minimalist back inflate BC?

[Scuba_Vixen]

At the surface, assume you are perfectly neutral with empty tank and No air in your bc and a 7mil suit with vest and hood....

Now let's fill the tanks and start the dive...

With a full Al80, all else the same, you'll be 6# negative at the surface...so you'll be descending....

As you descend, the wetsuit compresses..loosing the bouyancy it had at the surface, that you weighted for at the surface to counteract......

That much wetsuit, or a drysuit with undies and minimal inflation will loose at least 15# or more of bouyancy as it compresses with depth, or holes and can't inflate (respectively)

Keep in mind that a holed flooded drysuit (that can't inflate, or a leaking one with the gas exhausted) is negatively bouyant at any depth....A compressed wetsuit ends up at about neutral near max compression...

You're now at the bottom, AND at least 21# negative .... probably a bit more if you brought something you didn't have at weight check.. an extra light maybe...or suppose the suit swing is more than 15#, a 7mil 2piece is.

You're getting real close to the maximum lift a 30# wing can give you.....If you need to help a buddy, I'm glad it's not me....

If you think for a second that with a BC failure, (no lift) you could swim up even the minimum of 21#...... That's Insane!

You choose a bladder size that's comfortably conservative. About twice the rock bottom minimum seems a good rule of thumb....

Hence my suggestion of the Trek wing at 45#lift.... a bit more is better than a bit too little.. don't you think...


I hope I explained better this time. You really were missing the suit compression - loss of bouyancy thing..you wouldn't recover bouyancy from the wetsuit till you somehow finned 21# plus however far up off the bottom it is till you get into the 60 to 40' range.......with a drysuit as described, you'll never recover any bouyancy...


Darlene

 

[jhelmuth]

Well said ScubaVixen!

jplacson - not to hijack this thread, but your comment on the BCD NOT being a flotation device...

I just got back from a trip to the Bahamas (Bimini). On a sister-boat of the dive company I traveled with, 2 divers were lost at sea due to a really strong transient current and their lack of a signaling device at surface. They were swept away 7.5 miles from their entry and were not found until almost 2 hours from there expected suface time. They did use their BCs as a floatation device - it saved their life, and I'd say that you'd be foolish to not consider it a floation device under dire circumstances (like the ones they came into).
...and yes, I do use it to leisurely float at the surface - so I guess that's my bad!

 

[jplacson]

"With a full Al80, all else the same, you'll be 6# negative at the surface...so you'll be descending...."

A full AL80 tank is only -2, and +4 when empty

"Keep in mind that a holed flooded drysuit (that can't inflate, or a leaking one with the gas exhausted) is negatively bouyant at any depth....A compressed wetsuit ends up at about neutral near max compression..."

How can a flooded drysuit be negative? No exposure suit is negative at any depth... well, except for the chain-mail shark suit.


"You're getting real close to the maximum lift a 30# wing can give you.....If you need to help a buddy, I'm glad it's not me....

If you think for a second that with a BC failure, (no lift) you could swim up even the minimum of 21#...... That's Insane!

You choose a bladder size that's comfortably conservative. About twice the rock bottom minimum seems a good rule of thumb....

Hence my suggestion of the Trek wing at 40#lift.."

So what happens if your BC fails? Aren't you contradicting yourself by claiming you need a lot of lift in an emergency, but assume that your BC will never fail? If you can't fin youself up against your rig with a failed BC bladder you ARE SERIOUSLY overweighted, no matter what you claim your rig is. And in a life or death situation... you can still ditch your weightbelt... unless you value the cost of lead more than your life.

-jhelmuth... of course the thing CAN float you at surface if needs be...but don't get a BC with the intentions of using it as a floatation device... it was never designed for that. In a drift dive, always carry a redundant floatation device, whether it be a marker sausage, lift bag, or life raft. I read a story once about a diver who got lost, and surfaced...drifted all the way around a small island and was afloat for almost a week before the rescue team found him... yes your BC can float you... ditching your weight belt, and breathing your tank empty also floats you fine. But it's NOT advised. At the end of a dive, all the lift in your BC is ALL positive, since your tanks actually float you, and your weight should just keep you neutral. So even if you have a 5# bladder... that makes you 5# positive at the end of a dive.

Like I said, what happens if your bladder fails?

 

[jhelmuth]

jplacson - Again, I think we actually agree with everything except the lift size/requirement (however you might put it). Interestingly, I've never seen any adult BCD with less than 26lbs of lift and the more typical low-end of the lift capacities seem to be ~ 30-32 lbs. Based on your arguments, you don't need anywhere near this much lift. So while I've still yet to haer an argument against having the extra lift, I'd like to hear from you on why you think/feel/know the manufactures do not offer at least a couple of BCD models which use only 10 lbs of lift?
Also again, I can be pursuaded to think differently if given a good argument based on more than just opinion.

