Minimum Diving Weight

[randini]

Everything you wrote is true. It may be harder to defend as the "minimum" weight, but it works. Your procedure is certainly better if you are working in shallower water than a stop. Perhaps I should modify the procedure to specify "your shallowest stop or working depth"?

The lower tank pressure makes a little more difference on doubles, but your point is well taken. However, I do think new divers should experience what being out of air feels like under controlled conditions. It varies by regulator, but knowing what it breaths like and how much time you have in shallow water can be useful. I will take another cut at the procedure in a few weeks and hopefully incorporate everyone's input.

Thanks

Rather than a shallowest or working depth, I think every person is going to have individual preferences (just look at the conversations re. split fins vs blades, wrist mount vs console and so on). Therefore I think a personally "comfortable" depth would be better. Some might prefer to be a bit more buoyant at the surface for that swim back to the boat, while others might prefer to be a bit negative to help them get down in that new wetsuit (with all the air pockets) when they first jump in. Either way, and no matter what depth/conditions you decide to teach the skill in, the exercise sounds like a great learning tool and one worth exploring so long as the individual divers understand that they can fine tune it to their own needs and comfort levels.

*edit* as for the lower tank pressures, I don't know. I still remember the first time I sucked a tank dry at 45 ft and didn't see it coming. Later it was explained to me that my balanced piston reg breathes equally well on low tank pressure as high, leading to why I might not have noticed it. Apparently (from what I've heard, but I'd welcome some confirmation from divers experienced with them) using diaphragm regs (at least the unbalanced ones) you can tell the difference when the tank gets low whereas with piston ones it's more difficult.

I guess my question is what are you going for by having these new divers on low air? The psychological experience or do you you hope they notice a difference in air delivery?

*another edit: yea I'm sure that on doubles lower tank pressure does have a greater effect on buoyancy depending on the the tanks and so on, but since we're in the beginners forum I doubt that many reading this forum (or at least those to which it is applicable) are already on doubles. So it's kind of a red herring.

 

[peterbj7]

Sorry Akimbo, I'm rather losing track of what the point was. You were originally referring to "air" and its volume, and I had the impression you were confusing current "volume" with "mass". I'm sure you know the two don't go together. But if I, an advanced technical diving instructor with degrees in mathematics and physics am getting confused, then how much more will the average reader of this forum. Perhaps we should stick more to basics.

On that tack, this talk of how a regulator feels when the tank is nearing empty is perhaps rather out of place here. I would hope our target audience is monitoring its gauges rather more effectively so that the empty tank scenario never arises.

 

[Akimbo]

Rather than a shallowest or working depth, I think every person is going to have individual preferences (just look at the conversations re. split fins vs blades, wrist mount vs console and so on). Therefore I think a personally "comfortable" depth would be better…

True. How about something like this?

A diver's submerged weight should be no less than neutrally buoyant

• At a depth no deeper than your shallowest decompression or safety stop. Shallower is OK, but fully submerged
• With a fully deflated BC (if you use one)
• With drysuit deflated to minimum without discomfort (if you use one)
• With nearly empty Tank(s), like 200-300 Lbs or 14-20 Bar
• With lungs comfortably inflated to your normal respiratory inhalation peak

…*edit* as for the lower tank pressures, I don't know. I still remember the first time I sucked a tank dry at 45 ft and didn't see it coming. Later it was explained to me that my balanced piston reg breathes equally well on low tank pressure as high, leading to why I might not have noticed it. Apparently (from what I've heard, but I'd welcome some confirmation from divers experienced with them) using diaphragm regs (at least the unbalanced ones) you can tell the difference when the tank gets low whereas with piston ones it's more difficult.

I guess my question is what are you going for by having these new divers on low air? The psychological experience or do you you hope they notice a difference in air delivery?...

