Math is Scary - Drowning is (probably) Scarier

[boulderjohn]

I find time useful because many dive boats (usually cattle boat ops like Rainbow Reef) want you back on the boat after a certain amount of time - usually 1 hr.

I missed this originally. Why is this limit given the pejorative term "cattle boat"?

I have no problem with a dive operator giving me a time limit on a dive in most (but not all) recreational diving situations. I fully understand the need for it when you have a schedule to run.

• I remember standing on a dock in Aruba waiting waiting waiting for our scheduled trip, with our boat finally arriving and leaving us with a highly shortened schedule because someone on the earlier trip decided to dive to his own personal limits rather than the standard schedule.
• I was on a very shallow reef dive in Key Largo at the end of an afternoon, although not with the dive operation maligned in this post, and like almost everyone else, we got on the boat at the same time, as we were told in the dive briefing. We all began breaking down our gear as the captain called the role. Someone, a couple, was missing. Anxious eyes scanned the water as we put our gear away. Other boats in the area disconnected from their moorings and headed for home. Before long everyone was done packing. Everyone was scanning the water surface at 360° in search of bubbles. We were all terrified. Eventually someone shouted "Bubbles!" and pointed in the distance. The DM looked, donned mask and fins, and swam out furiously. At the spot he looked down, rose up with the OK signal, and then submerged. Eventually the couple arrived on board and did not seem to give a damn about the problem they had caused. By the time we reached the doc, it was well past dark. Many of us had plans for the evening that we had to change.

So I will dive those "cattle boats" in the future, and when they tell me what time to be back, I will be back at that time. Now, if I think their time is ridiculous, I will go somewhere else, but otherwise, I will understand the reason and follow their rules.

 

[Manatee Diver]

"But there’s always that one 80lbs woman on the boat who has been diving for 50 years and comes back with more gas than she left. @#$% that jerk."

Take the 50 years down to a more reasonable number and that sounds like @Scuba_Jenny I swear she was stealing air from my tank.

To add another story, I was in Japan, and on the last day they assigned me to the native Japanese DM, she didn't speak much english and my japanese was pretty limited too. So the briefing was done by someone else. We get in the water and she didn't ask for my pressure all day. I thought it was great that the DM trusted me enough to manage my own air. Found out later, Japanese DMs don't check air consumption as almost all Japanese have such low lung volume that they never run out of air.

 

[dmaziuk]

... Japanese DMs don't check air consumption as almost all Japanese have such low lung volume that they never run out of air.

I thought you were going to say "because it would be impolite".

 

[dmaziuk]

Let's say I am planning to do a recreational drift dive on a flat reef, such as is found in south Florida. Here would be my entire dive plan:

1. Jump into the water,
2. drop down to the reef,
3. swim with the current until either my gas supply reaches a certain point, my NDL reaches a certain point, or I have reached the maximum time allowed by the boat operator
4. Ascend

3a. If I'm still not at half on an Al80 after 30 minutes, start paying close attention to my SPG as it may be stuck.

 

[Storker]

You're going to want to look into breaking that habit sooner than later as/if you intend to ever dive deeper than about 30'/10M.

After I standardized on EAN32 as my breathing gas, I, too, only bother about monitoring my SPG. With a single tank and typical drysuit country RMVs, you really have to make an effort to exceed NDLs before violating min gas.

When I was breathing air, I used to monitor both my pressure and my remaining nitrogen time.

 

[boulderjohn]

After I standardized on EAN32 as my breathing gas, I, too, only bother about monitoring my SPG. With a single tank and typical drysuit country RMVs, you really have to make an effort to exceed NDLs before violating min gas.

My post above about dive planning for a simple reef dive was actually more complicated than what I actually do for most of my dives because I wanted to make it nicely generic. In most of my actual dives, I am using EANx 36 in an overfilled LP 85. I am not going to run out of gas, and I am not going to get anywhere close to NDL. The dive operator wants me to surface no later than an hour after descending, so the only thing I really do during the dive is check the time and try to have my head break the surface at exactly 60 minutes.

 

[Storker]

My post above about dive planning for a simple reef dive was actually more complicated than what I actually do for most of my dives because I wanted to make it nicely generic. In most of my actual dives, I am using EANx 36 in an overfilled LP 85. I am not going to run out of gas, and I am not going to get anywhere close to NDL. The dive operator wants me to surface no later than an hour after descending, so the only thing I really do during the dive is check the time and try to have my head break the surface at exactly 60 minutes.

I'm diving a 10L 300 bar steel (roughly 90 cu.ft), and with my RMV my air NDL and my min gas time correlate very nicely at nearly any depth. With EAN32, my NDLs are roughly 50% longer, so going into deco isn't an issue as long as I monitor my gas.

And since we dive independent buddy pairs without a DM in the water, and only have to make sure we surface within the run time we give to the dive leader, only thing I need is an inkling of my expected max depth. That tells me my expected run time and then I pad that number liberally before giving it to the dive leader.

 

[divezonescuba]

On the subject of 80 pound women divers’ gas consumption.

one of our recently certified dives went to Ramones in Belize. He is 6’ 5” and weighs 300 pounds. He actually looks like Mr. Clean. While he was down there, he was paired up with a very small woman who could have been a former pearl diver.

On his first post certification dive with her, he blew thru his gas forcing the two of them to ascend after 20 minutes.

Once back on the boat, she pointed her finger at him and said in a loud stern voice:

“Mister, you better get your s**t together!”

According to the diver, he was so scared of her, that he was afraid of breathing. We’re not really sure what he did, but now he has really exception gas consumption for his size.

 

[Marie13]

On the subject of 80 pound women divers’ gas consumption.

one of our recently certified dives went to Ramones in Belize. He is 6’ 5” and weighs 300 pounds. He actually looks like Mr. Clean. While he was down there, he was paired up with a very small woman who could have been a former pearl diver.

On his first post certification dive with her, he blew thru his gas forcing the two of them to ascend after 20 minutes.

Once back on the boat, she pointed her finger at him and said in a loud stern voice:

“Mister, you better get your s**t together!”

According to the diver, he was so scared of her, that he was afraid of breathing. We’re not really sure what he did, but now he has really exception gas consumption for his size.

Women generally use less than the guys. Even diving dry with doubles I still had a RMV that was 0.2/cft per min less compared with a guy of much the same size diving a 7mm with a single tank.

 

[Rickk]

...

I would argue that for a recreational diver, you don’t want their brain to be too task-loaded, so they don’t control for depth or trim or just enjoy the surroundings because they are keep doing math.

......

It doesn't task load my brain to look at a couple of numbers and do some simple arithmetic.

It also does not task load my brain to breath.

Both are very simple tasks.