View Full Version : Pls. Somebody post a good question

No Misses

03-17-2008, 12:54

I have zero ambition for work today. So, please post a good question that will cause me to do some research on my favorite subject (diving).

P.S. I got in late yesterday. check out the reason on the brags thread http://forum.scubatoys.com/hunting-gathering/10483-post-you-best-catches-bragg-about-them.html

ScubaToys Larry

03-17-2008, 13:48

I have a 400 pound object that is sitting in 85 feet of water - in the ocean - and it takes up 1 cubic foot of space. I have a small 2 cfm compressor that burns a pint of gas every 10 minutes. If I hook up an air lift bag to my object, and pump air down from the boat at the surface... how much gas will I need to get to get this thing coming up... and with the price of gas... I don't want to buy any more than what I need.

(That should take a few minutes.... :smiley2:)

No Misses

03-17-2008, 13:51

Ouch, I think I pulled a frontal lobe.

emcbride81

03-17-2008, 13:58

:eek2:

16.8 pints of gas....I think

No Misses

03-17-2008, 14:33

In honor of St. Patricks day. I will take Chads suggestion of 16.8 Pints and forget that Larry ever posted the algebra question

:fulle::drankere:

If a chicken and a half can lay an egg and a half in a day and a half, how long does it take to cross the road?

No Misses

03-17-2008, 14:38

I have a 400 pound object that is sitting in 85 feet of water - in the ocean - and it takes up 1 cubic foot of space. I have a small 2 cfm compressor that burns a pint of gas every 10 minutes. If I hook up an air lift bag to my object, and pump air down from the boat at the surface... how much gas will I need to get to get this thing coming up... and with the price of gas... I don't want to buy any more than what I need.

(That should take a few minutes.... :smiley2:)

Are you kidding? You don't want to buy more gas than needed? Gas is a great investment. You can buy it today for $3.35 and sell it tomorrow for $4. Show me a stock with that much growth. :smilie39:

WV Diver

03-17-2008, 15:10

It is 10 mins. till quiting time and the boss calls you in.

We have been monitoring your computer and it seems, that over the past 8 months, you have spent and average of 82% of your time posting on a site called Scuba Toys.

Yada, Yada, Yada,

I am so glad we could have this little chat. There are some upcoming layoffs in the near future (5 seconds) and we will no longer your services.

BTW, thanks for making my job easier. :smiley11:

:smiley2: :smilie39:

Joking but I have known of it to happen. Different scenarios but the end result is the same.

WV Diver

03-17-2008, 15:12

I have a 400 pound object that is sitting in 85 feet of water - in the ocean - and it takes up 1 cubic foot of space. I have a small 2 cfm compressor that burns a pint of gas every 10 minutes. If I hook up an air lift bag to my object, and pump air down from the boat at the surface... how much gas will I need to get to get this thing coming up... and with the price of gas... I don't want to buy any more than what I need.

(That should take a few minutes.... :smiley2:)

Are you kidding? You don't want to buy more gas than needed? Gas is a great investment. You can buy it today for $3.35 and sell it tomorrow for $4. Show me a stock with that much growth. :smilie39:

Answer.

You will always need more gas for something. Buy extra because I don't want to make two trips for gas.

And probably what Chad said or there abouts.

doczerothree

03-17-2008, 15:28

Huh!?

cummings66

03-17-2008, 18:14

I'll take a wild stab at it. .2625 pints of fuel.

cummings66

03-17-2008, 18:19

Tell me if I went south somewhere, but here's the guesses.

First, ocean water and displacement math. Ocean water is about 64 lbs per cf. That means our 400 lb object needs a lift of 336 lbs to get neutral. Divide the required lift by cf which is 336/64 and we need 5.25 cf of air. Your compressor puts out 2 cfm so it's going to take 2.265 minutes to fill a bag with that much air. Divide by 10 since it's burning 1 pint every 10 minutes and we get .2625 pints?

