Info A SATurner starts diving*... (*trials and tribulations of a 50+ year old out of shape guy learning to dive)

[SATurner]

Dives #7 and #8: (J&R Wall and Double Head Barrel outside of Belize City, Belize) continued

Dive #8: (Double Head Barrel)
After a surface interval (hour and twenty minutes) which included sandwiches, chips, pineapple, and cookies, it was time for a second dive. We had moved a small distance to the J&R Barrel.

I forgot to mention that the family of 6~8 stayed with their DM in the 30'~40' range while the others with my DM were allowed to go deeper. On the way to the second site, there was spot in the reef where there was a sand bottom with reef on both sides as we swam to the outside of the reef. There wasn't any overhead, but in a few places, the reef on each side got a bit close. Once again, the DM lead and the plan was same as previous, at 1000 psi, head for the anchor, do a safety stop, and exit with 500psi.

On this time, I "hung back" a bit more than on the first one. I also didn't try so hard to go deep. My personal goal was to extend my time a bit. At one point, I found myself at least 10' if not more above the instructor from CA. His exhaust bubbles were really a HUGE bubble along with some little ones. I was having fun popping the HUGE bubble as it rose toward me. Everyone else seemed to have a trail of bubbles while his was like one HUGE one and then a short trail of smaller ones.

Again, not a lot of wild life, but the reef was awesome. There was a green eel that was out for a swim that came toward us and through us, then turned back to check us out for just a second or two. We did see some of the largest lobsters I have ever seen.

On this dive I went to 70.8' and averaged 38'. I was able to stretch my dive out to 39 minutes and 44 seconds. Not a huge extension of time, but to be honest, those five minutes seemed like fifteen.

Then it was time to head back to port, grab a tender and get on the cruise ship. The next day I would wake up in Cozumel for another two dives.

 

[scubadada]

Hi @SATurner

Have you taken the time to calculate your gas consumption in volume/time/atm (RMV or SAC depending on your nomenclature)? It sounds like you might enjoy following improvement in your gas consumption with your continued diving. The value is very helpful in estimating your gas needs.

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

Question - Definitions for SAC and RMV?

This topic comes up over and over. Let's see what you think. Please vote once for SAC and once for RMV or vote for #5 and elaborate in your post or #6 if you don't know what this is all about.

scubaboard.com

Just as an example, if the 2 dives above were dived with an AL80 filled to 3000 psi and you surfaced with 750 psi, the 1st dive would have a RMV in the low 0.8s cu ft/min the the 2nd in the high 0.6s cu ft/min

Best of luck in your diving

 

[SATurner]

@scubadada, great question, and in asking, it pushes me to slow down and learn more. I had read both of the threads you linked earlier, but haven't participated in them.

So, let's go through my 10 dives to date calculating SAC and RMV for each and then come up with an average to date. I will provide data from Shearwater app, SAC calculator from divebuddy, and RMV calculator from chipoladivers. So far all tank sizes have been AL80s. I'll even provide start/end pressures, average depth, average temp, and time.

It's interesting that the three sources seem to be close to one another, but yet not equal. Some of that could be caused by rounding as in the SAC and RMV calculators, I had to round instead of using decimals. Extrapolating that out, it is a matter of breaths, but if underwater and needing one, I'd rather have it than not!

When using the SAC calculator, I used 80 ft³ and 3000psi for tank volume and tank pressure.

When calculating RMV, I used 80 for cylinder and 3000 for rated pressure of cylinder.

