BCD- Jacket/vest style vs back inflation

[DennisS]

You will read posts about "diver streamlining" or a BC that is "sleeker". Compared to other swimming creatures, a diver (regardless of gear) is not "streamlined". A shark or dolphin moves through the sea like a fighter plane through the sky. Even the turtle is speedy underwater. Relative to those, a diver goes through the water like an old bread truck.

There are reasons to buy each type of BC. But... if "streamlining" is your goal, you can compare it to streamlining an old bread truck.

Now if only we could "streamline" those cameras and flashes, lobster tickle sticks, nets, game bags and tow floats.

 

[RJP]

Look, without going into the arguments pro and con, anything back inflate or wing with an aluminum 80 is going to want to roll you face down. The tendency to do so depends upon your weighting, the amount of air introduced into the bladder etc.

TO OP: be sure to understand the difference between opinion and fact.

I started out with a back inflate and moved to a BP/W and have NEVER felt like I was being rolled face down.

As Nemrod does disclaim his opinion with some info about weighting and inflation, I suppose I could imagine some confluence of bad gear configuration and poor habits/skills that might roll you face forward (weights placed incorrectly, wing over-inflated, etc) but that does not mean that de-facto you'll be face-first in the water no matter what with a back inflate or BP/W.

 

[jonnythan]

TO OP: be sure to understand the difference between opinion and fact.

I started out with a back inflate and moved to a BP/W and have NEVER felt like I was being rolled face down.

As Nemrod does disclaim his opinion with some info about weighting and inflation, I suppose I could imagine some confluence of bad gear configuration and poor habits/skills that might roll you face forward (weights place incorrectly, wing over-inflated, etc) but that does not mean that de-facto you'll be face-first in the water no matter what with a back inflate or BP/W.

I agree with this post.

The claim doesn't really make sense when you think about it, either. Your exposure protection will invariably provide a great deal of buoyancy (unless you're diving somewhere super-tropical with no wet or drysuit), and your weighting is generally on or around your waist or center of mass. I've never, ever felt that a back inflate BC (I've used two back-inflate BCs as well as a variety of wings and backplates) was trying to push me face down.

Most weight-integrated back-inflate BCs also seem to put their weight pockets toward the rear, right where the wing will be giving its buoyancy.

I imagine that if you have little to no exposure protection and are severely overweighted it might be a possibility, but this is something that generally just doesn't exist in the real world. It's IMO a falsehood made up by ignorant divers and dive professionals.

 

[Nemrod]

TO OP: be sure to understand the difference between opinion and fact.

I started out with a back inflate and moved to a BP/W and have NEVER felt like I was being rolled face down.

As Nemrod does disclaim his opinion with some info about weighting and inflation, I suppose I could imagine some confluence of bad gear configuration and poor habits/skills that might roll you face forward (weights placed incorrectly, wing over-inflated, etc) but that does not mean that de-facto you'll be face-first in the water no matter what with a back inflate or BP/W.

And for the OP, please understand that some people's facts are opinion.

It would be best for the OP, if at all possible, to evaluate the BC with the other equipment, including tanks and exposure gear that will be utilized.

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.

Additionally, not all back inflate systems utilize a heavy BP, therefore they may well have a weight belt or weight system that places much of the weight forward of the bladder, on the hips etc, therefore, simple physics, there will be a rolling moment introduced. Usually this is easily managed by the diver to the point of being second nature but it still exists. With a heavy, negative steel tank, steel plate, the rolling moment might be reduced to negligible amounts.

As to the "ignorant" and other comments, I will leave that lay as I will put my experience as a diver against any, anywhere and those who have dove with me can vouch.

N

 

[Leejnd]

No I'm not.

I'm making the assumption that I care about streamlining underwater.

By the way, I don't care about speed and didn't say anything about speed. I did not make this assumption in the previous post, but I feel safe assuming that virtually every diver cares about gas consumption underwater.

