Advanced penetration of the Spiegel Grove Wreck

[scubadada]

Hi @Rearviewmirror

Do you know your average RMV? It can be a powerful tool to help you estimate your gas use. From your graphs, the RMVs shown are on the high side. As you pointed out, your dives on the Spiegel Grove were out of your comfort zone and stressful.

Gas consumption has been discussed frequently on SB. Two examples:

Why Surface with 500 PSI?

Every boat trip, the crew will brief the site before splashing, and finish with the warning, "Be back on the boat with no less than 500 psi in your tank!" Some boats are more dogmatic about it than others, and the consequences of surfacing with less will usually depend upon whether you also...

scubaboard.com

Average Gas Consumption

There has been extensive discussion lately regarding average gas consumption. A poll may help give us a better idea of what the normal distribution of RMVs is. 1 cu ft = 28.32 liters 1 liter = 0.035 cu ft 28.3 l/min

scubaboard.com

 

[Rearviewmirror]

@scubadada I only just upgraded to AI dive computer recently so don't have a huge dataset, but on easy reef dives totally relaxed SAC tends to be at around 0.6-0.7 cuft/min but average SAC for those dives tends to be around 0.75 cuft/min - with a good chunk of heavy consumption happening in the first ~2-3 minutes or if I'm concentrating on taking video of something cool rather than my breathing.

I'm really trying to work on my pre-dive mental visualization, relaxation, and prep to reduce sucking a bunch of gas early, and continue working on my breathing rate. In addition I do want to see if I can go even lighter on dive weights so I'm not spending as much gas on my BCD etc. after initial descent.

Here's a graph of a more "representative" shallow dive (this dive ended as others were low on gas):

 

[scubadada]

Hi @Rearviewmirror

You are right to expect that your gas consumption will improve over time and that the variation will decrease. Continue to follow your RMV and make note of factors that lead to a lower or higher value than usual. Besides exertion, I find that being cold is a major determinate in my gas consumption.

You're on the right track

 

[Rearviewmirror]

Hi @Rearviewmirror

You are right to expect that your gas consumption will improve over time and that the variation will decrease. Continue to follow your RMV and make note of factors that lead to a lower or higher value than usual. Besides exertion, I find that being cold is a major determinate in my gas consumption.

You're on the right track

Thanks @scubadada - honestly after this trip I decided to invest in a 5/4mm wetsuit as by the end of 4 days of diving the cold was getting to me. I think I might just be more susceptible to cold water than some others as most folks seem to dive 3mm in the Keys. I'm hoping that plus playing with my regulator's WOB and concentrating on my technique will yield results.

What would you consider a "good" SAC rate? (I'm going to read through those two threads now, so apologies if that is discussed therein.)

 

[scubadada]

@Rearviewmirror

A good RMV is individual, if you take a look at the thread with the RMV poll, you will see that the average RMV is somewhere in the 0.5s cu ft/min, with a fair amount of variation.

There are many determinants in your gas consumption, some of which are under your control, and some that are not. You can read about them, on SB and elsewhere.

I tolerate cold less well as I have become older. I dive a lot in SE Florida. I have a 3, 5, and 7 mm full suit as well as a 5/3 mm hooded vest. I wear them all every year, covering usual water temperatures from the high 60s to the low-mid 80s. I am fortunate that I have always had a relatively low RMV. It has improved only a little since I started following it routinely in 2010, at about 500 dives. I'm now just short of 2200 dives.

Let us know how you do as your diving progresses

 

[Rearviewmirror]

@Rearviewmirror

A good RMV is individual, if you take a look at the thread with the RMV poll, you will see that the average RMV is somewhere in the 0.5s cu ft/min, with a fair amount of variation.

There are many determinants in your gas consumption, some of which are under your control, and some that are not. You can read about them, on SB and elsewhere.

I tolerate cold less well as I have become older. I dive a lot in SE Florida. I have a 3, 5, and 7 mm full suit as well as a 5/3 mm hooded vest. I wear them all every year, covering usual water temperatures from the high 60s to the low-mid 80s. I am fortunate that I have always had a relatively low RMV. It has improved only a little since I started following it routinely in 2010, at about 500 dives. I'm now just short of 2200 dives.

Let us know how you do as your diving progresses

Thanks a lot Will do - I really appreciate all the constructive criticism and help I've received in this thread. I was a bit nervous to be that vulnerable and post when I possibly hadn't made the best decisions, but I really appreciate the opportunity to learn more for the experienced divers on the site.

 

[Edward3c]

Answers below:

• Yes - the primary guidance given was rule of thirds for the dive (i.e. turn the dive and begin our ascent at 2/3 of gas remaining, indicate when at 50% gas remaining, and keep NDL above 5mins at all times on the dives.
• I wondered about that at the time, but I think potentially his computer was set to a 5min safety stop, whereas I believe my computer adapts based on dive profile (Shearwater Teric) so it's possible my computer only asked for a 3min SS vs his 5min stop. I spent 5mins at that stop, so I'm guessing it was still a safety stop. I think he was diving a Suunto Zoop.
• Gas guidance
  • We did not set a target gas pressure for arrival at the SG - worth saying it was a calm day w/ close to zero current
  • We were not told to be at the surface with a specific pressure
  • 500psi was given as the min pressure for back on the boat
  • So with that said - it sounds like we didn't adequately discuss gas consumption/target pressures.
    

You description of the rule of thirds doesn’t sound like it was being used properly i.e., for a cylinder starting at 3,000psi, 2/3 (2,000psi) turn point, 1/3 (1,000psi) on the surface - not 500psi.

I have used Suunto for over 25 years, all by default ask for a 3 min SS. A SS is not mandatory and can be ignored. Another question it’s worth asking your buddy is what SS are they planning, better to know before you get in.

 

[BlueTrin]

@Rearviewmirror if that makes you feel better about it, I had about the same SAC rate than you, 0.75 (20 litres a min).

Now, I usually have 0.52 - 0.6 depending of how much effort is required during the dive. (15 to 17 litres a min), so it definitely improves as you becomes more efficient …