"Correct Weighting" Identified as #1 Needed Improvement in SCUBA Diving

[JamesBon92007]

Most of the diving I've done has been at Southern California beaches. The best spots usually have cliffs and surf. In order to get to some of these dive spots it is necessary to carry all of that gear down the bluffs, and, at the end of the dive, back up. I prefer to bring as little junk as possible. I prefer a steel 72 over an aluminum 80 because it weighs a few pounds less plus I don't need as much weight on my belt--this reduces my load by around 7-8 pounds. A typical jacket-style BC weighs around 5-8 pounds, possibly more. By eliminating the BC I have now removed around 14-16 pounds of stuff I don't need to carry. I have never gone through the surf wearing a BC but I cannot imagine that it is not more difficult with all of the added bulk and water resistance. I have gone beach diving with people who bought BCs but I have never felt the need to get one. If there was an advantage to having one for this type of diving it was not apparent. After all, I am just going scuba diving. I (and some others on SB) approach this kind of scuba diving as free diving with a tank strapped to my back. Some people here say that scuba diving is "inherently dangerous." If that is so, then why do they let 10-year-olds do it?

I have read many of the Incident Reports on SB and elsewhere and, on at least a few occasions, I could not help but wonder if the BC was responsible for the incident. My impression, in some cases, was that somebody pushed the wrong button and had so many different gadgets that they had to mess with that they got confused. I watched a video of a guy plummeting down into the Blue Hole. About the only thing I could think of was that he let all of the air out of his BC by mistake and kept pushing the wrong button. Of course he would have needed to be over-weighted to begin with, plus by having weights in several locations instead of just one it could be confusing to dump weight if someone is panicking. Dropping your weight belt is such a simple thing but trying to dump it and hope it doesn't get caught on a BC strap and figure out what to pull to dump the pocket weights seems to me to be a lot to ask of someone who is uncomfortable enough to be thinking about dropping their weights.

I just bought my first BC last week. One reason I bought it is because when I go on dive trips I am required to wear one. I have been renting them and they are all different. Sometimes the exhaust button is on the end and sometimes it's on the side. Sometimes the dump valve is on the shoulder, and sometimes it can be activated from the bottom in the back. Sometimes just pulling the hose will dump the air, sometimes it won't. At least now I'll know where the buttons are and which one is which. One BC I rented caused me to zip right past my safety stop because I could not get all of the air out. Fortunately that particular stop was not crucial (shallow dive). I was also under-weighted by about a pound or two which also contributed a little to the problem. At least that particular Dive OP was not into over-weighting.

Another reason I bought the BC is because, due to the general climate and attitudes of the industry I would not be surprised if someday soon someone told me I can't dive without one. This was the case on Maui a few years back. The dive shop told me it was a state law that you had to wear a BC and have a float with a diver's flag.

The BC I bought is a good, used one that didn't cost very much money. I consider it a temporary device and I'm looking into making or buying a back wing which will have a much smaller profile and should fit into my carry-on nicely. I will have to bring a checked bag with the BC I just bought. I figure I only need about 3-5 pounds of lift with the back wing and that is mainly because I have yet to use any tank other than an AL80 while on a dive trip so I need to add about 4 pounds of lead to my weight belt.

I believe that there are situations where a BC is very desirable especially where perfectly neutral buoyancy is critical but for the most part I simply don't need or want one. It is, however, nice to have pockets to put things in.

Additionally, due to the desirable buoyancy characteristics of the steel tanks vs the aluminum tanks (in general) I am surprised that nobody is making a modern version of the steel 72. All it would take is to make the same sized tank that can be filled to about 3000 psi instead of 2475 and it will then hold about the same amount of air (or more) as the typical AL 80 plus it will probably still weigh a little less and they seem to last longer. I realize that aluminum 80s are cheap but if they mass-produce enough steel 80s the price should come down. I don't think that the additional weight of 8 cu/ft of air will be much of an issue.

 

[kelemvor]

I think the discussion has become lost in the weeds. DAN isn't talking about perfecting weighting. Look at the quote from the article:

Investigation showed that the diver had 50 pounds of weights

50 lbs? I'm no pro and I've only been diving for a few years now. So far, the most I've ever seen someone use to my knowledge was closer to 25 and even then it raises many eyebrows.

It must have been on a private boat with no professionals.

 

[Joneill]

Not exactly. It doesn't matter what tank you use. If you are weighted to be neutral with a near-empty tank, then you will be negative by the amount of gas you're carrying. Whether you're using an AL80 that is floaty when empty or a steel HP80 that is negative when empty, if you are properly weighted, you will start the dive being about 6 pounds negative, as that is the approximate weight of 80 cu-ft of air.

