Proper weighting with doubles.

[nielsent]

This may be a bit of a silly question, but I have been getting some different answers and was curious what other think about this question.

After doing some experimenting, I have determined that my exposure suit makes me 34lbs positively buoyant.

My doubles kit is 35lbs negative when full. the tanks are LP120's which hold 20lbs of air.

So that means i am negatively buoyant at the start of my dive but am 19lbs positive at the end.

As it sits, the kit had very good trim and I have no problems in that department. I am mostly concerned about the weighting.

I have been told various things about the weight required to compensate for the variable weight of the air. How much weight would you add to compensate for the backgas? and where?

 

[Scott L]

Doc knows best...

 

[Doc Intrepid]

Hmm...well, according to Lloyd Bailey's site, the swing weight on a set of LP 120s is right at 9 lbs per tank, so assuming both tanks are drained the set would be some 18lbs more bouyant at the end of the dive than when both tanks were full at the start.

http://www.lloydbaileysscuba.com/PST E Series Tanks.htm

I weight myself with double E8-130s down at around 200 psi, and two nearly empty 40s, with no gas in my drysuit. If I can hold a 10' stop and control my ascent to the surface under those conditions, then I won't be concerned about being too light at the end of some difficult dive.

What I use in cold dark water is a 12 lb FredT plate and a 10 lb V-weight (with an argon bottle). In warmer water when I'm not wearing a Weezle Extreme+ I drop down to a 6 lb Halcyon plate and use an 8 lb V-weight. It works for me...

And it isn't a silly question at all. Being too light at the end of a dive and not being able to hold your stops sucks. Don't ask me how I know this.

 

[TSandM]

Don't ask any of us how we know it!

I've heard people say to weight yourself neutral, having used the amount of gas you intend to use in the tanks (so you don't carry so much weight). But I prefer to set myself up to be optimized for the worst case scenario. If I get delayed and use more gas than I planned, the last thing I want is to have trouble holding the longer stops I've gotten myself into (or crawling out on the ceiling of the cave). So I weight myself neutral at the surface with 500 psi in the tanks, and I carry a lot of weight.

 

[nielsent]

Don't ask any of us how we know it!

Don't worry, I have floated into that boat myself.

Where would the optimal places to put weight on the rig? I have a 11lbs v-wieght that covers part of it, but I need to place another 8lbs to cover the difference. Where would be the best place for the rest?

 

[sea2summit]

Don't worry, I have floated into that boat myself.

Where would the optimal places to put weight on the rig? I have a 11lbs v-wieght that covers part of it, but I need to place another 8lbs to cover the difference. Where would be the best place for the rest?

One way is to stick two backplates together. With the price of lead now days could be worth it

I used a DUI weight/trim for a long time for my extra lead. Don't think I ever needed it with doubles but it's been a while.

 

[spectrum]

I'm not a doubles diver but based on what I think I know and the first responses is this any different than single tank diving. Obviously the V weight option is exclusively multi-tank.

 

[Kern]

I only use doubles for staged deco dives. I weight myself so that no matter how much gas I use or lose I will be able to stay in control of my ascent.

I use 9lb on a belt for trim purposes. This all varies between individuals of course.

 

[Doc Intrepid]

"...Where would the optimal places to put weight on the rig? I have a 11lbs v-wieght that covers part of it, but I need to place another 8lbs to cover the difference. Where would be the best place for the rest?"

My humble opinion is "flat against your back". Unless you need to move weight further down your "lever" to trim out, weight flat against your back is less apt to roll you around your longitudinal axis at awkward times!

You might want to look at Tobin's heavy plate. What sets it apart is that there are panels that can be removed, so the same plate can be heavy or light depending on your requirements. Tobin is on this board, check with him for details:
https://www.deepseasupply.com/index.php?category=backplates

 

[ianr33]

And it isn't a silly question at all. Being too light at the end of a dive and not being able to hold your stops sucks. Don't ask me how I know this.

Thats what God made rocks for, or so I'm told