And I'm not advocating that anyone "replace all their gear." I'm simply stating facts, and stating which gear I think is better. If you don't want to "replace all of your gear" for "minimal benefit" I certainly don't care, and I won't tell you to do so. But this is a thread where a newbie asking opinions and asking which is better. And I think back inflate is unequivocally better.

Okay...you're saying that YOU care about streamlining, which is why YOU prefer back inflation. I'll buy that. And I'll even apologize for assuming you were assuming something you weren't assuming.

I'll even agree that every diver cares about gas consumption underwater.

However, what I disagree with is that having a back-inflated rig will have a noticeable impact on gas consumption for every, or even most, divers, to the point where it can be stated that back-inflation is "unequivocally better". I agree it's better for divers who dive in situations where being less streamlined is going to make a huge difference in gas consumption - but that is simply not going to be a factor for every diver.

By the way, not sure if you noticed in my earlier post, but I dive with a back-inflation BC. However, I didn't go to back-inflation for streamlining. I did it because it helps with my trim, and I prefer the unencumbered chest. I did not experience ANY noticable difference in my gas consumption...primarily because I'm simply not doing dives where I need to swim long distances or fight currents. I'm perfectly happy lumbering along like a slow bread truck, and have no need (or desire) to be a Lamborghini. My SAC rate didn't change. I might not go as far as you, but I'm enjoying myself just as much.

So, while I agree that every diver cares about gas management (or at least should), I disagree that caring about gas management will or should lead one to believe that back inflation is "unequivocally better". Sometimes it will...but sometimes it won't.

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.)

 

[jonnythan]

However, what I disagree with is that having a back-inflated rig will have a noticeable impact on gas consumption for every, or even most, divers, to the point where it can be stated that back-inflation is "unequivocally better". I agree it's better for divers who dive in situations where being less streamlined is going to make a huge difference in gas consumption - but that is simply not going to be a factor for every diver.

"Streamlining" is not the only issue. There are a number of advantages to back-inflate (and especially bp/w) that make it unequivocally better. I never said that was the only reason, but you appear to spend the bulk of your post here speaking as if I had.

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.)

Efficiency.

The Honda Insight isn't aerodynamic so that it can go really really fast. It's aerodynamic to improve its fuel efficiency.

I'm lazy and like to find diving as relaxing as possible. The less work I have to do to motate around underwater, the better.

 

[Leejnd]

"Streamlining" is not the only issue. There are a number of advantages to back-inflate (and especially bp/w) that make it unequivocally better. I never said that was the only reason, but you appear to spend the bulk of your post here speaking as if I had.

Um...just because the "streamlining" issue is the only issue *I* responded to, doesn't mean it's the only issue *you* posted. And I certainly never said that's the only reason you think it's better. Although, truth be told, I can't find a single other reason that you stated...all I'm seeing are a lot of posts about streamlining. But I'm sure there are plenty of other reasons you feel they are better, since you seem to feel so strongly about it. I'm sorry I haven't taken the time to address EVERY SINGLE ONE of your statements, but I guess the rest of them didn't inspire me to respond. So I didn't.

I simply disagree with you that the streamlining issue is one that is of concern to all divers, and should be construed as a reason that they are unequivocally better. Streamlining had no relevence in my decision to switch to back-inflation. And my husband, who continues to dive jacket, is happy enough with his streamlining, and his horizontal trim, and his gas usage, that he does not see a benefit (to him) in switching.

Efficiency.

The Honda Insight isn't aerodynamic so that it can go really really fast. It's aerodynamic to improve its fuel efficiency.

I'm lazy and like to find diving as relaxing as possible. The less work I have to do to motate around underwater, the better.

But if the Honda Insight is only moping along at 5mph, how much fuel is it really saving over the bread truck, also cruising along at 5mph? Neither is moving much air to begin with, so the aerodynamics really don't make much of a difference, do they?

Again, my gas consumption experienced no change whatsoever when I switched to back inflation. However, I found myself better able to maintain a horizontal position, which has helped dramatically with my ability to take decent photos underwater. Hubby, on the other hand, is perfectly comfortable in his jacket, and we are both ending our dives with about the same psi in our tanks...so that works for us.