 

[Scuba_Vixen]

If I take a drysuit and undies and throw it overboard from the boat.....once any air pockets are gone, don't you think it's going to sink?????... Without inflation, a drysuit's just a body bag... (crushed neo may be the exception, but that's another thread)

Let's try the wetsuit math again...

If you add enough weight at the surface, counteracting the positive bouyancy of the wetsuit to make you neutral, and suit compression as you descend reduces that positive bouyancy by 15#...you are now 15# negative, what's so hard to see about that????

Remedial math:

"With a full Al80, all else the same, you'll be 6# negative at the surface...so you'll be descending...."

A full AL80 tank is only -2, and +4 when empty


....Exactly what I said....the air weighs 6#....if you're neutral at the surface empty...then full..you'll be 6#negative ( you essentially have 4# of lead to offset the empty bouyancy of the tank to stay neutral)

The extra lift capacity is answered this way...

Assume you have a wing failure:.....
Since you agree that you can't swim up the 21#, then you have the option of dropping some weight......if you drop enough to swim up the few pounds left ( I doubt you could swim up more than 5 for very long), by the time you reach shallower depths to where the wetsuit starts to uncompress and becomes less negative, you'll reach a point at which you won't now have enough weight to even stay neutral,...you'll end up in an uncontrolled ascent.....probably the last 30' or so.....

Now let's do the same thing with a buddy with the 2X minimum required lift capacity.......
You're stuck at the bottom 21# negative, same as before, you're buddy grabs your bc and inflates his untill BOTH of you together are neutral... that's the 2X part.....now you can make a perfectly safe controlled ascent and safety stop with him venting air as you ascend...sweet simple piece of cake....

 

[jplacson]

jhelmuth- Well, for the simple reason that most divers feel safer with more lift. And most divers don't really bother getting their weight right... it took me 4 years before my DIR friend got to convince me how big a difference it makes. From my PADI classes way back, we were taught "Just wear 6-8 lbs, that's normal" ... so all these years, I've been using my BC more often to inflate and lift me against the 8# I was wearing... so when I borrowed his 27# Pioneer, it felt like I wasn't being lifted at all.

When I took the time to really experiment (had a DM help me out at 15" at the end of a dive) ... I dropped 6#! That's over half of what I've been wearing for 4 years!

I now dive with just 2#.

I even asked Halcyon why they stopped manufacturing their 18# "Batwing" ... they said it was due to demand... very few divers 'feel' confident with 18# of lift (tropical waters) ... and always opted for the bigger 27# bladder. So for economic/manufactuirng reasons, Halcyon discontinued the 18# bladder.

Other manufacturers do the same... haven't you noticed, most BC makers only make 2-3 bladder sizes? This is purely for business/manufacturing reasons. They round it off to people who need more lift... general lift capacities are 30, 40, and 50# bladders simply cuz they can't afford to make too many bladder sizes... scuba diving, as wide spread as it is, is still a niche market and people don't buy BCs every year so the turn over is still very slow.

scubavixen- a flooded drysuit only takes in water, so it will still be neutral even when completely flooded...water doesn't add weight in water... it will cause more drag, but it won't make you sink. A suit that sinks, in your own words, really is a body bag.


-in general- if you wanna dive with a 100# wing, go ahead. I don't subscribe to the whole "streamlined underwater" thing since we don't fin fast enough for it to really count. But the added bulk isn't worth it, specially if you're weighted properly.

 

[Scuba_Vixen]

I looked back over the posts, and I realized how poorly I behaved... the sarcasm was inexcusable. I wasn't wrong, but the delivery sure was, and I apologise.

It's nice to dive with so little weight, you must have a very low body fat percentage, but in reality, most folks need about 4% of their body weight in salt water (some a bit more)... and that's exclusive of what they need to neutralize the positive bouyancy of their exposure protection at the surface.

It's obvious, of course, that there is not sufficient demand for BC's with less than 30# lift to justify producing them. But conversely, if you have a 30# bladder, but only inflate it a small amount, it will Not displace any more space than an 18# bladder at a much greater percentage of inflation.

You mention a DIR friend helping you with bouyancy, they have great emphasis on trim, and for good reason... proper trim is the key to efficient motion...once you can remain horizontal in the water column without moving at all... you'll feel weightless and everything will seem easier.

Sounds like you have it dialed in well.


Darlene

 

[jplacson]

no harm done! I apologize as well for being so persistent.... but I used to dive large jackets... and once even wanted a 45# Zeagle since I felt that having more lift was 'safer'.

