Dumpable weight vs trim

[wetb4igetinthewater]

Overweighting to me is the current biggest problem in modern diving.
Combine this problem with no ditchable weights and you have a dormant disaster waiting to happen.

I think that overweighting and those diving a balanced rig (I hope that this is taught in all tec programs) are somewhat, but not necessarily, mutually exclusive.

 

[TMHeimer]

It’s been a long time since I’ve participated in any sort of class environment so I’m trusting what you say about the problem of overweighting is indeed getting better.
When I got certified we were overweighted - I found out later.
The training was thorough and good but overweighting was still the ugly duckling of the trade. One guy had 40# on! I think they slammed me with 35#. Later, after diving on my own for a while and gleaning info from other divers, I was able to shed that down to about 24# and that was in a 7mm with a jacket- no plates yet.

Just the other day during a shop sponsored fun dive, a couple newly certified guys showed up to get on a few dives. We were at a popular cove up on the coast. They ended up coming up way out in the ocean because they navigation skills were still a little weak. They got tired trying to fin in on the surface and kind of got pulled off course by currents and ended up getting caught up in a wash against some rocks. Both were in typical shop gear (jackets, integrated weights, aluminum rental tanks) and were overweighted. They made it in OK and didn’t need to be rescued, but all they kept saying was how they had to put enormous amounts of air in their jackets to stay afloat and that squeezed on them making it hard to get deep lungfulls of air. At one point one almost tried to figure out how to unclip the weights pouches and get rid of some weight but didn’t want to buy expensive replacement pockets for the BC, or a new BC if they weren't available. So apparently OW in my area hasn’t gotten the memo yet.
Back on the beach some of us made it into a learning moment and had a very positive conversation with them about what took place. They are very thankful for the insight and vowed to rethink their weighting strategies.

Thursday I'm taking wetb4's advice and seeing if I can swim up my 42 pounds from the bottom with empty BC. If I can, I suspect some will say I should not be ditching weights in an emergency. Either way, 42 pounds is a lot to be carrying up when you are OOA and maybe panicked or close to it. Obviously dropping 20 pounds and in that wetsuit would mean a much faster ascent, which would be important if diving very deep. I am properly weighted in my 7 mil farmer john wetsuit.
With less than 42 pounds it is impossible for me to descend with an empty BC. That has amazed several instructors when they observed it.

 

[Eric Sedletzky]

Thursday I'm taking wetb4's advice and seeing if I can swim up my 42 pounds from the bottom with empty BC. If I can, I suspect some will say I should not be ditching weights in an emergency. Either way, 42 pounds is a lot to be carrying up when you are OOA and maybe panicked or close to it. Obviously dropping 20 pounds and in that wetsuit would mean a much faster ascent, which would be important if diving very deep. I am properly weighted in my 7 mil farmer john wetsuit.
With less than 42 pounds it is impossible for me to descend with an empty BC. That has amazed several instructors when they observed it.

Describe your setup that takes 42 lbs to sink.
That seems awfully excessive.
is your BC empty at 15’ at the end of your dive?

 

[boulderjohn]

Describe your setup that takes 42 lbs to sink.
That seems awfully excessive.
is your BC empty at 15’ at the end of your dive?

He has said he needs 42 pounds repeatedly over the years. I would love to spend a day with him working on this.

 

[TMHeimer]

Describe your setup that takes 42 lbs to sink.
That seems awfully excessive.
is your BC empty at 15’ at the end of your dive?

7 mil farmer john wetsuit, hood of course. AL 80 tank. I weigh 190-205 pounds.
Haven't done a weight check since buying the new wetsuit 3-4 years ago.
With the old one I needed 42 back in 2006. Gradually decreased to 37 by end of it's life (due to loss of integrity, I guess).
Tried 37 with the new suit-- not a chance. Needed the 42 once again. I'd welcome the chance to work with anyone to change that. An instructor on staff who usually dives dry, said he uses 38 with the same setup as me wet. My instructor in FL during the PP Buoyancy course was confounded that I needed so much.
With my shorty in salt water I need 18 pounds.
With body suit only in tropics I need at least 10 pounds.

 

[Eric Sedletzky]

7 mil farmer john wetsuit, hood of course. AL 80 tank. I weigh 190-205 pounds.
Haven't done a weight check since buying the new wetsuit 3-4 years ago.
With the old one I needed 42 back in 2006. Gradually decreased to 37 by end of it's life (due to loss of integrity, I guess).
Tried 37 with the new suit-- not a chance. Needed the 42 once again. I'd welcome the chance to work with anyone to change that. An instructor on staff who usually dives dry, said he uses 38 with the same setup as me wet. My instructor in FL during the PP Buoyancy course was confounded that I needed so much.
With my shorty in salt water I need 18 pounds.
With body suit only in tropics I need at least 10 pounds.

