How much lift is really needed or is too much?BCD?

[IndigoBlue]

See the calculation of exactly how much lift you need in the following thread.

FYI I dive in salt water with 30 lbs. lift in a 7 mm full wetsuit and a AL 80 tank and 36 lbs weight.
ScubaRon

Sorry, this does not cut it. Your gear will sink, like a rock, since 36 + the full alum tank + the reg + the light more than exceeds your 30 lb B/C.

You are banking on being able to swim-up a negative trim, which is fine for an advanced diver. But this is not how we teach it to beginners. And this is not how I would recommend answering the question.

 

[ScubaRon]

Sorry, this does not cut it. Your gear will sink, like a rock, since 36 + the full alum tank + the reg + the light more than exceeds your 30 lb B/C.

You are banking on being able to swim-up a negative trim, which is fine for an advanced diver. But this is not how we teach it to beginners. And this is not how I would recommend answering the question.

This is the error many people make: you are forgetting the inherent buoyancy of my wetsuit and myself. I wear 36 lbs to offset this! Read the calculation I provided and you'll see that I have ample buoyancy. Swimming up negative trim is a definite NO!

One thing to consider with integrated weight systems is how much to put in it. In general it is better not to put more weight in the BC than it's lift capacity. That way it won't sink if you have to take your BC off at the surface (e.g. to board a boat in rough water).
ScubaRon

 

[LowTide]

Drag Schmag... My Recon has 75lbs lift and I love it. I have dove with BCs with less, I can't noticeably tell a difference on the drag of a 35lb lift or my 75lb lift - SAC rates are the same. I think it was Pug who wrote something like drag is proportional to speed, so if you are hauling ass it may be a factor. I don't haul ass, so all is good. I kind of like the feeling of having an emergency zodiac on my back

 

[IndigoBlue]

This is the error many people make: you are forgetting the inherent buoyancy of my wetsuit and myself. I wear 36 lbs to offset this! Read the calculation I provided and you'll see that I have ample buoyancy. Swimming up negative trim is a definite NO!

One thing to consider with integrated weight systems is how much to put in it. In general it is better not to put more weight in the BC than it's lift capacity. That way it won't sink if you have to take your BC off at the surface (e.g. to board a boat in rough water).
ScubaRon

I am not forgetting the inherent buoyancy of your wetsuit. Particularly since I believe that thick wetsuits are a hazard, predominantly because they have huge swings in inherent buoyancy, and therefore you could be buoyant near the surface, and yet were you to dive really deep, and then end up deeper than you thought you would end up, it would end you up in a downward spiral out of control that you could never return from.

Weight yourself at the surface, like I illustrated. Exactly like I illustrated, and THEN you will be safe in the water.

 

[ScubaRon]

I am not forgetting the inherent buoyancy of your wetsuit. Particularly since I believe that thick wetsuits are a hazard, predominantly because they have huge swings in inherent buoyancy, and therefore you could be buoyant near the surface, and yet were you to dive really deep, and then end up deeper than you thought you would end up, it would end you up in a downward spiral out of control that you could never return from.

Of course a wetsuit can never loose more than it's surface buoyancy, no matter how deep you go. But I think that the key is to know what this potential buoyancy loss is and make sure that your BC can easily handle this. That is why I promote that people actually calculate their minimum lift requirement, instead of going by what works for others.
ScubaRon

 

[mempilot]

...I promote that people actually calculate their minimum lift requirement, instead of going by what works for others.
ScubaRon

Right on! It's not prudent to copy unless everything is the same. Since we all have different equip and bodies, this is the best advice.

 

[IndigoBlue]

Of course a wetsuit can never loose more than it's surface buoyancy, no matter how deep you go. But I think that the key is to know what this potential buoyancy loss is and make sure that your BC can easily handle this. That is why I promote that people actually calculate their minimum lift requirement, instead of going by what works for others.
ScubaRon

Nice change of subject.

You are way too overweighted for your B/C in your thick wetsuit.

I strongly urge you to re-calculate.

 

[IndigoBlue]

I dive a 30lb wing with this single tank config (it is plenty of lift for me):

Single steel 80 tank
6lb Stainless Steel Backplate
My gear (lights, reels, etc...)
Scuba Pro Jet Fins (neg buoyant)
Wetsuit with 6lbs of weight or Drysuit with 8lbs of weight
Deep (135 or shallower)

I weigh 170lbs.

With doubles, I go to a 55lb lift wing.

Not knowing your size or other equip, it's hard to give you any advice.


The deeper and heavier you go, the more lift you'll need. When I go deeper than 135 for deco dives, I use doubles and a bigger wing (BC). I also dive deep with a drysuit which gives redundancy in the lift. I also carry a lift bag, which gives redundancy. But for recreational, 30lbs is more than enough for me and I could get away with much less. My last jacket style BC was 24lbs of lift.

Hope that helps a little.

With a drysuit you would probably be fine. You could not help anyone else off the bottom if they had a failure, but you yourself would probably be fine.

ScubaRon's thick wetsuit is a totally different story.

Drysuit = good.

Thick wetsuit = very, very bad.

I hope nobody confuses your post, about drysuit diving, with Ron's about thick-wetsuit diving.

 

[mempilot]

You could not help anyone else off the bottom if they had a failure, but you yourself would probably be fine.

Not true. I've simulated it in recurrent training with both wet and drysuit configs. You must be assuming complete BC failure of both the rescuer and the victim. For me, that would mean bladder failure, suit failure, and lift bag failure. Not likely. I am thinking of dropping 2lbs off both configurations, but that 2lbs isn't keeping me from swimming the rig up.

 

[IndigoBlue]

Not true. I've simulated it in recurrent training with both wet and drysuit configs. You must be assuming complete BC failure of both the rescuer and the victim. For me, that would mean bladder failure, suit failure, and lift bag failure. Not likely. I am thinking of dropping 2lbs off both configurations, but that 2lbs isn't keeping me from swimming the rig up.

You might be able to pull this off, as an extremely experienced advanced diver, with a cool head, and good arm and leg strength and technique.

I would not bet on a beginner doing this successfully, however.

You can forget about the lift bag issue. You won't have time to deal with a lift bag, for the real thing.

Like I said, you sound fine, taking care of yourself. But I would not bet on your configuration for taking care of students or inexperienced divers.