Cylinder type and proper weighting (SPLIT FROM 'Pull Dumps - Lose them')

[Celt]

Sorry--this is the post to which I responded:
In it, you clearly indicate that carrying weight to compensate for the lighter aluminum tanks means that people are "are carrying to [sic] much weight and trying to compensate with a wing or bcd." You clearly state that if you carry weight to compensate for an aluminum tank, then you are overweighted. that is the comment to which I was responding.

Im not saying if you use aluminium tanks your carrying to much weight, i clearly said your carrying to much LEAD. my point is by using steel tanks your carrying less dead weight. but in actual fact people do tend to carry to much weight especially when using aluminium tanks, and clearly in this post the diver was to heavy.

 

[boulderjohn]

Im not saying if you use aluminium tanks your carrying to much weight, i clearly said your carrying to much LEAD. my point is by using steel tanks your carrying less dead weight. but in actual fact people do tend to carry to much weight especially when using aluminium tanks, and clearly in this post the diver was to heavy.

So people who use aluminum tanks overweight themselves, but people who use steel tanks do not overweight themselves? I wonder why that is. What makes people with steel tanks more savvy about weighting than people with aluminum tanks?

Please note, as well, that people with aluminum tanks often have more of a choice about their weighting. Divers using steel doubles usually use some sort of redundant buoyancy because they have no choice but to be overweighted.

 

[Celt]

Do you think steel tanks do not change their buoyancy?

steel tanks don't have bouyancy, at least mine don't. if something is buoyant it will float to the surface. a steel tank will not float to the surface, the amount of air thats in the tank will only affect the speed that it will sink.

 

[Celt]

So people who use aluminum tanks overweight themselves, but people who use steel tanks do not overweight themselves? I wonder why that is. What makes people with steel tanks more savvy about weighting than people with aluminum tanks?

Please note, as well, that people with aluminum tanks often have more of a choice about their weighting. Divers using steel doubles usually use some sort of redundant buoyancy because they have no choice but to be overweighted.

why are you putting words in my mouth? i didn't say "people who use aluminium tanks overweight themselves" i said they carry more lead.

 

[Stoo]

I love how these discussions about a "near miss" always become so judgemental, so quickly. I've been diving a while (44 years) and have a few dives logged (roughly 5386 as of Saturday) and I can tell you, that I have seen many, many divers, who are highly experienced and skilled just about lose it when the excrement hits the oscillator. Just because it hasn't happened to you, doesn't mean it won't.

On Sunday, I pushed some ice pans out of the way and jumped in for a little solo dive in front of my place in Tobermory. Max depth was 53' and the water temperature was a toasty 36°F (2°C). At the 35 minute mark, my primary reg began to freeflow and even though I could have easily ascended without incident, for a brief moment, my heart skipped a couple of beats and and I was pretty sure I was about to die... OK, not really, and I quickly switched regs (I was wearing doubles), shut down my right post and carried on. I turned the gas back on again after a couple of minutes and continued my dive without incident. My guess though, is that a lot of people would have fired to the surface and mass bedlam would have ensued.

Anyway, until something "interesting" happens to you, maybe limit your comments to ones that are helpful. This dude could have drowned, and let's face it, diving is stupid.

Happy Easter, friends. Dive Safely.

 

[boulderjohn]

steel tanks don't have bouyancy, at least mine don't. if something is buoyant it will float to the surface. a steel tank will not float to the surface, the amount of air thats in the tank will only affect the speed that it will sink.

Well, it is now pretty clear that you are not going to understand this. I am responding for the benefit of others who might still be confused.

1. Buoyancy is the relationship between an object's weight and its volume. If it weighs the same as that volume of water, it is neutrally buoyant. If it weighs more than that volume of water, it has negative buoyancy. If it weighs less than that volume of water, it is positively buoyant. A steel-hulled ocean liner floats because its total weight is less than the volume of water it occupies. A steel tank sinks because it weighs more than the volume of water it occupies. All objects have buoyancy--it is just a matter of how much. This is Archimedes Principle.
2. This chart shows the buoyancy characteristics of different scuba tanks. It lists the degree to which the different tanks are positively or negatively buoyant, both when empty or full. In every case, aluminum or steel, that difference is based solely upon the amount of air in the full tank. The full tank is heavier than an empty tank, but it still occupies the same volume, so it is more negatively buoyant.
3. According to Archimedes Principle (see #1), the buoyancy of a diver is determined by the total weight of the diver and all the gear combined. During the dive, the diver's volume will not change, except for the adjustments made to the BCD and the compression of the thermal protection, but the diver will lose weight because of the loss of air in the tank. It is the loss of air in the tank that causes the change in buoyancy, and as the chart in #2 shows, that is true for all tanks, aluminum or steel.
4. It does not matter whether the tank being used will sink or float on its own, whether full or empty. What matters for the diver is the weight and volume of the diver plus all gear, including the tank. If the weight of that total package is not enough, the diver will be positively buoyant and must add weight without creating a significant increase in volume. That is usually done by adding lead.
5. Because it is the weight of the total package that counts, all factors have an impact, and no one factor is alone responsible for the buoyancy. A diver using a single aluminum tank with a 3mm suit and standard BCD in fresh water will need very little weight--perhaps none. That same diver using a single steel tank in salt water and wearing a dry suit will need a significant amount of lead to do the dive.

 

[CuzzA]

diving in 36°F (2°C) is stupid.

FIFY.

 

[Saniflush]

Sorry but all this discussion of buoyancy keeps making me think of "The Holy Grail" and whether a witch floats or not?

 

[boulderjohn]

Just a personal example for my most recent post:

When I taught OW classes in a warm pool using a 3mm shorty and an aluminum tank, I regularly demonstrated that I was correctly weighted and able to dive with no weights whatsoever.

The day I dived in Puget Sound using a dry suit and my warmest, fluffiest undergarment and a steel tank, I did not think there was enough lead in Seattle to sink me.

 

[Stoo]

FIFY.

LMAO. Ya. I find no fault in what yer saying. The thing is, it's pretty much that temperature year round below 70' up here. Well, maybe 39° but still....

Did I mention the wind was howling, and it was sleeting or something as well? Here's evidence and a nice beach shot.