2 more upper keys dive fatalities, 8/6/2011

[DoNotDstrb]

If you had really been interested in a PM conversation, you could have PM'd me.

For the following quoted post, how about backing up things you have said with facts and math, no hard science necessary.....



I own a couple 120 cft's and my concept of proper weighting is "neutral at surface with empty tank and empty BC, holding a normal breath." Please do the math to figure how negative I am at the beginning of the dive. If I make a two minute descent to 130 fsw, would the lost positive buoyancy of my Pinnacle Merino-Elastiprene 5 mm be more or less than the lost negative buoyancy of the air I have breathed to that depth?

I am pretty sure I could be properly weighted, diving more than 15 lbs negative (at depth) and I do not need different tanks.

I like AL100's, especially compared to AL80's. AL100's are less buoyant empty than typical AL80's.

Perhaps the "hard science" explains your "4lbs negative at the beginning and near neutral with 500 PSI" for your 102 cf @ 3500 psi tank.

Now look who's trying to start a pissing contest ...

I already explained that my "8-10lb" comment is in the context of WARM water diving with LITTLE or NO exposure protection. A 5mm suit or worse yet, a dry suit changes this altogether. I am not familiar with the buoyancy characteristics of the particular suit you mention and therefore cannot run the numbers.... Your 15lb heavy figure at the beginning of the dive sounds perfectly plausible to me in the configuration you mention.

As for tank buoyancy... A 3300 PSI Luxfer 100 is 3 lbs positive empty... A 3000 PSI Luxfer S80 is 2lbs positive empty. Yes, I'm sure you can show me an example that proves YOU right.... but why bother.... my point simply was that with a positive/empty tank you need more weight and this makes you heavier early and messes with your trim throughout... that was all.

I also already explained the buoyancy characteristics of MY setup and rationale for my weighing.... go back and read it if you are interested. Numbers are all there....

I invited you to PM me if you wanted to have a discussion -- the rest of what I said was meant to be a public post.

I am done with this pi$$ing contest as well.

 

[Splitlip]

So I'm somewhat confused by this statement; do most who dive in Palm Beach own their own BC's or do most who dive in Palm Beach rent BC's?

Yes.


On any given trip or site, most people own their BC's. And most of them are weight integrated.

 

[dumpsterDiver]

....my point simply was that with a positive/empty tank you need more weight and this makes you heavier early and messes with your trim throughout... that was all. I am done with this pi$$ing contest as well.

Still making ridiculous statements..... An aluminum tank will make you "heavier earlier".

 

[DoNotDstrb]

Still making ridiculous statements..... An aluminum tank will make you "heavier earlier".

I'm really pulling my F-in hair out here with you arithmetically-challenged so-called professionals!!!


Fact: A Luxfer AL100 is about 5 pounds negative full and 3 pounds positive empty --

Fact: A Faber steel 12L 102 is about 7 lbs negative full and 1 lb negative empty.

If I want to be 1 lb negative at the END of the dive --- regardless of what else I'm wearing, I have to carry 4 extra pounds of lead (or whatever) if I'm diving the AL 100 to make up for the 3lbs of lift THAT tank gives me versus the -1 lbs of lift I get from my 12L. This means that at the beginning of the dive, I am 2 pounds heavier in terms of buoyancy with the AL100....


Also with the AL 100, I am carrying about 15 lbs of additional TOTAL mass because the AL100 is 11 pounds heavier than my 12L PLUS I have the 4 extra pounds of ballast needed to sink the thing when empty, PLUS the whole thing is bigger...... this part doesn't have anything to do with buoyancy, but it DOES have something to do with trim and the energy needed to move me around and therefore gas consumption..... that's the Newton's law of motion stuff that you apparently did not understand either.

 

[TSandM]

DND, your math is completely correct. Aluminum tanks are pernicious, because they are both physically heavier and require more weight. That's why you just about never see them in use in Puget Sound except as stages. The only exception I took to your post was the idea that they mess with your trim, because that's more a function of where you put the weight.

 

[DoNotDstrb]

DND, your math is completely correct. Aluminum tanks are pernicious, because they are both physically heavier and require more weight. That's why you just about never see them in use in Puget Sound except as stages. The only exception I took to your post was the idea that they mess with your trim, because that's more a function of where you put the weight.

Thank you...... Yes, I agree that given the fact that you have the weight.... where you put it can easily mean the difference between awful balance and hardly noticing its there....

