View Full Version : Weight change when moving to doubles
May 15th, 2012, 10:51 AM
I am going to double up my AL80's and am trying to sort out how my ballast requirements will change. I am using a total of 23 lbs now with a single AL80 and a neoprene drysuit. I know that the additional AL80 will add positive buoyancy when empty but the addition of the manifold will off-set a little of that.
Can anyone share their experience with how their weighting changed when going from a single AL80 to double AL80's.
May 15th, 2012, 11:20 AM
It'll be hard to accurately do a weight check online :D
Looking at my notes here's what I have used with similar gear & exposure protection:
AL80 single tank, no weights
note: 3mm full wetsuit plus 3/5 hooded vest, SS backplate, Oxycheq 40lb single wing, fresh water
AL80 doubles, 2lb weight in trim pocket hanging from lower bolt (tail weight)
note: 3mm full wetsuit plus 3/5 hooded vest, SS backplate, Dual Bladder REC wing, fresh water
May 15th, 2012, 11:21 AM
Depends upon the AL80 and if you're using a single tank adapter (STA) now. The STA and manifold are pretty much the same. If you're using regular AL 80's, you're now +4# positive empty. If you're using neutral AL 80's, it's a wash.
You didn't mention if you're diving a BP/W or what.
Good thing about doubles is that it's easy to add a V-weight.
May 15th, 2012, 02:22 PM
Thanks guys. My current set-up is a BP/wing with an STA. I have a 7lb channel weight in the STA and the steel BP weighs around 6 lbs. I also have a total of 10 lbs in 2 pockets on the harness. I will do a proper weight check in shallow water once I am set up but I wanted to get a decent starting point from others who have doubled up their 80's. I dive exclusively fresh water in a neoprene drysuit.
May 15th, 2012, 02:43 PM
if you have the same kit then the only thing you need to figure out is the bouyancy change of the al80 and the manifolds and regs.
put a set of regs on the tank ,empty it to 20 bar and strap a 1lb weight on it to simulate the manifold.
throw it in a fresh water pool.
you are looking for it to be neutral-if it floats then you can add that amount of lead required to make it sink.
if it sinks then you can take off some lead.
i dont imagine there will be too much of a change.
you will feel heavy at the start of the dive because you have 6kgs of gas.
May 15th, 2012, 02:50 PM
Definitely do all this with 500psi in them or less ... you damn sure don't want to be trying to do a deco stop and fighting to stay at your stop depth, as you well know.
May 15th, 2012, 04:51 PM
If you do not have much experience diving with doubles, I strongly suggest a practice session in a very benign environment (as pool-like as possible) so that you can just get the feel of them. That will also give you the opportunity to get used to the weight characteristics at all points in the dive. Make sure you check it when nearly empty.
May 15th, 2012, 05:06 PM
I'll second what John said above about getting in a benign environment. My first dives with doubles had me turtling all over the place or face planting. A bit of help adjusting the bands and weight distribution to trim me out. Feels weird now when I go back to a single tank. lol
May 15th, 2012, 05:14 PM
I don't have exact numbers at my fingertips, but it seems to me that I wear very close to the same amount of weight with double 80's as I do with a single, maybe just a pound or two one way or the other. Which kind of makes sense, if you add it up. You're +8 on tanks when empty, but then you have the bands and manifold, which are about -5, and the extra reg, which is -1 or -2, so an empty set of Luxfer 80's is very close to neutral, or a couple of pounds positive.
May 16th, 2012, 08:55 AM
Thanks everybody...this great information as a starting point.