After a long discussion as well with my friend... I tried his 27# wing... it really felt weird... I felt I couldn't float at the surface, etc...etc... Then he told me to redo my weighting.

I did... I'd been diving 6# overweight (and I only dive tropical waters) ... so I can only imagine how much weight will be removed when diving dry...and one takes the proper time to really, really get your weighting down right. I'm very enthusiastic about it all since I only discovered the real difference recently!

I never thought it would make a big difference... but it does! And moving weight from your belt to other parts of your rig helps as well... finning suddenly became a lot easier.

with a minimalist BC or BP wing, you should try to move some weight to the BC itself, whether by using a SS plate (6#) and weighted STA (another 6#) ... then have the rest on your belt... your hips will be very thankful... and you will gain more leg movement... without having less lead. At the same time, ditching your belt, even at depth...won't create an uncontrolled ascent since you only ditched part of your weight.

I even wanted the 36# wing, but my friend really insisted I try the 27# instead and dump lead. My BC feels like I'm wearing a small backpack, rather than an arctic jacket, or those big camping backpacks. Right now, for redudndant lift at depth or at the surface, I carry a marker balloon... it gives me about 10# more lift... I'm saving up for the Halcyon Surf Shuttle (30# of lift) or Life raft (300# of lift) all without adding drag to my diving rig. The Surf Shuttle and a bigger balloon (40#) should be more than enough lift at depth for almost any emergency... If I got the raft, I could lift the entire team should ALL their BCs fail at depth!!! I highly recommend a quality balloon over a larger BC bladder... it's a lot safer at the surface, and increases your visibility to the boats.

 

[jhelmuth]

jplacson once bubbled...
jhelmuth- Well, for the simple reason that most divers feel safer with more lift. And most divers don't really bother getting their weight right... it took me 4 years before my DIR friend got to convince me how big a difference it makes. From my PADI classes way back, we were taught "Just wear 6-8 lbs, that's normal" ... so all these years, I've been using my BC more often to inflate and lift me against the 8# I was wearing... so when I borrowed his 27# Pioneer, it felt like I wasn't being lifted at all.

When I took the time to really experiment (had a DM help me out at 15" at the end of a dive) ... I dropped 6#! That's over half of what I've been wearing for 4 years!

I now dive with just 2#.

I even asked Halcyon why they stopped manufacturing their 18# "Batwing" ... they said it was due to demand... very few divers 'feel' confident with 18# of lift (tropical waters) ... and always opted for the bigger 27# bladder. So for economic/manufactuirng reasons, Halcyon discontinued the 18# bladder.

Other manufacturers do the same... haven't you noticed, most BC makers only make 2-3 bladder sizes? This is purely for business/manufacturing reasons. They round it off to people who need more lift... general lift capacities are 30, 40, and 50# bladders simply cuz they can't afford to make too many bladder sizes... scuba diving, as wide spread as it is, is still a niche market and people don't buy BCs every year so the turn over is still very slow.

scubavixen- a flooded drysuit only takes in water, so it will still be neutral even when completely flooded...water doesn't add weight in water... it will cause more drag, but it won't make you sink. A suit that sinks, in your own words, really is a body bag.


-in general- if you wanna dive with a 100# wing, go ahead. I don't subscribe to the whole "streamlined underwater" thing since we don't fin fast enough for it to really count. But the added bulk isn't worth it, specially if you're weighted properly.

So I dive with the Balance and would not change for larger lift (not needed - I don't know why you continue to refer to such large bladders with an implication that that is or would be my choice). You've cited the manufactures reasons (but I don't think that you know this as much as it is your speculation for theeir reasons), and you've still not given any reasons to not wear a 36 lb. lift BCD. I'll take that as "I'm not sure".
So let's just agree to not being on the exact same point of view.

 

[jplacson]

:lol: oh, again, I apologize... my response was not directed against you... I was giving you the explanationon that Halcyon gave me on why they discontinued their 18# Batwing.

There is no reason NOT to dive a 36, 45 or larger wing... as long as the person needs that much lift. Again, I'm not directing this against you... this is just stating my personal observation on how a lot of divers are seriously overweighted, and in return, usually look to a larger BC bladder to make up for their excess lead.

Having more lift than what you need isn't really bad... it causes some drag problems, and too much air shifting since partial inflating leaves a lot of room for a little air bubble to play around in... in that, I feel that having too big a bladder (10# or more than what you need) flops around too much and isn't really worth it... for extra lift at the surface, I prefer having a marker balloon which I can hang on to, and signal boats with.

I apologize again if my reply came off as aggressive in anyway.