Dive 01:
No data due to not having a DC during the dive

Dive 02:
Start Pressure: 2826 psi
End Pressure: 1712 psi
Pressure Change: 1114 psi
Average Depth: 18.5'
Time: 21min 46 sec
Average Temp: 66.2°F
SAC per Shearwater app: 32.88 psi/min
SAC per SAC calculator: 32.1 psi/min
RMV per SAC calculator: .857 ft³/min
RMV per RMV calculator: .8662 ft³/min
Average SAC to date per Shearwater: 32.88 psi/min
Average SAC to date per SAC calculator: 32.1 psi/min
Average RMV to date per SAC calculator: .857 ft³/min
Average RMV to date per RMV calculator: .8862 ft³/min

Dive 03:
Start Pressure: 1568 psi
End Pressure: 712 psi
Pressure Change: 856 psi
Average Depth: 17.3'
Time: 21 min 27 sec
Average Temp: 67.3°F
SAC per Shearwater app: 26.26 psi/min
SAC per SAC calculator: 26.9 psi/min
RMV per SAC calculator: .717 ft³/min
RMV per RMV calculator: .7246 ft³/min
Average SAC to date per Shearwater: 29.57 psi/min
Average SAC to date per SAC calculator: 29.5 psi/min
Average RMV to date per SAC calculator: .787 ft³/min
Average RMV to date per RMV calculator: .7954 ft³/min

Dive 04:
Start Pressure: 2882 psi
End Pressure:656 psi
Pressure Change: 2226 psi
Average Depth: 24.2'
Time: 38 min 35 sec
Average Temp: 66.2°F
SAC per Shearwater app: 33.41 psi/min
SAC per SAC calculator: 33.0 psi/min
RMV per SAC calculator: .881 ft³/min
RMV per RMV calculator: .8922 ft³/min
Average SAC to date per Shearwater: 30.85 psi/min
Average SAC to date per SAC calculator: 30.6667 psi/min
Average RMV to date per SAC calculator: .81833 ft³/min
Average RMV to date per RMV calculator: .82766 ft³/min

Dive 05:
Start Pressure: 3054 psi
End Pressure: 2080 psi
Pressure Change: 974 psi
Average Depth: 17.4'
Time: 20 min 52 sec
Average Temp: 62.7°F
SAC per Shearwater app: 30.55 psi/min
SAC per SAC calculator: 30.6 psi/min
RMV per SAC calculator: .816 ft³/min
RMV per RMV calculator: .8245 ft³/min
Average SAC to date per Shearwater: 30.775 psi/min
Average SAC to date per SAC calculator: 30.65 psi/min
Average RMV to date per SAC calculator: .81775 ft³/min
Average RMV to date per RMV calculator: .82688 ft³/min

Dive 06:
Start Pressure: 2006 psi
End Pressure: 482 psi
Pressure Change: 1524 psi
Average Depth: 13.6'
Time: 26 min 26 sec
Average Temp: 67.8°F
SAC per Shearwater app: 40.9 psi/min
SAC per SAC calculator: 39.6 psi/min
RMV per SAC calculator: 1.057 ft³/min
RMV per RMV calculator: 1.1071 ft³/min
Average SAC to date per Shearwater: 32.8 psi/min
Average SAC to date per SAC calculator: 32.44 psi/min
Average RMV to date per SAC calculator: .8656 ft³/min
Average RMV to date per RMV calculator: .88292 ft³/min

Dive 07:
Start Pressure: 2800 psi
End Pressure: 864 psi
Pressure Change: 1936 psi
Average Depth: 35.4'
Time: 34 min
Average Temp: 81°F
SAC per Shearwater app: 27.06 psi/min
SAC per SAC calculator: 27.6 psi/min
RMV per SAC calculator: .737 ft³/min
RMV per RMV calculator: .7482 ft³/min
Average SAC to date per Shearwater: 31.8433 psi/min
Average SAC to date per SAC calculator: 31.633 psi/min
Average RMV to date per SAC calculator: .8442 ft³/min
Average RMV to date per RMV calculator: .86046 ft³/min

