Overweight?

[Soggy]

SCUBedoobedoo once bubbled...
aluminum tank.......by teh way, wats cft stand for? i assumed 80 cubic inch tank was ci

cubic feet. An 80 cubic inch tank wouldn't hold much air.

If you were to let out all the air in an Al80, you would have enough air to fill a room that is 80cft. If the air in the tank were reduced to 14.7 psi, it would take up 80 cubic feet of space. It isn't a rating of the actually cylinder volume.

There are several types of 80 cft tanks. Low Pressure Steel 80s hold 80 cft, but store it at 2400 psi....you still have the same volume of air for the dive, but it is compressed to a lower pressure. High pressure 80s hold that same amount of air at 3500 psi...the tank is physically smaller than an Al80, but holds the same amount of air.

In reality an Al80 holds 77.4 cft of air, but that's a whole other discussion.

 

[Soggy]

SCUBedoobedoo once bubbled...
aluminum tank.......

FYI, an Aluminum 80 is approximately 2 lbs negative at the beginning of a dive and 4 lbs POSITIVE at the end when empty. This is part of why you need so much weight. Steel tanks are much heavier in the water.

 

[MikeFerrara]

I didn't read each post in detail so I don't know if it's been suggested but you should do a weighting check. You should have done this in the pool during your class and in OW both.

This is something that needs to be rechecked when things like equipment change.

 

[herman]

I am about your size and with a 2 piece 5mm I use 12-14lbs in fresh water. While it's hard to say for sure how much you need, 24 seems quite a bit. If your 7mm is a one piece, the wetsuits are about even. Saltwater will add a few pounds but not that much. You best bet is to do a good bouyance check. Just remember if you do it with a full tank, add 5 lbs or you will be light at the end of the dive and it makes it hard, esp for a new diver, to control your bouyancy. Bouyancy checks are great tools. I can nail my weight requirements without much trouble but I still do them every chanced I get. Take the time to log the results, including all the equipment, how much weight, water type and how you felt about your weighting. This makes a great guide to how much weight you need when diving conditions change.

 

[MarcHall]

A typical single tank goes thru about a 6lb buouancy shift from full to empty. This is true of Al and Steel tanks. It's the weight of the air.

You only need to have as much weight as is required to maintain your deco stop
(aka safety stop) at 10 feet at the end of the dive when your tank is near empty. Any additional weight will need to be offset by inflating your wings or BC during the dive. With more air in your wings or BC the less streamlined you are and you will spend more energy swimming and consume more gas resulting in a shorter dive.

Marc Hall
www.enjoythedive.com

 

[Big-t-2538]

SCUBedoobedoo once bubbled...
thanks for all of the info! it'l take a little while to process it all :doctor: in the meantime, i'm 5'9, 150 lb., 7mm wetsuit, 80ci tank, 5mm gloves, and a bibbed hood.

We usually tell our students (similar exposure protection to you....some have johns & shortys....others have what you have) 10% of their body weight....plus 2 or 3 as a MAX starting point. so I would suggest starting with no more than 18lbs of lead and going from there.

Next, at the end of one of your dives, bleed your tank to 500psi...go to 10 ft. Exhale completely, dump all the gas out of your BC/wing/etc. IF you sink...you can lose more weight....if not, you are properly weighted.

 

[SCUBedoobedoo]

thanks for all the good info!