minimalist back inflate BC?

[Scuba_Vixen]

You'll find the TP has more flexibility with regards to fitting adjustments and positioning for straps.....great for those who use multiple eposure protection schemes. If you get the weight pockets, they are cavernous, if you use soft weigh, you can get 20# in each of them if you want. I'd be a bit skeptical of a 30# lift wing, the Trek is 45#......if you end up on the bottom with 30# of weight and a holed drysuit with a full tank, you're better with a bit more than you need, than a bit less. The K'hawk is a sweet bc to dive, but you'll never get that much weight into it without a crowbar.

Overall, I think the TP2 is a notch above the recreational bc's for toughness and longevity, they have an excellent track record with demanding diving...... or....You could look at the new TransPlate...it's a Transpac2 harness on a BP..best of both worlds...comfort and stability.......



Isn't shopping fun,


Darlene

 

[jhelmuth]

Paul,

I'll conceed that your math "theoretically" provides enough lift. But there is more to it than that. There are safety issues (like having enough reserve lift to assist your buddy in a case of their BCD failing - and others that I can't cite here at this moment) which would demand that you have more lift than the minimum required to offset your lead at the surface.
The general rule I learned is that your lift requirements should be ~ 2x (or more if desired) the requirements for your most negative gear configuration at the surface (IE - 10lbs of lift required at surface sould indicate the need for a BCD with 20+ lbs of lift or more).
Even if you don't want to go with this premise, you may want to consider the drag from a fully inflated BCD at depth. The larger surface area will create a larger "hole" for you to swim against and will increase you SAC rate and workload. If this is your cup-of-tea, fine - I'll go along with that. It's just that I think there is a better answer - but that's me, and I wouldn't ask anyone to subscribe to my opinion just because it's mine. As a matter of fact, maybe it would be better to do it your way (seriously). Can you provide me with some information that might lead me to a different conclusion?

 

[jplacson]

I'm sorry jhelmuth, but I disagree... first of all, your BC is NOT an elevator... you're not supposed to inflate it to rise... nor are you supposed to use it as a life jacket.

And if you do need to lift your buddy... you, again, are NOT supposed to just float there motionless and inflate your BC... you FIN up.

Inflating to ascend is a VERY VERY dangerous practice. No matter what the situation. That's why we wear fins.

Should you need additional lift at the SURFACE... buy a lift bag or a closed circuit signal balloon (which should be standard) ... inflate it, then hug it... this will provide you with much more lift at the surface, better visibility for the boat, and buoyancy where you need it... in front of you!

I used to think it was cool to have a huge bladder... "Man, I can lift a small treasure chest if I just inflate!" ... but the more I learned... the less lift I needed! Your BC should just provide you with just enough lift to be a little positive. Remember that you're supposed to be neutral at 15' with 500psi, and a COMPLETELY EMPTY bladder. This means that at the beginning of the dive, the only additional weight you should have dragging you down is the weight of your air... and even diving doubles... that's not that much... 5# per tank or so at the most. It's very easy to fin up against 10# at the beginning of a dive..since you're not tired yet. By the end of the dive, your tanks are already positive and add buoyancy anyway.

Remember that the reason you wear weights is the NEUTRALIZE the positive buoyancy of your exposure suit, and to compensate for the lost weight of air by the end of a dive... it's not meant to DRAG you down.

 

[paulwlee]

jhelmuth once bubbled...
The general rule I learned is that your lift requirements should be ~ 2x (or more if desired) the requirements for your most negative gear configuration at the surface (IE - 10lbs of lift required at surface sould indicate the need for a BCD with 20+ lbs of lift or more).
Even if you don't want to go with this premise, you may want to consider the drag from a fully inflated BCD at depth. The larger surface area will create a larger "hole" for you to swim against and will increase you SAC rate and workload.

jhelmuth,

The 2x lift is something to be debated, as jplacson was saying. If my buddy is having problems and I inflate my BC to counter his 20 something pounds of negative bouyancy, I will do a Polaris if I lose my hold on him. Not something I want to do. But maybe it's a personal choice. I would feel OK with several lbs of positive lift, which is about the margin I would have with my choice of bladder size. That much is counterable with empty lungs and kicking down a little while emptying the bladder.

