New diver: Suggested conservatism settings for a Petrel?

[victorzamora]

When I compared my computers, I was using the default CF which on the Oceanic Pro Plus 3 is 0 and used DSAT. I also have an older veo 100 which I compared to, which previously I compared to my ancient Oceanic (1996 era). Those 3 computers compared similar. I then was trying to match my Shearwater in Rec mode to the rest of my family. I found that in all settings (even Low CF on Shearwater), the Shearwater was more conservative. I also found that using Z+ (CF 0) on PP3, the Shearwater was closest, differing by a minute or 2 to the conservative side.

I will need to go home tonight and run the numbers like croomrider.

Well the DSAT algorithm is a liberal algorithm for recreational divers that punishes depth and punishes ndl breaches. That's why the gap was closing as you increased the depth.

Pelagic Z+ is based on the Buhlmann that the Petrel is running..... which is why it closely matched the Petrel. I believe that with the right GFs, you can practically dive identical algorithms.

 

[packrat12]

Well the DSAT algorithm is a liberal algorithm for recreational divers that punishes depth and punishes ndl breaches. That's why the gap was closing as you increased the depth.

Pelagic Z+ is based on the Buhlmann that the Petrel is running..... which is why it closely matched the Petrel. I believe that with the right GFs, you can practically dive identical algorithms.

Yea that was also what I expected. My recreational rig is using my PP3 as the SPG. I still like to wear an use my Petrel as my primary computer and the PP3 as my backup. As a result of this, I use Z+ to match my computers and am now more conservative then my family :depressed: go figure. I have not checked how DSAT CFs work out with the Petrel settings either but I assume that in the end, the DSAT will still remain more liberal. All in all, this is indicating that any of the Low/Med/High settings of the Petrel settings should allow sufficient margin to DCS that they are all usable in the Rec mode, with Doppler's caution that is.

---------- Post added August 14th, 2014 at 09:29 AM ----------

I'm guessing you have nitrox gasses entered and turned on. The planner appears to default to the highest active mix.

This is the thing that users must be aware of with multi-gas computers, defiantly Shearwaters. They will plan for the best gas mix for the depth. Any indication of time to surface will include gas switching to the best gas mix for the depth and as you stated, NDL will also be calculated to best gas mix. Shearwater recommends turning off any gas you are not carrying, whether in Tech or Rec mode. One nice feature is that you can always set a new gas if necessary during a dive.

They are a well designed computer and they are very capable.

 

[DuboisP]

I'm guessing you have nitrox gasses entered and turned on. The planner appears to default to the highest active mix.

I agree
153 min at 50 feet without stop can be done with an EanX 32%, according my tables.

 

[rhwestfall]

Again, it is very important to read, re-read, and read again the manual. It is an awesome computer, but you need to be able to comprehend what it is showing you, and recognize if something just doesn't appear "normal". It has the ability to get you out of in trouble, but can also get you in trouble as it does not know your diving abilities or knowledge, nor can it verify you are equipped the way it is configured. It is up to you to operate it within the parameters of your diving.....

Magic Bracelet Syndrome.....

 

[DuboisP]

imho, we don't learn diving and decompressing by reading the dive computer manual.
learn first principles of physic, then read and read again the manual to know how it's applied.

 

[packrat12]

I looked at my computers:

50/60/70/80/90/100/110/120/130/140/150/160 Depth
81/57/40/30/24/019/016/013/011/009/008/007 Veo 100
76/51/35/25/19/015/012/009/008/006/005/004 Shearwater CF: Low
65/48/35/26/19/016/012/010/008/007/006/006 PP3 Z+ CF:0
81/57/40/30/24/019/016/013/011/009/008/007 PP3 DSAT CF:0

The DSAT CF:0 is default. It is considerably for conservative for NDL type diving. I cannot compare it to repetitive NDL diving. The Veo100 is an older computer matches an older yet computer that I have performed many dives to NDL on. Overall, the Shearwater is much more conservative even in CF:Low settings and considering doing a SS will improve the margin.

 

[C Dub]

Packrat, wow man, thanks for taking the time to check and type all that!!

This thread is making me more and more comfortable starting with "medium", and then doing as Doppler posted early on.

Anyone else have other computers and would be willing to post up a table???

I looked at my computers:

50/60/70/80/90/100/110/120/130/140/150/160 Depth
81/57/40/30/24/019/016/013/011/009/008/007 Veo 100
76/51/35/25/19/015/012/009/008/006/005/004 Shearwater CF: Low
65/48/35/26/19/016/012/010/008/007/006/006 PP3 Z+ CF:0
81/57/40/30/24/019/016/013/011/009/008/007 PP3 DSAT CF:0

The DSAT CF:0 is default. It is considerably for conservative for NDL type diving. I cannot compare it to repetitive NDL diving. The Veo100 is an older computer matches an older yet computer that I have performed many dives to NDL on. Overall, the Shearwater is much more conservative even in CF:Low settings and considering doing a SS will improve the margin.

 

[mruseless]

In case anyone is interested, here are the plan numbers from my D9 compared to my Petrel (another new Petrel owner!) Air numbers are NDL's starting at 60 ft and going to 130ft. 32% Nitrox numbers are from 60 ft to 100 ft (Suunto MOD on 32% is 106ft so the planner won't go below 100).

Gas: Air
Depth--------------60---70---80---90---100---110---120---130
D9-----------------50---36---28---22----17----13----10-----9
Petrel (45/95)-----45---31---22---17----13----10-----8-----7
Petrel (40/85)-----36---24---18---13----10-----8-----7-----5
Petrel (35/75)-----27---19---13---10-----8-----6-----5-----4


Gas: 32% Nitrox
D9-----------------75---55---41---32----26
Petrel (45/95)-----74---52---37---28----21
Petrel (40/85)-----63---42---30---22----17
Petrel (35/75)-----50---33---23---17----13

 

[cidcolada]

This conversation got me wondering about my Tusa Sapience II.

Air:
Depth------50---60---70---80---90---100---110---120---130
NDL CF-0--70---51---37---27---21--- 17---- 15--- 12--- 10
NDL CF-1--62---46---34---25---19--- 16--- 14--- 11--- 10

EaN32:
Depth------50---60---70---80---90---100--110
CF-0------130---79---59---44---35--- 26--- 21
CF-1------107---70---53---40---32--- 24--- 19

The Sapience II uses a TUSA Algorithm based on the 12 compartment Swiss-Bohrer model

 

[mruseless]

I was quite surprised when I found out the Petrel Recreational Nitrox Mode is more conservative than my D9, even when set to 45/95. The Suunto is routinely lampooned for being too conservative.