CAT calculation for GUE Fundies

[C Dub]

I didn't read the whole threat. But is this new? I wasn't taught this back. We were taught using the normal ascent profile for calculation, with higher SAC and additional minute for failure handling

I'm not an instructor, just a recent T2 guy, so grain of salt. The point of the new CAT formula is that you can get rid of all the variable ascent rates and profiles, which vary from Rec, to T1, and T2. You ignore them completely, and just use the same methodology (10fpm ascent rate), and a lower SCR of 0.75cfm per diver instead of 1.0cfm per diver. This just came out in the last batch up updates for the class materials. It is much easier to calculate, and is consistent as you progress from Rec to Tech1 to Tech 2.

 

[mer]

The SCR used in the new CAT method is 0.75cf/min (20L/min) at MINIMUM. Divers need to consider the environment, equipment, and experience level of their team and determine an appropriate SCR to use when calculating minimum gas. For some divers/situations, 0.75cf/min will not be enough.

 

[mainedvr]

I didn't read the whole threat. But is this new? I wasn't taught this back. We were taught using the normal ascent profile for calculation, with higher SAC and additional minute for failure handling

Yes its new (passing on information I have received from a GUE instructor) basically when figuring MG (only) you would use 0.75 cuft per min (old was 1 cuft per min), and instead of using the accent profile time to figure min gas you would use 1 min for every 10' of depth+1' and then the average ATA. So the SCR was lowered and the time was increased. But as I was told and is in the thread its for planning min gas. The accent profile stays the same at 30' per min to 1/2 max depth then 10' per min to surface.

When I first saw it it threw me off I had started studing two years ago and did not finish the class. Now that I finally am going to do it I started to go over the new worksheets and saw this. I have been using MG when planning so it was one of those things that make me go HMMM


Thanks again for all the input

 

[KevinNM]

The SCR used in the new CAT method is 0.75cf/min (20L/min) at MINIMUM. Divers need to consider the environment, equipment, and experience level of their team and determine an appropriate SCR to use when calculating minimum gas. For some divers/situations, 0.75cf/min will not be enough.

I remember someone asking us pointed questions about how long it took for us to actually do a team ascent vs how long should it have taken per our planning...

 

[Kevrumbo]

We tried to simplify it, across the board (rec 1 all the way to Tech 2) so we have one min gas calc that you don't need to remember ascent rules of thumb etc to use.

I'm not an instructor, just a recent T2 guy, so grain of salt. The point of the new CAT formula is that you can get rid of all the variable ascent rates and profiles, which vary from Rec, to T1, and T2. You ignore them completely, and just use the same methodology (10fpm ascent rate), and a lower SCR of 0.75cfm per diver instead of 1.0cfm per diver. This just came out in the last batch up updates for the class materials. It is much easier to calculate, and is consistent as you progress from Rec to Tech1 to Tech 2.

The SCR used in the new CAT method is 0.75cf/min (20L/min) at MINIMUM. Divers need to consider the environment, equipment, and experience level of their team and determine an appropriate SCR to use when calculating minimum gas. For some divers/situations, 0.75cf/min will not be enough.

You'll have to forgive me a little as I tend to work in metric, but no.

2 x 0.75 x 2.5 x 11
Use normal SCR for this calculation, so it should come out similar to the old calculation.

Recreational -Minimum Gas Reserve (MGR),
"CAT" vs old "Rock Bottom":

So as I understand it, the New GUE CAT using 100'/30m for example:

100'/30m, 1min;
(Ascent rate 10fpm, same as 3 meters per min, to surface takes -->10min);
Time to Ascend is 10 plus 1 equals 11min.

Therefore given the new Surface Consumption Rate (SCR) of 0.75 cfm, same as 20 liters per min,
CAT = 0.75 x 2 divers x 2.5 ATA x 11min = 41.25 cuft or 1200 liters in metric.

So the new ascent strategy in a gas sharing contingency (after 1 minute at operational depth to problem solve) is a 30 second hold/30 seconds to ascend for every delta 10'/3m from operational depth -for an ascent rate of 10 fpm (3mpm).

A somewhat simpler rote ascent rate, tactical wise, than UTD's Rock Bottom. . .

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By comparison for the 100'/30m example,
UTD recreational Rock Bottom procedure still retains the ascent strategy 30 fpm/9mpm rate from operational depth to 50% max operational depth, then 10 fpm/3mpm from there to the surface, and using the higher SCR of 1 cfm (30 liters per min):

Rock Bottom = 1 x 2 divers x 2.5 ATA x 8min = 40 cf or 1200 liters in metric.

(See 14:30 mark in video below):

 

[KeesBL]

So the new ascent strategy in a gas sharing contingency (after 1 minute at operational depth to problem solve) is a 30 second hold/30 seconds to ascend for every delta 10'/3m from operational depth -for an ascent rate of 10 fpm (3mpm).

A somewhat simpler rote ascent rate, tactical wise, than UTD's Rock Bottom. . .

A point of clarification: GUE's recommended minimum decompression profile hasn't changed with the introduction of the CAT formula. The CAT formula is intended only to be a conservative way of easily calculating minimum gas, and does not mirror the minimum decompression ascent profile perfectly.