If you are diving with a single HP120, you'll start off about 9 # negative. If you're wearing a 7mm wetsuit, and you dive your HP120 to 130', your suit will compress and you could end up being 20# negative at the bottom, at the start of your dive.

I am in NO way pushing the idea of diving or teaching scuba with no BCD. But, I think REVAN's point is not that you should use no BCD in all conditions (e.g. a steel tank and a 7mm wetsuit). His point was to teach that way in warm water with (I assume) AL80 tanks. In those conditions, the most negative you should be is 6 #, with little or no concern of additional buoyancy loss from suit compression. And, in those conditions, as Pete has already observed, you can compensate for 6# just with your breathing.

Thanks - I do understand that different tanks have different buoyancy characteristics (both full and empty/with remaining gas), so I was just throwing out the 3 lb for an AL80 as an example.

However, I'm, still struggling with the rationale that a BC teaches people bad habits/makes it harder to understand proper weighting. That has not been my experience at all, I see use of a BC and determining proper weighting as different topics (albeit with some inter-relation in use) as I determine proper weighting with an empty BC. Also, to me, compensating for 6 lb overweight through just breathing seems a lot to ask: If you are breathing as recommended, using the diaphragm (not puffing out your chest) with long, deep inhale and even longer exhausts, then you will experience minimal depth changes (up and down). If you are 6 lb overweight, how do you breathe through that? Physics would say that, just like putting a little air in your BC (to increase your volume/buoyancy), you'd need to permanently hold some air in your lungs to present more volume - I would think that would interfere with proper deep/diaphragmatic breathing - no?

Also, even in warm conditions, the BC allows you to be relaxed while negatively weighted at the surface pre-dive and is nice to establish strong positive buoyancy in rough seas (pre and post dive). It also allows for relaxed surface swims on your back when doing shore dives that are a little ways out from shore. During a dive, I typically only add a minimal amount of air as I reach depth and then it's normally only dumped as the dive progresses - I'm not constantly fussing with it.

All in all, I'm not seeing any downsides to use of a BC and any impact of BC use on getting your weighting right if you understand the concepts? Of course, to each his own, but I'll keep the W in my BP/W.

 

[stuartv]

Thanks - I do understand that different tanks have different buoyancy characteristics (both full and empty/with remaining gas), so I was just throwing out the 3 lb for an AL80 as an example.

Right. I was only quibbling with this statement.

That required weight makes you negatively buoyant at the start of the dive.

It seems like I often see posts that are somehow implying that using an AL80 makes you light or a steel tank makes you heavier. Which is wrong. If you are properly weighted, then you will start the dive negative by the amount of gas you're carrying. It has nothing to do with aluminum vs steel tanks.

Similarly, if you use an AL80 and 3 pounds of lead or an HP80 that has the 3 pounds of "lead" built in, none of that is what makes you negatively buoyant at the start of a dive. It's only the gas in the cylinder that makes you negative. You use it during the dive, it's gone, and you're neutral at the end.

Whether you understood that or not, it seems like statements like the one you made lead some people into confusion about weighting and cylinder materials.

I dived with someone once who was using an HP100 for the first time. She'd always used AL80s before. She blamed her feeling of being heavy and struggling to control her buoyancy on the tank being heavy and steel. She didn't get that that had nothing to do with it. Being heavier than she was used to was simply from carrying more gas. She was used to starting 6# negative, but with a 100 (whether it's steel or aluminum), she was starting 8# negative. And that means it required more gas in her BCD at the start of the dive than she was used to putting in. And more gas in your BCD makes it harder to control your buoyancy.

Anyway, my apologies for being didactic. I'll shut up now.

 

[dmaziuk]

If I wanted to control my buoyancy with my internal organs, I'd evolve me a swim bladder.

Also, to me, compensating for 6 lb overweight through just breathing seems a lot to ask... If you are 6 lb overweight, how do you breathe through that? Physics would say that, just like putting a little air in your BC (to increase your volume/buoyancy), you'd need to permanently hold some air in your lungs to present more volume - I would think that would interfere with proper deep/diaphragmatic breathing - no?

I often enough jump into the diving well with a 10 lb brick, and occasionally: with 2. I can swim around with them (with 2: not for very long) but here's the thing: I can let go and drop them any time. That's not quite how it works with the weight strapped to your back in a 5-point harness. So I'm not sure I'd care to dive without an aircell outside of a very controlled environment with hard bottom at 12 feet and lifeguard watching etc.

Aside from the practicality of using just your lungs for control.

 

[REVAN]

So, one misconception I've seen more than once around here is that you will need 6 pounds of extra weight to offset the buoyancy of an 80 when empty. This is the kind of thing that only people who have experience diving with a harness will likely understand to be false.

