Jacket BCDs, BP/W and bouyancy question

[dmaziuk]

Judging by how people who go from jackets to BP/W, as opposed to how many BP/W people go to jackets, I'd say the plate/wing system would be a pretty darn strong contender.

That is of course faulty logic: by your own assertion almost everyone starts with a jacket BCD so they can't go from BP&W.

 

[Diver0001]

Luckily, I don't wear my BC around my entire body so my legs and arms are free to bend. It is a feel/personal preference thing, and selling it as jackets are restrictive seems to be a stretch.

30 years ago the BCD's on the market were like this. Modern BCD's come in various shapes and sizes and have fitting options that the older ones didn't. There are certainly some lousy BCD's out there even today but there are some good ones as well. Painting them all with the same brush is just another example of what I was trying to say in earlier posts.

R..

 

[BoltSnap]

Jacket BC's are popular with beginners because:
1) That's what the dive shops tell them they need - economics for the dive shop
2) In most cases that's really all that's available when they first are exposed to the sport, as in walk-ins to an LDS and no awareness of the alternatives in the beginning. There are a few exceptions with shops that carry alternative gear but they are very few world wide.
3) That's what's in most rental fleets
4) They feel good and comfy when trying them on on dry land.
5) They place the diver upright (high and dry) on the surface making hanging around pleasant when they listen to their instructors.
6) They look nice to a beginner, complex, like they are getting something for their money.

Mostly I would say, Jacket BC's are popular to the rest of the dive world (besides Scubaboard) because they don't know any different.
How many alternatives have you seen on dive boats world wide? And if there are who's actually paying attention? If most divers never go on dive related websites, and their LDS's never carries anything else, rental fleets only have jackets, magazines only show jackets in pictures, articles, and gear reviews, how are they going to know anything else even exists?

It is a dive industry conspiracy for world domination for sure, the damned communist Soviets are at it again!!!!!!!!!!!!!!!!!!!!!!!


Give me a freaking break!!!

 

[dmaziuk]

It is a dive industry conspiracy for world domination for sure, the damned communist Soviets are at it again!!!!!!!!!!!!!!!!!!!!!!!

As a former dam Soviet I can assure you that economics for the shop is pretty much the opposite of the "it" the commies were again at.

 

[Diver0001]

I do see several advantages to a BP:

a) fabric BCDs, be they jacket or back-inflate, are generally positively buoyant. That translates to an additional weight requirement for the diver, unless they are inherently negatively buoyant, which most of us are not. In contrast, metal backplates with simple harnesses are usually negatively buoyant - unless that is altered by the additional of (unnecessary) padding- and the total weight obligation for the diver is less;

b) a metal backplate places much of the weight of the BCD where it optimally belongs, adjacent to the diver's center of lift (thorax / lungs). If you have a 'floaty' fabric BCD, even if it is weight-integrated, the weight is usually placed below that center of lift (e.g. on the waist on a belt, or in pockets at the bottom of the BCD). The use of trim pockets on cam bands - for jackets, 'soft' back-inflates. and BPs - has helped correct this to some extent, but it remains an issue with regard to trim. You can be perfectly weighted, but the distribution can still be 'off' and create a foot-low diver - a 'Forty-fiver', if you are adding a substantial amount of weight to compensate for the 'floaty' fabric;

c) wearing a SS BP i need virtually no added weight in certain configurations (fresh water, salt water with AL cylinder and 1 mm exposure suit), or i only need a minimal amount of added weight;

d) the plate is versatile, and allows for changing the lift (wing), to suit different exposure suit / weight combinations (e.g. diving both warm and cold water);

e) the BP is amenable to easy addition of a crotch strap, which serves to enhance the security of the scuba unit to the diver, and the overall stability of the rig. Yes, you can add a crotch strap to a jacket BCD with a little sewing (yourself or a shoe repair shop) and I have done this with two jacket BCDs over the years, so that is not an exclusive advantage of a BP. But, it is easier to add a crotch strap to a BP than a jacket;

f) I find it much easier to properly fit a BP with a single piece harness to a variety of torsos (mine included) than it is with a jacket. A perfectly fitting jacket is great. Getting a perfect fit with a jacket may be a bit more challenging than with a BP.

