BCD- Jacket/vest style vs back inflation

[Leejnd]

Yeah, but think about all the DRAG on those jagged teeth!

 

[stargazer61]

An aluminum tank, as I stated, in all back inflate/wing units I have used or own, do indeed push me face forward, the higher I want to float, the more air introduced, the more torque forward, face down, applied.

N

That makes some sense, you must get pushed over to an extent with a back inflate if you are using the BC to lift your head well clear of the surface, perhaps in heavy chop? If you dive with a snorkel it reduces the need for this. It might also vary depending on your natural bouyancy, weighting etc. Personally, I have never noticed a significant tendency for my back inflate to push me over and I am pleased I chose a back inflate when I bought my first gear. The advantages of the back inflate are experienced under the water - where we want to spend most of the dive.

If the OP can find a shop which allows him to try out some options, that would be worth spending a few extra bucks if necessary.

 

[elmer fudd]

I am curious, tho...if speed isn't of concern to you, why do you care about streamlining? Isn't the purpose of streamlining to allow you to move faster through the water with less effort? (I'm not being patronizing - I actually want to know.)

Speed isn't an issue for me 99% of the time, but I do appreciate being able to move quickly when I want to. When surge or a current is sweeping me somewhere I don't want to go or I see a nice big Dungeness crab running away I really like being able to go a little faster than I otherwise might.

 

[MauiScubaSteve]

AFAICT, streamlining is a red herring discussion with regards to the three BC categories, since there is no scientific data on the subject. I'd venture to say there isn't even any non-scientific data on the subject. All I see on this subject is opinionated anecdotes.

My "other" job is pool cleaning, and I hope to someday find an "endless pool" that I can make some tests in.

My anecdotal opinion is that since a good majority of the leading edge of the vest BC bladder is drafting in the divers shoulder "shadow" and NONE of the other two BC's have any part of the leading edge of the bladder drafting at all, it is hard for me to imagine that either of the two that have the entire leading bladder edge dragging are going to have less drag than the one with the majority of bladder leading edge drafting.

 

[vladimir]

One quesion i have is that when completely inflatated and at the surface how does a back bc differ from a vest?

When completely inflated a back-inflate will tend to push you forward, in my experience. I always dive with aluminum 80 tanks, usually in a diveskin or 3mm wetsuit. The strategy is to not inflate it more than necessary, to have a crotch strap to keep the air-cell from riding up, and to lean back a little. It's a non-issue for me; I don't expect my bc to serve as a life-preserver and I am comfortable sitting on the surface, just beneath, or just above it. You do have a regulator available.

 

[herman]

AFAICT, streamlining is a red herring discussion with regards to the three BC categories, since there is no scientific data on the subject. I'd venture to say there isn't even any non-scientific data on the subject. All I see on this subject is opinionated anecdotes.

My "other" job is pool cleaning, and I hope to someday find an "endless pool" that I can make some tests in.

My anecdotal opinion is that since a good majority of the leading edge of the vest BC bladder is drafting in the divers shoulder "shadow" and NONE of the other two BC's have any part of the leading edge of the bladder drafting at all, it is hard for me to imagine that either of the two that have the entire leading bladder edge dragging are going to have less drag than the one with the majority of bladder leading edge drafting.

I totally agree. Like you, I often see claims of BPs being much more streamlined but as far as I have seen there is no research on the subject. My bet is a well sized jacket BC with hoses properly stowed is actually more streamlined than any other with the exception of the horse collar which is most likely the most streamlined of them all. Now by streamlined, I am not talking about how it looks but how it actually cuts through the water. While the jacket style and to some extent most back inflates (BI)have pockets and other irregular surfaces on the front, the BP and BI have a large floppy bladder with a large surface area as opposed to the smooth transition from the shoulder down the bladder of a jacket style. The jacket style may have more actual surface area but it is more rounded and flowing than the bladder of a BP or BI. The actual surface area of the BC is not the surface area that needs to be considered. A couple of thin straps on a divers chest of a BP may look more streamlined but when you take into consideration the area of the divers chest covered in a wetsuit it is basically the same total area as the frontal area of a properly fitting jacket BC the difference becomes small. The real difference in streamlining between the 2 is in the rear of the BC and that is where the jacket style wins. From personal observation I do know (or maybe feel is more correct) that the bladder on a BP adds a huge amount of drag. I often remove the bladder -fairly small 24 lb one- from my BP and dive with no bladder. I can tell a big difference in how I glide between frog kicks. If anyone has links to a study on the streamlining of BCs I would love to read it.

 

[BDSC]

Well I'm a person who recently purchased a back inflate bc (Scubapro Seahawk)and used it for the first time when I went to Little Cayman and a second trip off the coast of NC recently. I had been diving jacket bc's (Scubapro's) for the past 19 years. It is an absolute FACT that as compared to the jacket bc, the back inflate did tend to push me forward a little at the surface. It wasn't bad and nothing I couldn't deal with but the sensation was there. Now I suppose if a person had never dove anything but a BI bc and didn't know how a jacket bc felt or held you at the surface, then maybe they wouldn't pick up on the difference because they would have nothing to compare their style of bc to. But the feeling is there and my weighting is spot on.

