Getting rid of my weight belt?

[DocWong]

Hi, Thanks everyone for your input, here's what happened:

I did 5 dives this weekend! I ended up putting 6 lbs in between my tanks, getting rid of my weight belt and got some unexpected results:

1. Ability to swim up: With my wing empty and drysuit giving me a good squeeze, I could not swim up. Then with a bit of argon in my drysuit, I could swim up. So getting back up to the surface without my wing is not a problem, especially with a working dry suit and 2 SMBs (small and large).

2. Trim: I was utterly surprised that by shifting my weight from my belt to in between my tanks that it drastically decreased my tendancy to roll left or right. Before with weight on my belt, a slight roll to the right or left would have me on my back without some finning to keep from unrolling! I was much more comfortable and could tell that I took a significant step to achieving perfect trim.

3. The rig felt awesome without the bulk of a weight belt. It also seemed to make it a lot easier to clip on and off my D ring at my left hip.

Note: I'm diving in Monterey Bay, CA with temps at around 50 degrees, drysuit, stainless steel backplate, double Faber 85s with 6 lbs between the tanks, cannsiter light, Luxfer 80 Cu Ft deco bottle, and Evolve wing.

Dive well!

Harry (doc) Wong www.docwong.com
President: Northern Caifornia Oceans Foundation
Proj Mgr: Warships to Nurseries

 

[TomR]

The following is not necessarily a position, just my thoughts as I've been considering the same issue...

There have been a few mentions of SMBs as a safeguard to get you to the surface in the event of a buoyancy failure. I'm not sure if this would work in a real emergency. If, for example, you jump in with your gas turned off and no air in the BC or drysuit and you're overweighted, you're probably going to the bottom unless you can swim the rig up unassisted. By the way, from the accident reports I've read, this seems to be one of the more common reasons for buoyancy system "failure" (you forget to turn your air on or someone tries to do you a favor and actually turns it off). I certainly believe in the buddy system, but if you're first in the water, your buddy might not be able to catch you on your way down. Yes, the pre-dive check should identify this problem, but what if you have enough pressure in your hoses to make for a good test of the regulator and wing, or what if (as humans do) you screw up for forget to make such a check?

By the time you get to the bottom, it's probably too late to blow up the SMB, especially since you only have the air in your lungs. Reaching your valve and getting the gas turned on or ditching weight seems like the only way out. Ditching a belt seems a lot easier in a stressful situation. Yes, using argon cuts the odds of this type of failure scenario in half, but it's plausible to assume that you would forget to turn on both gasses if you forgot one of them.

I've been grappling with this same issue, considering the ditchable vs. non-ditchable question. I like non-ditchable for its lack of clutter and secure nature, but I also don't want to be sinkin' to the bottom in case Murphy strikes. I took DIR-F a couple of weeks ago and it was suggested that if you are at any point during your dive more than 10lbs. negative, that you probably won't be able to swim that up from 30ft. I haven't had a chance to do the swim-up experiment or completely balance my rig, but once it is, I will definitely try the experiment. Since I'm diving a PST 119, which has about a 8.5lbs. buoyancy swing, I'll be right below that threshold with a perfectly weighted rig. By the way, I require a fair amount of weight so I've got all options on the table (having any sort of tank and weighting combo) so for me only the buoyancy swing is important. For those not requiring much weight, the actual buoyancy of the tank in the dive beginning is obviously just as important.

With doubles, the problem is multiplied - out of the common doubles options it looks like only doubled Neutral Aluminum 80s have under a 10lbs. buoyancy swing (my research indicates it's 9.6lbs. combined for two cylinders). If 10lbs. negative is the magic number for the average Joe, it seems like those are one of the few choices or you're forced to make a trade-off between the perils of ditchable weight or too much non-ditchable weight. I am going to figure out my magic number of swim-up-able weight before I buy anymore tanks. This number will definitely affect my cylinder choice. I might sell the HP119 and get an HP100. If/when I get doubles, I might get neutral 80s as opposed to HP100s. We'll see.

