Comparing ST doubles to Al doubles

[ianr33]

Be wary of this train of thought. Yes, of course the bigger tank you get the heavier it weighs, but as another member pointed out it's bouyancy that matters. Look at Faber tanks vs PST or especially Worthington, and you'll find they're very light in water.

Faber LP121's are monster sized tanks, yet they're only -5 lbs full and actually QUITE positive when empty. [

But................They will swing around 9 pounds from full to empty. Cave Fill them and the swing is around 13 pounds. Doubled up and you have 26 pounds of gas. Add a stage and thats 32 pounds of gas. Even if you are perfectly weighted i.e neutral with empty tanks a 40 pound wing is getting marginal.(Even if it is really 40 pounds) Dont even think about what would happen if you flooded your drysuit! If you are positive with empty tanks then you are going to have an interesting time doing a 10 or 20 foot deco stop. (And if you are not doing deco why are you bothering with double 121's ??)

I have found empirically that with well filled 104's An 80 stage plus a 40 deco bottle I float with about 1/2" of the top of my head out of the water. Thats with an Al plate and a puffed up drysuit.

I'm fine with a 40 pound wing in a cave as the deco bottle gets dropped right away and the surface is flat. I would NOT want to be in large swells in the Ocean with that configuration.

 

[DA Aquamaster]

I have found empirically that with well filled 104's An 80 stage plus a 40 deco bottle I float with about 1/2" of the top of my head out of the water. Thats with an Al plate and a puffed up drysuit.

I'm fine with a 40 pound wing in a cave as the deco bottle gets dropped right away and the surface is flat. I would NOT want to be in large swells in the Ocean with that configuration.

That is a well stated argument for a larger 55 -60 lb wing, and is exactly why I switched to a 55 lb wing.

As stated many "40 lb" wings will not actually provide a full 40 pounds of lift. Many are narrower than larger 55-60 lb wings and end up getting partially pinched between the plate and large diameter tanks.

In the above mentioned, doubles, stage and deco bottle scenario, I can at least get my head above water with a 55 lb wing and dry suit (and the average human head weighs about 15 lbs.)

 

[tgsmith]

But................They will swing around 9 pounds from full to empty. Cave Fill them and the swing is around 13 pounds. Doubled up and you have 26 pounds of gas. Add a stage and thats 32 pounds of gas. Even if you are perfectly weighted i.e neutral with empty tanks a 40 pound wing is getting marginal.(Even if it is really 40 pounds) Dont even think about what would happen if you flooded your drysuit! If you are positive with empty tanks then you are going to have an interesting time doing a 10 or 20 foot deco stop. (And if you are not doing deco why are you bothering with double 121's ??)

I have found empirically that with well filled 104's An 80 stage plus a 40 deco bottle I float with about 1/2" of the top of my head out of the water. Thats with an Al plate and a puffed up drysuit.

I'm fine with a 40 pound wing in a cave as the deco bottle gets dropped right away and the surface is flat. I would NOT want to be in large swells in the Ocean with that configuration.

I think you missed what I'm saying.

 

[ianr33]

I think you missed what I'm saying.

Quite possible. Care to edjucamate me?

 

[DA Aquamaster]

I think what he is saying is that, swing weight aside, some tanks can be very heavy out of the water, but can be very light and even buoyant in the water when empty - so a large wing would not be required due to excessively negatively buoyant tanks.

One thing to consider is that excessively negative tanks can cause you to become over weighted, especially if you dive a thin wet suit, so it is important to look at the whole system. With negative tanks and a thin wet suiot for example, you may want to avoid a stainless plate and go with alumium or kydex instead to keep from being too negative. Again, the idea is to be neutral at 10 ft with no air in the wing and almost no gas in the tanks.

On the other hand, if those really heavy double 121's are positive at the end of the dive, you'll need some kind of weight to offset that bouyancy at the end of the dive - potentially increasing the total gear weight you have to carry up the ladder.