The only advantage I found with a BI bc was I felt I may have had a little more freedom of movement with my arms. I shoot video and so that's a plus although it still is not a significant difference from my jacket, but a little better. Other than that one item, I found no additional benefit to a BI BC. No change in my air consumption and no better trim. By the way, for probably the vast majority of people who dive, if you want to make a real difference in your air consumption, exercise and get in better shape. That will have a far greater impact on your air than any equipment configuration you will choose.

So my overall impression of my BI is a good one. I like it and will continue to use it but will probably switch back and forth between my bc's. But I certainly didn't see enough of a difference between the two that I would say one is better than the other. Not even close. And while I have only tried a BP/W on four dives so my experience with them is limited, now that I can somewhat compare all three, I certainly don't see all the hoopla about a BP/W for the diving I do. (Warm water Caribbean style of diving) They may be the "do all - end all" for other styles of diving but not my style of diving. I can even dive doubles with both of my current bc's if I want to.

So I guess what I have learned from my experience diving all three is that all the many advantages that folks will go on and on about from using a back inflate or BP/W over a jacket style makes for a great read on ScubaBoard and probably other such internet sites but for me it had no bearing on reality. I see way too many excellent DM's who make hundreds and hundreds of dives a year with jacket BC's and even fullfoot fins and their skills, trim, buoyancy, and breathing are off the charts.

 

[diveanytime]

I have a ScubaPro KnightHawk and a Oceanic Chute2 both back inflate BCDs. I use them but don't like them. I favor the jacket style and now I see newer BCD's called Hybirds that have a small bladder pocket that will open up on the sides to help prevent the pushing of your face downward by the back inflation BCD's. I also like BIG pockets on the outer side of the jacket bladders but haven't found any weight intergrated jackets that I can brag about. So I favor still using my old BCD from 25 yrs ago for wetsuits. When I drysuit dive, the back inflation BCD's don't bother me as much since I can inflate my drysuit to counter act the pushing of my face downward.

 

[dumpsterDiver]

Well I'm a person who recently purchased a back inflate bc (Scubapro Seahawk)and used it for the first time when I went to Little Cayman and a second trip off the coast of NC recently. I had been diving jacket bc's (Scubapro's) for the past 19 years. It is an absolute FACT that as compared to the jacket bc, the back inflate did tend to push me forward a little at the surface. It wasn't bad and nothing I couldn't deal with but the sensation was there. Now I suppose if a person had never dove anything but a BI bc and didn't know how a jacket bc felt or held you at the surface, then maybe they wouldn't pick up on the difference because they would have nothing to compare their style of bc to. But the feeling is there and my weighting is spot on.

The only advantage I found with a BI bc was I felt I may have had a little more freedom of movement with my arms. I shoot video and so that's a plus although it still is not a significant difference from my jacket, but a little better. Other than that one item, I found no additional benefit to a BI BC. No change in my air consumption and no better trim. By the way, for probably the vast majority of people who dive, if you want to make a real difference in your air consumption, exercise and get in better shape. That will have a far greater impact on your air than any equipment configuration you will choose.

So my overall impression of my BI is a good one. I like it and will continue to use it but will probably switch back and forth between my bc's. But I certainly didn't see enough of a difference between the two that I would say one is better than the other. Not even close. And while I have only tried a BP/W on four dives so my experience with them is limited, now that I can somewhat compare all three, I certainly don't see all the hoopla about a BP/W for the diving I do. (Warm water Caribbean style of diving) They may be the "do all - end all" for other styles of diving but not my style of diving. I can even dive doubles with both of my current bc's if I want to.

So I guess what I have learned from my experience diving all three is that all the many advantages that folks will go on and on about from using a back inflate or BP/W over a jacket style makes for a great read on ScubaBoard and probably other such internet sites but for me it had no bearing on reality. I see way too many excellent DM's who make hundreds and hundreds of dives a year with jacket BC's and even fullfoot fins and their skills, trim, buoyancy, and breathing are off the charts.

One of the best ways to lower yoour sac is to get a pair of very efficient (long) freedive fins, fiberglass is probably best for this application. I see a bigger difference with the big fins than the type of BC.

 

[Saudi-Diver]

Many years ago I saw a feature in the British Sub Aqua Club Magazine addressing the issue of Jacket style Bcds v BP/W style jackets. They towed a manikin dressed in both through a ship test tank and measured the drag at typical diver speeds which were very slow 0.5 knots to 1.5 knots. There conclusions were body position in the water and trim were more important than the style of BCD. I have been hunting for a link to the story but have been unable to find it, perhaps it was just my imagination or too many beers over the years