Can I dive to 40m (130ft)?

[Neilwood]

Ironically, this is exactly the dive site I had in mind when I wrote the previous post. We were there last month and really didn't understand why the dive plan had us dipping down to 130 feet. So I take it the sharks there generally prefer such depths? We figured it was that, but the divemaster never explicitly said so. Anyway, my wife and I duly began the dive as the divemaster had planned, reaching a maximum of 130 feet, but then looked at our gauges, looked at each other like "there's nothing to see here," and started ascending to a depth that would allow our gas to last a bit longer. We really did see almost nothing on that dive but blue water.

Similar dive there myself - dive master trying to find hammers (which generally prefer deeper water) but didn't spend too long down there.

Seeing some sharks on other dives on the trip was amazing but I spent too long looking at blue water for my liking. Give me some rust or reef and I am a lot happier!

Spent a short while at 34m on the last trip - wasn't really worth it but I had increased my depth gradually from 25-30-31-33 etc over the trip so had a good idea what my consumption was going to be.

 

[Diver0001]

I guess it depends on what "planned" means here. If these dives were fully planned out, with contingencies like what you do when you have a free flow at depth and your guide or buddy isn't paying attention, or whether you have enough gas to complete deco if you exceed your planned bottom time by five minutes, and what you'd do if you lose your gas while having a deco obligation, and you have practiced the skills involved in dealing with these scenarios, then those dives are good data points for assessing whether you can go deeper or not. But if they were just "follow the guide" dives, hoping that noting would go wrong, then getting away with it doesn't really tell you much.

I've made a great many dives at the 35-50m range and I'll add my vote to the people who suggested that the main issue will be narcosis. At 30m most divers can handle narcosis fairly well. At 40m the narcosis is markedly more pronounced. Personally I usually never feel overly narced until I'm deeper than about 35 meters. Some days I can function fine up to about 50 meters and other days I have trouble focusing my attention at 40 meters.

The funny thing is, it's a crap shoot. You literally can't plan for, or do anything that I've ever discovered, to influence how you're going to feel at depth on a given day. Well, that's not entirely true. You can used Trimix but if you don't have that and you're diving air, then it's a crap shoot. The only thing you can really do (and should do) is have a plan-B if you're not feeling sorted. It's a good idea to talk about that plan-B with your buddy before the dive.

R..

 

[tridacna]

Here is a video of two divers going deep in search of something specific (in this case, fish) in a location where light is obviously not an issue (although they are using lights). In this case, it is noticeably colder at depth than in the shallower water. The point is that each location is different, and you have to make individual diving decisions based upon the individual site you are planning to dive.

Warning--video has adult content!

I wonder how RP is making out in HI sans Reco Chamber?

 

[Diver0001]

Here is a video of two divers going deep in search of something specific (in this case, fish) in a location where light is obviously not an issue (although they are using lights). In this case, it is noticeably colder at depth than in the shallower water. The point is that each location is different, and you have to make individual diving decisions based upon the individual site you are planning to dive.

Warning--video has adult content!

I can guarantee you that if they are diving in wetsuits without gloves on, the water is not that cold. They just made some bad equipment choices.

R..

 

[MXGratefulDiver]

I can guarantee you that if they are diving in wetsuits without gloves on, the water is not that cold. They just made some bad equipment choices.

R..

I wouldn't be so sure. A few years back I was diving on the Numidia (Big Brother, Red Sea). When we left the surface the water temp was round 80 (Fahrenheit). At around 160 feet we swam into a rather dramatic thermocline. I was in a 3mm wetsuit, and unable to remain there for more than a few minutes. I think the water temp dropped about 12-15 degrees in just a few feet. Fortunately, and although the wreck goes well below 200 feet, there's plenty of it to explore back up in the warmer, shallower water as well.

