Question on tank bouyancy and weights
- Thread starter black1
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LeadTurn_SD
Contributor
Hi black1,
I think the discussion we are having (regarding you
) is just to make sure you are not over-weighted in your 3mm wetsuit in the event of a total wing failure (rare, but possible).
There are two schools of thought regarding "correct" weighting:
1. Current PADI, etc.: With a full tank, find neutral weighting at surface (float eye-level holding normal breath), then add the weight of your gas. Then re-test at the end of the dive at about 500psi @ 15 feet.
2. "Oldtimers" like me, Tobin, etc.: With a full tank, find neutral weighting at the surface as in #1, but do not add much, or any, additional weight. The idea here is that wetsuit compression and bouyancy-loss during the dive will not "rebound" completely as you ascend (takes hours to overnight?), thus your suit will be less bouyant at the end of the dive, and at 15' you'll be able to hold a safety stop.
Number 2 works with thicker wetsuits, but for a 3mm I think you need to "split the difference" between #1 and #2 and add some weight.... I add about 1/2 the weight of gas for diving with my 3mm.
So, at the beginning of your next dive, try a bouyancy check with a full tank, no weights. Are you "close" to neutral, or pretty negative? Then adjust weighting (including no weights at all) from there.
Best wishes.
I think the discussion we are having (regarding you
) is just to make sure you are not over-weighted in your 3mm wetsuit in the event of a total wing failure (rare, but possible).There are two schools of thought regarding "correct" weighting:
1. Current PADI, etc.: With a full tank, find neutral weighting at surface (float eye-level holding normal breath), then add the weight of your gas. Then re-test at the end of the dive at about 500psi @ 15 feet.
2. "Oldtimers" like me, Tobin, etc.: With a full tank, find neutral weighting at the surface as in #1, but do not add much, or any, additional weight. The idea here is that wetsuit compression and bouyancy-loss during the dive will not "rebound" completely as you ascend (takes hours to overnight?), thus your suit will be less bouyant at the end of the dive, and at 15' you'll be able to hold a safety stop.
Number 2 works with thicker wetsuits, but for a 3mm I think you need to "split the difference" between #1 and #2 and add some weight.... I add about 1/2 the weight of gas for diving with my 3mm.
So, at the beginning of your next dive, try a bouyancy check with a full tank, no weights. Are you "close" to neutral, or pretty negative? Then adjust weighting (including no weights at all) from there.
Best wishes.
rstofer
Contributor
Simply adding weight to your weight belt and counteracting it with air in your wing is not the solution. The problem is the tank. It is just too negative for use with a 3mm wetsuit.
Of course you could make the stop with a 500 psi tank as long as you had air in your BC. Did you try to dump all of the air? Did you sink like a stone? Remember, the PADI method is eyeball level at the surface with 500 psi and an empty BC. Try it... Your wetsuit buoyancy won't change a heck of a lot between 0' and 15' since it doesn't have much buoyancy in the first place.
I'm still arguing with myself over an HP 100 and a 7/8mm wetsuit. Even it is a little too negative and my wetsuit produces a lot more lift than a 3mm suit. But at least I have 20# of ditchable weight.
Try the PADI test just to see if you are highly negative at the end of the dive.
Richard
Of course you could make the stop with a 500 psi tank as long as you had air in your BC. Did you try to dump all of the air? Did you sink like a stone? Remember, the PADI method is eyeball level at the surface with 500 psi and an empty BC. Try it... Your wetsuit buoyancy won't change a heck of a lot between 0' and 15' since it doesn't have much buoyancy in the first place.
I'm still arguing with myself over an HP 100 and a 7/8mm wetsuit. Even it is a little too negative and my wetsuit produces a lot more lift than a 3mm suit. But at least I have 20# of ditchable weight.
Try the PADI test just to see if you are highly negative at the end of the dive.
Richard
rstofer
Contributor
Changing to a Worthington HP119 will improve your situation by about 5#. Full the tank is -11# and empty it is -2#
Richard
Richard
rstofer
Contributor
When you work through the details, there are two further considerations: First, your wetsuit should support you and any weight you wear on your body. Second, the wing should support the BC and everything attached.
This makes it hard to come up with a weightbelt or weight harness solution for 3mm wetsuits and warm water diving. This is one of the cases where integrated weights (ditchable weights attached to the harness) makes sense.
Richard
This makes it hard to come up with a weightbelt or weight harness solution for 3mm wetsuits and warm water diving. This is one of the cases where integrated weights (ditchable weights attached to the harness) makes sense.
Richard
Thank you gentleman for all your help and suggestions, there's only 1 way to find out wether i need weights or not and i will check this this weekend. My thoughts are that i will NOT need any additional weights because at 16lbs full tank i can easily get down and stay down and at 500psi at 7lbs i can easily hold my safety stop and in case of BC wing failure i can swim up on my own power, this is of course just my way of thinking but will have to see if it's correct by trying it out, i need to jump in my pool maybe because jumping overboard on a dive boat to simply check my weight is going to be frowned upon, especially if i need to get back out and ditch some or add some weights, fresh water will be different but will give me an idea i think.