Ok so we know an aluminum 80.
What about BC? What type and what brand? Jacket - s/s plate?
Farmer John suit, beaver tail - step in?
Hood - hooded vest or bib style?
Body composition? How much body fat? At 190 a 205 I suspect not much but an insulation layer could have an effect.
You still need to answer about your 15’ stop at the end of the dive, do you have any air in your BC or not?

 

[Zef]

Ok so we know an aluminum 80.
What about BC? What type and what brand? Jacket - s/s plate?
Farmer John suit, beaver tail - step in?
Hood - hooded vest or bib style?
Body composition? How much body fat? At 190 a 205 I suspect not much but an insulation layer could have an effect.
You still need to answer about your 15’ stop at the end of the dive, do you have any air in your BC or not?

One would think that if 42lbs of lead is needed to get down at the beginning of the dive that @TMHeimer would be positively buoyant and struggling to stay down at the end of the dive if his tank down around reserve pressure (50 bar / 500psi) given the buoyancy characteristics of an AL80.

-Z

 

[johndiver999]

One would think that if 42lbs of lead is needed to get down at the beginning of the dive that @TMHeimer would be positively buoyant and struggling to stay down at the end of the dive if his tank down around reserve pressure (50 bar / 500psi) given the buoyancy characteristics of an AL80.

-Z

It sounds like you think that he would experience a different swing in buoyancy than anyone else who uses the same tank?

 

[Zef]

It sounds like you think that he would experience a different swing in buoyancy than anyone else who uses the same tank?

No that is not what I am implying...I am implying that if one needs X amount of weight to descend at the beginning of the dive while using a tank that has a buoyancy characteristic of being positively buoyant when near empty, that one would need X+Y amount of weight to be able to hold a safety stop within the top 33ft/10m of the water column at the end of the dive. Y would be roughly equal to or greater than how positively buoyant the tank is at the reserve pressure one plans to surface with.

Perhaps I am wrong, but I inferred from TMHeimer's post that he needs 42lbs of lead at the beginning of his dives due to the buoyancy of his body, his exposure suit, and any other gear that may be contributing positive buoyancy. I did not infer that the 42lbs considered end of dive conditions....perhaps that factor is taken into account in the amount of ballast he uses...but if not, the end of dive may be a struggle due to the positive buoyancy characteristic of AL80 tanks.

Now, I may have it all wrong, as I am assuming that AL80 tanks generally become positively buoyant as they are depleted....perhaps there are versions of AL80 tanks that do not...AL80s seem few and far between where I dive....the most common single tank setup, based on my observations, is 15L 232 bar steel tanks....this is chosen as it provides even those with high consumption rates an adequate supply of air for at least 30 min or more of diving, while at the same time it reduces the amount of lead they need in pockets or on a belt.

The next most common setup seems to be twin 10L or twin 12L....its is not so easy to differentiate between 10L and 12L tanks from a distance when they are banded and attached to BC or backplate.

-Z

 

[johndiver999]

No that is not what I am implying...I am implying that if one needs X amount of weight to descend at the beginning of the dive while using a tank that has a buoyancy characteristic of being positively buoyant when near empty, that one would need X+Y amount of weight to be able to hold a safety stop within the top 33ft/10m of the water column at the end of the dive. Y would be roughly equal to or greater than how positively buoyant the tank is at the reserve pressure one plans to surface with.

Perhaps I am wrong, but I inferred from TMHeimer's post that he needs 42lbs of lead at the beginning of his dives due to the buoyancy of his body, his exposure suit, and any other gear that may be contributing positive buoyancy. I did not infer that the 42lbs considered end of dive conditions....perhaps that factor is taken into account in the amount of ballast he uses...but if not, the end of dive may be a struggle due to the positive buoyancy characteristic of AL80 tanks.

Now, I may have it all wrong, as I am assuming that AL80 tanks generally become positively buoyant as they are depleted....perhaps there are versions of AL80 tanks that do not...AL80s seem few and far between where I dive....the most common single tank setup, based on my observations, is 15L 232 bar steel tanks....this is chosen as it provides even those with high consumption rates an adequate supply of air for at least 30 min or more of diving, while at the same time it reduces the amount of lead they need in pockets or on a belt.

The next most common setup seems to be twin 10L or twin 12L....its is not so easy to differentiate between 10L and 12L tanks from a distance when they are banded and attached to BC or backplate.

-Z

the magnitude of the buoyancy swing of ALL tanks is the same (assuming the same capacity).