I just wanted to touch briefly on this post. I'll cover it point for point.

a) Most modern jackets, and certainly all of the well designed ones, have 1-2lbs of inherent positive lift. There are exceptions. The worst ones on teh market have about 4lbs of inherent positive buoyancy. On these threads people make it sound like you have a lift balloon attached to your body, but you don't. These days it's normally in the 1-2lb range. 20 years ago this was not the case but people have trouble letting it go. It is true, however, that a BP/W is generally negatively buoyant because of the metal backplate. This can make a difference to your total need for ballast weights. If this is really a big issue then you can also deal with ballast weight by changing the tank type. Aluminium cylinders are considerably more positive than steel cylinders, for example. In fact, your choice of tanks (and suit) will affect your stability in the water a lot more than your choice of BCD.

b) this point makes no sense at all. If it fits, it fits. If it doesn't, it doesn't. You wouldn't buy a BP/W that didn't fit properly or wasn't properly adjusted and you wouldn't buy a jacket that didn't fit properly or wasn't properly adjusted. Trim is a total NON issue if you take the time to trim yourself. Your trim in ANY gear is only as good as the time you put into dialing it in. If you don't put in the time to trim yourself, then don't blame the gear. The type of BCD is utterly irrelevant to this.

c) you will need less ballast weight with a SS backplate as compared to a jacket. However, the discussion about ballast weights is going to depend much more on the SUIT you're using and not on the BCD you're using.

d) This is true. If you need this feature, a jacket will not offer that.

e) you might need a crotch strap on a BP/W for floating on the surface. Under water, it has virtually no function unless you're wearing 40 or 50kg of tanks that you need to keep from moving around too much. A jacket is a BCD intended and designed for one tank and no stages and the manner in which it is designed makes a crotch strap an unneeded feature. This is really a case of comparing apples and oranges.

f) This will depend on the jacket. Personally I adjusted my BP/W ONCE in 2002 and haven't touched it since and I adjusted the straps on the jacket ONCE the day I bought it and haven't touched it since. The exception are the shoulder straps on the jacket that you generally need to tighten when you put it on before every dive. This is about as complicated as putting on the seat belt in your car. My advice would be that if you aren't able to tighten a shoulder strap or put on a seat belt by yourself, that diving might not be the sport for you. Again, this is over-reaching in the quest to find arguments that sound on the surface like they make any sense.

R..

 

[cool_hardware52]

I just wanted to touch briefly on this post. I'll cover it point for point.

OK, I'll play.

a) Most modern jackets, and certainly all of the well designed ones, have 1-2lbs of inherent positive lift. There are exceptions. The worst ones on teh market have about 4lbs of inherent positive buoyancy.

I've actually tested a "few" +5 lbs is not uncommon for a "full featured" high end bc with a back pad, shoulder pads, cumberbund etc. It's the foam padding. In addition many jackets are hard to full vent. This requires even *more* ballast to offset.

It is true, however, that a BP/W is generally negatively buoyant because of the metal backplate.

Er, ah, well, no. A well designed BP&W has no inherent buoyancy *without* the plate. It's pretty simple, no foam pads means no inherent buoyancy. Nylon webbing, nylon fabric, and urethane films are not less dense than water, foam padding is. The plate provides ballast, but it is simply false to claim that a BP^W is net negative because the plate is offsetting *any* inherent buoyancy.

b) this point makes no sense at all. If it fits, it fits. If it doesn't, it doesn't. You wouldn't buy a BP/W that didn't fit properly or wasn't properly adjusted and you wouldn't buy a jacket that didn't fit properly or wasn't properly adjusted. Trim is a total NON issue if you take the time to trim yourself. Your trim in ANY gear is only as good as the time you put into dialing it in. If you don't put in the time to trim yourself, then don't blame the gear. The type of BCD is utterly irrelevant to this.

One of the primary benefits of a BP&W is the huge range of adjustment possible, easily exceeding that available from most Jackets. That directly leads to a better fit for many.

c) you will need less ballast weight with a SS backplate as compared to a jacket. However, the discussion about ballast weights is going to depend much more on the SUIT you're using and not on the BCD you're using.

No, an inherently buoyant jacket, and one that cannot fully vent, will require more ballast than a BP&W that can easily be fully vented and is without any inherent buoyancy.


Tobin

 

[Diver0001]

Er, ah, well, no. A well designed BP&W has no inherent buoyancy *without* the plate. It's pretty simple, no foam pads means no inherent buoyancy. Nylon webbing, nylon fabric, and urethane films are not less dense than water, foam padding is. The plate provides ballast, but it is simply false to claim that a BP^W is net negative because the plate is offsetting *any* inherent buoyancy.

This is actually what I meant. The thing in it's entirety will be negative.

One of the primary benefits of a BP&W is the huge range of adjustment possible, easily exceeding that available from most Jackets. That directly leads to a better fit for many.

For some, yes. For many would be reaching.

No, an inherently buoyant jacket, and one that cannot fully vent, will require more ballast than a BP&W that can easily be fully vented and is without any inherent buoyancy.

