Descending Vertically Vs Horizontally

[Charlie99]

If you did two dives, one with the steel 80 and one with the AL80 and you ran down to 500 psi on each dive, you would need more lead at the end of the dive with the AL80 to offset its buoyancy than you would with the steel.

OK, lets try this.

Assume a diver has worked out his weighting and is wearing the proper amount of lead. --- in other words, he can maintain his final stop and ascend to the surface in a controlled manner with a near empty tank. Assume that he has worked out the proper amount of lead (which will NOT be the same number) for both a steel PST 80 and for a Luxfer AL80.

When wearing the proper amount of lead for an AL80, and no air in his BCD, how negatively buoyant is he at the beginning of a dive with the AL80?

When wearing the proper amount of lead for a PST 80, and no air in his BCD, how negatively buoyant is he at the beginning of a dive with the PST 80?

My answer, in both cases, is 6 pounds.

 

[stoddu]

No; look at the links for the charts I posted. The amount of the swing may be the same but the end result is different. An empty HP80 has more negative buoyancy than an empty AL80; an AL80 is positively buoyant when empty.

If you did two dives, one with the steel 80 and one with the AL80 and you ran down to 500 psi on each dive, you would need more lead at the end of the dive with the AL80 to offset its buoyancy than you would with the steel.

I see how this "if you have a tank that swings negative to positive as the air is depleted" isn't clear; yes all tanks do but some more than others; sorry if I wasn't clear.

The swing weight will be the same for both tanks. The swing weight will not be changed by the bouyancy characteristics of the tank. You will have to carry extra lead during the whole dive to compensate for a bouyant tank, but you would not need extra lead just at the end of the dive. If you don't understand the point these guys are making, you should consider turning in your instructors certificate.

 

[Tanked Monkey]

fftopic: Alright you guys, give it up. Take "The Great Tank Swing Debate" to another thread. Let this thread get back to the original topic of descending horizontally or vertically.

Mike

 

[Xanthro]

You add no air to get neutral...so what do you do when you go deeper? Do you add air then? How about when you come up to a shallower depth? I'm sorry but if you are nuetral at 60 ft with no air in your BC then there is no way in the word that you can be nuetral at 15 ft. Not happening in this world.

Of course that could happen. You can be nuetral at any depth without changing air levels in your BCD.

He often doesn't wear a Wetsuit, so there is little to compress and thus he changes bouyancy to such a small amount that he can compensate merely by breathing.

I don't have to add or subtract air from by BCD from between 40' and 100' wearing a 7mm. I can easily change my bouyancy by breathing and relaxing.

In a 3/5 I hardly ever have to use air to change bouyancy.

 

[Xanthro]

Topic was beaten to death and the confusion was recoginzed by the time I posted, so I edited my post and deleted the information.

 

[pants!]

No; look at the links for the charts I posted. The amount of the swing may be the same but the end result is different. An empty HP80 has more negative buoyancy than an empty AL80; an AL80 is positively buoyant when empty.

If you did two dives, one with the steel 80 and one with the AL80 and you ran down to 500 psi on each dive, you would need more lead at the end of the dive with the AL80 to offset its buoyancy than you would with the steel.

I see how this "if you have a tank that swings negative to positive as the air is depleted" isn't clear; yes all tanks do but some more than others; sorry if I wasn't clear.

Yeah, but dude, you need more lead at the beginning of the dive as well so that's irrelevant. You're missing the forest for the trees.

The swing on both tanks is 6 pounds positive.

 

[Tanked Monkey]

fftopic: Just let it die.

 

[P_Abercrombie]

OK, lets try this.

Assume a diver has worked out his weighting and is wearing the proper amount of lead. --- in other words, he can maintain his final stop and ascend to the surface in a controlled manner with a near empty tank. Assume that he has worked out the proper amount of lead (which will NOT be the same number) for both a steel PST 80 and for a Luxfer AL80.

When wearing the proper amount of lead for an AL80, and no air in his BCD, how negatively buoyant is he at the beginning of a dive with the AL80?

When wearing the proper amount of lead for a PST 80, and no air in his BCD, how negatively buoyant is he at the beginning of a dive with the PST 80?

My answer, in both cases, is 6 pounds.

I agree; but you do agree that the amount of lead would be different?

 

[P_Abercrombie]

The swing weight will be the same for both tanks. The swing weight will not be changed by the bouyancy characteristics of the tank. You will have to carry extra lead during the whole dive to compensate for a bouyant tank, but you would not need extra lead just at the end of the dive. If you don't understand the point these guys are making, you should consider turning in your instructors certificate.

...and you should consider learning how to read and review all the posts; you got it completely wrong *******; tell you what; go get some more dives in before you offer your 2 cents

 

[stoddu]

OK, back on topic. A higher capacity tank will make it easier for you to descend at the beginning of a dive (assuming the tanks are full). The extra air that you are carrying gives you a greater swing weight which means you are more negative at the beginning of the dive. Maybe that's why scubafool, who is diving doubles, has air in his BC when descending?