Mares Dive Organizer consumption spike at start of dive?

[zoranb]

Hello,

I've noticed that every single of my dives logged with the Icon HD Net Ready starts with a huge consumption spike in the range 122 - 190 L/min.


Has anyone else noticed this?

Z

 

[Kharon]

Don't know that I'd take it too seriously. There are at least one serious and many more trivial math errors in Dive Organizer (which Mares seems uninclined to fix). It almost seems like the programming is being done in Integer Basic. Some of the errors are that crude.

 

[Jim-SAR]

I'm not sure how it calculates the usage, so I'm not sure if it's measuring your usage before you enter the water and actually "start" your dive? If it is, then maybe the spike is from filling the BCD prior to your entry. Or it could be the air you add to your BCD when you reach your depth, and then again when you surface at the end of the dive.

 

[pasley]

You add air to your BCD at the start of the dive during your decent and more as your are approaching the depth you want to level off at. That will show up in your consumption of air as the computer is not looking at where the air goes, only the reduction in PSI.

 

[fda483]

Not sure where you dive but it could be do to the pressure drop as your tank cools at the start of a dive.

Joe

 

[zoranb]

Hey guys/gals,

Thanks for the suggestions.

Without Mares confirming I can't be sure, but my guess is that the consumption is based on the calculation of the difference in tank pressure at certain depth.

It makes sense the starting consumption is higher, but it's not from the cooling of the tank. I've ruled that one out as with the last couple of dives, I've been in the sea (on the surface) for a couple of minutes before diving.

I also thought it might be the BCD inflating, as mine is quite big (large volume), and I tend to start the dive completely deflated, and inflate at the level-off depth, but I tried starting the dive with some air in the BCD and using fins, but the spike is still there...

Looking at the physics of it does make sense.

The pressure difference in the First couple of meteres is the highest, so the difference in the consumed air (calculated as surface consumtpion) will therefore also be the highest...

Z

 

[brutus_scuba]

surface Consumption is normalized for the surface and math is math!

 

[Kharon]

... Looking at the physics of it does make sense.

The pressure difference in the First couple of meteres is the highest, so the difference in the consumed air (calculated as surface consumtpion) will therefore also be the highest...

Correct - but you should observe a spike going down and a negative spike coming up (pressure drop) if that's the reason.

 

[zoranb]

@Kharon
And I don't, which is why this puzzles me...

 

[Kharon]

Only thing I can think of for not having the negative spike going up is the difference in pressure. If it's a set percentage of the pressure then going down (lets use 10% to make it easy) going down with 3000psi it's a 300 psi change and coming up (@500psi) it would only be a 50 psi change. Maybe it's there but too small to see?

Here's a couple of experiments I'd try (depending on how curious you are): Do you get the spike if you drop to 10' and hang there? What happens if you drop to 30' then come right back up (essentially the same pressure up and down)?