Tom

 

[DocWong]

The following is not necessarily a position, just my thoughts as I've been considering the same issue...

There have been a few mentions of SMBs as a safeguard to get you to the surface in the event of a buoyancy failure. I'm not sure if this would work in a real emergency. If, for example, you jump in with your gas turned off and no air in the BC or drysuit and you're overweighted, you're probably going to the bottom unless you can swim the rig up unassisted. By the way, from the accident reports I've read, this seems to be one of the more common reasons for buoyancy system "failure" (you forget to turn your air on or someone tries to do you a favor and actually turns it off). I certainly believe in the buddy system, but if you're first in the water, your buddy might not be able to catch you on your way down. Yes, the pre-dive check should identify this problem, but what if you have enough pressure in your hoses to make for a good test of the regulator and wing, or what if (as humans do) you screw up for forget to make such a check?

Yes, this is a nightmare. Sinking to the bottom, gas turned off, wings deflated, no air in drysuit, overweighted, regulator out of mouth, light off, panicked and getting your ears squeezed...all in a panic. Bad news and it's happened, from what I hear.

That's why my gearing up procedure has a redundant check before I get into the water. Here's what I do. Before putting my doubles on, I'll turn on my back gas and inflate my wings partially (too full and I'll have trouble getting them on). Then when I put the rig on, I'll inflate the wing more, then route my hoses (drysuit inflator, backup reg on the neckless, light and my long hose) Then I take 2-3 breaths looking at my guage. If I miss any of the 2 checks, I know I'm out of it a bit and recheck things just to be sure. Sometimes we get a bit distracted and forget something, but noticing I forgot something in my redundant checks it'll alert me to the fact that I'm a bit off and will recheck things.

<<<<<< By the time you get to the bottom, it's probably too late to blow up the SMB, especially since you only have the air in your lungs. Reaching your valve and getting the gas turned on or ditching weight seems like the only way out. Ditching a belt seems a lot easier in a stressful situation. Yes, using argon cuts the odds of this type of failure scenario in half, but it's plausible to assume that you would forget to turn on both gasses if you forgot one of them.

I've been grappling with this same issue, considering the ditchable vs. non-ditchable question. I like non-ditchable for its lack of clutter and secure nature, but I also don't want to be sinkin' to the bottom in case Murphy strikes. I took DIR-F a couple of weeks ago and it was suggested that if you are at any point during your dive more than 10lbs. negative, that you probably won't be able to swim that up from 30ft. I haven't had a chance to do the swim-up experiment or completely balance my rig, but once it is, I will definitely try the experiment. Since I'm diving a PST 119, which has about a 8.5lbs. buoyancy swing, I'll be right below that threshold with a perfectly weighted rig. By the way, I require a fair amount of weight so I've got all options on the table (having any sort of tank and weighting combo) so for me only the buoyancy swing is important. For those not requiring much weight, the actual buoyancy of the tank in the dive beginning is obviously just as important.

With doubles, the problem is multiplied - out of the common doubles options it looks like only doubled Neutral Aluminum 80s have under a 10lbs. buoyancy swing (my research indicates it's 9.6lbs. combined for two cylinders). If 10lbs. negative is the magic number for the average Joe, it seems like those are one of the few choices or you're forced to make a trade-off between the perils of ditchable weight or too much non-ditchable weight. I am going to figure out my magic number of swim-up-able weight before I buy anymore tanks. This number will definitely affect my cylinder choice. I might sell the HP119 and get an HP100. If/when I get doubles, I might get neutral 80s as opposed to HP100s. We'll see.

Tom >>>>>

At the bottom, with both wing and drysuit deflated (100 feet) I could not swim up. With my drysuit inflated, I could. Even then it was hard.

I'm at least 14 lbs negetive at the beginning of the dive. My LP Faber 85s alone are -13 or 14 lbs negetive full and zero empty.

On checking out my weight at 10 feet, I'm not sure if I should include an empty 40 and an empty 80 deco bottles. They are both the standard Luxfers and are 2 lbs and 4 lbs positive empty.