Dive 08:
Start Pressure: 2740 psi
End Pressure:918 psi
Pressure Change: 1822 psi
Average Depth: 38'
Time: 39 min 44 sec
Average Temp: 80.4°F
SAC per Shearwater app: 21.41 psi/min
SAC per SAC calculator: 21.2 psi/min
RMV per SAC calculator: .565 ft³/min
RMV per RMV calculator: .5735 ft³/min
Average SAC to date per Shearwater: 30.3529 psi/min
Average SAC to date per SAC calculator: 30.1428 psi/min
Average RMV to date per SAC calculator: .8042 ft³/min
Average RMV to date per RMV calculator: .81947 ft³/min

Dive 09:
Start Pressure: 2884 psi
End Pressure: 674 psi
Pressure Change: 2210 psi
Average Depth: 51.6'
Time: 34 min 29 sec
Average Temp: 79.4°F
SAC per Shearwater app: 24.85 psi/min
SAC per SAC calculator: 24.5 psi/min
RMV per SAC calculator: .654 ft³/min
RMV per RMV calculator: .6852 ft³/min
Average SAC to date per Shearwater: 29.665 psi/min
Average SAC to date per SAC calculator: 29.55 psi/min
Average RMV to date per SAC calculator: .7855 ft³/min
Average RMV to date per RMV calculator: .80268 ft³/min

Dive 10:
Start Pressure: 2780 psi
End Pressure: 492 psi
Pressure Change: 2288 psi
Average Depth: 31.4'
Time: 44 min 31 sec
Average Temp: 80°F
SAC per Shearwater app: 26.33 psi/min
SAC per SAC calculator: 26.2 psi/min
RMV per SAC calculator: .699 ft³/min
RMV per RMV calculator: .7092 ft³/min
Average SAC to date per Shearwater: 29.294 psi/min
Average SAC to date per SAC calculator: 29.177 psi/min
Average RMV to date per SAC calculator: .776 ft³/min
Average RMV to date per RMV calculator: .7923 ft³/min

Not sure I am ready to fully dip my toe in SAC vs. RMV quite yet. It is my understanding that RMV varies with depth where as SAC is normalized at surface pressure. Stating it that way, in my opinion, SAC would be a more averaged number while RMV would be a more exact depending on depth.

So, I answered your poll with ".7 to 0.79ft³/min, 19.8-22.5 l/min votes= 67 10.4% of the votes." Given the nature of the curve and my limited experience, I am satisfied with my rate. The trend I seem to see is first tank higher than second tank on any given day EXCEPT on dives 5 and 6 and 9 and 10. Dive 6 was a navigation dive and we were also calculating kick cycles so I get that one. Dive 10 was along Paradise Reef in Cozumel. The current was less than Dive 9 along San Francisco Reef, and I saw more wildlife so I was more excited. The numbers seem to tell a good story to me, but I would welcome comments from those with more knowledge.

Thank you again for the challenge. It is also showing me that I need to double check some settings on my DC to make sure that it isn't telling me to head up before I need to. On only one dive did I surface with less than 500 psi.

Edited to close quotation of poll result and notate edit...

 

[SATurner]

@scubadada, I have a post under review due to me editing a typo, I really need to let those slide....

In the mean time:

Reflecting on dives #7 and #8:
The dive plan was simple, long stride off the boat, descend, follow the DM. Let him know when at 1000 psi so he could lead back to the anchor point and then ascend to safety stop around 750 psi.

The waves were at least 4'~6' on the outside of the reef. There were breakers coming over the reef. Once below the water by say 10'~15' I didn't feel any of the surge or current. It might have been there, but I didn't "sense" it.

The water clarity was awesome! It was easily > 40'. At my deepest depth of the two dives (just under 71') there was (I would estimate) at least another 30'-40' to the sandy bottom before it sloped off into unknown depths. So, there I was, deeper than I had ever been, in water clearer than I had ever seen, with waves going crazy above me while I was just happy as a clam in awe of it all.

I knew I was going deeper than I had previously. I had no issues clearing my ears or mask. Everything felt "right."

