Oceanlog 2.1.8 SAC calculation problem

[vondo]

OK - 2.2.0 is ready for scubaboard review -

Oceanic Worldwide - Owner Services - Software

Ok, I couldn't resist downloading this and checking out. Here are some concrete comments:

1) Switching between metric and imperial still displays nonsense for the tank in the units you did not enter it in. This is due to the way tanks are referred to in metric and imperial. I think I explained this above, but if it doesn't make sense, please ask.

2) Dive and Dive Details in the menu bar don't accurately describe what they are. One is the details or the summary (the one labeled "Dive") and the other is the graph or "Dive Data" perhaps. Please re-think the names of these things. I'd suggest "Dive Summary" and "Dive Data." I'm constantly clicking on the wrong thing.

3) In "Dive", the Location should restrict the Dive Site pulldown. If I've told OL that I was diving in Key Largo, I don't need to select from a list of sites that includes dive sites in Thailand.

4) I would like to see my average SAC under "History"

5) Although I can query on my SAC under Queries, it doesn't display it in the resulting list. (I want to figure out my average SAC for dives deeper than 40').

More later.....

 

[ocpaul]

OK - 2.2.0 is ready for scubaboard review -

Oceanic Worldwide - Owner Services - Software

Doug,

Downloaded, installed and ran version 2.2.0 this AM. Imperial SAC calculation appears to be correct. I then switched units to metric. All of the conversions (psi to bar, cubic feet to liters and feet to meters) appear to be correct, but the SAC calculation in metric cannot be right.

As an example, I had a dive that started at 3052 psi, ended at 734 psi, averaged 69.26feet deep, and lasted 44 minutes. Tank working pressure was 3000 and size was 77.8 cubit feet. This results in a SAC of 0.441 cubic feet / minute, a value that appears to be correct.

Switching over to metric gives 210.4 bar start, 50.6 bar end, 2203 liter cylinder size, 21.11 meter average depth - all of those values appear to be correct. However SAC calculates to 2572 liters / minute - a nonsensical value since the 2203 liter tank would be drained in less than a minute! 0.441 cubic feet / minute is about 12.5 liters / minute.

 

[vondo]

Doug,

Downloaded, installed and ran version 2.2.0 this AM. Imperial SAC calculation appears to be correct. I then switched units to metric. All of the conversions (psi to bar, cubic feet to liters and feet to meters) appear to be correct, but the SAC calculation in metric cannot be right.

As an example, I had a dive that started at 3052 psi, ended at 734 psi, averaged 69.26feet deep, and lasted 44 minutes. Tank working pressure was 3000 and size was 77.8 cubit feet. This results in a SAC of 0.441 cubic feet / minute, a value that appears to be correct.

Switching over to metric gives 210.4 bar starat, 50.6 bar end, 2203 liter cylinder size, 21.11 meter average depth - all of those values appear to be correct. However SAC calculates to 2572 liters / minute - a nonsensical since the 2203 liter tank would be drained in less than a minute!

Yes, this is one effect of OL not understanding how tank sizes are different in metric and imperial. Your tank is not 2203L, it is 2203/(working pressure in bar). Assuming you had a full fill, not over or under, your tank is about 10.5L.

 

[Dan Watkins]

doug, can you add the 's' and submit 2.2.1?

Thats probably not neccessary from Oceanic's side. It's their text output, they have the right to put it in whatever format they want.

The fact that it messes up a 3rd party app isn't neccessarily Oceanic's issue, it's the 3rd party app's responsibiliity to adjust, imho.

 

[ScubaMarc]

I wrote a excel spreadsheet that will read the oceanlog database and displays many graphs.

If you would like to try it. download it here: http://www.mwdives.com/dive.zip

 

[ocpaul]

Yes, this is one effect of OL not understanding how tank sizes are different in metric and imperial. Your tank is not 2203L, it is 2203/(working pressure in bar). Assuming you had a full fill, not over or under, your tank is about 10.5L.

Sorry Vondo - what does OL mean?

77.8 cubic feet is indeed 2203 liters, both values at 1 atmosphere.

3000 psi is 204.1 atm, so 2203 liters at 1 atm would be 10.79 liters at 204.1 atm. That all makes sense to me.

So I guess the real problem is the calculation of the "cylinder size" in metric as a conversion from Imperial.

If I enter the cylinder size as 10.79, the SAC then calculates to 12.815 liters / minute which is 0.452 cubic feet / minute, which is certainly starting to get close to the originally calculated value of 0.441 cubic feet / minute.

OC

 

[vondo]

Sorry Vondo - simply don't understand what you are saying. 77.8 cubic feet is indeed 2203 liters. If a full tank is 10.5 liters, you are not going to have a very long dive!

Metric people measure a tank by the volume of the inside of the tank, not how much compressed air it holds.

So, in metric the total quantity of air held in the tank is (Volume in L)*(Pressure in Bar) and the amount of air used in L is (Volume)*(Begin Pressure - End Pressure). You'll notice the rated pressure of the tank is nowhere in the calculations needed in metric for the SAC. Personally I think this is easier.

But if you ask a European "How big is your tank?" They don't say "80 c.f." (to mis-quote Jules, "No man, they got the metric system. They wouldn't know what the **** a cubic foot is!")

The also don't say 2200 liters. They say "10.5L" or "12L."

In any case, software should adjust to this difference in specification.

"It's the little differences."

 

[ocpaul]

Metric people measure a tank by the volume of the inside of the tank, not how much compressed air it holds.

So, in metric the total quantity of air held in the tank is (Volume in L)*(Pressure in Bar) and the amount of air used in L is (Volume)*(Begin Pressure - End Pressure). You'll notice the rated pressure of the tank is nowhere in the calculations needed in metric for the SAC. Personally I think this is easier.

But if you ask a European "How big is your tank?" They don't say "80 c.f." (to mis-quote Jules, "No man, they got the metric system. They wouldn't know what the **** a cubic foot is!")

The also don't say 2200 liters. They say "10.5L" or "12L."

In any case, software should adjust to this difference in specification.

"It's the little differences."

Yep - figured that out on my own - I revised my post almost immediately - you must have read it and responded prior to my repost.

OC

 

[vondo]

Yep - figured that out on my own - I revised my post almost immediately - you must have read it and responded prior to my repost.

OC

Yes, I must have. By OL I mean Ocean Log.

As for why the calculations don't quite agree, a bar is not quite an atm, I think, and I get 207 bar. That closes half the distance.

 

[ocpaul]

Yes, I must have. By OL I mean Ocean Log.

As for why the calculations don't quite agree, a bar is not quite an atm, I think, and I get 207 bar. That closes half the distance.

Learn something every day! I must admit I always thought bar and atm were the same thing - I see that they are slightly different as you noted.