Test Data on Back-Inflate vs Jacket-Style

[Don Quixote]

Hi,

Have seen statements that back-inflate has lesser drag but is there any real test data or comparative number on this?

Thanks,

Don Q

 

[tursiops]

There are so many variables that you'd need to test them both, on you,. with your kicks and exposure suit and body position, doing the kind of diving you usually do. The issue is what is the cross-sectional area seen by the flow....so even how you hold your head matters.

 

[Kharon]

Real data or comparative numbers - not me, but ... Anecdotally

I've used a jacket type BC for all my diving up to the last year. Then I switched to a soft backpack/harness with an orally inflatable vest (with a dump valve) underneath the harness. I noticed about a 25% difference in how long my dives lasted with comparable profiles.

I found the oral inflation to be a wee bit problematic when towing a dive flag and handling a GoPro type camera. So I got a very small donut/bladder for the backpack. I haven't had a trip yet and only 2 short dives this summer, but I expect it to fall somewhere between the jacket BC (which does have a lot of drag on surface swims) and no donut/bladder. For surface swims I'd expect it to be nearly as good as the vest.

 

[divad]

Hi,

Have seen statements that back-inflate has lesser drag but is there any real test data or comparative number on this?

Thanks,

Don Q

No. Maybe.....no.

 

[fmerkel]

Dive drag is BIG. The rest is pretty much quibbling. You will find absolutely no data.
The real question is do you like it better....or not. You will also find no data, just anecdotal tales.
I've owned and used them all. I like a BP&W best, but I do take a fairly standard BC to the tropics. It was inexpensive, it's lighter, it's fine when I'm not carrying cold water gear+weight, AND it has honest to goodness usable pockets.

 

[Eric Sedletzky]

I very seriously doubt any companies have done any sort of scientific drag comparison tests. Why would they? All it would do is invalidate their products since all they are interested in doing is selling overstuffed poodle jackets with lots of bells and whistles to the general public and maximizing profits. Between jackets and back inflates: My perception is that there *might* be a slight difference in streamlining between the two since back inflates lack the side inflation areas, but they still have big integrated weight holders and a lot of fluff which does stick out and cause drag. If you’re into going fast then there are other options, but many divers don’t care about fast they just cruise slowly and look at things. In that case jackets and back inflates are just fine. Fast would be for hunters who need to cover a lot of ground, or those that need to go head on into strong currents, etc.
There is a whole separate school of minimalist style diving that deals with streamlined, maximum enhanced slipstream, body positioning that maximizes slick movement, etc. but you won’t hear or learn about this stuff at any dive shop or standard training agency. This is a tie over from the old ways/days and is practiced by a small group who is into this type of thing. There is no “official” training for this style of diving, you just have to get in with the right group of people and get mentored. One of the tenets of minimalism is diving with no BC and only a tank mounted on a back pack, proper weighting, using lungs, and other principles.
Very controversial and usually ends up in a huge flame war here on SB.

 

[Don Quixote]

Thank you for all the response. The reason I asked is my LDS has been pushing me to go backplate for some time now saying it has less drag and can reduce air consumption. ERIC SEDLETZKY reflects my thoughts as I am mainly an underwater tourist. I like to have my flashlight, knife, Lifeline and SMB inside the pocket making it a lot handier for me and the dive busboys as it is preferable to doff the BCD before climbing back on the dinghies. FMERKEL also points out something I thought. Believe that the back-inflate is better for cold water in a dry suit as it will balance better and the big lift capacity will balance out the extra weight. I only dive warm water, a lot in Indonesia. Never had a problem engaging the currents even in Komodo. With regards to air consumption, I used to be the number one air hog and guilty of being the dive terminator. But nowadays, my air normally last a lot longer than the DM's. There is no need for more air as I have many times nearly break my bottom time. More air time might actually get me into trouble.

 

[dmaziuk]

Remember that in the formula for drag, velocity is squared. Less drag is great, but on a drift dive you'd have to go against the current to actually notice the difference. I think for us underwater tourists who mostly drift with the current, the choice of BP&W is 99% personal preference: steel plate offers somewhat better weight placement, and if you're between sizes you get much better fit, and that's about it.