The logic is that 80 cubic feet of air has a weight of 5.7 pounds, so round that up to 6 and that's what you need. However, that 5.7 pounds is to completely empty the tank (like for doing a VIP). This is not something you are EVER going to do while underwater. And believe me, if you do empty a tank that far, you want that condition to make you buoyant and force you to the surface. Better to risk some possible, but unlikely, bubbles in the blood, than a certain case of water in the lungs. The actual shift in buoyancy you plan on an 80 for is 4.4 pounds (I personally use 4). The 6 pound allocation is in error of what works best by 50%. Keep in mind that I am only referring to recreational diving here, not technical or planned deco diving (which should not be done on a basic harness in the first place).

One other area from the DAN list of improvements had to do with air management, and overstaying the dive. If a diver is weighted right, they will get a reminder, in the form of feeling too buoyant to stay down. There is a noticeable feeling that something is not right and it's time to call the dive. This will tend to happen even if the diver does not check their tank pressure gauge.

This 6 vs. 4 pound issue is one example of the little things that can add up to contribute to overweight diving. There are others involving suit compression, finning and dynamic forces, etc.... Of course, the really bad cases of overweight diving, I'm thinking, have more to do with a basic gross negligence of weight management more than any misconceptions like I described here.

And, I too wish that a 3000 psi rated version of the old steel 72 was the standard recreational tank. Steel is, volumetrically, a more efficient material from which to make scuba tanks, and it can last longer than aluminum as well.

 

[REVAN]

If I wanted to control my buoyancy with my internal organs, I'd evolve me a swim bladder.

Umm... That's what lungs are.

Seriously. The difference between fish and sharks is that the ancestors of fish gulped air and crawled in the mud like the lungfish, whereas sharks never left the water. A fish's swim bladder is an vestigial lung that has been re-purposed.

 

[dmaziuk]

Umm... That's what lungs are.

Yup. The point is, fishes don't have 'em doing double-duty of breathing and buoyancy control. And neither would I.

 

[stuartv]

So, one misconception I've seen more than once around here is that you will need 6 pounds of extra weight to offset the buoyancy of an 80 when empty. This is the kind of thing that only people who have experience diving with a harness will likely understand to be false.

The logic is that 80 cubic feet of air has a weight of 5.7 pounds, so round that up to 6 and that's what you need. However, that 5.7 pounds is to completely empty the tank (like for doing a VIP). This is not something you are EVER going to do while underwater. And believe me, if you do empty a tank that far, you want that condition to make you buoyant and force you to the surface. Better to risk some possible, but unlikely, bubbles in the blood, than a certain case of water in the lungs. The actual shift in buoyancy you plan on an 80 for is 4 pounds. The 6 pound allocation is in error of what works best by 50%. Keep in mind that I am only referring to recreational diving here, not technical or planned deco diving (which should not be done on a basic harness in the first place).

You can weight yourself to be positively buoyant when your tank gets to 100 psi if you want to. Personally, I'm going to weight myself so that if something happens and I need to get to 10 or 15 feet and breathe my tank down until the very last dregs, my weighting is not going to prevent (or even make it difficult/tricky/whatever) me from doing that.

And before I hear "you can't breathe it down to 100 anyway!" Let me note that ambient pressure at 15' is 21.4 psi and I (as most people) use air-balanced 1st and 2nd stage regs.

And, I too wish that a 3000 psi rated version of the old steel 72 was the standard recreational tank. Steel is, volumetrically, a more efficient material from which to make scuba tanks, and it can last longer than aluminum as well.

What is the difference between this imaginary tank you're talking about and an HP80? Or maybe I should just ask why would you prefer that to an HP80?

 

[Miyaru]

Teaching neutrally buoyant has advantages. Since most learning is done by monkey-see-monkey-do, students will try to mimic your position. During the first lesson you make some adjustments for the students (like you'd do on a DSD), and they will hover. Without knowing why. It's their first feeling under water, so it becomes the feeling they're used to. Does it have to be perfect? No of course not. But having a student off the floor is a big win and time-saver during confined. You don't need to teach buoyancy anymore, you just need to teach fine-tuning buoyancy.

Unfortunately, there are other instructors (in this same pool) who take the easy approach by overweighing students so they stay kneeled down, hover in a Buddha position and fiercely reject my suggestion to demonstrate skills neutrally buoyant. I guess because they just can't do it...

...
After that, PADI obviously experimented on their own, for two years later they began to advocate our approach as the best way to teach. Unfortunately, they still allowed the traditional approach on the knees, and that is still what most instructors do.
....

I'd really like to know where I can find this statement. It would back up my suggestion to other instructors.