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

[grf88]

A lot easier to just ditch those weights.

To each their own I guess. Most of my diving is cold water in a drysuit and my primary singles tank is a 130 HP. If I was using double 80's aluminum I am not sure where I would put all the lead comfortably.

 

[boulderjohn]

steel tanks have negative buoyancy, they have no buoyancy to compensate for. you cant breath lead why carry it.why would you have to ditch weight?

This is apparently a very difficult concept.

Your buoyancy is based on your entire package--your body, your thermal protection, your BCD, your fins, your mask, your light, your tank, your regulators, your weights--everything. That whole package has a certain total weight. It also has a total volume. If the total weight of your total package is equal to the weight of that volume of water, then you are neutrally buoyant. If it weighs more, you are negatively buoyant.

In your total package, there are individual items that are negatively buoyant. There are certain items that are positively buoyant. The negatively buoyant items include your thermal protection, the fat in your body, some BCDs (especially with air). The negatively buoyant items include all tanks at the beginning of the dive, some BCDs, and the weights you carry. To be properly weighted, you need to consider all the factors over which you have control. Ideally, you want to be slightly negatively buoyant with no air in the BCD at the end of the dive so that you only need a minimum amount of air in the BCD to remain at depth.

• Let's say that a diver's total package needs to weigh 250 pounds in order to be be properly weighted at the end of the dive. If the diver uses a PST 80 steel tank, the tank will be 9.3 pounds negatively buoyant at the beginning of the dive. If the diver uses 4 pounds of gas during the dive, then that diver must make sure he or she weighs 254 pounds at the beginning of the dive to compensate for air loss. That weight can be achieved by adding lead or by using a different BCD.
• Let's say that a diver needs to weigh 250 pounds in order to be be properly weighted at the end of the dive. If the diver uses a Luxfer 80 aluminum tank, the tank will be 1.4 pounds negatively buoyant at the beginning of the dive. If the diver uses 4 pounds of gas during the dive, then that diver must make sure he or she weighs 254 pounds at the beginning of the dive to compensate for air loss. That weight can be achieved by adding lead or by using a different BCD.

If we are talking about the same diver in each case, the diver with the aluminum tank will need to have about 7 more pounds of added weight in the form of lead (or a different BCD) to achieve the needed weight. If the diver adds that extra weight, he or she will be in exactly the same situation throughout the dive as the diver with the steel tank.

I mentioned that I don't use any additional weight when using one of my steel 85s with a 5mm wetsuit in salt water. That is because I use my steel back plate. If I used my aluminum back plate, I would have to add some lead to achieve the same buoyancy. If I used an aluminum tank, I would have to use more weight to achieve the same buoyancy. But it all comes out the same.

 

[Dan]

To each their own I guess. Most of my diving is cold water in a drysuit and my primary singles tank is a 130 HP. If I was using double 80's aluminum I am not sure where I would put all the lead comfortably.

In your case, having back up buoyancy compensator like DSMB will be helpful.

 

[grf88]

In your case, having back up buoyancy compensator like DSMB will be helpful.

I always have at least one backup even when diving wet and usually at least two.

 

[Celt]

Supposed you have the following problem during a dive, your BCD leaks (e.g., vent valve spring broke, a small dirt jammed on the vent valve seat, old plastic valve plate got brittle & cracked, etc.), starts to take in water & you become negatively buoyant in the blue water, then what would you do? Since you have no weights to ditch, you’d just keep finning on the surface to keep you a float until a boat rescue you?

are you serious, how would you break a vent valve spring in the water? what kind of dirt would outpace a power inflater? you check your gear for cracks and you would have to putting serious pressure before you opened that crack. why would have to keep finning on the surface would you not dump it and why would you leave the surface negatively buoyant in the first place

 

[Dan]

are you serious, how would you break a vent valve spring in the water? what kind of dirt would outpace a power inflater? you check your gear for cracks and you would have to putting serious pressure before you opened that crack. why would have to keep finning on the surface would you not dump it and why would you leave the surface negatively buoyant in the first place

May be those are bad examples for BCD not being able to hold air. Ditching lead seems to be a lot easier to do than ditching the negatively buoyant gears when the tank almost empty, especially when you are lost at sea & you’d be floating for a while. I carry lots of safety gears (6’ DSMB with 100’ line in spool, Dive Alert, Signal Mirror, Nautilus Marine Rescue GPS, PLB1, Dive light, Strobe, Glow stick with 6’ string, reef hook), I don’t want to ditch the whole gear. Best signaling devices from the searcher’s point of view - update

 

[Celt]

This is apparently a very difficult concept.

