Circular Wing vs Horseshoe Wing

[hongrace]

All other things being equal, what is the difference between a circular wing and a horseshoe wing? Thanks.

 

[TSandM]

Well, the theory behind circular wings is that you can move air from one side of the wing to the other at either the top or the bottom of the wing. It IS possible, if you are in perfect horizontal trim and using the butt dump, to dump one side of a horseshoe wing to the point where you want to float left-side down. (It is trivial to correct by going a little out of trim and moving air across the upper arc of the wing, though.)

As Tobin George of Deep Sea Supply often points out, the theory and practice with a doughnut wing are somewhat different. Air never goes DOWN, unless pressure pushes it there. And because the lower channel of a doughnut wing is trapped beneath the tank or tanks, it will ALWAYS be lower than the side pontoons, and lower than the upper arc unless you are distinctly head down. So, in practice, little or no air will actually move from side to side through that lower connection under normal diving conditions.

 

[beanojones]

Though the reasoning for why a donut should not work better than a horseshoe is sound, in my experience, donuts work more than a little bit better than horseshoes (as long as the butt dump is properly mounted facing away from the diver.)

The reason for this is that butt up to dump is just simply easier than head up in many diving situations.

But then you get back to the fact that wings manufacturers (as opposed to BCD manufacturers) now always put the butt dump on the diver's side /inside of the wing which means that there is air trapped by the placement of the butt dump away from the high point of the bladder.

Basically with non dual bladder wing, you can't count on the butt dump to fully dump anyway because it is on the inside facing the diver.. (Dual bladder BCDs can be flipped to put the butt dump on the outside/away from diver's side of the wing). Since you cannot count on the butt dump to fully vent anyway, you are going to have to use the shoulder dump, so in practice there is no difference between most donuts and most horseshoes.

Old DiveRite Travel wings used to have the Butt Dump outside facing away from the diver, and they work great. When DiveRite moved the butt dump to the inside to match what everyone else was doing, the butt dump became a lot less useful, since it can no longer be used to vent all the air in the BCD.

 

[gsk3]

But then you get back to the fact that wings manufacturers (as opposed to BCD manufacturers) now always put the butt dump on the diver's side /inside of the wing which means that there is air trapped by the placement of the butt dump away from the high point of the bladder.

Basically with non dual bladder wing, you can't count on the butt dump to fully dump anyway because it is on the inside facing the diver.. (Dual bladder BCDs can be flipped to put the butt dump on the outside/away from diver's side of the wing). Since you cannot count on the butt dump to fully vent anyway, you are going to have to use the shoulder dump, so in practice there is no difference between most donuts and most horseshoes.

Butt dumps are in the proper location when they are on the diver's side. To use them properly, pull *away* from you rather than towards you, so that you pull the dump into the highest position when you dump. Works like a charm.

 

[SDAnderson]

Circular design relative to the horseshoe:

1. Easier to dump without the gymnastics. As discussed, the real-world with a horseshoe requires you to pitch up, roll to the side, then pitch down whenever you want to dump. This is a pain.
2. If you actually dive prone, they make you more head-heavy. All that lift at your butt means your trim is pitched forward. This may or may not be a good thing, depending upon your natural trim.

 

[beanojones]

Butt dumps are in the proper location when they are on the diver's side. To use them properly, pull *away* from you rather than towards you, so that you pull the dump into the highest position when you dump. Works like a charm.

No it doesn't "work like a charm" since the facing the diver mounting means that the dump can never actually become the highest point when the diver is facing down. The highest point will always be the fold of the wing full of air above the dump when pulling back. It is constrained by the shorter length of fabric/bladder on the lower side than the higher side. If the dump is rear mounted, the dump starts at the highest point, and when it is pulled back it becomes the apex of the wing. Try pinching some fabric of your shirt over your nipple and pulling it towards your back. You might be able to make it to to a point even with your back, but then imagine an air bubble that is pulling your shirt away from your body in back. You will see that you can dump some air, but not all air. Now reach around to your back and pull the fabric away from your body to the rear, and you will see that there is no way to trap air since that can easily become the highest point.

People who think a front mounted butt dump actually works have found a way to work around the design by not counting on it to vent all the air in the wing, probably because they use their corrugated hose. If one expect the butt dump to vent all the air, front mounted designs fail to do so.

Cold water divers carry so much weight, and so much buoyancy due to exposure protection, they may not really notice the air trapping, or perhaps they have just become accustomed to using the corrugated hoses. Warm water divers, who frequently dive without exposure protection, notice it quickly when a front mounted butt dump will not release the last 2-5 pounds of buoyancy in a wing with a front mounted butt dump design.

There are reasons why someone started using a front dump (it has been previously stated are that a rear mounted butt dump is hard to reach, like reaching for a point in the rear of your shirt in the back in the above example). Overall, it is better to think of a front mounted butt dump as an OPV (over pressurization valve) rather than a fully functional dump, and count on using the corrugated hose for buoyancy control.

At least one manufacturer of wings with front dumps does acknowledge that there is some air trapping caused by front mounting the dump in the typical place on the wing. He has stated his wings have the dump mounted closer to the edge of the BCD to minimize the trapping. Never dove his wings so they might work better than most, but he does recognize the need to overcome the usual front placement of the butt dump problems.

 

[Rainer]

I own and regularly dive both. In my experience, there is absolutely no difference in how they dive. I really don't know what people are talking about with "gymnastics" required to dive a horseshoe wing. If you're diving dry, you're going to have to raise your left arm slightly anyways to vent the suit, at which point the wing will equalize. I think most people fail to realize just how head down they have to get to equalize across the bottom arc of a donut wing.