LeadTurn_SD i like your number 2 suggestion and feel this will be the correct one, thanks again everyone and safe diving to you all.
LeadTurn_SD i like your number 2 suggestion and feel this will be the correct one, thanks again everyone and safe diving to you all.
rstofer
Contributor
It's a good idea to experiment but I doubt that a pool is deep enough to get much wetsuit compression.
Simulating a wing failure (empty out the air) at depth with a full tank will give you an idea about whether you can swim to the surface. Personally, I doubt it. If you are really 19# negative at the start of the dive, that's a heck of an anchor.
The #2 approach to buoyancy works for thick wetsuits. In effect, you can remove from your weighbelt an amount of weight equal to the weight of air in the tank (or close to it). This also means that getting down isn't as simple as just letting the air out of the BC. It's already out. So, you have to swim down.
In kelp, inverting and swimming down is probably a good way to get entangled. So the idea is to kick upwards as hard as possible and bounce down.
But the #2 approach requires that the wetsuit be compressed enough to enable the diver to hold a safety stop. If the suit doesn't compress enough, the diver is buoyant and not carrying enough weight to stay down.
The #2 approach allows the diver using an HP100 to remove as much as 8# of lead. But that assumes they were carrying a bunch of lead to begin with. In the case of cold water wetsuit divers, this is always true.
Richard
Simulating a wing failure (empty out the air) at depth with a full tank will give you an idea about whether you can swim to the surface. Personally, I doubt it. If you are really 19# negative at the start of the dive, that's a heck of an anchor.
The #2 approach to buoyancy works for thick wetsuits. In effect, you can remove from your weighbelt an amount of weight equal to the weight of air in the tank (or close to it). This also means that getting down isn't as simple as just letting the air out of the BC. It's already out. So, you have to swim down.
In kelp, inverting and swimming down is probably a good way to get entangled. So the idea is to kick upwards as hard as possible and bounce down.
But the #2 approach requires that the wetsuit be compressed enough to enable the diver to hold a safety stop. If the suit doesn't compress enough, the diver is buoyant and not carrying enough weight to stay down.
The #2 approach allows the diver using an HP100 to remove as much as 8# of lead. But that assumes they were carrying a bunch of lead to begin with. In the case of cold water wetsuit divers, this is always true.
Richard
Leo53214
Registered
"I really don't like the idea of no ditchable weight. As I recall, the very first step when you rescue a diver and get them to the surface is to ditch their weights to establish positive buoyancy".
- rstofer
This response is as much for fun as it is informational (aka: no soapbox here)
As I just took my Rescue Diver final exam last night (literally!), I can tell you that you only drop their weights if it signifigantly increases your ability to get them accross/out of the water quickly. Your first move is to fully inflate their BCD. Then, if you MUST, because for some reason the BCD does not provide adequate lift, drop their weights. It is definately NOT your first step or choice if you can avoid it. ~Leo
- rstofer
This response is as much for fun as it is informational (aka: no soapbox here)
As I just took my Rescue Diver final exam last night (literally!), I can tell you that you only drop their weights if it signifigantly increases your ability to get them accross/out of the water quickly. Your first move is to fully inflate their BCD. Then, if you MUST, because for some reason the BCD does not provide adequate lift, drop their weights. It is definately NOT your first step or choice if you can avoid it. ~Leo
rstofer
Contributor
But suppose the diver doesn't require any weight? What do you do then?
I dive with no weight in nearly every coldwater/warmwater or singles/doubles configuration. Should I add weight just so it can be ditched? (Of course that makes no sense for a number of reasons.)
Obviously, it makes no sense to add weight such that you can ditch it and wind up right back where you started.
But it does make sense to balance the weight in such a way that some of it is ditchable. Or use tanks that aren't so negative. Certainly not the most negative possible tank of a particular capacity.
That's why the Al 80 is perfect for warm water. It is sufficiently buoyant that a diver will almost always require some weight. T shirt diving in south east Asia, I would wear about 6# of weight with an Al 80 and a somewhat floaty jacket BC. With an empty tank and no weights I would be at least 10# positive on the surface - more than enough to keep my head above water even if the BC had failed.
It would make no sense to put that 6# on a tank band and not have any ditchable weight.
As to whether a rescuer should ditch the victim's weights or play with a possibly non-functioning regulator/inflator is a choice. More often than not, it is faster to ditch the weight belt. Personally, I would do both but I would do the weight belt first. We're almost certainly not going back down.
I am not the world's expert on balancing dive gear but I want to be able to swim off the bottom with a failed BC. I'm not sure how much I could swim up but maybe the weight of air in an HP 100. I certainly couldn't swim 20# off the bottom. Of course, it gets easier as I ascend and the wetsuit expands. But I have to get off the bottom first.
Doubles are a different problem. Here the double bladder wings make sense. At least there is some redundancy in lift. I suppose the other option is to ditch the entire rig and swim up on the pony bottle. Redundant buoyancy in a drysuit would be an another good idea.
Lift bags and SMBs are another way to get off the bottom. Both assume that the diver has air. That may be a good assumption. Or not...
Everybody gets to pick their own configuration. For mine, I have no intention of giving up substantial ditchable weight.
Richard
