension, realising that many things occur despite what one knows, which will make DCS avoidance not as simple as 1,2,3.

My compliments - that is a very cleverly disguised logical fallacy - in this case, the attack ad hominen (personal attack). Before there is protest, check out some definitions. I have found an adequate definition and examples at Fallacy: Personal Attack . Drawing attention to my limited dive history may make you feel superior (assuming that you have a dive history, see my sig file) but it does nothing to change the underlying physiology or physics upon which I have tried to predicate my responses.

You are correct that DCI is imperfectly understood. Many people "do everything right" and still get bent. I suspect that a larger number do many things wrong and don't get bent. If you read the OP that you maligned (see http://www.scubaboard.com/forums/ask-dr-decompression/358076-do-undeserved-hits-happen.html ) you would have seen that I addressed the fact that DCI varies from individual to individual, and even from dive to dive within an individual.