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

[Mike126]

Looks like you are double counting the tank. 10# for tank and 10# for gas? Based on the buoyancy calculator the tank full is 10# neg in the water.

What type of BC are you wearing now? You may shed some buoyancy depending on the type of BC (jacket).

How much lift does your current BC have?

Regardless, call Tobin




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[halocline]

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.

This is correct, but add the weight of the gas, because at the beginning of the dive you will be negative by the weight of the the gas, assuming you're weighted properly.

OP, how much you weigh or your tank weighs on land is not part of the equation. Just figure out how much buoyancy your wetsuit has, you can do this by putting it in a mesh bag, floating it, and tying weights to the bag and determine how much weight it takes to sink it. Then add the weight of your gas and this is the total lift you'll need. For a single tank it rarely exceeds 30 lbs.

"Balanced rig" doesn't mean 'properly weighted'. It means that you split up ballast between your body (like a weight belt) and your rig (like a steel plate, weights in pockets, or camband weights) so that both your rig and yourself are reasonably neutral. That way if you ever had to take your rig off under water, maybe to fix a camband or something, you wouldn't go flying to the surface while your rig headed for the bottom. This also helps tremendously with the issue of floating your rig without you in it.

In cold water with a thick wetsuit, usually you have enough buoyancy on the surface so that it's not hard to keep your head out of the water.

 

[dumpsterDiver]

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?

I've dove deep in cold water with a thick wetsuit. I would want more than 30 lbs of lift. 40 lbs would be OK for me. I personally like to have a little extra lift incase I need to drag a buddy up or provide help, or more likely, be able to pick up something heavy during a dive.

Also I would definitely have a good portion of that lead ditchable, in case of a major problem.

 

[FM1520]

I dive in SoCal (coldish), 7mm wetsuit, LP95 steel tank, Deep Sea Supply BP and 30# wing - no problem.

 

[pasley]

... I personally like to have a little extra lift ... or more likely, be able to pick up something heavy during a dive. .....

Warning SLIGHTLY OFF TOPIC discussion follows. Disclaimer: The following is IMHO and is not meant as instruction in lifting objects or conducting rescue. See your local instructor for instruction in these topics. The following is for entertainment purposes only.

Not opposed to having a little (but not much) additional lift. But for newer divers who might be reading this I would point out that:
1. Lifting heavy objects in water is best done by individuals trained in how to use a lift bag.
2. If you need to lift an object in the water having the proper equipment makes it both easier and somewhat safer. The proper equipment for lifting a heavy object in the water is a....lift bag. Small objects could be lifted with an Submersible Buoy (SMB) with a venting device of some sort on it. In a pinch an extra BCD could be attach to the item for lift.
3. In all cases it is recommended that the object being lifted has its own separate lifting device that is not attached to the diver. If you and the object you are attempting to lift using your own BCD should become separated....well you will be given the opportunity to join the rocket to the surface club in short order as you suddenly and unexpectedly become 5, 10 , 20 or what ever pounds lighter.


Pulling up your buddy and/or a rescue scenario was also mentioned. IMHO In a rescue scenario we have two possibilities:
1. Victim has air - If Victim has air, use their BCD for assisting them not yours.
2. Victim is OOA. If they are OOA we again have 2 possible scenarios
A. Their BCD is inflated for neutral (or nearly so) buoyancy at their current depth. No additional air/lift required only venting during ascent.
B. If the victim is OOA and negative, then I would orally inflate their BCD to get them neutral and then vent as required during ascent.

In either case, I would not want to add air to my BCD to do the rescue. If I use my BCD to bring both myself and the victim to the surface the victim I place us both at risk. IF I and the Victim become separated (hand slips, victim becomes disoriented and puts up a fight etc) I could end up rocketing to the surface and then there are two victims, one on the surface, and one not. Better to deflate the rescuers BCD and use the victims BCD for the ascent (so here having a bit of extra lift available on the victim BCD might be good.). That way if we become separated the victim (who is already in deep stuff) ascends to the surfaced alone where they can be rescued while the rescuer safely swims up at the appropriate assent rate. Better to have one victim than two.

