Ditching the poodle jacket

[Deep South Divers]

Do you have some data to back this up?

Sure. It's a matter of atmospheres absolute - the compression of gasses at depth.

At sea level, you're at one atmophere absolute: or 1 ATA.

At 33 feet, 2 ATAs. 66 = 3 ATAs, and 99 = 4 ATAS. You know the math... I'm sure this isn't news to you.

So if your wetsuit is 20 pounds positive at the surface, then at 33 feet, it's going to be 1/2 of what it was on the surface, or 10 pounds positive. At 66 it's going to be 1/3 of what it was on the surface, or 6.66 pounds positive. At 99 it's going to be 1/4 of what it was on the surface, or 5 pounds positive.

So the difference between 0 and 20 feet or so is about 7 or 8 pounds' lift or so. The difference between 20 and 100 feet is slightly less - 7 pounds or so.

...So in the case of a 7 mil 20-lb bouyancy suit, with a full tank, in saltwater, the very worst a diver could ever be negative is by about 13 pounds, if he's correctly weighted. (Since my personal suit is only 16 pounds positive at the surface, it makes sense why I'd only see an 11 pound difference in my previous post.) Again, no reason to need to ditch weight in a catastrophe. Keep in mind, too, that any negativity LESSENS as he comes up, LESSENS with freshwater, LESSENS with a thinner suit, and LESSENS with a "less full" tank. Again, there should never be a need to ditch at depth. If there is, then something's wrong.

If it is only a few pounds difference, why are we buying wings with 25-30lbs of lift, why not go the the smallest travel wing we can find. If I follow your logic a 10-11lb wing should be enough for any wetsuit diver

Hey, great question. An even better one is, "Why are they making 60-pound lift wings?" Why would anyone ever want to have to push one of those things through the water? I've even seen for sale 80 and 100 pound wings!

The reality is that people buy big wings because it sounds macho. Even our original poster here was asking, "Did I buy too small of a wing?" Doesn't it sound better to have a 50-pound lift than a 30-pound lift? The 30-pounder sounds wimpy...

Yet, the 30-pounder is probably considerably smaller and more streamlined.

That said, any lift that the diver has that is MORE than what he needs is additional lift that he can use at the surface - the more "extra lift," the higher he'll float out of the water at the surface. This can be very comforting to some people.

Also - I can tell you that when I'm diving with a thick suit or drysuit, I like to have all of my weight on my rig. I don't like to wear weight belts. Even correctly weighted, sometimes my rig (with backplate, tank, STA, and whatever weight I need) can be surprisingly heavy... And I like to be able to float my rig sometimes so that I can get in or out of the boat (wimpy dive ladder). Thus - my wing's gotta have enough lift to support everything WITHOUT me and the suit.

...I can tell you that a 30-pound Eclipse just barely held my rig up yesterday. I hate winter.

I do find more than a couple of pound difference in lift from 15' to 100' in my gear.

No you don't. It's the laws concerning atmospheres absolute. They don't work on you any different than they do on the rest of the world.

I do admit, I am XL and dive Farmer John+Jacket in cold water so I expect a bit more than you might in the deep south.

Dunno - 41* water temps yesterday. 29* air temp here this morning. Is it colder where you are? I don't envy you, then... Did I say that I hate winter?

I'm diving my 7 mil, hood, booties, and gloves. I'd rather be dry at the moment, but I holed the crap out of my drysuit and don't have a choice but to dive wet at the moment.

For what it's worth, I've never found a Farmer John to be as warm as a one-piece. Yeah, they're thicker, but there's so many more seams on a Farmer John than a one-piece that they leak more... With the result being that I get colder. Maybe it's different for you.

I do agree with you, over weighting is a huge issue for many divers. I do think that in you drive to eliminate over weighting you have over simplified the issue and ignored the reality faced by divers in environments outside your corner of the world.

I dunno... I travel quite a bit and don't necessarily have a "corner." Admittedly, I've never dived the Pacific Northwest, but I'll get to that soon.

I tire of the "around here" mentality, though... The laws of physics apply no matter where you are on the globe, and yes... If you stand back and look, you'll see that all of the water is connected. There is no "around here."

 

[diver 85]

With a BP/W you'll want a crotch strap---some harnesses have them, some have them as optional....

 

[Deep South Divers]

Oh, and SeaJay, my number of 20 lbs for buoyancy loss on the thick wetsuit was from data presented during my GUE classes -- apparently JJ took a 7 mil suit to 100 feet and actually measured how much buoyancy it lost, and it was 23 pounds.

Cool new avatar, Lynne.

Yeah, I don't doubt it... If he was using a really large, low-end two-piece farmer john, then yeah, that makes complete sense. I could see 23 pounds.

...But then instead of losing 7 or 8 pounds' buoyancy from 15 or 20 to 100, you might lose 8 or 9 pounds. So what? You should still be able to swim that up. If a diver has to ditch to swim up, there's something really wrong, and he/she needs to go back and visit the basics.

 

[GrumpyOldGuy]

Sure. It's a matter of atmospheres absolute - the compression of gasses at depth.

At sea level, you're at one atmophere absolute: or 1 ATA.

At 33 feet, 2 ATAs. 66 = 3 ATAs, and 99 = 4 ATAS. You know the math... I'm sure this isn't news to you.

So if your wetsuit is 20 pounds positive at the surface, then at 33 feet, it's going to be 1/2 of what it was on the surface, or 10 pounds positive. At 66 it's going to be 1/3 of what it was on the surface, or 6.66 pounds positive. At 99 it's going to be 1/4 of what it was on the surface, or 5 pounds positive.

So the difference between 0 and 20 feet or so is about 7 or 8 pounds' lift or so. The difference between 20 and 100 feet is slightly less - 7 pounds or so....