I'm currently using an 8 lb V-weight which as proven awesome as far as trim and rotational stability goes, and I'm definitely overweighted without deco bottles, but with 2 deco bottles that are around 6 lbs positive, I'm about right.

Anyone know if this is correct? Or should I weight myself without the deco bottles?

 

[DIR-Atlanta]

With doubles, the problem is multiplied - out of the common doubles options it looks like only doubled Neutral Aluminum 80s have under a 10lbs. buoyancy swing (my research indicates it's 9.6lbs. combined for two cylinders).

I'm a little confused. The "buoyancy swing" on a tank is a function of two things - its filled capacity in cubic feet, plus the density of the gas being used. The material from which the tank is made has no effect on this, and neither does the tank's overall buoyancy characteristics.

Assuming that you are talking about Air (which weighs about 0.08 lbs/cf at STP) the buoyancy swing of an 80 cf tank should always be about 6.4 lbs, be it steel, aluminum, NB, or "other". Double a pair of 80s up and you get a total swing of 12.8 lbs. Of course, if you're using a 30/30 trimix, then that will be closer to a 9.6 lb swing in a set of doubles - 30/30 weighs about 0.061 lbs/cf, which works out to about 4.88 lbs for a single, 9.76 lbs for doubles.

And it should probably be noted that most "80" cf tanks really only hold about 77 cf, so the swing for an air fill is actually closer to 6 lbs for a single, 12 lbs for doubles. The swing for 30/30 is closer to 4.7 lbs for a single, 9.4 lbs for doubles.

The issue of the "balanced rig" seems to confuse a lot of people, but it's really very simple. If you are diving wet, you need to be able to ditch enough weight to swim the rig up comfortably, in the event that your BC fails at the most inopportune point in the dive (which is usually near the beginning - full tanks, max depth). It shouldn't really matter what type of tank you are wearing or what its buoyancy characteristics are, as long as you can ditch the weight and swim the rig up. You need to consider the overall buoyancy of the "total package" (diver + all gear), plus the tank swing to determine what amount of weight needs to be ditchable.

And of course the weight needs to be truly ditchable. Some people talk about ditching their canister lights or deco bottles, but I personally consider deco gas and a light to be items of critical need, so I would be reluctant to ditch those unless it were an absolutely necessity.

 

[Tanked Monkey]

If I have a broken leg, or lost fins, the other members of my team better be helping me. Since this is DIR forum, we don't dive alone...

Chris - Nicely said, dude.



DocWong - I'm not trying to be a big old meanie (or a troll), but are you really sure you want to post in this particular subforum? Your profile says you are a solo diver. Solo diving and DIR don't really mix too well. I'm trying to give you the benefit of the doubt. Maybe DIR is something you're working towards?

Mike

 

[DocWong]

Chris - Nicely said, dude.

DocWong - I'm not trying to be a big old meanie (or a troll), but are you really sure you want to post in this particular subforum? Your profile says you are a solo diver. Solo diving and DIR don't really mix too well. I'm trying to give you the benefit of the doubt. Maybe DIR is something you're working towards?

Mike

Thanks for pointing out that oversight. I used to dive solo, but no longer. gone too are the days of dangling guages, wrap around BCs, Air2s, snorkles, swimming vertical and flailing.

Yes, DIR is definitely something I'm working towards and will be doing a fundies class in the Monterey area later this year. In the meantime I'm really trying to get my skills up to a point where I'm not a total clutz when the class comes up. I'm waiting for the next scheduled on in the SFor Monterey Bay Area.

 

[Tanked Monkey]

Awesome! I see that you have changed your profile for the "better" (ie. no more solo diver). If you have any questions about Fundies, drop me a PM and I'd be happy to help you out.

Since I'm not from California, I'm guessing Redwood City is in Norther Calif, right? There's a great group of DIR divers in California called SoCal DIR. They might not be exactly in your area, but it's a heck of a lot closer than I am here in TN. The forum is special, in that you have to "apply." It's a subforum within the California Kelp Divers forum, located here: http://www.scubaboard.com/forumdisplay.php?f=441. If you need help getting into the group, send me a PM and I can point you in the right direction.

