First Time Pony Bottle, Bouyancy Questions

[Ronniemu]

I am a new diver and for the first time, will be using a pony bottle. Although these questions may seem simple to most, I found out a long time ago, it always helpful and educational to ask the pros. So here goes!

1) I tried a buoyancy check at the surface of my pool with a (80 cu ft HP steel tank) and a 5 mil wetsuit. At the time I had 500 PSI of air left. The weight I needed to be at eye level with no air in my BCD and holding a normal breath was 4 pounds. Using the same configurations in salt water, to my knowledge I would then add 5 pounds additional weight to a total of 9 pounds. Can someone let me know if this would be correct?

2) I purchased a 30 cu ft pony bottle. It has a full buoyancy of (-2.5 pounds). I attached the pony bottle to my gear as listed above and wanted to try the pony bottle in my pool. I removed the 4 pounds of weight that I had installed in my BCD as mentioned above. I then installed 3 pounds of weight in the left side of my BCD as the pony bottle was mounted on the right of my main steel tank. I wanted to balance my gear as the mounting of the pony bottle made everything lopsided. I then tried a buoyancy check at the surface. I was somewhat heavy, I now had a total of 6 pounds (3 lbs of weights in the left side of my BCD and almost 3 pounds of negative buoyancy fro the pony bottle). Instead of the four pounds of needed weight, I now had a total of 6 pounds. Is it correct to say I would now need only three more additional pounds for salt water?

 

[divad]

Is this a trick question?

 

[jeraldjcook]

 

[Nemrod]

You know, I nearly flunked sixth grade thanks to those word problems, I much preferred taunting the girls with bugs and snakes. N

 

[divad]

If that's a Catalina AL 30 then it's about neutral when empty so maybe you shouldn't count the -2.5 lbs as weight and don't really have a question.

 

[TheRedHead]

I find removing 2 lbs with a 30 cf bottle ideal. You don't really need to move any to one side.

 

[TheRedHead]

The difference between fresh and salt is estimated at .015 times your diving weight - body weight plus gear. It is something you'll have to tweak for yourself.

 

[Bruce3]

i dont use a pony bottle but may i suggest you dont take weight off to compensate for your bottle. reason being you might pass the bottle off or need to ditch it. you would still want to maintain proper buoyancy. however like i said ive never dove with a pony but i would imagine. i could be totally wrong.

 

[markfm]

I weight for the pony being empty, but trim (where the weight goes) for clean balance when it's full.

My S19 is close to 0 lb buoyancy empty, so I don't actually need more weight -- it would be OK to move a bit of weight from the front to the back. Full, that's a 1/4 tank, compared to an AL80 -- about 1.5 lb of air. An S30 is similar, effectively neutral when empty, about -2.5 lb full.

End of the day, for me it's a lot easier to not fiddle too much. Put the pony on whichever side you want, then add either 2 or 3 lb to the other side to trim, leave your basic (non pony) weight there (unless you have a turtle issue). At most, you could remove a total of 3 lb of weight from your starting setup, due to the 3 lb going in the trim pocket, but you may find you have a bit of turtle -- too much weight on your back, relative to what's up front.

Removing weight, by counting the gas in the full pony as part of your weight system, is not something I would do. For me, the bailout is supposed to be usable gas in an emergency, which is precisely when I don't want to be short 2 or 3 pounds, unable to maintain a safety stop.

A 5 lb weight change going from fresh to salt is reasonable, for someone in say the 130 - 160 pound range, given their gear is the same. The conversion is about 1/40 (this varies in places like Salt Lake, but is a good starter for most oceans) of total dry weight. A tank is worth 1 lb, so it's then a case of what you on the scale, in all gear (including weights) except tank, weigh. A 145 lb person with about 6 lb of base weight, wetsuit, etc, will be about 160 total; 1/40 of that is 4 lb. 4 lb + 1 lb (tank delta) is 5 lb total.

 

[hudson]

If the pony is strictly for your use, you can remove the weight corresponding to the negative buoyancy of the regulator that's on the pony, which should be around 2lbs (unless the pony is too big for your needs that you don't expect to empty it in which case you can maybe remove another 1lb but that's pushing it). You may also have better results performing your buoyancy checks underwater at 10 or 15ft.