As with all things SCUBA there are many ways to do and you may use a different technique. You and you alone are responsible for your diving decisions.

We now return you to the topic.

 

[dumpsterDiver]

I would prefer to use the victim's BC as well. However. what if their BC failed? Would you like to have an extra 8 or 10 lbs of extra lift to rescue some idiot who runs out of air, dives a steel tank, has no ditchable lead and his BC hose has ripped or the OPV spring failed or a zip tie came off or.. or...? Also, if you pick up things like lobsters or something, having some extra lift is going to be useful.

 

[decompression]

This is correct, but add the weight of the gas, because at the beginning of the dive you will be negative by the weight of the the gas, assuming you're weighted properly.

OP, how much you weigh or your tank weighs on land is not part of the equation. Just figure out how much buoyancy your wetsuit has, you can do this by putting it in a mesh bag, floating it, and tying weights to the bag and determine how much weight it takes to sink it. Then add the weight of your gas and this is the total lift you'll need. For a single tank it rarely exceeds 30 lbs.

"Balanced rig" doesn't mean 'properly weighted'. It means that you split up ballast between your body (like a weight belt) and your rig (like a steel plate, weights in pockets, or camband weights) so that both your rig and yourself are reasonably neutral. That way if you ever had to take your rig off under water, maybe to fix a camband or something, you wouldn't go flying to the surface while your rig headed for the bottom. This also helps tremendously with the issue of floating your rig without you in it.

In cold water with a thick wetsuit, usually you have enough buoyancy on the surface so that it's not hard to keep your head out of the water.

Just to clarify, a "balanced rig" has nothing to do with distributing your weights. It is simply a calculation of positively buoyant items vs negative items (to include lead). This ensures you are neutral throughout your entire dive. When it comes to lift, the BCD compensates for the weight of gas and ensures you have enough lift for the weight of gas you are bringing and keep you buoyant at the surface. If you are using a thick wetsuit for deep dives you've lost the positive buoyancy it has and if you suffer a wing failure you are massively overweighted. If you drop weights you become massively positive as you ascend and loose control of your buoyancy. This is why I advocate a balanced rig and caution if diving deep, cold and wet.


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[halocline]

Just to clarify, a "balanced rig" has nothing to do with distributing your weights. It is simply a calculation of positively buoyant items vs negative items (to include lead).

No, what you're talking about is simply being weighted properly and having enough lift. The term 'balanced rig' as I've always heard it specifically refers to splitting ballast between the scuba rig and the diver's body so that neither is excessively positive or negative. Its a fairly standard concept in technical diving circles.

 

[decompression]

Sorry, the agency I teach for has it that way.....what agency teaches a balanced rig as weight distribution?
Maybe I should try this "technical" diving thing....or you could read my profile.
I could email you a pp of a balanced rig that I teach everyday, that might explain it better.

 

[PfcAJ]

Balanced rig has to do with total weighting, not weight distribution. It can involve weight distribution, however.

For instance, if you're weighted in such a way that you can't swim up your kit with a full tank and empty wing, some of your weight needs to be ditchable or your
kit needs a major overhaul. The flip side os that if you dont need ditchable weight, thats ok too. You can still have a balanced rig without any ditchable weight. I do this all the time cave diving or single tank reef reef diving.

If you tried to add weight so you're neutral in just your dry suit and no tanks you'd be way overweighted when you put your tanks on. No thx.

---------- Post added June 6th, 2014 at 11:11 AM ----------

Balanced rig = able to swim up full tanks from depth with no gas in wing and able to hold a stop at 10ft with no gas in the tanks. Kit should be able to float at the surface without you in it.

If you can do all those things, you have a balanced rig.