Best,
Mike

 

[TomR]

DIR-Atlanta,

I was referring to filling the tanks with Air. Also, I was referring to "Neutral 80's", which have some different buoyancy characteristics than regular aluminum 80's. I believe they are lower volume, higher pressure, accounting for the differences in the swings we both arrived at. Course, I could still be wrong, but those were my assumptions.

Also, the reason I focused on buoyancy swing in the context of the balanced rig is that if you need to carry a fair amount of weight, the swign seems to be the only variable that really matters when selecting tanks. Anyway, hope I'm not confusing things. This is my second week of crunching numbers to balance my rig. Before that I just carried a lot of ditchable weight.

Tom

 

[DIR-Atlanta]

I was referring to filling the tanks with Air. Also, I was referring to "Neutral 80's", which have some different buoyancy characteristics than regular aluminum 80's. I believe they are lower volume, higher pressure, accounting for the differences in the swings we both arrived at.

The tanks have different buoyancy characteristics, but they have the same buoyancy swing, because they are the same capacity tank (80 cf). In fact, if you look at the product description page on the Luxfer website, you'll see exactly what I mean:

A regular S80 tank has a capacity of 77 cf. Its buoyancy in salt water is -4.4 lbs full, +1.4 lbs empty

An NB80 tank also has a capacity of 77 cf. Its buoyancy in salt water is -5.75 lbs full, +0.05 lbs empty

So the full and empty buoyancy is different in both cases, but the swing (i.e. change in buoyancy from full to empty) is exactly the same - 5.88 lbs. That's because they are the same capacity tanks. And in fact, every tank that has a capacity of 80 cf and is filled with Air will have a buoyancy swing of about 6 lbs. That's because 80 cf of Air always weighs the same, no matter what type of container it's in or what pressure it's at (van der Waals forces notwithstanding).

Also, the reason I focused on buoyancy swing in the context of the balanced rig is that if you need to carry a fair amount of weight, the swing seems to be the only variable that really matters when selecting tanks.

Again, the swing is not really "variable" as long as we are talking about a consistent combination of tank capacity and breathing gas. The important thing to realize is that you can only add weight to the rig, not take it away (except by using the gas or ditching equipment). So if your tanks are too negative to start with, then that can throw the whole system out of whack, because there's no adjustment that will make them less negative.

The trick is to make sure that you are not too positive in shallow water, and not too negative in deeper water. I don't know if you have a copy of JJ's book, but he sums it up pretty well on page 94:

The ideal configuration for a diver is one that, while being as light as possible, allows him/her to remain neutral at 10' (3m) with a nearly empty set of tanks (to allow decompression/safety stops). [In addition] divers should be certain that, without any air in their buoyancy compensators, they are capable of swimming against the weight of their configuration with full tanks and all weight in place.

In essence, you really have to balance the rig for both situations - beginning of dive / max depth / full cylinders, as well as end of dive / min depth / empty cylinders.

Anyway, hope I'm not confusing things. This is my second week of crunching numbers to balance my rig. Before that I just carried a lot of ditchable weight.

OK, this is going to sound like a flippant response, but my suggestion is that the best place to resolve this issue is in the water. See if you can borrow some different types of tanks from a local shop and just spend a day trying different combinations (make sure you do this with a buddy!). That will ultimately give you a lot more useful info than a page full of tank specifications.

 

[TomR]

I've read that book and definitely understand the concept and your logic sounds right, but how do you explain the info I'm finding on SCUBA.com. I checked SCUBA.com and here's what they have to say about two different tanks:

Neutral 80

BUOYANCY FULL: = -5.9lbs
BUOYANCY EMPTY: = -1.4lbs
SWING = 4.5LBS

Aluminum 80

Buoyancy Full = -1.9lbs
Buoyancy Empty = 4lbs
SWING = 5.9LBS


http://www.scuba.com/shop/product.asp_category_200