I don't think anyone is claiming otherwise. The point about not being able to fully vent it will have to do with the design. A jacket that's significantly positive and can't be fully vented is a lousy design. I've said over and over on this thread that there are lousy jackets on the market but the "anti jacket" crowd takes those designs as the baseline by which all jackets are compared and judged.

I'll just be clear again that I have nothing at all against a BP/W. I like mine just fine. The reason I'm cutting against the grain here has to do with the huge allergy I have to the way these discussions are waged on the internet. If people were arguing in favour of a BP/W due to its inherent advantages (as few do) then it would come across very differently than arguing against a jacket based on a lot of misinformation and parroting of that misinformation. The whole issue has become highly biased and highly clouded by people treating it more like a political/religious discussion than a discussion involving logic.

R..

 

[Skeptic14]

The whole issue has become highly biased and highly clouded by people treating it more like a political/religious discussion than a discussion involving logic.

R..

Yeah, the "thou must convert" attitude is so prevalent among bp/w proponents. Again this morning checking new posts... a new diver was asking SPECIFICALLY about din vs yoke and how to get in the habit of checking air and in 7 posts someone was urging them to go get a bp/w... really???

I'm beginning to expect a knock on my door with someone asking if I've heard the great news about our diving savior, the BP/W


And regarding mobility and restriction which was a big reason earlier in the thread that BP/W were better...

Once you put on a wet suit/dry suit the limitation of mobility isn't going to be either the jacket or the bp/w... And yet somehow the smooth, controlled motion necessary for diving is possible even when wearing something like a 7mm wet suit over your arms/legs but a jacket on your torso is going to restrict your movement????

 

[Diver0001]

Once you put on a wet suit/dry suit the limitation of mobility isn't going to be either the jacket or the bp/w... And yet somehow the smooth, controlled motion necessary for diving is possible even when wearing something like a 7mm wet suit over your arms/legs but a jacket on your torso is going to restrict your movement????

It's true that the suit generally restricts your mobility to an extent.

There is, however, a big difference between a wing and a jacket in this regard. A wing is fully behind your back and when you fully inflate it, it doesn't push against your body at all. Many jackets will push against your body when fully inflated on the surface, especially if you over-tighten the waist strap and/or it doesn't fit you very well. Hybrid designs reach a middle ground.

The argument that this affects your diving, however, is completely absurd. There are only two times that you might fully inflate the jacket. (1) during the buddy check and (2) on the surface before or after a dive. During a dive the jacket is never fully inflated because doing so, by definition, would cause you to float to the surface. Nevertheless, on every single one of these threads, someone says it and the believers all nod in agreement without thinking it through. As I said before I dive with both a jacket and a BP/W and under water, if you're trimmed and your gear is well thought out to balance itself, then you'll literally feel no difference.

When I stop moving in a BP/W I hang in the water like I'm hung on a string. I have *exactly* the same thing when I'm using a jacket. There's a picture of me diving with a dolphin if you click through my profile to the photos and I'm in a jacket on that. Also, when you open my profile you'll see a picture of me diving through a coral cavity (in a jacket). Do I look like I'm uncomfortable or struggling in either of those pictures?

That said, however, there *is* a difference to how a jacket acts on the surface as compared to a wing. A wing won't push against your body at all, even when fully inflated and a jacket ordinarily will if you fully inflate it. Apparently some people find this so uncomfortable that they believe that a jacket is not suitable for diving. I've never felt this way but I have a jacket that's the right size and it's properly adjusted for me....

R..

 

[cool_hardware52]

This is actually what I meant. The thing in it's entirety will be negative.

No at all what you implied in your previous post.

For some, yes. For many would be reaching.

For many it is a key point. I routinely hear from my happy customers how much better a fit they achieved with a BP&W.

I don't think anyone is claiming otherwise. The point about not being able to fully vent it will have to do with the design. A jacket that's significantly positive and can't be fully vented is a lousy design. I've said over and over on this thread that there are lousy jackets on the market but the "anti jacket" crowd takes those designs as the baseline by which all jackets are compared and judged.

I've never suggested otherwise, but the fact remains that you can walk into most dive shops, and leave with a 60 lbs lift, super delux jacket to end all jackets with ease.

I'll just be clear again that I have nothing at all against a BP/W. I like mine just fine. The reason I'm cutting against the grain here has to do with the huge allergy I have to the way these discussions are waged on the internet. If people were arguing in favour of a BP/W due to its inherent advantages (as few do) then it would come across very differently than arguing against a jacket based on a lot of misinformation and parroting of that misinformation. The whole issue has become highly biased and highly clouded by people treating it more like a political/religious discussion than a discussion involving logic.

R..

So you are going to treat your "huge allergy" by providing mis information about BP&W's ?

Why don't you start a thread on what to look for in a well designed jacket?


Tobin