Hence, I think that pretty much clarifies that back inflation is "unequivocally better" for YOU, and for ME, but not for EVERYONE.

Can we agree on that?

 

[jonnythan]

However, what I disagree with is that having a back-inflated rig will have a noticeable impact on gas consumption for every, or even most, divers, to the point where it can be stated that back-inflation is "unequivocally better".

Let's be perfectly clear: I completely agree with this statement. The 'streamlining' issue by itself certainly does not make BI unequivocally better.

I'm perfectly happy disagreeing with your opinion that it's not something important to all divers.

But if the Honda Insight is only moping along at 5mph, how much fuel is it really saving over the bread truck, also cruising along at 5mph?

If they were moving at 5 mph through water, the answer would be "an incredibly large amount."

See, at 5 mph on a road, drag due to fluid (air) resistance is negligible - rolling friction is much more significant, so increased aerodynamics will have virtually zero impact on fuel economy. However, when a human being is scuba diving, drag due to fluid resistance is really the only impediment to movement worth talking about. So a much more apt analogy would be the Honda Insight and bread truck both moving at 50 mph.

Though an even better analogy would be a regular bread truck compared to a slightly streamlined bread truck that gets 15% more gas mileage.

We're having an unfortunately large argument about a terribly small point. I think we can both agree that to divers who find maximum streamlining an important consideration (I think that should be everyone, and you don't), it's a big "pro" under the back inflate category.

In any case, I think it's a relatively minor point compared with other issues such as simplicity, comfort, trim, etc.

I've already stated that back inflate is, in my opinion, unequivocally better. For everyone. Even if they disagree

 

[Leejnd]

If they were moving at 5 mph through water, the answer would be "an incredibly large amount."

Okay now that's simply unfair. You and I both know that you can't compare movement underwater to movement in the air - and that I was referring to those vehicles moving at that speed in the air. OBVIOUSLY anything attempting to move 5mph in the WATER is going to be dramatically impacted by streamlining. So that was just playing dirty. :cool2:

Just to be clear...I really DID mean moving at 5mph on land. Which, in the water, might translate to, oh, barely moving forward at all. Which is how I spend most of my dives.

By the way, I also disagree with your suggestion that going to back-inflation is going to cause a 15% decrease in gas consumption. Where did you get that number? And I guess you didn't read the part where I said that it had NO impact on my gas consumption? So there's an actual case, not just theoretic numbers thrown out at whim.

I've already stated that back inflate is, in my opinion, unequivocally better. For everyone. Even if they disagree

This is where you lose me. Like so many other other topics on SB, this one is like a religion - people have their minds made up, and nothing, not even facts, will change it. This is what gave DIR such a bad name way back when - it was the implication that if they're "doing it right", the rest of us must be "doing it wrong". (Fortunately in recent years this type of zealotry seems to have lessened, as people realized that "different" isn't always "wrong".)

I have no problem with anyone's personal opinion about what gear configuration works best for them. What I have a problem with is anyone telling me that what I prefer (or my husband, or anyone else for that matter) is simply wrong, or less desirable, or inferior.

I love my back-inflation BCD, for reasons that matter to me. My husband loves his jacket BCD, for reasons that matter to him. Does that mean he's diving an inferior rig? Is he somehow in the wrong? No. He's diving in what he prefers, which is perfectly fine. He's not causing harm to anyone, or to himself. His choice is not negatively impacting his gas consumption, his trim, his safety, or his comfort. So, given that, how can anyone say that he would be better off with a BP/W or back-inflation?

That's what drives me nuts about "all or nothing" stances on this topic. It's the implication that the *other* choice is the *wrong* choice.

And since this is a thread originally started by a newer diver looking for opinions, I will reiterate: There is nothing inherently wrong with EITHER choice. Try them both, learn the pros and cons of each for the type of diving you'll be doing, and make your own choice. Don't allow anyone to tell you one is ALWAYS better than another, for ALL divers, because that is simply not true.

 

[Stu S.]

Gotta transform your shape.