New Shearwater AI transmitter - the Swift

[Diving Dubai]

Bravo! RTFM wins again. Thanks!

One other thing is that the gas consumption at the beginning of a dive can be off based on the initial inflation of the BC while descending.

Which is the reason stated in the manual
View attachment 674380

I would argue, that the first 5 mins of a dive offer provides rather meaningless SAC, given all the above and the time it can take for a diver to relax'

gtr is a guess at a constantly moving target.

Pretty much what I've been pointing out all along, and as the manuals state, it's only based upon the last 2 mins of data anyway people should watch what happens if they inflate a dsmb from a reg, GTR crashes until that data sample disappears and normal service is resumed

 

[Hoag]

Of course GTR is an approximation. It is the DC's best guess based on available information at the time and it has no way of predicting the future aspects of the dive profile. The same it true of the NDL, but NDL is looked at as if it was gospel. NDL will fluctuate if you go up or down a few feet (or more).

Both of these times have their uses and they are both approximations based on the best available info at a given time. They give the diver an indication of how much time they have before they either run out of gas or start to incur a deco requirement. Some divers will be hard on their air in which case GTR will be the limiting factor. Others may be good on their air and may find NDL is their limiting factor. Both readouts provide relevant information based on what has occurred up until that point.

 

[scubadada]

So this ATR/GTR, SAC, RMV topic has proven to be of interest to several of us.

I have over 2000 dives with Oceanic computers reporting out ATR. I've been diving a VT3 since 2010, the vast majority of those dives. The ATR is displayed on the computer during the dive. I do not get start pressure, end pressure, average depth, SAC, or RMV until I download the dives. I'm still using the OceanLog application, more than adequate for my use.

I only have 266 dives on my Shearwater Teric. The GTR is displayed on the computer during the dive, current SAC can also be viewed. The start pressure, end pressure, average depth, and SAC can all be found in the onboard log or after downloading, I've been using the Shearwater Cloud applications. RMV must be calculated by multiplying the SAC by the tank factor.

I dive the VT3 and the Teric using a single PPS transmitter, they receive identical information. The start pressures, end pressures, average depth, SACs and RMVs are essentially identical for the two computers.

For my VT3, I am able to see the ATR at any point in a dive from the dive details in the download, marked with the red arrow. The dive time remainig (NDL) is marked with the yellow arrow.

Unfortunately, I don't see that you can review GTR during the dive on the Shearwater download to compare. I'll have to do it the old fashioned way

Edit: I just heard back from PPS and they do not correct for deviations from the ideal gas law

Morales (Pelagic Pressure Systems)

Aug 3, 2021, 11:02 MST

Hi,
Please accept our apology for the misunderstanding. Pelagic Pressure Systems air time remaining algorithms do not correct for nonlinear compression of gas at higher pressures.

Kind regards,
Support team

 

[Hoag]

So this ATR/GTR, SAC, RMV topic has proven to be of interest to several of us.

I have over 2000 dives with Oceanic computers reporting out ATR. I've been diving a VT3 since 2010, the vast majority of those dives. The ATR is displayed on the computer during the dive. I do not get start pressure, end pressure, average depth, SAC, or RMV until I download the dives. I'm still using the OceanLog application, more than adequate for my use.

I only have 266 dives on my Shearwater Teric. The GTR is displayed on the computer during the dive, current SAC can also be viewed. The start pressure, end pressure, average depth, and SAC can all be found in the onboard log or after downloading, I've been using the Shearwater Cloud applications. RMV must be calculated by multiplying the SAC by the tank factor.

I dive the VT3 and the Teric using a single PPS transmitter, they receive identical information. The start pressures, end pressures, average depth, SACs and RMVs are essentially identical for the two computers.

For my VT3, I am able to see the ATR at any point in a dive from the dive details in the download, marked with the red arrow. The dive time remainig (NDL) is marked with the yellow arrow.

View attachment 674416
View attachment 674417 View attachment 674419

Unfortunately, I don't see that you can review GTR during the dive on the Shearwater download to compare. I'll have to do it the old fashioned way

I am not disputing that in the example which you gave, the DTR would be the NDL, however, IIRC, the DTR is the lesser of ATR and NDL for Oceanic. At least that is how I think it was on my PP3.

 

[scubadada]

I am not disputing that in the example which you gave, the DTR would be the NDL, however, IIRC, the DTR is the lesser of ATR and NDL for Oceanic. At least that is how I think it was on my PP3.

Hi @Hoag

What you say is true of the computer display. On the main screen, the lesser of NDL or ATR will be shown, the other is shown on the 1st alternate screen.

In the downloaded log, the ATR is always the ATR and the dive time remaining is the NDL. This is from the same dive I posted above, later in the dive, at a shallow depth. My ATR is around 40 min while the NDL is very long at this depth. Just the way the downloaded log is constructed.

