Determining the best size wing

[MikeS]

If you have ditchable weight that is making you negative... why do you have it? What does ditching it solve?

I wasn't referring to ditchable weight I meant equipment that happens that to be negatively buoyant that you could detached for some reason.

For example a stage slung pony bottle carried as a bailout. If you can hand it off it should not be used in determining weighting since you want to be able to be able to achieve neutral buoyancy just below the surface at the end off the dive without it. So at the beginning of the dive, before you use any gas, you will need lift to compensate for the negative buoyancy.

I would think this true for any equipment with negative buoyancy that you could detach to include reels, cameras, lights, etc.

Mike

 

[Spectre]

I wasn't referring to ditchable weight I meant equipment that happens that to be negatively buoyant that you could detached for some reason.

Ok... I see your point... sorta.

For example a stage slung pony bottle carried as a bailout. If you can hand it off it should not be used in determining weighting since you want to be able to be able to achieve neutral buoyancy just below the surface at the end off the dive without it. So at the beginning of the dive, before you use any gas, you will need lift to compensate for the negative buoyancy.

Well, there is a couple factors at play here. You're handing off negative bouyancy that is already compensated for. I'm not handing off an empty bottle, but rather a full bottle. It becomes an issue if you are handing off a tank that is going to be negative empty.. but even then it most likely doesn't matter.

If you have a stage bottle, you need to be able to compensate for it in your wing _and_ in trim. So if you have a full stage bottle that is, for example, 2 lbs positive empty and 2 lbs negative full, then you're going to have 2 lbs to compensate for the positive 2 lbs. Which leaves you 4 lbs heavy from the gas. Take that bottle away and you loose 2 negative lbs, but you already have space for 4 lbs.. .well, 8 actually because that 4 lbs needs to be able to fit in the side of the wing that the bottle is on so that you don't end up rolling.

The only time it might become an issue is if you are using stages that are negative empty, and you are treating that empty weight as part of your weighting needs. But I don't know of _any_ tanks where the empty negative weight is greater than the weight of the gas [e.g. if you've got 4 lbs of gas, you need to have 4 lbs of lift on the side of your wing to keep your attitude in the water, so you need 8 lbs of available lift. If the bottle is 9 lbs negative full, and 5 lbs negative empty, then you got a lb you gotta deal with... but I don't know any tanks that have that sort of characteristic except the Heisers... and I wouldn't get near those tanks in the first place.

I would think this true for any equipment with negative buoyancy that you could detach to include reels, cameras, lights, etc.

It comes down to what you _would_ be ditching inadvertantly. I'll buy the stage bottle hand-off. My canister light is going to be part of my overall weight, and I'm not going to compensate for loosing that, because I'm not losing that unless I _need_ to ditch _that_ weight. I'm not handing it off for any reason.

On top of it all, you'll have some extra room in your wing anyway. When your on the surface with a full wing, you'll be plastered face first in the water. If you have some extra space in that wing, then you'll get a better vertical float.

Of course we've completely gone beyond what the original poster was looking for. You really only need to deal with the big items. How much gas you are going to be carrying? What about unevenly distributed weight [like a can light, or the weight from a stage bottle], and most importantly... is your exposure suit thick, and compressible?

 

[MikeS]

Jeff,

I guess I’m still missing something. Here’s my line of reasoning, where have I gone astray?

You work out weighting so that with a near empty tank you are very slightly negative just below the surface with no gas in the bladder. Your bladder is sized to accommodate the swing weight of your gas plus the loss of buoyancy due to compression at depth, with some safety margin.

Now you decide to add a stage slung bail out bottle, it may be the same for a stage bottle. My stage slung AL 30 cu. ft. pony with a DS4/TX40 and SPG is about 4 pounds negative full. Forgetting about trim for a second, how do you address weighting? I propose that you do not change weighting so that if you hand off the pony you are still correctly weighted. This means that at the start of the dive you need an additional 4 pounds of lift.

Mike

 

[GoBlue!]

Another thing to consider, from what I'm told, is that with Oxycheq wings, the 30# & 45# wings have exactly the same underwater profile. So, if you want to err on the side of additional lift, I can't see any horribly bad reason to go with the 45# lift if you choose this brand. Clearly, other wings are excellent as well, but the profiles will vary with different size lifts.