IMHO, both. If they are using a balanced piston or diaphragm first stage, they should know that they only have a few breaths left once they notice increased inhalation resistance. Divers using an unbalanced piston first stage will notice increased breathing resistance much sooner, but not as dramatic an increase until they get down to around their IP (intermediate pressure). Either way, not knowing what it is like could make a new diver who is already out of their element more likely to respond poorly, maybe even panic. That is one reason I frequently question the wisdom of new divers using balanced first stages.

 

[Akimbo]

They do hold up OK to salt water. They are a cheap mix of different metals so once they get exposed saltwater they do start to rust fast (read they're good for a few weeks unless you maintain them properly). The ones I used in the experiment I mentioned worked fine for months after almost continuous use on the shore and constant battering by waves. Just give them a good rinse in freshwater, spray the heck out of em with WD-40 and recalibrate before re-use. For about $4 a pop, don't expect them to last forever (hence why I said you could buy a dozen of them and consider them disposable). Recalibrating is easy, just hang weights of known denominations from it, see what it indicates and make sure it's still reading what it should. ...

That looks like the best option for a diver readable solution so far. You would think that the digital fish scales would be water resistant enough to take 10'/3M. The advantage of the digital is they are much more accurate and hold accuracy much longer than a spring scale. A lot of dive boats carry fish scales already, but I don’t see them taking care of a spring scale well enough to tolerate submersion. In fact, most spring scales rust out just from being stored onboard which is a big reason the digitals are taking the market.

Having a setup for dive instructors would probably be the most useful. I am concerned that it won’t be worth it to them if maintenance is too high.

…Personally I don't think that this degree of accuracy is necessary. It's all about how you feel in the water. But if you wanted to use a system like this to help a friend/buddy realize when they gain neutral buoyancy, what I was thinking is that you could have one of these at a stage (say 10 ft below the surface or whatever your depth of preference is) and given the conditions you want (low tank, empty BC, etc) hook it onto the diver (not directly, but via a long enough rope that the diver could hang from it like if on a trapeze) and see how negative they still are. That should give both of you an indicator of how much lead they theoretically could shave off.

These scales aren't that precise, but at 1/2 kg (about 1lb) increments that's good enough considering the range of dive weight increments (generally about the same).

From my limited observation, many new divers are not sensitive enough to the environment yet to reliably sense neutral buoyancy without a lot of attention from instructors — which is probably why most are so over-weighted. Reading posts on this board reinforces my observations, in my mind at least.

Above all, I would like to see a method evolve from this discussion that dive instructors and boats can offer that would allow new divers experience neutral buoyancy well before getting a c-card. To be accepted; it has to be fast, low maintenance, and not require excessive instructor time.

Here is a procedure I posted before that works, but requires the divers to have a better sense of neutral than using a scale.

http://www.scubaboard.com/forums/5341680-post12.html

 

[Akimbo]

Sorry Akimbo, I'm rather losing track of what the point was. You were originally referring to "air" and its volume, and I had the impression you were confusing current "volume" with "mass". I'm sure you know the two don't go together. But if I, an advanced technical diving instructor with degrees in mathematics and physics am getting confused, then how much more will the average reader of this forum. Perhaps we should stick more to basics…

You are probably right. I just don't know how when questions are asked that deserve explanation.

I tried to be careful to always use phrases like "the weight of water displaced by air", but may have missed some. It is probably worth requesting the moderator to make corrections to prevent future confusion. Who knows how long these posts will linger and resurface thanks to search engines? Please let me know of errors you see.

…On that tack, this talk of how a regulator feels when the tank is nearing empty is perhaps rather out of place here. I would hope our target audience is monitoring its gauges rather more effectively so that the empty tank scenario never arises.

Having been distracted and sucked my bottles down on too many occasions to count, how can I expect all new divers to be so vigilant? I know that I am very happy to have been taught what "empty" feels like and how to perform a blow & go. Alas, the days of teaching free ascents are long gone, but experiencing low air does not strike me as unreasonable. Perhaps it is and this "peer review" is serving the purpose.

