Weighting difference from double to single

[mikerault]

I am diving a Bare NexGen with a six pound SS BP with the diverite manifold (just under 6 pounds ) and a set of Luxfer AL80s with SS bands. If I drop to a 2 pound aluminum plate with a pound STA and a single AL80 (also losing a 2 pound regulator in the process) how will that affect my weighting? I currently use 16 pounds (which actually is a bit heavy for full tanks and I haven't breathed the doubles down to 500 to check empty yet).

So I will be seeing a drop of weight for hardware alone of at least 11 pounds for the bands, first stage regulator, manifold and switch to the aluminum plate (6+2+3) The AL80 is about 1 pound negative when full and 1.1 pounds positive when at 500 according to the docs, so I lose another pound of negative when full making for 12 pounds. This seems to indicate I need 28 pounds? I used 25 pounds using a Oceanic Back Inflate BCD with the drysuit and a single.

Diving an Oceanic Signature 50 pound wing and no STA with the aluminum plate with a single tank and everything else the same I used 25 pounds and was ok throughout dive. I will be using the TrekWing 35# wing instead of the Oceanic, will that reduce the weight since less air volume for trapping, and of course it is bungeed so it should collapse a bit more?

This weighting stuff is a bit confusing at times...


Mike

 

[dsteding]

Hmmm, weight check time?

I went from 24 pounds of total weight (plate, lead) with a single 119 to 9 pounds with double 119s, everything else being equal. In other words, you are right, the 'fold, bands, and extra reg (not to mention the negative weight of the second tank, and the 500 psi of air in it) add up (almost 15 pounds of negative buoyancy in my case).

One thing I'd check is the weight of that AL 80, air is what, .8 pounds per 10 cubic feet? So, an 80 is going to see a ~6 pound shift from full to empty . . . not the 2 pound shift you have.

At the very least, I'd stick with the steel plate (unless travelling). What the above does demonstrate is the need for more dead-weight ballast (plate or lead) with a single rig, keeping all else equal.

 

[Kendall Raine]

I am diving a Bare NexGen with a six pound SS BP with the diverite manifold (just under 6 pounds ) and a set of Luxfer AL80s with SS bands. If I drop to a 2 pound aluminum plate with a pound STA and a single AL80 (also losing a 2 pound regulator in the process) how will that affect my weighting? I currently use 16 pounds (which actually is a bit heavy for full tanks and I haven't breathed the doubles down to 500 to check empty yet).

So I will be seeing a drop of weight for hardware alone of at least 11 pounds for the bands, first stage regulator, manifold and switch to the aluminum plate (6+2+3) The AL80 is about 1 pound negative when full and 1.1 pounds positive when at 500 according to the docs, so I lose another pound of negative when full making for 12 pounds. This seems to indicate I need 28 pounds? I used 25 pounds using a Oceanic Back Inflate BCD with the drysuit and a single.

Diving an Oceanic Signature 50 pound wing and no STA with the aluminum plate with a single tank and everything else the same I used 25 pounds and was ok throughout dive. I will be using the TrekWing 35# wing instead of the Oceanic, will that reduce the weight since less air volume for trapping, and of course it is bungeed so it should collapse a bit more?

This weighting stuff is a bit confusing at times...

Mike

1 lb negative full and 1.1 positive at 500 psi? A 2.1 lbs swing? Mike, how much does 64 cu. ft. (the amount of gas you breathe to get from a full AL80 -77 cu. ft.-to 500 psi) of air weigh? Answer is a bit under 5 lbs. That's your delta from full to 500 psi. Your docs are BS. If they're wrong about the swing they may be wrong about the empty weight, too.

Put down the pencil and get wet. You can test the tank weight empty with a fish scale in a water filled trash can or, better yet, jump in the water with all your gear and dial the buoyancy. You want to be neutral at 15 feet with an empty tank. By establishing your neutral weighting empty, you know you can complete a stop while buddy breathing OOA. You also can then ignore the swing factor when you alter the gas mix. Don't forget the 2.3% adjustment (on total weight-you plus gear) from fresh to salt if you test in a pool and dive in the ocean.

Why are you using a 50 lb wing with AL tanks, anyway? That's like grocery shopping in a Hummer. Lots of extra drag. All you need is enough lift to offset the amount of gas you carry plus any compressability of your suit-if any-plus a bit more if you want to float higher in the water. I use an 18 lbs wing with a single and it's ample.

