Teach me warm weather weighting

[DA Aquamaster]

As noted above 2-4 pounds is probably all you'll need at most with a pair of AL 80s after it's all said and done with the swing weight, regs, tank rigging, residual gas, etc if you are pretty much neutral in the water with no tanks on at all.

Thee are two schools of thought with AL 80s.

One is to add any needed weight to the tank to normalize the tank relative to other steel tanks you might use that end the dive near neutral or a couple pounds negative. In this case adding the weight to a cam band near the bottom of the tank also helps offset the tail light trim of AL 80s when they get low on gas. And that also tends to be the simple solution as the lower clip is often secure with a cam band when you bring your own rigging to put on rental AL 80s.

The second is to attach any needed weight to a weight belt or to your harness in some manner. I think this approach makes the most sense in terms of divers who do not need ay weight at all, something that is not uncommon in fresh water, in a 3mm or well crushed from use 5mm wet suit when the diver is carrying reels, back up lights and a can light, and is diving in a manner that leaves a 1/3rd reserve (1000 psi) in each tank at the end of the dive. In that case in particular, it makes a lot more sense to carry no weight on the tank and just clip them to a waist D-ring when the tails start to float to avoid any over weighting.

Both approaches work fine, but in both cases whether it makes sense or not for you depends on the entire picture of what you are diving and how you configure for it.

 

[The Chairman]

I should put the caveat that I am relatively buoyant, and I'm not just talking about my personality. I added another 8 pounds after the ten on the tanks. I usually dive with 14 with a single AL80, so this was an additional 4 pounds.

The best part of the weight on the tanks was really at the surface. While waiting for the chase zodiac to come pick me up, I unclipped the tanks from the butt plate and they just dangled straight down allowing me to recline easily in the water. I took the time to stow my right reg and hose and then did the same on the left.

 

[Karl_H]

The actual buoyancy of aluminum tanks depends on the model and manufacturer, the compact style tanks tend to have nicer buoyancy characteristics but are generally harder to find. I’d use 2.5lbs negative when full and 3.5lbs positive when empty as a general rule.

In warm water diving I’d avoid putting weights on the tanks, the tanks do move as you do so weight on the tanks is just going to give you headaches with balance and trim, in most cases I’ve seen anyone who says they don’t have an issue with using weights on the tanks tends to have problems with balance and trim anyway so they don’t notice too much difference.

I’d suggest starting with 6l or 8lbs of weight mounted on your spine axis, this can be shifted along this axis to suit your trim to get to a point where you feel comfortable. At the end of your first (or maybe second) dive finish by free flowing both regulators to 30-50bar/ 500-700psi and see if you can hold a stop at around 5m/15ft. If you can, the weight is fine or can be reduced, if you can’t – it’s time to add more weight!

Don’t forget sidemount in warm water needs a different d-ring configuration to sidemount with steel tanks, you’ll need to shift the tanks as they become buoyant, letting them rise up of the cold water d-rings looks terrible, adds drag and messes with your trim. Also try to get the tank band mounting point as close to the bottom of the tank as is comfortable with your harness and bungee set-up, having the bands too close to the tank vales means a little lift on the tank results in a big angle deflection, moving the band lower on the tank means the same lift has a lower angle of deflection.

If you're using a warm water BC with lower lift the tip NetDoc gave on letting the tanks hang at the end of the dive is really useful, with a smaller capacity BC the weight of the tanks out of the water adds up, as does the weight pulling you forwards. Letting them hang keeps the cylinders in the water where they should be positive or neutral by the end of the dive.

Hope that helps!

Karl

 

[DevonDiver]

What I use - Warm Water Sidemount w/2x AL80's:

Rash Guard/Board Shorts = 2lbs of weight only, on my shoulder straps.-

3mm Full Wetsuit = 2lbs of weight on my shoulder straps + additional 2x 2lbs (for rec/non-penetration/quickie dives, just on the tank cams), otherwise on the spine strap (or equiv).

Nothing beats a full weight check though - post-check-out dive, nearly empty tanks (<35bar), empty BCD and remove weights until you float neutral whilst breathing naturally.

 

[Paul S]

Thanks everyone for the examples.

I just got back last night from Cyprus having had 6 great dives on the Zenobia. Everyone came back safe and sound although we did have some unwanted excitement having to take Ian, our host, to the hospital. He trapped his finger catching a tank that slipped out of his hands loading the truck up. 18 stitches later he was back on the boat with us for the second dive of the day. There's no stopping that man.

Hope everything heals nicely Ian, and thanks to Chris at Alpha Divers for stepping up, filling the gap, and taking us out once we had Ian in good hands.

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On the side-mount side:

The tanks Ian had for me were Luxfer AL3000-S80, and first dive out I just had 2x4lbs on my waist. That was pretty good as a first guess, but I realised the tails were getting high towards the end of the dive. I then moved them from the door handles to my waist d-rings, which got them more under control. Still a bit "fly away" though.

The Zenobia has a trapeze on it at 6m (20ft) and having taken the bottles down to about 1/3 full I was finding that, with an empty wing, I needed to apply slight pressure to keep me down. Definitely under weighted, but only by a tiny amount (at that instant). Now I knew an S80 holds about 6 pounds of gas <80 cu ft of air in lbs - Wolfram|Alpha>, so I had a couple of pounds of air left in each tank when I did this test.

(Ok it's a bit more than 6lbs, but this was on site, in my head, between dives)

Next dive I moved the two 4lbs weights I had on my waist on to the cam-bands of the tanks to keep the tails down. I also added 2x2lbs onto my waist to compensate for the gas in the tanks when I'd done my test. That was it. 4+2+2+4 = 12lbs total. That got it spot on, and it was sweet!

The reason I could tweak it in one go like that was because I'd thought through my options before hand, and you guys had given me the benefit of your experience. So thanks!

One minor change I will be making is to flip one of my cam-bands over, so the two truly mirror each other. Then I can get the weight in the same place on each cylinder. I had one on the inside of one cylinder, and the other on the outside, just because of where the cam, rigging, etc fell on the band. I could feel the imbalance during the dives, but it was so small it wasn't an issue.

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The total package: LOVELY!

This was the wreck that made me go "In a year I'm coming back and diving this side-mount", and it worked. The work has paid off and I'm really happy. We do some dives that I think are not for the feint hearted (or those not trained). 40+ metres (120+ ft), overhead environments. All the penetrations were easier. There were a couple of people who thought I'd be struggling with a couple of narrow windows, but I flipped onto my side and no issue, and I knew I could swing one forward if I needed, but never did. Never squeezed, never pushed it.

In fact, that's what felt so great. At all times I knew I had better margins of safety. I always KNEW I had redundant gas for me and my buddy. I always KNEW I could slim down and get out of that small hole. I always KNEW I had a complete redundant set of everything. I felt like my buddy could rely on me, but I didn't need to rely on them (although I'd always want them there).

I really feel I had the right kit for the job.

...and nobody ever waited for me to be ready

 

[offroadr1]

that was a great story. thanks for sharing it!