 

[peterbj7]

Experiencing low air is a good thing, notwithstanding that (as has been said by you and others) it feels quite different depending on the regulator in use. The s**t can always hit the fan, no matter how careful you are. But teaching basic good housekeeping, not just WHAT to do (as all agencies teach) but WHY (lamentably few agencies do this, and diminishing) can later on be a life saver.

 

[Eric Sedletzky]

From my limited observation, many new divers are not sensitive enough to the environment yet to reliably sense neutral buoyancy without a lot of attention from instructors — which is probably why most are so over-weighted. Reading posts on this board reinforces my observations, in my mind at least.

Above all, I would like to see a method evolve from this discussion that dive instructors and boats can offer that would allow new divers experience neutral buoyancy well before getting a c-card. To be accepted; it has to be fast, low maintenance, and not require excessive instructor time.

Here is a procedure I posted before that works, but requires the divers to have a better sense of neutral than using a scale.

The reason instructors overweight their students is so they don't have to mess with them not being able to get down to perform skills. The problem is they never undo that training so the diver keeps diving overweighted thinking that's the way it should be done in the real world.

A lot of this new gear is not really the best choice for minimal weight diving. Minimal weighting means a lot of times the diver would need to decend in a heads down position with fins behind the direction of travel.
From what I see with the rigs hanging in the dive shops these days is that they are more designed for elevator diving where the diver decends horizontally or in a feet down position. Most if not all are weight integrated and do not have crotch straps. This means that if the diver gets inverted at all the rig will have a tendecy to want to slide down off the diver's head if the diver is in a heads down position, so these rigs are not designed to be all position.
This makes it really difficult to get down to absolute minimum weighting because the rig requires a certain amount of weight just by itself to work properly, and that's without the weight needed to offset the exposure protection of the diver.

Diving with drysuits also adds to the problem of absolute minimal weighting because they too are not optimum for heads down decents due to air migration to the lower legs and feet.
To be able to strip weight down to the absolute minimum to be completely neutral at the last 15 foot stop at the end of the dive with 300 - 500 psi means that at the start of the dive it would mean having to force yourself down by swimming down head first, at least where I live and the suit thickness I wear.

I prefer to dive with as little weight as I can get away with for several reasons:

1) It's less weight I have to hike around on land.
2) It's less weight I need to drag around underwater pulling my waist down.
3) It's easier for me to surface swim around as light as possible to crawl over kelp and navigate the surface.
4) it's safer. If there was ever a problem with an inflator hose coming off or something leaking, even with no air in my wing I know I will be able to float.

Not that jacket or back inflate weight integrated BC's and drysuits are bad, they're just different and may require additional weight to make them work properly.

 

[Akimbo]

The reason instructors overweight their students is so they don't have to mess with them not being able to get down to perform skills. The problem is they never undo that training so the diver keeps diving overweighted thinking that's the way it should be done in the real world...

I couldn't agree more, but was reluctant to say it since I was expecting a lot of flack in the first place.

To be fair, over-weighted with a BC sucks less than underweighted. Giving the benefit of the doubt, I figured a fast, one-step, low-skill method of finding what most of us consider "proper" weighting would solve the problem. Classes are so short that it appears that explaining more than "here are the up and down buttons on the BC" is disappearing from many new basic Scuba courses.

…A lot of this new gear is not really the best choice for minimal weight diving. Minimal weighting means a lot of times the diver would need to decend in a heads down position with fins behind the direction of travel.
From what I see with the rigs hanging in the dive shops these days is that they are more designed for elevator diving where the diver decends horizontally or in a feet down position. Most if not all are weight integrated and do not have crotch straps. This means that if the diver gets inverted at all the rig will have a tendecy to want to slide down off the diver's head if the diver is in a heads down position, so these rigs are not designed to be all position.
This makes it really difficult to get down to absolute minimum weighting because the rig requires a certain amount of weight just by itself to work properly, and that's without the weight needed to offset the exposure protection of the diver.

