How much lift?

[farmyou]

I’m getting ready to purchase a BC and have been getting mixed recommendations from my local dive shops.

Here is the question: I am looking at the Apeks WTX harness. I’ll be running a single steel 100 tank with no back plate. One shop recommends the WTX3 cell with 32Lbs of lift, another recommends the WTX6 with 60lbs of lift.

The argument goes something like this, The WTX3 will provide less drag, travels better, and will provide enough lift for your setup. On the other side, the WTX6 will support you if/when you go to doubles, back plates, etc. Because the thing deflates, it really doesn’t make that much difference for travel, and it’s only $25 to upgrade now.

Currently I carry 26# of weight with a traditional vest BC and an aluminum 80 tank. I wear a 7mm farmer john 2 piece wet suit, gloves, boots, and hood. I normally dive in cold, fresh water (Minnesota lakes, 40-70 degrees)

It seams like the WTX6 would be the logical choice, but I’m seeking advice before I spend money on something I am disappointed with.

 

[TheRedHead]

You're not going to use a SS backplate when you are carying 26 lbs. of lead? I couldn't imagine using a 60 lb wing for a single tank.

 

[PerroneFord]

A wing designed for use with doubles is shaped differently than one designed for a single tank and will be problematic. If you are diving with a single tank, buy a wing designed for a single. If at some point you move to doubles, buy a wing for doubles.

While I personally don't think much of the WTX, that's your call. There are a lot of BP/W options out there. Is there a reason you won't be using the backplate? Not only would it take some lead off your belt, you'll need it if/when you go to doubles anyway.

To be honest, I'd try finding a different shop that knows more about BP/W. Doesn't sound like the shop that recommended the 60# wing knows very much.

 

[runamonk]

I just recently purchased my first BP/W configuration and after talking with the guys there they recommended a OMS BP (AWESOME BTW) and a Apex WT3 wing with 34lbs of lift.

I tested it all out a couple days ago and LOVE the new configuration. Even with a pony I won't need more than 34 is what I've been told.

Seems lately everyone thinks you need to have more lift, bigger seems to be better. I went with this bladder because I really like it because it's not bulky (less drag).

 

[BSea]

A wing designed for use with doubles is shaped differently than one designed for a single tank and will be problematic. If you are diving with a single tank, buy a wing designed for a single. If at some point you move to doubles, buy a wing for doubles.

To be honest, I'd try finding a different shop that knows more about BP/W. Doesn't sound like the shop that recommended the 60# wing knows very much.

Well said.

You don't buy off road tires for your 2 door coupe, and you don't buy a doubles wing for diving singles. People that dive doubles, have a rig for doubles, and a rig for when they dive singles. It may be only switching a wing, but then it's a different rig.

Just out of curiousity how much more is the 60# wing than the 30# wing? That might be why he suggested the 60# wing.

 

[cool_hardware52]

I’m getting ready to purchase a BC and have been getting mixed recommendations from my local dive shops.

Here is the question: I am looking at the Apeks WTX harness. I’ll be running a single steel 100 tank with no back plate. One shop recommends the WTX3 cell with 32Lbs of lift, another recommends the WTX6 with 60lbs of lift.

The argument goes something like this, The WTX3 will provide less drag, travels better, and will provide enough lift for your setup. On the other side, the WTX6 will support you if/when you go to doubles, back plates, etc. Because the thing deflates, it really doesn’t make that much difference for travel, and it’s only $25 to upgrade now.

Currently I carry 26# of weight with a traditional vest BC and an aluminum 80 tank. I wear a 7mm farmer john 2 piece wet suit, gloves, boots, and hood. I normally dive in cold, fresh water (Minnesota lakes, 40-70 degrees)

It seams like the WTX6 would be the logical choice, but I’m seeking advice before I spend money on something I am disappointed with.

Farmyou,

First I suggest that you run, don't walk, away from any shop that would seriously recommend a 60 lbs wing for use with a single tank.

Any BC needs to be able to do two things;

1) Float your rig at the surface without you and your buoyant wetsuit in it.

You can estimate the maximum negative buoyancy of your rig; a full AL 80 is ~2 lbs negative, the BP will be ~6 lbs, ~2 for regs, and maybe another 2lbs for a light / reel etc. Rig weight is about 12 lbs. If you attach more ballast to the rig via weight pockets etc. add this also. It's still unlikely your rig will be more than ~22-26 lbs negative. That means a 30 lbs wing will float it no problem.

2) Compensate for the compression of your wetsuit as you descend.

The second thing any Buoyancy Compensator needs to do is Compensate for the compression of your wetsuit. The most buoyancy your suit can loose is initial buoyancy it has at the surface. How do you determine this? Roll it up and throw it in the pool, add lead until it's neutral. That will represent the max initial buoyancy your suit can loose. You should test your own suit. Various grades of neoprene varies quite a bit, and the cut of the suit, and age of the suit etc are all variables.

In general, for cold water diving single tank diving, it is the exposure suit that dictates the minimum lift required. This may not be true if you choose to hang all you ballast on your rig, but will usually be true if you choose to carry some portion in a weight belt.

Regards,



Tobin

 

[*Floater*]

The most buoyancy your suit can loose is initial buoyancy it has at the surface. How do you determine this? Roll it up and throw it in the pool, add lead until it's neutral. That will represent the max initial buoyancy your suit can loose. You should test your own suit. Various grades of neoprene varies quite a bit, and the cut of the suit, and age of the suit etc are all variables.