But for your full-bladder argument, I wasn't saying he should dive with the exact lift that he would need, so he would be fully inflated. I am in favor of some margin, in which case the bladder will not be fully inflated, and thus will present a similar profile to a larger capacity bladder. (if it is holding the same amount of air)

 

[Scuba_Vixen]

Jplacson said:

"Remember that you're supposed to be neutral at 15' with 500psi, and a COMPLETELY EMPTY bladder. This means that at the beginning of the dive, the only additional weight you should have dragging you down is the weight of your air... and even diving doubles... that's not that much... 5# per tank or so at the most. It's very easy to fin up against 10# at the beginning of a dive..since you're not tired yet. "

First, you're better off being able to hold a 10' stop with virtually empty tanks...(the worst case scenario)

Secondly, we're talking 7 mil wetsuit here for some dives...This thing swings about 15# in bouyancy (probably a bit more with hood and vest, etc.) from surface to 60' where it's well compressed.

Add 10# for an Al80 full and the reg.

Now swim up the 25 to 30# ....Good Luck


You may want to rethink your recommendations on lift requirements


Darlene

 

[jplacson]

Scubavixen... why will you be finning up against 30#? The 15# additional will be negated by your wetsuit. That's why you wear the additional weight to begin with...just to negate the buoyancy of the suit at surface... if you are properly weighted, no matter what your exposure suit... your only negative buoyancy at the beginning of a dive should be the air in your tanks. Remember that at the end of a dive, you should be able to float at eye level with one full breath, and an empty BC bladder... regardless of how much weight you're wearing.

The only time it becomes annoying to wear weight is actually on la

 

[jplacson]

Scubavixen... why will you be finning up against 30#? The 15# additional will be negated by your wetsuit. That's why you wear the additional weight to begin with...just to negate the buoyancy of the suit at surface... if you are properly weighted, no matter what your exposure suit... your only negative buoyancy at the beginning of a dive should be the air in your tanks. Remember that at the end of a dive, you should be able to float at eye level with one full breath, and an empty BC bladder... regardless of how much weight you're wearing.

The only time it becomes annoying to wear weight is actually on land. Other than that, 3mm suit with 6#, or 7mm suit with 15# shouldn't make a difference in water at all since the weight you wear is cancelled by the suit you wear.

You said so yourself that wetsuits gain buoyancy as you ascend.

Now, if you're overweighted, that's another story.

You have to first calculate how much weight you REALLY need. What I did when I decided to buy a BP/wing setup... I did one fun dive with more weight than I normally wear... then at the end of the dive, I asked the dive master to help me as I emptied my bladder and waited for my tank to hit 500psi... I slowly handed him the weights in 2# increments until I stopped sinking, and I no longer had to fin upwards.

Its a misconception (even with me, up until a few weeks ago) that more weight is better, hence you need more lift as well. This increases the overall bulk of your gear... why clutter yourself with extra bulk? It takes just one planned 'weight' dive to get your buoyancy perfect. After that, you realize that more lift and more lead isn't really better. And remember, a flooded drysuit becomes NEUTRAL, not negative.

30# of lift and below is more than enough for MOST 3-5mm dives. 30-40# of lift for 5-7mm dives. 40 and above is either for extreme cold water dives, or if you're lugging around a lot of extra gear that's negative (equipment, cameras, scooters, tools, etc)

 

[jhelmuth]

jplacson once bubbled...
I'm sorry jhelmuth, but I disagree... first of all, your BC is NOT an elevator... you're not supposed to inflate it to rise... nor are you supposed to use it as a life jacket.

I never said that you do (where did you get this from?)

jplacson once bubbled...
And if you do need to lift your buddy... you, again, are NOT supposed to just float there motionless and inflate your BC... you FIN up.

Yes - but if their BCD is not providing any lift, you may have to compensate with yours. Hopefully this will never come into play - it was just one example of a possibility of needing additional lift.

jplacson once bubbled...
Inflating to ascend is a VERY VERY dangerous practice. No matter what the situation. That's why we wear fins.

Again - never said that this is the way to ascend. You're implying that from the "useless BCD" example (I'm sorry now that I cited it because your not getting it)

jplacson once bubbled...
Should you need additional lift at the SURFACE... buy a lift bag or a closed circuit signal balloon (which should be standard) ... inflate it, then hug it... this will provide you with much more lift at the surface, better visibility for the boat, and buoyancy where you need it... in front of you!