A bungied wing?? That's like grocery shopping in Bagdad. The bungies make orally inflating more difficult. If you have a leak in the wing, the bungies simply facilitate the expulsion of gas through the leak. Their purpose is to make the wing more streamlined but the best solution is to achieve streamlining by avoiding a wing that's bigger than you need.

 

[mikerault]

Wrong columns...that should be -3.4 to +2.2 so just about a 5.6 pound swing...

The OxyCheq is the 50 pound non-bungeed...the TrekWing comes that way and is the 35 pound wing. I use the 35 pound wing with singles and the 50 with doubles and the drysuit.

 

[cool_hardware52]

I am diving a Bare NexGen with a six pound SS BP with the diverite manifold (just under 6 pounds ) and a set of Luxfer AL80s with SS bands. If I drop to a 2 pound aluminum plate with a pound STA and a single AL80 (also losing a 2 pound regulator in the process) how will that affect my weighting? I currently use 16 pounds (which actually is a bit heavy for full tanks and I haven't breathed the doubles down to 500 to check empty yet).

So I will be seeing a drop of weight for hardware alone of at least 11 pounds for the bands, first stage regulator, manifold and switch to the aluminum plate (6+2+3) The AL80 is about 1 pound negative when full and 1.1 pounds positive when at 500 according to the docs, so I lose another pound of negative when full making for 12 pounds. This seems to indicate I need 28 pounds? I used 25 pounds using a Oceanic Back Inflate BCD with the drysuit and a single.

Diving an Oceanic Signature 50 pound wing and no STA with the aluminum plate with a single tank and everything else the same I used 25 pounds and was ok throughout dive. I will be using the TrekWing 35# wing instead of the Oceanic, will that reduce the weight since less air volume for trapping, and of course it is bungeed so it should collapse a bit more?

This weighting stuff is a bit confusing at times...


Mike

Mike,

Much good advice here already.

My 2 cents: Find out what it takes to get you and your Drysuit neutral, and adjust from there.

Ex: Lets say we stick you in your undies and DS and put you in the water. Add lead until you are neutral. For the sake of this example lets say it takes 24 lbs.

You are going to need gear + ballast that equals 24 lbs + the weight of your gas.

It all starts with the buoyancy of exposure suit.


Tobin

 

[Kangy]

Why would you switch to an AL plate for single tank if you need so much weight for your twins?
to balance my rig, I had to do the opposite, I was using a SS for my singles rig, but on my doubles that made me too top heavy, so I switched to an AL for Double AL 80's and put a few extra pounds on my waist to trim out.
I'm diving a 2 piece 5mil suit and with singles and SS I need about 7lbs. For my doubles with same suit and AL plate I use about 6lbs. I know this will be alot different for diving dry but my advice is before making any more questimate adjustments, at the end of your next dive, even if your not at 500psi, purge and drain some air during your 15ft stop and do a proper weight check

 

[mikerault]

A 2 pound aluminum is much easier to pack for travel than a 6 pound steel.

I plan on doiung some playing next dive including testing with a 5mm wetsuit as well as the dry...

 

[Kendall Raine]

Wrong columns...that should be -3.4 to +2.2 so just about a 5.6 pound swing...

5.6 lbs is the right number 3,000 to 0 for air.

FWIW I use a 36 lbs wing with double AL 80's in fresh water wet. Plenty of lift unless I'm also using more than one stage (or an old AUL Spectrum or Pro 14 canister) at which point I switch to a bigger wing to counteract roll.

I use a 55 lbs wing for double 104's plus stages-typically helium back gas so a lot less weight full. Steel tanks means diving dry. Never needed more lift despite multiple stages and scooters.

The 18 lbs wing serves just fine for singles even diving wet.

If you have a chance to experiment with downsizing the wing (borrowing one) you might try it to see what you think. From what I've seen. some people subscribe to the more is better view on BC lift-note the 80 lbs dual bladder James Bond life rafts-and then wrap them in bungie cord to deal with the excess drag.

DIR means slick.

 

[mikerault]

I picked up both of them used for less than one new...so I am playing the hand dealt me...I may be in the market for a smaller one later.

Mike

 

[amascuba]

For double AL80's I actually wear the same amount of lead that I would in a single AL80. AL80's typically are 2-4 lbs positive when they are empty and if I'm light I will notice that the tanks get floaty at around 1200 psi.

I typically wear 10 pounds (#6 backplate + #4 tail weight in double AL80's)