You are playing with the numbers trying to make them support your argument. That is why I asked for your data. Using more words does not make your argument valid.

My thickest wetsuit is 28lbs positive at the surface with the the goodies (hood, gloves, booties). I measured it in a trash can (fresh water), so in s/w, it is a bit more.

Since I set myself to be neutral at 15', suit compression would be 1/4 of the total (7lbs), leaving it 21lbs positive. In reality, Boyles law is hindered by the elasticity of the suit, but this is probably close enough and the same elasticity effects the compression at depth also.

Sorry if reality is getting in the way...

 

[JeffG]

...But then instead of losing 7 or 8 pounds' buoyancy from 15 or 20 to 100, you might lose 8 or 9 pounds. So what? You should still be able to swim that up. If a diver has to ditch to swim up, there's something really wrong, and he/she needs to go back and visit the basics.

add in 10 lbs of gas for a full 130. Things are getting a little tougher to swim up.

 

[Deep South Divers]

You are playing with the numbers trying to make them support your argument. That is why I asked for your data. Using more words does not make your argument valid.

There's no "playing with the numbers." Do you have different numbers? How do you figure it?

My thickest wetsuit is 28lbs positive at the surface with the the goodies (hood, gloves, booties). I measured it in a trash can (fresh water), so in s/w, it is a bit more.

Hmmm... That's a tough one to swallow, but okay, let's assume that's true.

Since I set myself to be neutral at 15', suit compression would be 1/4 of the total (7lbs), leaving it 21lbs positive.

Not exactly, but close enough.

In reality, Boyles law is hindered by the elasticity of the suit, but this is probably close enough and the same elasticity effects the compression at depth also.

Okay, close enough... Let's go with that, then.

Sorry if reality is getting in the way...

Not sure where this came from, but you forgot to finish your math:

28 lbs positive at the surface.
21 pounds positive at 15' (1 1/2 ATAs, or .75 * 28) - where you weighted to be neutral with zero gas.
7 pounds positive at 100' (4 ATAs, or .25 * 28).

...So the difference is 14 pounds... Still easy to swim up - and as you do, it gets lighter.

...Again, you're making an example out of the very worst case scenario... Absolute catastrophic wing failure (no lift at all) with a FULL tank, and the thickest suit you can find, at one of the deepest points that your typical diver will go...

...But even with that, there's STILL no reason to ditch at depth.

Let me ask you, GrumpyOldGuy (great name - funny)... How much weight are you wearing with that 28-pound bouyant suit on? How much of it is ditchable?

 

[GrumpyOldGuy]

My argument is not about ditching weight at depth! I don't go there.

You originally stated using a D/S or SMB was not a viable option for redundant flotation and states very clearly you should not be diving if you cannot swim up your rig with no BCD. This is the statement I disagree with.

I did finish my math! I just don't assume a hard bottom like you do.

I keep 1/2 to 2/3 of my weight in a harness I can ditch on the surface. For my 7+7 suit, I wear 26 or 28lbs of lead total, depending if I carry a pony. I prefer my 7m jump suit in water over 50F, it is a heck of a lot less lead.

 

[Deep South Divers]

Tell y'all what... Instead of talking math and theory, why don't y'all try it and see if y'all can figure out a need to ditch weight at depth?

I'm not recommending that you DO ditch at depth, of course. I'm just saying, weight yourself correctly, then dive to 100 feet, dump all the air out of your wing or BC, and simulate a complete failure... Then try to swim it up and see what happens.

It'll tell you a lot - and if you do need ditchable weight.

There y'all go... A reason to step away from the computer and go diving.

Optionally, you can read the Open Water manual of the agency of your choice again and see what it says about ditching weight at depth...

More fun if you find out for yourself, though, while diving.

 

[H2O 70]

With a BP/W you'll want a crotch strap---some harnesses have them, some have them as optional....

Couldn't tell if this has been answer yet amongst the debating!

Yes, you'll want a crotch strap. Personally I have a 2" wide crotch strap. It doesn't rub if you know what I mean. I have a d ring on the front of it and there is a d ring on the rear. The read d ring is for scootering (which I don't yet do) and the rear is where I clip my reel and SMB or lift bag. It is out of the way and doesn't cause drag.

 

[Deep South Divers]

My argument is not about ditching weight at depth! I don't go there.

Oh, my bad... Sorry, I got hung in the "ditch weight at depth" discussion.

You originally stated using a D/S or SMB was not a viable option for redundant flotation and states very clearly you should not be diving if you cannot swim up your rig with no BCD. This is the statement I disagree with.

For what it's worth, I believe that anyone, any time can have their own opinion and should be able to express it within the ScubaBoard TOS... So it's your right to disagree, and even if we end up always disagreeing and never see eye-to-eye (which I think we really do), that's fine. It's anyone's right to have their own opinion!

Can you use a lift bag or SMB to pull yourself off the bottom? Can you walk out of a spring? Can you use your drysuit as a backup means of bouyancy? Of course... I just don't believe it should ever be done or need to be done - there are simply better methods of handling a catastrophic wing failure, which is a pretty remote issue anyway.

"Viable?" You know, if something happened to me and I was completely stoned and went diving totally overweighted, and that was my only option for getting back to the surface, then... Yeah, I guess it would be "viable." There are, after all, ALWAYS options, and in my opinion, it's not an emergency until you're out of gas.

Try the "swimming up" technique and see what happens. I believe it'll lend creedence to the mantra of "never ditch weight at depth."

I did finish my math! I just don't assume a hard bottom like you do.

Heh - fair enough. The original discussion was "a catastrophic wing failure at 100 feet," so I plugged that into the equation.