I'm hoping I got it right.

Aquatrax

03-17-2008, 19:11

Being in salt water, we know that 64 lbs. of buoyant force is exerted on the object (64 x 1 cubic feet = 64). However, as it weighs 400 lbs., there’s 336 lbs. more negative buoyancy than positive (400 - 64 = 336). Therefore, you must apply an additional 336 lbs. of positive buoyancy to make the object neutral. From the constants, we know that for each cubic foot of air you add to the lift bag, an additional 64 lbs. of positive buoyancy is applied. By dividing 64 into 336 you find that 5.25 cubic feet of displacement will provide the required positive buoyancy to make the object neutrally buoyant. Take the cubic feet needed and divide by 2cfm and we get 2.625 minutes of compressor run time. Divide by ten to get the pints per minute and arrive at 0.2625 pints.

I am new at this so do we need to factor in the diameter of the 85’ hose or the volume difference based on depth?

MY HEAD HURTS!

what is the ambient temperature of the water, and what colour is the lift bag?

Splitlip

03-17-2008, 20:49

I have zero ambition for work today. So, please post a good question that will cause me to do some research on my favorite subject (diving).

P.S. I got in late yesterday. check out the reason on the brags thread http://forum.scubatoys.com/hunting-gathering/10483-post-you-best-catches-bragg-about-them.html

Am I the only one who checked no misses' link?

(great day.)

cummings66

03-17-2008, 21:53

I am new at this so do we need to factor in the diameter of the 85’ hose or the volume difference based on depth?

So, are you agreeing with my post then? You think I did it right?

Doghouse

03-18-2008, 09:11

I have a 400 pound object that is sitting in 85 feet of water - in the ocean - and it takes up 1 cubic foot of space. I have a small 2 cfm compressor that burns a pint of gas every 10 minutes. If I hook up an air lift bag to my object, and pump air down from the boat at the surface... how much gas will I need to get to get this thing coming up... and with the price of gas... I don't want to buy any more than what I need.

(That should take a few minutes.... :smiley2:)

I don't know if this was answered, but I did not want to cheat and look before trying to figure it out.

Please check my theory and inform me of any mistakes.

1. lift of 1cf of air is 64# salt water 62.4 fresh.

2. 85' of water equates roughly to an additional 2.58 atm's

3. I am not including the inefficency that would be generated due to increased pressure.

4. lift needed for 400# is 6.25 cf salt, 6.41 cf fresh at 1 atm

5. lift X atm = 16.125 salt 16.54 fresh

6. 1 cfm is created by 1 pint of fuel, you would need 2 pints for either including a minor safety margin.

cummings66

03-18-2008, 12:12

Your figures for the fuel are wrong. The compressor runs 10 minutes on 1 pint of fuel, it produces 2 cubic feet per minute, that's 20 cubic feet on one pint of fuel. Using 2 pints gives you 40 cubic feet of air.

I also see you forgot to take into consideration the amount of water displaced by the 1cf square block. So the 400 lbs is only 400 lbs above water and under the water it should be lighter because it displaces water.

That much I know, but I'm not 100% my answer is right .

cummings66

03-18-2008, 12:20

I'm not sure where to look for the correct answer, am I being obtuse? Is there an answer posted that I overlooked?

The link was just pictures as far as I could tell, didn't read the whole thing.

And you thought you had time to waste Dave (No misses). :smilie39:

Luckily I can say I didn't have time to read the question.

The correct answer is "D" question did not contan enough information to be solve IE How much BEER are you bringing to get us to jump in the water and fetch your over grown rubixcube?

Aquatrax

03-20-2008, 17:50

I am new at this so do we need to factor in the diameter of the 85’ hose or the volume difference based on depth?

So, are you agreeing with my post then? You think I did it right?

I think so

mark44883

03-20-2008, 20:25

i don't know ,i can't see the guy sitting next to me papper

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