 

[gsk3]

I'm pretty picky about my buoyancy and it works fine for me. Using the dump that enables a horizontal diving style matters a lot more to me than getting out the last few drops of air, and I really doubt that there's 5 lbs of buoyancy being trapped in there.

Three arguments that the true number is so tiny as to be ignorable:
-Anecdotal - When I come up empty, I come up really empty. I've felt my wing before and there's just not really any air in there.
-Theoretical - Take a look at the inflator on a common wing.

The dump will empty from all sides, so look at the outermost edge of the rear dump. Draw a line from the outer edge of the rear dump to the edge of the wing, and then draw a line from the edge of the rear dump perpendicular to the other line. That perpendicular line should encompass the entire area that can't be dumped. It's a heck of a lot less than 5/40=1/8th of the wing by volume.
-Hypothetical - When you pull up and back to dump, you compress the small area where the last remaining air might be trapped, forcing another good bit of it out.

In short, this is one of these things where the current design works quite well when used properly and it's just not worth fretting about.

 

[cool_hardware52]

Circular design relative to the horseshoe:

1. Easier to dump without the gymnastics. As discussed, the real-world with a horseshoe requires you to pitch up, roll to the side, then pitch down whenever you want to dump. This is a pain.

1. 
   
   
   No, not really. A properly designed wing, horseshoe or donut will have no more tank wrap than absolutely necessary, and neither will require any "gymnastics" Many older wing designs, which are often horseshoe style, are either too wide, or much to high capacity, or both. This makes venting difficult. The very same would be true for a donut wing that suffered from the same design flaws.
   
   
   
   

   If you actually dive prone, they make you more head-heavy. All that lift at your butt means your trim is pitched forward. This may or may not be a good thing, depending upon your natural trim.

   
   This is complete nonsense. Wings provide lift only where there is gas in them. Donut wings do not automatically provide more lift at the hips. The lower arc of a donut wing contains no gas for a horizontal diver. As others have pointed out the lower arc of a donut wing is between the cylinders and the divers rear end.
   
   We build donut style wings that specially increase the lift closer to the divers shoulders (top biased) and others that specially increase the lift near the divers hips (bottom biased)
   
   Where the lift is placed is a function of the overall shape of the wing, in plan view where the wing is widest is where it will first fill with gas for a horizontal diver. It has nothing to do with whether the wing is a horseshoe or donut.
   
   We offer both horse and donut wings. Either can be made to work, and neither is a magic instant better diver piece of gear.
   
   Far more important than horseshoe vs donut is proper capacity and overall shape.
   
   Tobin

 

[Splitlip]

Another conspiracy perpetrated on the dive community I suppose; like split fins.

Only wing I have ever seen with a rear facing butt dump was a Dive Rite Venture It wrapped the tank so at the OPV,the dump was not facing the rear, but rather to starboard. The Wing had a cord thread through a sleeve so it could be reached on the front of the wing. When the guy tried to dump by pulling the cord, (he did not have monkey arms) he lowered the valve which from my perspective seemed ineffective. I suspect Dive Rite joined the other manufacturers because when all was said and done, front facing is right. (I have all the respect in the world for Lamar.)

I dive a front facing donut. I dump exclusively from the butt during my dive. As gsk3 said, pulling away from your butt (back) brings the valve to the high point and works like a charm.

Oh..and FTR, the gas in my very narrow donut wing DOES move through the lower arc. If the wing is completely inflated, it lifts the bottom of the tank off my butt. If not fully inflated I can slide my hand behind the bottom of my tank. Maybe we do it stupider in Jupiter, but my donut works. Is my rig "too loose"? Doubt it.

I admit, when I dump, I give a little hip bump to raise the left side of the bottom arc.

No it doesn't "work like a charm" since the facing the diver mounting means that the dump can never actually become the highest point when the diver is facing down. The highest point will always be the fold of the wing full of air above the dump when pulling back. It is constrained by the shorter length of fabric/bladder on the lower side than the higher side. If the dump is rear mounted, the dump starts at the highest point, and when it is pulled back it becomes the apex of the wing. Try pinching some fabric of your shirt over your nipple and pulling it towards your back. You might be able to make it to to a point even with your back, but then imagine an air bubble that is pulling your shirt away from your body in back. You will see that you can dump some air, but not all air. Now reach around to your back and pull the fabric away from your body to the rear, and you will see that there is no way to trap air since that can easily become the highest point.

People who think a front mounted butt dump actually works have found a way to work around the design by not counting on it to vent all the air in the wing, probably because they use their corrugated hose. If one expect the butt dump to vent all the air, front mounted designs fail to do so.

Cold water divers carry so much weight, and so much buoyancy due to exposure protection, they may not really notice the air trapping, or perhaps they have just become accustomed to using the corrugated hoses. Warm water divers, who frequently dive without exposure protection, notice it quickly when a front mounted butt dump will not release the last 2-5 pounds of buoyancy in a wing with a front mounted butt dump design.

There are reasons why someone started using a front dump (it has been previously stated are that a rear mounted butt dump is hard to reach, like reaching for a point in the rear of your shirt in the back in the above example). Overall, it is better to think of a front mounted butt dump as an OPV (over pressurization valve) rather than a fully functional dump, and count on using the corrugated hose for buoyancy control.

At least one manufacturer of wings with front dumps does acknowledge that there is some air trapping caused by front mounting the dump in the typical place on the wing. He has stated his wings have the dump mounted closer to the edge of the BCD to minimize the trapping. Never dove his wings so they might work better than most, but he does recognize the need to overcome the usual front placement of the butt dump problems.