Sudden and uncontrolled acsent.

[radinator]

I'm thinking it's possible they were overweighted (as many many divers are). To compensate for this, there was extra air in the BC, so when his depth changed a little, there was lots of expansion taking place.

If you have 1 liter of air in the bc, and go up a bit, you have 1.1, but if you have 2 liters, and go up the same amount, you have 2.2 (the expansion volume is twice as much, so 2x the change in bouyancy).

At near the end of the dive the weight should be such that you are neutral at 15' with no air in the BC. Since you were close to the end, but deeper, you should have only had a little air in there. I'm guessing you had more than a little bit. Try checking that.

Of course, I could be wrong on everything I've ever said. Just something to check.

 

[H2Andy]

An Al80 will gain less buoyancy than an E7-100, and the SAME amount as an HP-80.

hmmm... ok... i'm missing something then

so when a Luxfer 80 goes from -3.6 to 2.2 bouyancy (net gain 5.8 lbs)

and a Pressed Steel 80 goes from -5.5 to -1 (net gain 4.5 lbs)


they have both gained the same bouyancy?

is it because they are different sizes and are displacing different
amounts of water relative to the weight gained?

 

[H2Andy]

Get a refund from your instructor.

please

 

[pants!]

I'm thinking it's possible they were overweighted (as many many divers are). To compensate for this, there was extra air in the BC, so when his depth changed a little, there was lots of expansion taking place.

Ding ding ding! Brilliant observation and almost certainly true.

Overweighted, lots of extra air in the BC, acrobatics which result in the diver losing SA and ascending a bit = diver in uncontrolled ascent.

 

[pants!]

hmmm... ok... i'm missing something then

so when a Luxfer 80 goes from -3.6 to 2.2 bouyancy (net gain 5.8 lbs)

and a Pressed Steel 80 goes from -5.5 to -1 (net gain 4.5 lbs)


they have both gained the same bouyancy?

is it because they are different sizes and are displacing different
amounts of water relative to the weight gained?

PST HP80 goes from -9.3 to -3.3, net gain 6 lbs.

PST E7-80 goes from -8.5 to -2.5, net gain 6 lbs.

Makes sense because an Al80 holds 77.4cf, slightly less than 80cf, so slightly less shift than the steel 80s which actually hold 80cf.

http://www.huronscuba.com/equipment/scubaCylinderSpecification.html
http://members.aol.com/jsuw3/tankspecs.html

Any chart saying an 80cf tank only gains 4.5 from empty to full is lyinig.

 

[pants!]

PST HP80 goes from -9.3 to -3.3, net gain 6 lbs.

PST E7-80 goes from -8.5 to -2.5, net gain 6 lbs.

Makes sense because an Al80 holds 77.4cf, slightly less than 80cf, so slightly less shift than the steel 80s which actually hold 80cf.

http://www.huronscuba.com/equipment/scubaCylinderSpecification.html
http://members.aol.com/jsuw3/tankspecs.html

Any chart saying an 80cf tank only gains 4.5 from empty to full is lyinig.

Also from those charts, an E8-130 gains 9.8 lbs of buoyancy, and an E7-65 gains 4.9 lbs.

 

[H2Andy]

pants!, but aren't those both steel cylinders?

it's like comparing apples to apples

we were comparing steel and aluminum, and the aluminum has a larger
bouyancy gain (from what i can see) than the steel total and percentage
of original way, either way

 

[Evric]

Thanks for the reply everyone.

Just to clear a few things.
While at 55 feet, we weren't at 500 psi. We had about 5-7 minutes worth of air before getting to 500 psi. Our air planing this time and every other time is to be on the shore or the boat with 500 psi left. My mistake for bad wording at the original post.

Gear,
full 7mm suit, steel air tanks, weighted just enough to go down at the begining.

I have boyancy control, but I have been working on it and its getting better.

Thanks all,
Will practise your advice.

 

[pants!]

pants!, but aren't those both steel cylinders?

it's like comparing apples to apples

we were comparing steel and aluminum, and the aluminum has a larger
bouyancy gain (from what i can see) than the steel total and percentage
of original way, either way

The Al80 gains 5.8 lbs
The HP80 gains 6 lbs

What do you think now?

 

[H2Andy]

wait... you're right

luxfer 80 gains 5.8
luxfer s80 gains 5.9
catalina s80 gains 5.8
catalina c80 gains 5.7