Your buoyancy is based on your entire package--your body, your thermal protection, your BCD, your fins, your mask, your light, your tank, your regulators, your weights--everything. That whole package has a certain total weight. It also has a total volume. If the total weight of your total package is equal to the weight of that volume of water, then you are neutrally buoyant. If it weighs more, you are negatively buoyant.

In your total package, there are individual items that are negatively buoyant. There are certain items that are positively buoyant. The negatively buoyant items include your thermal protect, the fat in your body, some BCDs (especially with air). The negatively buoyant items include all tanks at the beginning of the dive, some BCDs, and the weights you carry. To be properly weighted, you need to consider all the factors over which you have control. Ideally, you want to be slightly negatively buoyant with no air in the BCD at the end of the dive so that you only need a minimum amount of air in the BCD to remain at depth.

• Let's say that a diver's total package needs to weigh 250 pounds in order to be be properly weighted at the end of the dive. If the diver uses a PST 80 steel tank, the tank will be 9.3 pounds negatively buoyant at the beginning of the dive. If the diver uses 4 pounds of gas during the dive, then that diver must make sure he or she weighs 254 pounds at the beginning of the dive to compensate for air loss. That weight can be achieved by adding lead or by using a different BCD.
• Let's say that a diver needs to weigh 250 pounds in order to be be properly weighted at the end of the dive. If the diver uses a Luxfer 80 aluminum tank, the tank will be 1.4 pounds negatively buoyant at the beginning of the dive. If the diver uses 4 pounds of gas during the dive, then that diver must make sure he or she weighs 254 pounds at the beginning of the dive to compensate for air loss. That weight can be achieved by adding lead or by using a different BCD.

If we are talking about the same diver in each case, the diver with the aluminum tank will need to have about 7 more pounds of added weight in the form of lead (or a different BCD) to achieve the needed weight. If the diver adds that extra weight, he or she will be in exactly the same situation throughout the dive as the diver with the steel tank.

I mentioned that I don't use any additional weight when using one of my steel 85s with a 5mm wetsuit in salt water. That is because I use my steel back plate. If I used my aluminum back plate, I would have to add some lead to achieve the same buoyancy. If I used an aluminum tank, I would have to use more weight to achieve the same buoyancy. But it all comes out the same.

a full aluminium tank is buoyant on the surface, a steel tank of the same volume has a negative bouyancy empty. If you use steel twins of the same volume as an aluminium 80, not only will you not need lead to sink the AL80 but the extra weight of the steel twins will negate the buoyancy of other essential gear and dramatically cut the amount of lead needed. Also the aluminium tank is heavier to carry on the surface. The only reason aluminium tanks are used for diving is there cheap to buy and maintain so the dive resorts and schools like them.

 

[Celt]

May be those are bad examples for BCD not being able to hold air. Ditching leds seems to be a lot easier to do than ditching the negatively buoyant gears when the tank almost empty, especially when you are lost at sea & you’d be floating for a while. I carry lots of safety gears (6’ DSMB with 100’ line in spool, Dive Alert, Signal Mirror, Nautilus Marine Rescue GPS, PLB1, Dive light, Strobe, Glow stick with 6’ string, reef hook), I don’t want to ditch the whole gear. Best signaling devices from the searcher’s point of view - update

Dan, if my life depended on it i would dump everything that wasn't buoyant except my fins mask and snorkel,

 

[BRT]

steel tanks have negative buoyancy, they have no buoyancy to compensate for. you cant breath lead why carry it.why would you have to ditch weight?

Do you think steel tanks do not change their buoyancy?

 

[BRT]

a full aluminium tank is buoyant on the surface, a steel tank of the same volume has a negative bouyancy empty. If you use steel twins of the same volume as an aluminium 80, not only will you not need lead to sink the AL80 but the extra weight of the steel twins will negate the buoyancy of other essential gear and dramatically cut the amount of lead needed. Also the aluminium tank is heavier to carry on the surface. The only reason aluminium tanks are used for diving is there cheap to buy and maintain so the dive resorts and schools like them.

If you mean a full aluminum tank floats you are wrong.