Overweighted at beginning of dive but underweighted at end in shallows

[Zach The Diver]

FTFY
Stop digging

You’re cherry-picking to cherry-pick. That’s not only insufferable but you just proved my point.

Congratulations.

Grown adult divers do indeed need to change their weighting before their dive based on their configuration. If not, they’re improperly weighted. I’m not sure what you were trying to achieve with that.

 

[inquis]

Actually read what I said

We did, which is what sparked much of this latest flurry. In msg #131, you quoted this:

the difference of upward force between beginning and end of a dive is only driven by the amount of gas used.

And then said this:

The composition of the cylinders holding that volume of gas also plays a role.

which is simply wrong in the quoted context. Cylinder composition does NOT play a role in "the difference of upward force between beginning and end of a dive".

It also riles people up when you call their attempts to rectify a common misunderstanding "senseless arguing", and then seemed to perpetuate the misunderstanding with your very next sentence --

A lot of senseless arguing here…

No, nobody is doubting that all tanks will become “more” buoyant with less gas, but with AL80s the effect becomes more noticeable

(I did see that you acknowledged that your statement about "more noticeable" was wrong, and I appreciate that.)

Hopefully you understand that being in the Basic area, errors will tend to be corrected. Your later posts have adopted a position of essentially "tank composition should be considered in the weighting", and I think everyone would agree with that.

 

[Zach The Diver]

What part of the link you provided?

An HP80 is approximately 6 pounds less buoyant than an AL80 either empty or full and they hold approximately the same amount of gas. Strap 6 pounds of lead to the AL80 and they will have the same bouyancy characteristics throughout the dive. Or you can take the 6 pounds and attach it to the diver and the system bouyancy will be the same.

Trim will obviously be different as I already stated.

Yes… so the diver must adjust their weight accordingly. lol. That’s what I’m saying.

18th paragraph down. It is a longer read so I should have specified that.

 

[lowwall]

You’re cherry-picking to cherry-pick. That’s not only insufferable but you just proved my point.

Congratulations.

Grown adult divers do indeed need to change their weighting before their dive based on their configuration. If not, they’re improperly weighted. I’m not sure what you were trying to achieve with that.

We are responding to what you have actually written. You are the one changing your arguments as you go.

 

[tursiops]

A diver improperly weighted for aluminum at the beginning may be unable to compensate and avoid an ascent even with a fully deflated wing.

LOL. This is also true for steel! Just start your dive with a steel tank neutrally buoyant, see what happens.
The point is to be properly weighted, not to use AL or steel.

If you were not properly weighted to begin with, then that’s a potential problem. Particularly if you were properly weighted for steel but failed to adjust when switching to aluminum.

Did you do this once? Is this why you are so obsessed with it?

 

[Zach The Diver]

LOL. This is also true for steel! Just start your dive with a steel tank neutrally buoyant, see what happens.
The point is to be properly weighted, not to use AL or steel.


Did you do this once? Is this why you are so obsessed with it?

That was the point I was attempting to make to begin with.

No. But it’s a very common mistake with rookie divers so it warrants mentioning, particularly those doing their first tropical dive who may have received their initial training inland or in a coldwater environment. Almost as common as strawman attempts on Scubaboard.

 

[Zach The Diver]

We are responding to what you have actually written. You are the one changing your arguments as you go.

The only thing I stated that upon rereading comes off as incorrect was my “more noticeable” statement which I already acknowledged. You read into it what you wanted to read and formulated a very condescending tirade from it. Also the argument I keep reading about steel and aluminum being identical in terms of buoyancy characteristics is absolutely wrong.

 

[Zach The Diver]

We did, which is what sparked much of this latest flurry. In msg #131, you quoted this:

And then said this:

which is simply wrong in the quoted context. Cylinder composition does NOT play a role in "the difference of upward force between beginning and end of a dive".

It also riles people up when you call their attempts to rectify a common misunderstanding "senseless arguing", and then seemed to perpetuate the misunderstanding with your very next sentence --

(I did see that you acknowledged that your statement about "more noticeable" was wrong, and I appreciate that.)

Hopefully you understand that being in the Basic area, errors will tend to be corrected. Your later posts have adopted a position of essentially "tank composition should be considered in the weighting", and I think everyone would agree with that.

From beginning to the end of the dive you are correct, it doesn’t. I was bemused that people actually thought I meant that, but given how many did I should have been more clear in my choice of words.

To the OP, sorry this has turned into a toxic tirade lol.

 

[RobPNW]

The implication is that the “buoyancy swing” is likely rooted in poor weighting from the outset of the dive, which is easily masked in underweighted divers until they start running low on gas at a relatively shallow depth.

Wouldn’t buoyancy swing from beginning to end of the dive be identical regardless of the equipment used and whether properly weighted or not, assuming the same amount of gas is consumed? Maybe I’m interpreting the term buoyancy swing differently.

 

[Zach The Diver]

Wouldn’t buoyancy swing from beginning to end of the dive be identical regardless of the equipment used and whether properly weighted or not, assuming the same amount of gas is consumed? Maybe I’m interpreting the term buoyancy swing differently.

Proportionally speaking the swing would be identical assuming the same volume of gas is used, yes. What matters is how the diver is weighted at the back end of that buoyancy swing. If the swing exceeds the weighting of the diver with an empty wing at the end of the dive then the logical conclusion is a positively-buoyant diver with little to no means of compensating for it.