Tank Bouyancy

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Trwmodela

Trwmodela

Contributor
Messages
178
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0
Location
Fort Myers, FL
# of dives
100 - 199
Ok, I keep hearing some divers talk about dropping their tank if they are having trouble at the surface. Your BCD should keep you on the surface unless it fails. We all know about dropping your weights FIRST.

I did read a report on a diver with a leaking low pressure hose that also contributed to a problem keeping his BCD inflated. You should be able to manually inflate your BCD if your tank is empty or your low pressure hose fails. But if your BCD fails to hold air then why would I drop my BCD & tank? To me your tank would provide some positive bouyancy at the surface and maybe the only piece of equipment besides your wet suit providing bouyancy. Dropping your tank even when empty of air makes no sense to me. I always dive with aluminum tanks and I believe the extra weigh from a steel tank would make a difference in bouyancy.

Tim
 
See:
http://www.huronscuba.com/equipment/scubaCylinderSpecification.html
Look in the column "Buoyancy Empty"
As you'll see, many of the numbers, especially the steel tanks, are negative, meaning the tanks aren't actually buoyant. For example, the steel Faber 100 is -7.26 pounds when empty -- ditching that tank would make you 7 pounds more buoyant.
 
ditch my tanks....?
thats why i have a dual bladder
 
In warm fresh water, with only a core warmer, I only have 8 lbs with an AL80, of which 2 lbs is my pony. If I switched to a Faber 100 there's an 11 pound swing on empty tanks -- that means I'm -3 pounds. Bleed the pony and I'd still be negative.
You betcha, if the dung hits the fan, my butt is worth more than a tank.
 
markfm:
In warm fresh water, with only a core warmer, I only have 8 lbs with an AL80, of which 2 lbs is my pony. If I switched to a Faber 100 there's an 11 pound swing on empty tanks -- that means I'm -3 pounds. Bleed the pony and I'd still be negative.
You betcha, if the dung hits the fan, my butt is worth more than a tank.
Click to expand...
o yeah if it was to come down to it.......
C-ya
 
If I'm diving my bp/w with any tank, the only way for me to ditch any weight is to lose the whole kit, as I don't have any ditchable weight. *shrug* Works for me....
 
It gives your buds something to do a search and recovery exercise :)
 
Unless you are aborting a dive you will encounter surface distress either at the begining or end of the dive. At the beginning even the AL-80 is negative.

Thinking of things I've read a BC failure may be most likely at the start of the dive due to dump valves being damaged or mis-assembled in cleaning and things like that. Make sure it's holding air before you're in the water.

The as others have said if it needs to go then it needs to go, Now it all depends where you are and what your wearing, For skin-diving with 5mm in salt water I wear 16 pounds of weight to comfortably surface swim but dive down at will. Given any significant wetsuit 5 pounds of negative cylinder may not be the end of your world. Add trim weights and such and it becomes a different story.

Pete

Trwmodela:
Ok, I keep hearing some divers talk about dropping their tank if they are having trouble at the surface. Your BCD should keep you on the surface unless it fails. We all know about dropping your weights FIRST.

I did read a report on a diver with a leaking low pressure hose that also contributed to a problem keeping his BCD inflated. You should be able to manually inflate your BCD if your tank is empty or your low pressure hose fails. But if your BCD fails to hold air then why would I drop my BCD & tank? To me your tank would provide some positive bouyancy at the surface and maybe the only piece of equipment besides your wet suit providing bouyancy. Dropping your tank even when empty of air makes no sense to me. I always dive with aluminum tanks and I believe the extra weigh from a steel tank would make a difference in bouyancy.

Tim
Click to expand...
 
Ok, I was never concerned about ditching a cylinder and the cost $$$ of replacing. This would not even enter my mine if bouyancy was effected by the cylinder. Based on the cylinder chart it really depends of the size, manufacturer, material and how much air is in the cylinder. One thing I have learned is the idea of just removing the cylinder and testing if it is bouyant and worth keeping. If not I would just drop the cylinder and keep my BCD. It looks like most steel cylinders would not provide positive bouyancy.

Thanks,
Tim
 
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