I was a bit surprised to hear one of the DMs make a comment that "if you don't have a dive computer, don't worry, just stick close to us, we'll keep you safe." To put that in perspective, that DM was staying with the group that was staying shallower.

When asked how much weight I needed, I explained my experience in fresh and what was needed for that, and that I guesstimated needing 16#. On the first dive, 16# seemed heavy so I dropped 4# and went down to 12#. At the safety stop for the second dive, I was a bit light, so, I likely should have been at 14# with a full lycra skin and rental BC. Prior to this, I had been in fresh water with a full 3mm wetsuit and 10# of weight. Logging this information will be key to me dialing myself in as I am not sure when I will have my own gear. Between certification in mid January and the cruise, I also likely added 5# around the waist. Most of that was from being a glutton on the cruise though. I really need to start trimming down some of the excess.

Said all of that to say, there wasn't a lot of hand holding from the shop or the DMs as they expected me to know what I needed. That said, I didn't get the impression that if I claimed total ignorance they wouldn't have helped me. To be honest, I actually appreciated that the attitude was one of "you should know or you should ask, we're not here to spoon feed you."

The second dive was much a repeat of the first. I did push to go from 68.7' to 70.8' on the second dive, but I went deep early and then shallowed up to be around 3' deeper than the first dive on average. I wanted to test myself more than anything else, but it was very much like early days when first learning to swim in the pool. Down to touch bottom at 5' then 8' then 10', just brief touches, but always growing in capability.

While we saw some sea life, most of what we saw was simply reef. The corals were awesome! The eel swimming by was a cool occurrence. That it spun around after going through the whole group to double check us was neat too.

All in all, I wish I had more time in the area to explore more of the area. While initially the dive shop was pushing for a visit to the Hol Chan/Shark Ray Alley, I am glad we were able to go to the reefs. Going to a place less visited was a bonus in my book.

 

[NeilA.]

It looks like you got a couple of short fills. What is up with that?

 

[SATurner]

Dives 2 and 3 were on the same tank.

The tank from dive 6 had someone on it prior to me? Happened during training, and the valve cover wasn't on the valve when I set up. If any air has been used from the tank, the shop I dive with doesn't cover the valve.

Are those the short fills you are seeing?

 

[Searcaigh]

The blue IKEA bags were a great idea but were out of place with everyone else's gear.

Not if you dive in Sweden.

Very enjoyable read, thanks for posting.

 

[NeilA.]

Dives 2 and 3 were on the same tank.

The tank from dive 6 had someone on it prior to me? Happened during training, and the valve cover wasn't on the valve when I set up. If any air has been used from the tank, the shop I dive with doesn't cover the valve.

Are those the short fills you are seeing?

Yes, that explains it. Sorry if I wasn’t following close enough.

and there is nothing wrong with utilizing Ikea or Costco bags especially when traveling. They are very practical. We almost always take one.

 

[scubadada]

@scubadada, I have a post under review due to me editing a typo, I really need to let those slide....

Ha, I approved it The suspense was killing me

As you work on your buoyancy, trim, propulsion, relaxation, breathing... no doubt your gas consumption will decrease, It will be interesting, having values from the beginning.

Gas consumption in volume/time/atm (RMV, cu ft/min in your post) is most useful. It is at 1 atm. To calculate gas consumption on a dive you multiply the atm at depth (60 ft = 60/33 +1 or 2.8 atm)

Best of luck in your diving

 

[SATurner]

Rofl, that's funny!! I'll try to be better about letting my typos slide to reduce the moderator load.

@NeilA., no apology needed, you were drilling down into a huge mess of data. That you noticed the oddities is a great tribute to your attention to detail.

The Ikea bag was fun, and it served well for the first trip. No knowing what I needed, I was way over packed. I have dialed in on an Akōna Globetrotter. I had been looking at them heavily prior to the cruise and ad luck would have it a diver in Cozumel had one and raved about it.