weights on aluminum 80s?

[ShootnStr8]

I weight the AL80s with 4 lbs but I do so with reservations. I appreciate SanDiegoSidemount's comment: "Your tanks are not part of your weighting system."

 

[SWAMPY459]

The whole issue of putting weights on cylinders seems scary to me. It seems like there's a danger of "passing the buck" for weight that should rightfully live on the belt or harness.

I have been strictly trained that in SM "your tanks are not part of your weighting system". This allows bottom gas and/or stages to be attached/detached/ditched/added as necessary while remaining safely balanced. The rest of your rig must be balanced even without the tanks.

If you have heavy tanks, that's fine: the BC is there to counteract. This is why steel tank SM divers -- or those who dive lots of stages -- need more lift: to balance heavy tanks and the gas in them.

Adding a little weight to the lower part AL80s to make them trim out more flat... I can see an argument for that. I also see a danger in assuming that this weight is part of your overall weighting system.

I have been trained to deal with the buoyancy characteristics of AL80s as they come, with no extra weight. When full, the bottom bolt snap attaches to my hip d-ring. Below around 2500psi, the bottom moves to a sliding D-ring forward of those. By 500psi per side, the sliding D-rings are forward almost to my waist buckle. This keeps the AL80s trimmed pretty well.

I don't see weights on tanks as a big issue as long as there's still enough weight on the rest of your rig to be balanced. I do think that relying on tank weights could limit your ability to switch, mix, and match tanks.

Proper balance without the tanks allows you to get rid of one or more of your tanks in an emergency situation (worst case, all of them) share air with a buddy and safely make all your stops to the surface. I would hope that all SM divers who dive heavy steel or weighted AL tanks are still able to do this.

I'm curious to know if you have the same thoughts about a backmount diver diving a pair of 108's with a manifold. Should they wear a weight belt just in case they suddenly feel the need to ditch one or both tanks?

Most of the divers I've seen who do wear doubles don't have any weight other than their tanks... and the weight on their tanks IS part of their weight system. (all of their weight system actually)

thoughts?

 

[Razorista]

thoughts?

I would assume that the sidemount tanks are part of the weight system, too.
This is just an hindrance with aluminum cylinders, however.
When using steel cylinders I remove weight from the harness before dives, to get as neutral as possible with weights only countering the buoyancy from used gas.

First of all this is against the principle of putting all weight near or at the small of the back, leading to a more unpredictable weight distribution.

Main reason (or most cited) for not using them is of course the 'snagging risk', but since that is not very relevant to most, even most cave divers, I try ignore that aspect here.

I am an open water diver myself, but it does not work with my diving style as well.
Since I squeeze through most small openings encountered, I would get stuck very often (and did during testing).
That would not be much of a risk, but a hazard for the environment when trying to free oneself, silting and constantly smashing tiny organisms on edges of openings.

Not putting weights on the tanks makes it possible to swap or cache them during the dive, if one diver puts weights on them this would not work equally well.

There is also the aspect of the weight turning the cylinder so that the weight becomes the lowest point on it, this can help with tank positioning, but mostly it negates some of the the pull of the bungee on the valve, reducing its effectiveness significantly.
I never found a way to get to a continuously stable position using weights, but it is rather easy to successfully do that with a good bungee system and without weights on cylinders.

When weighting your tanks you just exchange high hanging tanks at the end of the dive for low hanging ones at the beginning of the dive.
The first situation is easy to avoid without weights and there are also next to no problems if ignored and the tanks are left bottom-light.
In contrast heavy low-hanging tanks make most maneuvers much harder.

 

[SanDiegoSidemount]

I'm curious to know if you have the same thoughts about a backmount diver diving a pair of 108's with a manifold. Should they wear a weight belt just in case they suddenly feel the need to ditch one or both tanks?

Most of the divers I've seen who do wear doubles don't have any weight other than their tanks... and the weight on their tanks IS part of their weight system. (all of their weight system actually)

thoughts?

Backmount doubles are a different thing entirely. In this case, the weight of the tanks absolutely figures into your overall rig balance. You can't ditch them, reposition them, etc. They are there, locked in position along with your backplate and harness, for the duration of your dive.

However, there's a reason that divers with heavy backmount doubles still tend to prefer AL80s and AL40s for stage/deco bottles. This is so the extra bottles don't radically alter buoyancy and trim.

Sidemount offers the diver much more flexibility in bottle positioning and configuration. It also is a configuration that supports "trim fanatics" really getting things dialed.

My feeling is that using heavy tanks for sidemount -- whether HP steels or AL80s with weights -- work against these two benefits of sidemount.

This may be just fine for some divers, especially recreational sidemounters who never have a need to remove/reposition their tanks during a dive. However, you'd be defeating some nice benefits of sidemount if moving tanks around to "pistol" or "superman" throws your trim out of whack. And defeating another benefit if you can't remove a tank (to ditch, or to offer to another diver) without becoming dangerously buoyant.

Again, some sidemounters don't need or care about these types of maneuvers, but diving more-or-less neutral tanks allows you to maximize the flexibility that the sidemount configuration offers .