Beating a Dead Horse: BP/W Lift for Deep, Cold, Wet Dives

[jreilly2120]

I'm currently shopping for my first bp/w (going it solo on the internet because my LDS only sells jacket style BCs), and I'm having a lot of trouble determining required lift for a deep dive, primarily because I dont know how much buoyancy my suit will lose. Here are my weights:

Me: 5'10 - 225
Tank: HP 80 or 100 single
Suit: 2 peice 7mm henderson with gloves, boots and a hood all in 7mm
Lead: 28 lbs (possible 26 with a HP 100).

If I calculate based on a 100% loss of buoyancy at 100-130 feet, I am looking at needing:
28 lbs lead + 10 lbs tank + 10 lbs tank gas = 48 lbs lift,

But if I assume my suit loses only 2/3 buoyancy, on a full tank Im looking at
18 lbs lead + 10 lbs tank + 10 lbs gas = 38 lbs lift,

and on top of that, people have suggested that I add 10 lbs to bring my head out of the water. Both of these are much greater values than what I see other people diving, and much more than the 32 lb wing that comes with the kit I am looking at. I'm not even sure they make 50 lb lift singles wings. Anyone else have a similar gear set up that could shed some light?

 

[MaxBottomtime]

I'm 225# and dive Steel 119s and 130s. My wing is 27# lift. When I dive doubles I use a 55# wing

 

[rhwestfall]

trial & error, but you are going to be -6# with just a SS bp (your jacket might be a couple pounds buoyant). That can be a large swing in required lead....

For singles here in fresh water I use 30-34 # lift, and 50# for doubles including my double HP120's

 

[pasley]

Make life simple, call Tobin George at Deep Sea Supply. DSS makes an excellent Backplate and wing right here in the USA (Pasadena CA) and at a reasonable price. Before you buy from Tobin he will run through things with you: Type of diving you are currently doing and plan to do in the future, Thermal Protection used, weight worn, weight of the gear etc. Then he will tell you what you need to buy in terms of wing to have the right amount, but not have a larger than you need wing creating drag. https://www.deepseasupply.com/

 

[JohnN]

If you're worried about total buoyancy loss, the size of your wing won't make a difference . . . FWIW 100 cu ft of gas is only 8 lbs, and as rhwestfall points out, your poodle jacket is buoyant, so a SS backplate+wing is probably another -8 lbs in your total weight. So make at least 10 lbs of your lead ditchable and you're down to neutral.

If this still bothers you, carry a DSMB of sufficient size to provide some lift

 

[eelnoraa]

You are double counting some of the weight. Assume you are currently weighted properly, meaning that with empty tank and empty wing on surface, you are neutral. HP100 is -2lb empty, reg set is -2lb, Lead -28lb => total positively buoyant items you are carrying (BC, wetsuit, etc) is +32lb. Let's assume your BC is +4lb and its buoyance doesn't change with depth. This makes your wetsuit +28lb. For 100% wetsuit buoyancy at depth (not likely), you will be -28lb. If at the beginning of a dive, 8lb of air/nitrox to a full HP100, you will be -36lb only (which is alot). A 40lb wing will do just fine for this extreme case consideration.

Head above water is at the surface, you will not lost any wetsuit buoyancy there.

 

[fbk]

people have suggested that I add 10 lbs to bring my head out of the water?

Well by the time your head is at the surface you will have all your suit buoyancy back...

 

[decompression]

You need to google a "balanced rig" to see what you actually need for lift and lead....as well rethink diving to 130 in a 7mil wetsuit


Sent from my iPhone using Tapatalk

 

[jreilly2120]

The wet suit is a non option right now. I don't see how i could be more balanced though. 28 lbs is perfectly neutral at 10 ft, so i can't go down. Is there any way a 32 lb wing could be made to work? I've had a couple very experienced people mention that they thought 38 was too large.

 

[ams511]

Your wing needs enough lift to do two things:

1) Float the rig on the surface without you in it.
2) Compensate for the change in buoyancy of the wetsuit.

1) According to what you posted you need a 48 lb lift wing whiich is not made. That means either something is off (I too think you are double-counting the air in the tank) or you need to carry some weight on a belt .

2) The buoyancy of the wetsuit can be measured by rolling it up and seeing how much weight sinks it in a pool.

Usually for cold water you are looking at a 30 - 40 lb lift wing.