Wing recommendations
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I see how donut wings would help in your situation but being tail heavy is not my problem at the moment.
I hope my excellent paint diagram will show what i feel is going on:
Yes I understand that's the concept, but most divers are tilted slightly shoulders up, so they can see forward. So unless you tilt over so your butt side is higher than your shoulder side, the air will never migrate to collect at the tail end. If you're in 0-degree trim, your shoulders will be higher than your butt. And if you add air in that trim position, the air will collect into the upper part of the wing, until you tilt yourself to migrate that air.
Trapezoid wings do have the trait that they will trap air in the lower extremity, but it does not migrate the air to that region. If you're already in a feet down position, adding air to a Trapezoid wing will not always float your hips, you still have to put the air in the region, and hopefully the air will trap and help your hips to float.
Donut wings can be the exact opposite, they don't trap air at the bottom of your lower half; air goes to where ever the highest point is. You do have circular wings from DSS that are shaped in a Trapezoid shape, but not to the extent of say the Dive Rite. They still work the same though, you have to put air in that lower half region for it to trap and float your hips.
But even then when it claims to float your hips, bouyancy wise it put bouyancy at your hips, but does it really add that much effect? I know all the air collects at my head in my Halcyon Eclispe wing, but I'm not head floaty, and I know I'm feet heavy normally. I wouldn't recommend a Trapezoid wing to a feet heavy diver, because quite simply, you're not going to get enough air in that region to float you AND keep your neutrally buoyant. If you grab your wing, you'll realize there's really minimal air in it at depth, unless you weight heavy and require a lot of air in the wing. Otherwise it [shape] doesn't have that great an affect. So is it really helping you in that extent or would simply trimming your weight differently solve the issue?
Unfortunately it's not so simple. You have to remember, that at the start of dive buoyancy of your BCD is much bigger, than in the end of dive when your cylinders are near empty. (I don't mean the maximum buoyancy, but the actual buoyancy in the certain moment of the dive).
I'll try to explain what is the problem, but at first three fundamental rules of trimming:
The first rule of trimming is: The BCD is not a "trimming device". The only purpose of the BCD is to compensate the gas in your tanks and eventually loose of wetsuit buoyancy if you don't use drysuit.
The second rule of trimming is: The centre of buoyancy of the BCD must be in exactly the same place as centre of gravity of the gas in the cylinders.
The third rule of trimming is: Use weight for trimming.
If you use the BCD for trimming, you'll never get perfect trim for the whole dive. Why? If you do that, in most cases you'll get the relation between centre of buoyancy and centre of the gravity like on the right picture here:
When you start the dive, your cylinders are heavy because they are full of gas and you have also a lot of gas in the BCD. If you'll trim perfectly in such configuration, when you use most of your gas the centre of buoyancy and centre of gravity will move and you will loose your perfect trim. Of course many divers gets perfect trim after playing with moving BCD/weight until they succeed or use the drysuit for help, but the shortest way to get perfect trim for a whole dive is to forget using the BCD for trimming and at first achieve perfect trim with empty cylinders by moving the weight and then fill the cylinders and properly position the BCD to keep the perfect trim with the full tanks.
The second issue is the BCD's shape. The following picture shows the problem of trapezoidal BCDs:
As you can see, the centre of buoyancy is far from centre of the gravity, so it will solve the problem of the heavy head or heavy legs, but only for the first part of dive. Why? Because in the end of dive the BCD is near empty and it stops helping
Some of wings are very square. Unfortunately they aren't so stable as they should be, because when diver gets more vertical position, the centre of the buoyancy tends to move rapidely to the front or back:
Thinking about all of these issues, the most perfect shape for the BCD is symmetrical like on the following picture:
Wow thanks for the excellent post! Lots of information, and confirmed alot of what I suspected.
Now a follow on question, sticking with that optimum shape, what horseshie wings are available? The xdeep hydros and frog midnight look right but are donuts..
Thanks again
Now a follow on question, sticking with that optimum shape, what horseshie wings are available? The xdeep hydros and frog midnight look right but are donuts..
Thanks again
just an observation, without practical experience (I use a donut wing).
If you are diving aluminum tanks, they get buoyant at the end of the dive, but because of the valve, they are top heavy. The horseshoe style has less buoyancy at the bottom and may help compensate for this.
As for the donut wing, being able to balance gas between the sides without going head up, IMHO is more important.
If you are diving aluminum tanks, they get buoyant at the end of the dive, but because of the valve, they are top heavy. The horseshoe style has less buoyancy at the bottom and may help compensate for this.
As for the donut wing, being able to balance gas between the sides without going head up, IMHO is more important.
chrpai
Contributor
If I'm understanding you correctly, you don't want to buy a separate singles wing and a doubles wing. Is that correct? If so, I'd caution you that's a fairly common mistake to try to use a doubles wing (wtx6) on a single tank. It usually doesn't end well and you'll be getting another wing anyways. Maybe 2 more wings if you decide you really want the evolve instead of the wtx6.
If it was me, I'd decide if single tank or double tank diving is more important to you and get that wing then get the other wing later.
FWIW I dive a 28lb donut wing on a single tank and love it. Find some good deals on used wings to compensate for the fact you have to buy 2.
In aluminium cylinders, the center of the gravity is far from the center of it's buoyancy as the valve and top of the cylinder is heavy. It's bad idea to use BCD to trim cylinders. The best way is to put some weight in the bottom area of the cylinders (trimming of course should be done on the empty cylinders) and then find the best location for BCD when the cylinders are full.
What is important, most of horseshoes are quite short, so it means they are far from being perfect BCD as the centre of buoynacy is not in the right place (to much in the valve direction). Here's the drawing explaining the problem:
With diving dry and being too light in the legs, what fins do you use?
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