I would add that let the suit soak for a bit first and make sure there's no trapped air in it. Perhaps you could even measure it's buoyancy slightly above 10ft since 10ft is where most people do their last safety stop - being a little positive after may be okay as you probably just want to make a slow ascent anyway. Also, you should factor in the buoyancy swing of your tanks: http://www.huronscuba.com/equipment/scubaCylinderSpecification.html

Say your suit is 24# buoyant close to surface and your tanks change buoyancy by 8#. Then you'd need about 32# of total weight (or negative buoyancy) to be neutral close to the surface with almost empty tanks and suit almost fully buoyant (and this negative buoyancy can come from your body, bp, regs, fins, lights, and everything else on you in addition to the weights).

Now if at the beginning of the dive you drop straight down to about 165 ft. then your tanks are still almost full, but your suit has lost almost all it's buoyancy (or so I'm told) so you'd need almost 32# worth of gas in your wing + lungs to stay neutral. Of course, this would be the worst case scanrio and generally most correctly weighted people dive with their BC's close to empty.

 

[cool_hardware52]

I would add that let the suit soak for a bit first and make sure there's no trapped air in it. Perhaps you could even measure it's buoyancy slightly above 10ft since 10ft is where most people do their last safety stop

We are discussing minimum required wing lift. If we use your method, i.e. at 10 ft. we will find out how much lift we need to get from the bottom back to 10 ft. I'd prefer to have enough to get back to the surface. The effect of the first 10-15 of depth on the compression of a wetsuit is fairly dramatic.

- being a little positive after may be okay as you probably just want to make a slow ascent anyway. Also, you should factor in the buoyancy swing of your tanks: http://www.huronscuba.com/equipment/scubaCylinderSpecification.html

Air weighs 8 lbs per 100 cuft regardless of tank type, pressure, or material, if you know the capacity of the tank you know the "swing". For single tank diving with a 5mil or thicker wetsuit one can basically ignore the weight of the gas.

What's the max swing one might see with a single tank from full to empty? ~7-8 lbs, usually much less, because tanks usually aren't empty at the end of the dive.

Will a 5 mil or 7 mil wetsuit loose 7-8 lbs from the surface to 15 ft? Absolutely, if you don't believe me try it. Get neutral at the surface and swim down to 15 ft. Do you need to add gas to your wing?

What I shoot for is: Neutral (eyelevel) at the surface with no gas in my wing and a full cylinder. If I need to I'll swim down a little to start the dive. I can always hold my shallow stop (10 ft) due to wetsuit compression if I have at least a 5 mil on.

If I ever find I'm "light" at 10 ft at the end of a single tank NDL dive, I'll just swim down to 15 or 20 ft and hang a little longer.


Tobin

 

[*Floater*]

We are discussing minimum required wing lift. If we use your method, i.e. at 10 ft. we will find out how much lift we need to get from the bottom back to 10 ft. I'd prefer to have enough to get back to the surface. The effect of the first 10-15 of depth on the compression of a wetsuit is fairly dramatic.

My idea is to weigh yourself so that you are neutral at 10 ft. say, (or little above), with almost empty tank/s. Then make sure that have enough lift in your wing and lungs to return to 10 ft. even if your wetsuit looses all its buoyancy. Obviously you can continue from there to the surface without problem. This is cutting it a little close, but it's still sufficient imo since rec divers generally do not go down to depth of 165 ft or beyond where they would loose all wetsuit buoyancy, nor do they usually return to 10 ft with almost empty tanks.

Air weighs 8 lbs per 100 cuft regardless of tank type, pressure, or material, if you know the capacity of the tank you know the "swing". For single tank diving with a 5mil or thicker wetsuit one can basically ignore the weight of the gas.

What's the max swing one might see with a single tank from full to empty? ~7-8 lbs, usually much less, because tanks usually aren't empty at the end of the dive.

Will a 5 mil or 7 mil wetsuit loose 7-8 lbs from the surface to 15 ft? Absolutely, if you don't believe me try it. Get neutral at the surface and swim down to 15 ft. Do you need to add gas to your wing?

If you weighted to be neutral at 10 ft with empty tanks, then yes you'll need some gas in the wing to offset the gas in the tanks, plus the extra 5 ft worth of wetsuit compression from 10 ft. down to 15 ft. But I think I'm missing the point of your question?

What I shoot for is: Neutral (eyelevel) at the surface with no gas in my wing and a full cylinder. If I need to I'll swim down a little to start the dive. I can always hold my shallow stop (10 ft) due to wetsuit compression if I have at least a 5 mil on.

If I ever find I'm "light" at 10 ft at the end of a single tank NDL dive, I'll just swim down to 15 or 20 ft and hang a little longer.


Tobin

That sounds similar to what I do in end result. I go to 10 ft with empty wing (and drysuit when applicable), run my gas out until my tank/s are near empty and then dump weight off the belt until I become neutral, or can raise up with a full breath.

By the way, do you know how much lift average people can generate with a full inhale of air after a full exhale?

 

[cool_hardware52]

Floater,

There is no need to try and measure the buoyany of your wetsuit at 10 ft. That's hard to do, and could leave you with too little wing. One might not plan on descending to 165, but I like knowing I have enough wing to get back.

Again this thread concerns Lift, not weighting. Minimum lift is the greater of in water rig weight, or initial buoyancy of your exposure suit at the surface.

Keep it simple.


Tobin