Jim

 

[Spectre]

Now you decide to add a stage slung bail out bottle, it may be the same for a stage bottle. My stage slung AL 30 cu. ft. pony with a DS4/TX40 and SPG is about 4 pounds negative full. Forgetting about trim for a second, how do you address weighting? I propose that you do not change weighting so that if you hand off the pony you are still correctly weighted. This means that at the start of the dive you need an additional 4 pounds of lift.

Well, there's a couple questions to answer. What is the empty weight, and is that part of your weighting or not. e.g. if you just add the bottle, and it's negative 4 lbs, then you need to be able to compensate for 4 lbs. If it's 3 lbs of gas, and -1 lb empty, then you can either 1) compensate for the full 4 lbs or 2) take 1 lb from somewhere else and use the -l lb of the empty tank as part of your weighting.

I would go with option 2... because 1) if I'm handing that bottle off, I got plenty of gas in my tanks... definately more than a pounds worth. And even if not, I can handle 1 lb of positive bouyancy with my lungs anyway.

Now the other part that I was talking about is.... lets say your bailout bottle is 2 lbs negative. Do you compensate for 2 lbs? Depends. Is it neutral empty? Lets say it's 2 lbs positive empty. That means you need to compensate for 4 lbs of weight that could get used during your dive [the weight of the gas]. Now since the bottle is 2 lbs positive empty, you'll want to add another 2 lbs to compensate for that. So now you've added 2 lbs positive, and 2 lbs negative [making it neutral] and 4 lbs of gas. You still only need to compensate for 4 lbs of gas. If you hand off the bottle, you're negative 2 lbs now, instead of negative 4 lbs. but since you could handle the 4 lbs, you can handle the 2 lbs.

Now if you're slinging, say a heiser tank, and lets say it's 8 lbs negative empty, and 12 lbs negative with gas. Now if you take that bottle away, you've got an 8 lb swing. If that weight was part of your weighting, then you're positive. If you have an extra 8 lbs somewhere else so you can hand off that bottle, then you've got 12 lbs you have to compensate for instead of just the 4 lbs that the gas weighs.

But the last little thing is the weight difference... the trim part. In your example, we've got 4 lbs negative on one side of your body. So you need 4 lbs positive on that side of your body [in your wing/bc]. Since your wing is going to be symetrical, and you want to be able to get 4 lbs of lift on your left side, then you need the space in the wing to be able to get 4 lbs of lift on that side [if your fully inflated, you'll have it distributed through the wing]. But if you've got 8 lbs of lift capacity left, and you put for lbs of gas in one side, you'll get it in there.. because it doesn't get distributed since the wing isn't full [make sense?]

So with my example, I've got a -2 lb tank with my gas. So I need 4 lbs of lift to be able to distribute 2 lbs over to the left side to compensate. But I need 4 lbs of lift to handle the gas anyway... so it's not an issue.

But the last example is using 4 lbs of gas, but 12 lbs negative on one side. So if your weight is evenly distributed, and you've got that 12 lbs on that one side, you need an extra 24 lbs to be able to compensate for 12 lbs on one side. If you add, say, an 8 lb canister light on your other side... now you're even, and only need to compensate for 4 lbs on one side...unless you hand that tank off.

Make sense?

 

[Uncle Pug]

I use a 27# wing with a single 104
I use a 70# wing with double 104s (+ deco bottle and at times scooter)

I've used 55# with doubles and 45# with singles.

I like what I have now. The 70# is a nice raft and doesn't create anymore drag than a 55#. When it is cold and lumpy out and the drysuit has completely flooded... it is nice to have the extra.

 

[Spectre]

*chuckle* Good point pug.

I used a 55# wing for singles. Way too big.
Went 36#. Kept it after I went dry.
diving 55# with double 130s.

 

[Genesis]

Dive an Oxy45 for singles. No difference in the profile than the 30, and I like the extra in rough seas on the surface.

Just picked up an Abyss 55 and like it for doubles. Plenty of lift with doubles. My Oxy 70 is on eBAY - not because I don't like it, but I found that I like the Abyss 55 even better.

 

[Snowbear]

For double HP120's I use a 59# DiveRite Classic. It has a problem with the taco shell effect when used for single tanks, so I got a nice little DiveRite Jr. I think it's 40# lift, but the wing is nice and small, only cost $40 and is more than adequate for any single as well as a small set of doubles if I ever stumble across any.