I agree with you on this point. Of course IMHO, you might consider having some additional lift capability (not a gross amount - just a bit more) from you BCD - just my opinion.

jplacson once bubbled...
I used to think it was cool to have a huge bladder... "Man, I can lift a small treasure chest if I just inflate!" ... but the more I learned... the less lift I needed! Your BC should just provide you with just enough lift to be a little positive. Remember that you're supposed to be neutral at 15' with 500psi, and a COMPLETELY EMPTY bladder. This means that at the beginning of the dive, the only additional weight you should have dragging you down is the weight of your air... and even diving doubles... that's not that much... 5# per tank or so at the most. It's very easy to fin up against 10# at the beginning of a dive..since you're not tired yet. By the end of the dive, your tanks are already positive and add buoyancy anyway.

Well, I've never thought it was cool to have a huge blader - partly why I like and chose the Balance. And we both agree that the BCD should provide enough just enough lift to make you neutral. So you've just disagreed with me on the "excess" lift capability. I have failed to find an argument against having the extra capacity - this was all I asked for to be convinced otherwise. Please let me know what your argument is against the general rule of ~ 2x the lift.

jplacson once bubbled...
Remember that the reason you wear weights is the NEUTRALIZE the positive buoyancy of your exposure suit, and to compensate for the lost weight of air by the end of a dive... it's not meant to DRAG you down.

I really think we agree on most all points. I'm sorry you've misinterprited or read mine. My apologies in advance if I've mis-read yours.

 

[jhelmuth]

paulwlee once bubbled...


jhelmuth,

The 2x lift is something to be debated, as jplacson was saying. If my buddy is having problems and I inflate my BC to counter his 20 something pounds of negative bouyancy, I will do a Polaris if I lose my hold on him. Not something I want to do. But maybe it's a personal choice. I would feel OK with several lbs of positive lift, which is about the margin I would have with my choice of bladder size. That much is counterable with empty lungs and kicking down a little while emptying the bladder.

But for your full-bladder argument, I wasn't saying he should dive with the exact lift that he would need, so he would be fully inflated. I am in favor of some margin, in which case the bladder will not be fully inflated, and thus will present a similar profile to a larger capacity bladder. (if it is holding the same amount of air)

Paul - I think we are actually in agreement. I posted this because his lift requirements were very close to the capability for the Balance. I'd simply recommend against it - but it's his choice. My personal opinion and choice is for a minimal size wing with the greatest lift capacity without being obtuse. The Balance (which was my personal choice) is great for me and my typical dive conditions. With a 3mm shorty and 500 psi ALU80 I wear 4 lbs of weight. I don't need much lift at depth and this is a great consideration to me as it really sets me up for a nicely trimed, low workload, easy to manage dive (wrt bouyancy control). I have no problem holding a 15 ft stop in most any suface conditions (really heavy waves at surface are a bit of an issue, so I usually choose to stop at 20 for an additional 2 mins and minimize the ascent rate from there as best as possible by losing some lift and slowly swiming up the remainder.

 

[jplacson]

:lol: it seems we do! :lol: my apologies as well...

I just didn't agree with your "There are safety issues (like having enough reserve lift to assist your buddy in a case of their BCD failing - and others that I can't cite here at this moment) which would demand that you have more lift than the minimum required to offset your lead at the surface.
The general rule I learned is that your lift requirements should be ~ 2x (or more if desired) the requirements for your most negative gear configuration at the surface (IE - 10lbs of lift required at surface sould indicate the need for a BCD with 20+ lbs of lift or more)." statement.

Generally, your BC is not what keeps you at the surface, it's still your finning. The BC helps but since it's not called a lift device (it's called a compensator) ... it shouldn't be treated as a floatation device either.

I do inflate at the surface to float, but it's mainly for convenience, not safety. At your most negative config at the surface, the only thing keeping your negative should be the weight of the air in your tanks, nothing more (unless you have camera equipment, tolls, and the like that are required on that dive) From what I know, 80cf of air weighs about 6# (am I right?) So, even diving doubles should give you a -12# buoyancy at the beginning of the dive, that means a 24# bladder should be enough.... now if this is what you meant by 2x you lift requirement, then ... hehehe... sorry, my bad. I guess we do agree on most points! :lol:

This is for everyone who wants more lift at the surface to help float (not at you jhelmuth) ... get a suface marker, or lift bag (ideally, closed circuit) ... inflat this at surface and hold on to it! Halcyon owners, get a Surf Shuttle or Lift Raft!