Spreadsheet for helping pick a pony bottle

[johndiver999]

I’m still thinking about it, wish I was better at math, but still think there is an issue in the logic, but can’t quite get there.

In any case, your table is very useful and shows the required components and allows a valid estimate of air needed. The issue I’m looking at makes no material difference. The real unknowns are the rmv and precise control of ascent rate, and these are unavoidably imprecise estimates necessary to get an answer.

 

[scubadada]

I’m still thinking about it, wish I was better at math, but still think there is an issue in the logic, but can’t quite get there.

In any case, your table is very useful and shows the required components and allows a valid estimate of air needed. The issue I’m looking at makes no material difference. The real unknowns are the rmv and precise control of ascent rate, and these are unavoidably imprecise estimates necessary to get an answer.

Your example of direct surface from 130 feet works the same way

You ascend 130 feet, half of that is 65 feet
From the bottom 130-65=65
From the surface 0+65=65

 

[wetb4igetinthewater]

You are correct, here is the correct version of the spreadsheet, thanks you are quick

View attachment 504748

I don't see the point of dividing up to the ascent to safety stop and from the safety stop to the surface. It doesn't change the final numbers and adds unnecessary complexity.

I'll spin this spreadsheet and upload. If I can't replace, I'll just start another thread referencing this one.

 

[scubadada]

I don't see the point of dividing up to the ascent to safety stop and from the safety stop to the surface. It doesn't change the final numbers and adds unnecessary complexity.

I'll spin this spreadsheet and upload. If I can't replace, I'll just start another thread referencing this one.

I agree with you, conceptually, to illustrate all the phases of ascent. Combining the 2 segments of ascent would look like this

For more complex ascents, gas switches for instance, it is necessary to break the ascent into all the segments to calculate gas use. The ability to do so is requisite, just not required in this case.

 

[johndiver999]

You need to break up the ascent so as to be able to account for a safety stop of duration 0 to x minutes. This is useful information and helps the user to decide if he can afford one or not. Similar for the delay in initiation of ascent time

 

[wetb4igetinthewater]

You need to break up the ascent so as to be able to account for a safety stop of duration 0 to x minutes. This is useful information and helps the user to decide if he can afford one or not. Similar for the delay in initiation of ascent time

Absolutely. Just no need to break up the ascent into two parts. Will post later the updated spreadsheet for users to specify in addition the safety stop time and time to prepare to ascend.

 

[johndiver999]

I apologize for my mistake wrt to calculation of the average depth during the initial ascent. Scubadada presented the correct method and I got tripped up on erroneous thinking of a simple concept. It took a good bit of pm explanation from him to get through to me:

 

[wetb4igetinthewater]

I apologize for my mistake wrt to calculation of the average depth during the initial ascent. Scubadada presented the correct method and I got tripped up on erroneous thinking of a simple concept. It took a good bit of pm explanation from him to get through to me:

Working on the next rev. Need to shovel some snow first.

 

[wetb4igetinthewater]

So I have a new version that takes into adding time at depth and adding a safety stop. Just need to figure out how to address when values go negative due to insufficient capacity.

 

[johndiver999]

Why not just have simple input and simple output. the output only needs to be the volume used, we don't need tabulations for the various bottles. I like the idea of seeing the volume used on each phase of the ascent, so the user can adjust those values and see the exact effect - like scubadada did. I don't think it adds value to tabulate a whole slew of ascent rates, just have the user enter the one he wants.. would make it far easier to understand.

Also, if you wanted to improve the flexibility of the calculation, you might consider having three different multipliers for the RMV/SAC corresponding to bottom, ascent and (safety stop and ascent from 15 feet). It is quite reasonable to assume that initially the breathing rate would be elevated, but by the time the diver reaches the safety stop, their respiration should/could return to a more normal value.