Still confused about lift

[dumpsterDiver]

While I don't agree having extra lift for rescue others, I however think 17lb or 20lb wing is very small. In warm water minimal suit, full AL80, you are 6lb negative by the gas only. You have 11lb of lift total for staying above water. Now the part of the wing above water provide no lift and the stuff above water is heavier than if they are underwater. You ended up having 7-8 lb of lift for floating above water. I found my head isn't comfortably above water with DSS17. I just don't understand what is the gain of having a 17lb wing vs a 30lb where drag, venting are practically the same.

some people on this board crack me up. they want a recreational diver who ventures below 100 feet to have a HUGE pony bottle,,, 40 cu-ft is often recommended and 30 is very commonly suggested. Zero regard for the extra drag of this large cylinder and the considerable weight on the boat.. And you need this larger tank to be "safe" to handle all kinds of unlikely scenarios... All this because a little 13 cu-ft pony just doesn't give the diver enough options in a true emergency....

Yet when i suggest a BC that has 12-15 lbs excess lift capacity above the absolute minimum that a diver will need for their own use... I am advocating unsafe practices and the moderators should be called in (again)..

 

[halocline]

While I agree with you that a 20 lb or less wing is very small, your analysis is not quite correct. It is not the weight of the gas that matters but the buoyancy of the cylinder. A 80 CF cylinder is roughly 2 lbs negative, however when you add the plate, regs, D-rings, etc. you are at 6 lbs or more.

I think what he was saying is that when you are weighted properly (neutral at surface with an empty tank) then you add 6lbs for the weight of the gas in the cylinder. The total weight of the gas in an AL80 is 6 lbs. It doesn't matter if the empty cylinder is 2 lbs negative or 4 lbs positive, you still have to adjust ballast to be neutral at the surface.

But, the old 'eye level' bit does not mean neutral, it means positive by part of the weight of your head, which is sticking out above the water. I like the DIR approach of being neutral at 10-15 feet with 500 PSI; that's where you need to hover for a stop, and that puts the diver a bit more positive on the surface which IMO is better.

 

[ams511]

I think what he was saying is that when you are weighted properly (neutral at surface with an empty tank) then you add 6lbs for the weight of the gas in the cylinder. The total weight of the gas in an AL80 is 6 lbs. It doesn't matter if the empty cylinder is 2 lbs negative or 4 lbs positive, you still have to adjust ballast to be neutral at the surface.

I didn't quite get that from his post but it was early for me. Darn thunder storm woke me up. However the buoyancy of the cylinder matters more for wing selection than the weight of the air. Remember the rig needs to float by itself. If the OP switches from an AL-80 to a steel tank which are popular in N. Florida that rig may not float on its own. Especially with a steel plate.

But, the old 'eye level' bit does not mean neutral, it means positive by part of the weight of your head, which is sticking out above the water. I like the DIR approach of being neutral at 10-15 feet with 500 PSI; that's where you need to hover for a stop, and that puts the diver a bit more positive on the surface which IMO is better.

From what I remember the other part of eye level is that when you exhale your head should sink below the water. So basically the weight of your head sticking out above water is offset by the air in your lungs.

 

[ronscuba]

While I don't agree having extra lift for rescue others, I however think 17lb or 20lb wing is very small. In warm water minimal suit, full AL80, you are 6lb negative by the gas only. You have 11lb of lift total for staying above water. Now the part of the wing above water provide no lift and the stuff above water is heavier than if they are underwater. You ended up having 7-8 lb of lift for floating above water. I found my head isn't comfortably above water with DSS17. I just don't understand what is the gain of having a 17lb wing vs a 30lb where drag, venting are practically the same.

The 17lb and 20lb wings are for buyers who want the advantages of a smaller and lighter wing. How important those gains are, is different person to person. Duffle bags, backpacks, dry bags. They come in capacity sizes small, medium and large. Why buy a small bag when a medium is only a little bigger but is more versatile ?

As discussed, I have an Oxy 30. I wanted something for travel that also vented easier. You and others mentioned the Halcyon 30 vents as well as a 17 or 20 wing. That might be, but I believe the Halcyon requires a STA ? I use a softplate for travel. So, in addition to paying the premium $ for Halcyon, I also have to buy a STA and travel with the extra weight of the STA and a hardplate. It's not the right setup for my travel needs. A DSS 17 or 20 is the best solution for me. My wife and I did not experience any problems with head clearance at the surface. You did, so something about us and our setups is different than yours.

When traveling, every pound matters. 50 lb limits on checked bags. Some international flights have 15 lb limits on carry-on's and yes, I had to pay a weight penalty because my carry on was overweight. Ever buy something when on vacation ? That's extra weight you have to travel back with.

My DSS 17 wing and Oxy softplate.
[vimeo]72577747[/vimeo]

 

[cool_hardware52]

However the buoyancy of the cylinder matters more for wing selection than the weight of the air.

No. The buoyancy numbers for the cylinder can impact plate material, i.e. stainless plate vs lightweight plate.

A diver in a 3mm suit with a HP 100 needs a lightweight plate. His rig will be about - 14 with a full tank.

a Diver in 3mm suit with an al 80 will benefit from the ballast a stainless plate provides. His rig will be about -10 with a full tank.

Either can use the smallest wings commonly sold today 17-18-20 lbs.


Tobin

 

[TSandM]

Why a 17 pound wing? Because it's tiny. Venting it is effortless, because the air has nowhere to get away from the dumps. You can also tell the difference in streamlining. It's just plain fun.

 

[buddhasummer]

Why a 17 pound wing? Because it's tiny. Venting it is effortless, because the air has nowhere to get away from the dumps. You can also tell the difference in streamlining. It's just plain fun.

That's exactly why I love to dive my 18lb wing whenever possible.

 

[ams511]

No. The buoyancy numbers for the cylinder can impact plate material, i.e. stainless plate vs lightweight plate.

A diver in a 3mm suit with a HP 100 needs a lightweight plate. His rig will be about - 14 with a full tank.

a Diver in 3mm suit with an al 80 will benefit from the ballast a stainless plate provides. His rig will be about -10 with a full tank.

Either can use the smallest wings commonly sold today 17-18-20 lbs.


Tobin

I do understand that, what I wrote was incorrect and not what I meant. Thank you for the correction.

 

[eelnoraa]

My wife and I did not experience any problems with head clearance at the surface. You did, so something about us and our setups is different than yours.

Maybe my head is heavier.

 

[ronscuba]

Maybe my head is heavier.

Could be. I drank a lot in college and I'm getting kind of old. I have less brain cells now. More empty space adds buoyancy.