... Bob (Grateful Diver)

 

[J-Vo]

I really have no words to express how many things are wrong with this... You most likely went into mandatory deco, hence the 2 stops. Did you have any sort of gas plan? Obviously not, if one of the other divers had to share. Did you discuss your "safety stops" on the surface. Did anyone look at tables or planning mode on a dive computer to see how long you could stay at depth without going into deco as from the sounds of it you are not decompression trained. Or did you just take what the guide said as gospel?

I'm showing a total of 31 minutes of mandatory deco using GF 50/80. I would want doubles and a tank of 50% for this dive plan. The plan still has 18 minutes of deco with 50% nitrox. In my opinion it is dangerous and irresponsible for the dive master to be attempting this profile with sport divers.

 

[divinh]

I really have no words to express how many things are wrong with this... You most likely went into mandatory deco, hence the 2 stops. Did you have any sort of gas plan? Obviously not, if one of the other divers had to share. Did you discuss your "safety stops" on the surface. Did anyone look at tables or planning mode on a dive computer to see how long you could stay at depth without going into deco as from the sounds of it you are not decompression trained. Or did you just take what the guide said as gospel?

At the time, I hadn't had that much experience and trusted the guide fully, who, as I said, was an instructor. I fully expected him to bail on the dive had any of us looked questionable. In some sense, I didn't know enough to be worried, which maybe in hindsight, I should have been.

Yes, we went into mandatory deco. We were informed in advance that we would be doing two safety stops, hanging off the mooring line. We also knew about the bottle hanging off the bottom of the boat. The guide regularly had us tell him our air and whoever reached half tank first was noted. From what I recall, I ended the dives with what I considered a normal amount of air, 70-80 bar. (I'll look up my dive log tonight and update this post with the numbers.)

Edit:

Okay, here are the numbers:

Dive 60: 43m, 29 min, 200 bar -> 50 bar
Dive 61: 41m, 30 min, 200 bar -> 50 bar

As for descent , bottom and ascent time, I thought I had written about it in my dive log, but I guess not. I wrote it down somewhere, but maybe in a travel log some four years ago.

 

[divinh]

I'm showing a total of 31 minutes of mandatory deco using GF 50/80. I would want doubles and a tank of 50% for this dive plan. The plan still has 18 minutes of deco with 50% nitrox. In my opinion it is dangerous and irresponsible for the dive master to be attempting this profile with sport divers.

Wow, you have me really worried now! Let me dig up my dive log tonight and make sure the bottom time was correct.

Edit:

We did one of our safety stops with these divers, who had a line attached to the mooring line. I guess they're equipped with what you're talking about? (One of my favorite pictures since it's like something from outer space.)

This is what was down at 43m... the U.S.S. Emmons...

 

[Lorenzoid]

Wow, you have me really worried now! Let me dig up my dive log tonight and make sure the bottom time was correct.

That was my first thought--that your "recollection" of "about" 15 minutes of swimming around at the bottom might be erroneous. Let us know.

 

[Diver0001]

I wouldn't be so sure. A few years back I was diving on the Numidia (Big Brother, Red Sea). When we left the surface the water temp was round 80 (Fahrenheit). At around 160 feet we swam into a rather dramatic thermocline. I was in a 3mm wetsuit, and unable to remain there for more than a few minutes. I think the water temp dropped about 12-15 degrees in just a few feet. Fortunately, and although the wreck goes well below 200 feet, there's plenty of it to explore back up in the warmer, shallower water as well.

... Bob (Grateful Diver)

So... you're saying that the temperature dropped to 18C/65F.

In my local area the PEAK water temperatures in the height of summer are +/- 18C. This is what Dutch divers call "warm water". I can dive for hours in this temperature.

In the winter the water typically drops to 2C/35F. The lowest temperature my computer ever recorded was -2C/28F. Wave action stopped ice from forming on the surface.

At the height of summer, lakes here have typical temperatures of about 5-6C/42F under the thermocline.

So again.... I say their problem wasn't the temperature, it was their equipment choices.

R..