Diving with drysuits also adds to the problem of absolute minimal weighting because they too are not optimum for heads down decents due to air trapping in the feet and lower legs.
To be able to strip weight down to the absolute minimum to be completely neutral at the last 15 foot stop at the end of the dive with 300 - 500 psi means that at the start of the dive it would mean having to force yourself down by swimming down head first, at least where I live...

I have not observed people descending feet first, outside of surface supplied divers on a down-line — usually in Wellies instead of fins. I can’t remember the last time I actually watched a basic course being conducted off a beach. Most of the new divers I have actually been on the same boat with… wait a minute. I am usually first overboard and last up the ladder so how would I know? Head-up descents sure strikes me as an uncomfortable way to dive.

I have had to dive drysuits a lot and never even considered avoiding head-down. Why is it different now? (that is a real question, not a statement)

There are sure a lot of people on this board asking about proper weighting. What say the newbie's?

 

[Eric Sedletzky]

I couldn't agree more, but was reluctant to say it since I was expecting a lot of flack in the first place.

To be fair, over-weighted with a BC sucks less than underweighted. Giving the benefit of the doubt, I figured a fast, one-step, low-skill method of finding what most of us consider "proper" weighting would solve the problem. Classes are so short that it appears that explaining more than "here are the up and down buttons on the BC" is disappearing from many new basic Scuba courses.



I have not observed people descending feet first, outside of surface supplied divers on a down-line — usually in Wellies instead of fins. I can’t remember the last time I actually watched a basic course being conducted off a beach. Most of the new divers I have actually been on the same boat with… wait a minute. I am usually first overboard and last up the ladder so how would I know? Head-up descents sure strikes me as an uncomfortable way to dive.

I have had to dive drysuits a lot and never even considered avoiding head-down. Why is it different now? (that is a real question, not a statement)

There are sure a lot of people on this board asking about proper weighting. What say the newbie's?

Yes instructors do overweight their student religiously. It happened to me when I got certified, and I saw it done all the time as I was later DM'ing.
The standard protocol was (and still is) if a student can not sink when they dump their air they are then loaded up with clip on weights out of a float tube or similar recepticle until they can. This means going down feet first.
I guess this is the new way to dive, but I don't buy into it. I think it's wrong and unsafe.
For some reason instructors will not teach to weight so that when all air is dumped the student should be able to float at eye level at least, then flip foreward and swim down. I could see how this opens up a whole can of worms and further teaching; just on proper weighting alone, then the whole heads down decent and trying to equalize as you're decending. At the rate students are run through a class there is no time for this.

Also what I'm saying is the new BC's are too floppy and not configured correctly for minimalist techniques of weighting therefore is not compatible with this style of diving, so the elevator method is what's taught. Unfortunately this is all that's sold in 99% of dive shops and what instructors are forced to use to teach with so this is why it is.

Those that choose to step forward beyond this mindset need to explore answers on their own because they will not get it from any of the standard agencies, IMO.

When I was diving dry it was difficult to flip foreward to do a heads down decent. I suppose if the suit was empty and shrink wrapped on my body I could do it but at some point the squeeze becomes so intense that air must be inserted into the suit which then will all go to the feet because they are the highest thing. This is one reason why I decided to go back to diving wet because I wanted absolute freedom in choosing body attitude/ positioning in the water column and not have it dictated by my gear.

 

[Hatul]

The empiric way I use to fine tune my weights is to use a couple of 1lb weights. Subtract 1lb of wt and do a regular dive and check buoyancy at the end. If still negatively buoyant at the end, on the next dive remove another 1lb of wt. By using a 1 lb weight change, the error is forgiving enough that it won't ruin your dive.

Using 1lb weights is also useful for adjusting trim.

Adam