 

[Wibble]

@scubadada - curious as to what kind of dive that is. Is it a wreck where you go around the bottom and come up to the deck?

 

[scubadada]

@scubadada - curious as to what kind of dive that is. Is it a wreck where you go around the bottom and come up to the deck?

No, this dive was out at Malpelo, just more than 300 miles off the coast of Colombia. Like Cocos, only accessible by boat, a 30+ hour cruise. This particular dive started at the islet of D'Artagnan, north of the main island. We went down to the bottom for interaction with Galapagos Sharks, and there were plenty. The rest of the dive is around the three islets known as the Three Musketeers, Athos, Portos, and Aramis. Here we interacted with huge schools of fish, Bonito, Jacks, Mullet Snapper.

 

[Wibble]

No, this dive was out at Malpelo, just more than 300 miles off the coast of Colombia. Like Cocos, only accessible by boat, a 30+ hour cruise. This particular dive started at the islet of D'Artagnon, north of the main island. We went down to the bottom for interaction with Galapagos Sharks, and there were plenty. The rest of the dive is around the three islets known as the Three Musketeers, Athos, Portos, and Aramis. Here we interacted with huge schools of fish, Bonito, Jacks, Mullet Snapper.

I bet you'll use words like warm, clear, blue water too!

Thanks - means I can live my life vicariously through other people's dives -- one day we'll be able to travel the globe and I can try for myself! Sounds a great site.

 

[scubadada]

I bet you'll use words like warm, clear, blue water too!

Thanks - means I can live my life vicariously through other people's dives -- one day we'll be able to travel the globe and I can try for myself! Sounds a great site.

Actually, this is the most wild place I've dived. I've dived Red Sea, Cocos, Galapagos, and Revillagigedos. There was current, very strong at times, surge, tremendous at times, thermoclines with 10 degree F changes, and visibilty changes between blue 100 feet and green 20 feet. However, there was a huge number of Galapagos sharks, a fair number of hammerheads, several whale sharks, a large number of Eagle Rays, and a humongous number of schooling fish and usual reef fish. For me, this was the best diving I've ever had.

 

[ATJ]

My point is also a very simple concept too: having too much information means that you're overloaded and may come to over rely on that information when it's clearly inaccurate.

You are making too many assumptions about me and my dives!

First of all, I am not receiving too much information and I am far from overloaded. In fact, I have selected just the information I need and it is perfect.

Second, as I have said a number of times already, the GTR from the Oceanic computers is accurate. I have done hundreds of dives with Oceanic computers have have found these data to be extremely useful on my dives.

In fact, for most of my dives at my regular dive sites I really only concentrate on three data: GTR (on the Oceanic), elapsed dive time and NDL. Almost all my dives are non-deco and my most frequently dived site I usually dive with EAN25% and really don't have to worry about NDL. On my last dive at that site, my NDL never got below 30 minutes!

For me, GTR gives me more information that my tank pressure or SAC. About the only time I look at the tank pressure is if the GTR is higher or lower than I expect at that time of the dive and I check the tank pressure ton understand why it is not what I expected - which is usually a short burst of exertion.

I cannot remember a single dive where the bottom phase is constant depth, stress and workload. It's different for an hour of deco at 6m/20' where nothing changes.

Clearly, your diving is not even close to my diving. For a large number of my dives I stay with in a narrow depth band for the whole dive (other than descent at the start of the dive and ascent at the end of the dive). Sure, there are small changes in depth (plus or minus 2 metres) but these changes make little difference to the GTR and what changes they do make are obvious and understandable. My workload barely changes on a dive. Certainly, if there is current or surge I use more air but that those conditions tend to be consistent for my dives and so, again, the GTR is consistent and understandable.

As has been said before; this is a philosophical discussion. You like more info that has variable quality, I like more relevant information that is useful to me. TTS is pretty accurate, certainly within 20%. GTR is highly inaccurate until the deco phase. My planning is accurate enough for risk aversion and is backed up by appropriate contingency.

Again, you are making assumptions about me and my diving.

For me and my diving TTS gives me very little value at all. As most of my dives are non-deco, all that TTS tells me is how quickly I could surface right now. Why would I care about knowing how quickly I could surface when I'm 10 minutes into a 2 hour dive? TTS also doesn't give any indication how long my gas is going to last.

Perhaps, the only time TTS MAY be of value is that if I went into deco, however, I would rather know what my deco commitment (what depth and how long) is rather than how quickly I could surface. Interestingly, TTS would be useful in conjunction with GTR as you could make sure you have enough gas to surface as slow as you need to surface. i.e. you have a problem if TTS is greater than GTR.