Question Do you ever practice dropping weights and handling the unexpected ascent?

[boulderjohn]

I was chosen as an assistant instructor and the cert they had was YMCA ( does YMCA even have a SCUBA certification program anymore?)

The YMCA program ended in 2008 and was continued independently as SEI.

I don't know much about the old YMCA program but I read years ago that one of its problems was that the local shops were fiercely independent about instruction, so what happened in YMCA #1 might be different from YMCA #2.

 

[Nick_Radov]

What is your definition of "uncontrolled"?

Inability to stop at a particular depth if desired. Flaring to slow down the rate of ascent is still uncontrolled.

We never got an objective definition of "overly thick" yet either?

Have either of you two ever dropped a "heavy" weightbelt while wearing a "thick" (5-7mm) wetsuit at depth?

This depends on the exact model and cut of the wetsuit but in practice anything thicker than about a 5mm full suit makes it effectively impossible to really have a balanced rig. If you need more thermal protection than that then you really need a shell drysuit. I am aware that some divers do use 7mm wetsuits combined with hooded vests (I used to do it myself) but those make it effectively impossible to have a balanced rig and involve safety compromises.

There is no good reason to have much more ditchable weight then the weight of the gas in your back tank(s) at the start of the dive. If you think you need more than that then you've screwed up something else in your equipment configuration.

 

[dmaziuk]

There is no good reason to have much more ditchable weight then the weight of the gas in your back tank(s) at the start of the dive. If you think you need more than that then you've screwed up something else in your equipment configuration.

On the flip side, in warm water with little to no neoprene and an Al 80, you're looking at 6lb buoyancy swing. If you can't swim up with 6 lbs, you really should consider swimming lessons at the local Y.

PS. Assuming a well-calibrated perfectly spherical diver of uniform density, of course. For actual human people the math may vary; women, for instance, with their lighter bone structure and higher proportion of body fat, tend to need a bit more ballast than the above.

 

[Nick_Radov]

On the flip side, in warm water with little to no neoprene and an Al 80, you're looking at 6lb buoyancy swing. If you can't swim up with 6 lbs, you really should consider swimming lessons at the local Y.

The issue isn't getting up, it's staying up. In many fatal incidents the victim made it back to the surface but failed to establish buoyancy and sank back down. Hence why for recreational diving without a deco ceiling it's safer to configure your gear such that if your wing fails at the beginning of a dive you can get neutral on the surface by ditching weight. Even being 6lbs negative can be problematic in rough surface conditions if you have a long swim back to the beach or boat.

PS. Assuming a well-calibrated perfectly spherical diver of uniform density, of course. For actual human people the math may vary; women, for instance, with their lighter bone structure and higher proportion of body fat, tend to need a bit more ballast than the above.

Obviously carry as much lead as necessary to have a balanced rig. The point is that you shouldn't have much more ditchable weight than the maximum weight of the gas in your back tank(s). If you need more lead than that then it's safer to have it securely attached to your rig precisely so that you can't drop it unintentionally causing an uncontrolled buoyant ascent. That additional lead might still be somewhat removable for transport or handing up to a small boat, but it shouldn't really be ditchable in the sense of easily removable during a dive.

 

[dmaziuk]

The issue isn't getting up, it's staying up. In many fatal incidents the victim made it back to the surface but failed to establish buoyancy and sank back down.

Yes, and until you have an actual CODs in a table we can analyze, this doesn't mean much: if you swim up and have a heart attack from the effort, your survival chances aren't good whether you ditch 6 lbs or not.

 

[boulderjohn]

The issue isn't getting up, it's staying up. In many fatal incidents the victim made it back to the surface but failed to establish buoyancy and sank back down.

That is indeed the reason the last changes in the PADI OW program emphasized both dropping weights at the surface and oral inflation.

On the other hand, consider the long time description for determining proper weighting before a dive. Divers are told to hold a normal (not deep) breath and dump air from the BCD. A properly weighted diver should float at eye level. Opinions differ as to whether to add the weight of the expected air loss during the dive or assume that there is at least that much air trapped in your system. Either way, if you are properly weighted and arrive at the surface with an empty tank, you should have no trouble staying there. In fact, you should have trouble descending if you wanted to. A diver who cannot stay on the surface at the end of the dive with an empty tank has to have been overweighted.

 

[Nick_Radov]

Yes, and until you have an actual CODs in a table we can analyze, this doesn't mean much:

Considering the poor state of diving accident analysis and lack of public data availability you're never going to get a table that breaks down diving causes of death in a useful way. However, I am aware of multiple local cases where a diver had some kind of problem, made it to the surface, failed to establish buoyancy, and drowned.

if you swim up and have a heart attack from the effort, your survival chances aren't good whether you ditch 6 lbs or not.

Correct, the DAN Annual Diving Reports show that heart attacks (or major adverse cardiovascular events in general) and poor physical fitness are a major cause of diving deaths. Overall this appears to be a larger risk than improper weighting or accidentally ditching weights. But now we're getting quite off topic from the original question. The point is that being improperly weighted with either too much or too little ditchable weight is a safety problem for recreational open-water diving.

 

[boulderjohn]

Yes, and until you have an actual CODs in a table we can analyze, this doesn't mean much: if you swim up and have a heart attack from the effort, your survival chances aren't good whether you ditch 6 lbs or not.

Yes.

A DAN/PADI analysis of fatalities more than a decade ago found that the most common cause of a fatality that could be attributed to a training issue was an embolism following a rapid ascent to the surface, with the assumption that the rapid ascent included holding the breath. This often followed an OOA incident.

Note that this is essentially a badly done CESA. I have often written about my belief that the way we teach CESA contributes to this--students do not have confidence that it works. You will see this in the gazillion SB threads on CESAs.

 

[johndiver999]

Obviously carry as much lead as necessary to have a balanced rig. The point is that you shouldn't have much more ditchable weight than the maximum weight of the gas in your back tank(s).

Why is this? Where does this rule of thumb come from? Why is it safe for a diver with two tanks to have double the ditchable weight that a single tank diver does? I am really curious, how this guideline has been developed and exactly what logic is a being applied, when we are talking about a recreational diver?

 

[Nick_Radov]

Why is this? Where does this rule of thumb come from? Why is it safe for a diver with two tanks to have double the ditchable weight that a single tank diver does? I am really curious, how this guideline has been developed and exactly what logic is a being applied, when we are talking about a recreational diver?

Some divers do recreational dives with double tanks. If you have a total BC failure at the start of a dive with full tanks then you should be able to ditch enough weight to get neutral on the surface. This doesn't necessarily mean carrying extra weight with doubles, but relative to using a single tank it usually means shifting more of your total weight to be ditchable versus non-ditchable. And it becomes even more critical to have reliable gear to avoid accidentally dropping weights.

Anyway I don't want to take this discussion totally off topic for the Basic Scuba forum. Suffice it to say that assembling a balanced rig becomes more complex with multiple tanks and if you want to get into the details it would be better to ask on a different forum. Search the archives for "balanced rig" and you'll find a lot of prior discussions that should get you clear on the basics.