My whole trim comment in regards to weight could be said like this: Trim/balance is improved by carrying as little weight as you need for the dive in question and properly distributing the weight you DO have....... proper/poor tank choice can have a positive/negative effect on this condition.

 

[dumpsterDiver]

.... This means that at the beginning of the dive, I am 2 pounds heavier in terms of buoyancy with the AL100....


.....that's the Newton's law of motion stuff that you apparently did not understand either.

I told you F = ma has little to do with a diver moving through the water.

So you are claiming that you must dive with more negative bouyancy at the start of a dive with an aluminum tank because it becomes light (floats) at the end of the dive (as compared to a similar capacity steel tank)??? Is that what you mean?

 

[DoNotDstrb]

I told you F = ma has little to do with a diver moving through the water.

f=ma has to do with anything that begins moving from rest and continues to move under its own power or from external stimulus -- whether its a diver finning through water, a rocket in space, a 747 flying to London, or a 90mph fastball. Its not the ONLY thing that affects motion -- drag from the medium the object is moving through plays a huge part as well.... BOTH reasons are why a well-trimmed, streamlined, smaller diver (I'm counting equipment in "smaller" -- a smaller tank makes a difference) uses less energy than the 250lb guy in a dry suit decked out in doubles with an additional pair of stage tanks under his arms and 50 lbs of lead.... Moral of the story: Be as small, as streamlined, and as light as you possibly can be and still accomplish your desired dive safely and you will make the most efficient use of the energy supply (gas) you have.

So you are claiming that you must dive with more negative bouyancy at the start of a dive with an aluminum tank because it becomes light (floats) at the end of the dive (as compared to a similar capacity steel tank)??? Is that what you mean?

I'm saying that more often than not (depending on the exact pair of tanks you are comparing), you end up that way because you must overcome the positive bouyancy at the end of the dive when the AL tank is near-empty....

In my example above, the difference was 2 lbs. How much does 2lbs matter? In a warm environment with little or no exposure protection, an additional 2 lbs represents 35% additional weight (I dive with 6lbs on the steel with either a 1mm shorty or skin) I can feel 2 additional pounds. When diving with students, I often carry an extra couple of pounds in case one needs it... this is how I know I can feel it. OTOH, if you are already wearing 40lbs to sink your dry suit or 7mm wet, hood, etc, then you're only adding 5% to the total, which probably (I don't dive like that, so IDK) can't even be felt.

 

[fisheater]

AL80s also have the annoying characteristic of getting very light in the base when they empty. That tends to mess with effortless trim.


---
- Sent from my iPhone using Tapatalk

 

[DoNotDstrb]

Sorry that is incorrect, maybe somebody else has the patience to explain to you why.

Only if the buoyancy tables published by the various tank manufacturers are also incorrect. I didn't make up those numbers, you know....


Back on topic..... IMHO... lessons learned from this incident:


1. Don't dive so heavy that you cannot do a controlled emergency swimming ascent WITH ALL YOUR GEAR INCLUDING WEIGHTS. That said, we're all big boys and girls here.... If you CHOOSE to do this in order to facilitate some other underwater activity such as lobster hunting or spearfishing --- KNOW that you are risking your life for an $8 lobster tail. IF you are OK with that, then go ahead and do it. Personally, I'm not OK with that.....

2. Become intimately familiar with any new piece of equipment BEFORE diving with it anywhere other than a pool.

3. Become and remain intimately familiar with weight-ditching procedures. Practice it on land or in a pool WITH ALL YOUR OTHER GEAR ON.....

4. Become and remain intimately familiar with the procedure for removing your entire SCUBA unit underwater.

5. Always dive with an octo or octo/inflator so you don't have to worry about buddy-breathing and the added complexity/stress that goes with it.

6. Check your SPG often -- specially when engaging in distracting or exciting activities such as spearfishing or lobster hunting. The old saying "time flies when you're having fun" applies here 1000%. I know a diver that sets an alarm on her watch to go off every 5 minutes. That's her queue to check gas supply. She is one of the most successful spearfisherpersons (is that a real word?!?!?) that I have ever met.... and she's still quite alive.

Tragedies like this are preventable. Beyond the obvious sense of loss at the premature death of any human being -- it pains me doubly so to see people die because of simple mistakes and apparent lack of knowledge.

Its our job as dive professionals to do everything we can -- inside or outside formal training situations -- to insure that recreational divers have the needed knowledge and experience to stay alive in any situation they may encounter.