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August 11, 2008

Dogs, tanks, suits and Nitrox

Sometimes you go diving and it's just for fun. Other times you learn a bunch of new things as I found out this past weekend at Lake Tahoe. Instead of Meeks Bay which is usually overrun with certification classes, we went back to the D. L. Bliss State Park just a few miles away from Meeks. That's the site of the (in)famous Rubicon Wall that plunges down from 60 feet or so to a depth of 1,500 feet within just a quarter mile. Unfortunately, the trail from the Callawee Cove parking lot is a plunge all by itself, and quite a pain with scuba gear on. Still, the lure of the secluded beach and the wall were enough to make us go back.

Parking at D.L. Bliss is just six bucks a day, a real bargain when you consider the giant size of the park (it takes a mile on a narrow, winding forest road to even get to the park entrance gate) and the gorgeous vistas. It's a bit like Big Sur with lots of woods and nature. We arrived at the smallish Callawee Cove lot at 9:30AM when you can still pick your spot. As always with diving, the closer to the beach you can get the better.

This time, with the memory of lugging those giant 104-cubic foot steel tanks down (and up!) the steep trail, we brought comparatively tiny high pressure steel-80s. They don't look very manly, those tanks, but on this trip I certainly got to appreciate them. Sure, I only had 80 cubic-foot of air instead of 104, but that was enough, and the big difference in size and weight made this trip about diving and not about scaling what seems like 700 steps up a vertical cliff.

I never really realized before how important picking the right tank is. As much as I had read about tanks, when I bought my own first tanks I got my two used low-pressure steel-95s because Robert at Diver's Cove in Folsom recommended them, and my metallic-blue anodized aluminum 80 because it looked great. The steel 95s are good but I don't think I ever got a full 2,400 psi charge, and when you begin with 2,100 psi or so, there just isn't all that much air in them. The blue alu tank does look great, but it's actually even longer than the steel-95s, so it's quite a handful for just 80 cubic feet of air, and that's before the annoying buoyancy issues of aluminum tanks (I'll get into that!). So I think I'll relegate the pretty blue tank to pool duty, sell the steel 95s, and invest in high pressure steel 100s if we can find them at a reasonable price. High pressure tanks have their own issues (filling time, availability of high pressure fills, etc.) but at this point weight and length of a tank have become important to me. If you routinely have to carry tanks by the valve, having one that you can carry without it dragging the ground makes things so much easier.

But it's not only tanks where there is no substitute for practical experience. The same goes for wetsuits. While I liked the first wetsuit I ever bought, a 7mm Telos, the thing was so difficult to get into that I started all my dives already exhausted. And pulling the recalcitrant material up your arms and legs practically guarantees sore fingertips as the side of the nails dig into the soft parts. The answer there is to get a suit that really fits. My Telos, for example, was a "medium," which meant it fit my 6-foot, 155 pound frame snugly, but arms and legs were too short. No fun.

Well, Carol pointed out that some wetsuits come in "medium-long," though dive shops don't usually carry the size. My new 7mm Scubapro "Form" wetsuit does come in that size and it fits great. It's also made from a material that is super-stretchy and therefore goes on a whole lot easier. Nothing is ever perfect, though. Somehow it must have escaped Scubapro that Velcro grabs this material like crazy. When you pull the velcro off, it rips the surface layer of the wetsuit material. Scuba gear uses lots of velcro, and so it won't be long before suits made of this material look all chewed up. Anyway, I love the suit and we'll see how it holds up.

The water temperature at Tahoe was 68 degrees as it usually is in the summer. However, I knew from prior dives that it gets colder quickly as you go down and so I used my hood and gloves. I had some concerns about the gloves as we took a test camera along, the new DC800 from SeaLife. The folks at SeaLife have this amazing ability to retrofit ordinary digital camera equipment for underwater duty by tweaking the software and adding special underwater modes that go well beyond what consumer cameras with an underwater setting or two offer. A lot of their magic comes from special white balance modes that correct for the way water filters out different colors as you go deeper. They also know that divers do wear gloves on occasion, and so the buttons on their underwater housings are always spaced to accommodate gloves. It may have escaped them, however, that older divers need reading glasses to see fine print and tiny icons, and so that can be an issue.

I had used Nitrox at the quarry in Tennessee, but this was the first time at altitude. I had contemplated the impacts of altitude on diving before, taken the PADI altitude diver class (twice, really), and read up on the subject. It's hard enough to wrap your mind around the logic of altitude diving on air (it's the ratio of the pressure differences between surface and a certain depth underwater that determines nitrogen absorption, and not the absolute pressure!), and it's worse for Nitrox where you essentially have to determine equivalent air depths twice. From talking to various people and also reading bulletin board posts on the matter, it seems that very few really know how it works. It makes no difference, of course, as everyone relies on their dive computer.

It's interesting to see just how much dive tables and dive computers differ when it comes to the real world. NAUI, for example, sells tables for diving at altitude with 32 and 36% Nitrox as well as for air dives. There are two sets of tables, one for altitudes between 6,000 and 10,000 feet and one for 1,000 to 6,000 feet. My dive eventually took me to 64 feet. Rounded up to 70 feet, the NAUI sea level tables would allow for a maximum dive time (MDT) of 45 minutes. The altitude air table cuts that to 21 minutes. That's because diving 64 feet at 10,000 feet of altitude is more like diving 100 feet or so at sea level as far as nitrogen uptake goes. This is where Nitrox comes in handy. Its lesser percentage of nitrogen increases maximum dive time from 21 to 32 minutes with 32% Nitrox, and 37 minutes with 36% Nitrox. So when diving at altitude, using Nitrox increases maximum bottom times when compared to air, just as it does at sea level.

Now how does all that theory translate into what the dive computer shows during an actual dive? Well, at no time did my no-decompression time fall below 60 minutes. And once set to 36% Nitrox, my Uwatec SmartZ also correctly showed an altitude-adjusted maximum oxygen depth of 100 feet. That's about six feet more than at sea level. Most people would expect less, but as far as oxygen goes, absolute pressure matters and so you reach the recommended 1.4 atmosphere partial pressure of oxygen a few feet deeper at Tahoe altitudes.

It's definitely a good thing to plan one's altitude dives, but once you're down there, the dive computer takes over. And at least in my case, maximum allowable dive time was a lot longer than my air would have lasted. I am getting better with my air consumption, but I am still sucking it up at an alarming rate when I get tense, and diving that wall at Rubicon point is still a somewhat scary experience for me.

The beach at Callawee Cove is shallow. You can dive along the rock cliffs and never reach more than 15-18 feet or so. However, swim away from the beach at the point, and there's the wall. Part of it is just a sheer wall, stark and forbidding. Other parts are giant boulders. All in all, it goes from 60 feet or so down to a 1,500 foot abyss within just a quarter mile. Visibility was far less than when we dove the wall last year. We had at least a hundred feet then, but this time it was just 50 or so, as we had already noticed during other Tahoe dives this year. I am not sure why that is; it must be some sort of local phenomenon as I cannot imagine clarity going down by that much within a single year. Tahoe is totally clean and clear, and pollution simply cannot be a sizable problem. Maybe it was ash and dust from all the California wildfires, and that may also account for the lower water temperatures.

Anyway, I never like low visibility, and its worse when there are severe thermoclines. This time we hit two, each gripping one's entire body. At 65 feet it was already down to 50 degrees. I wasn't uncomfortably cold with the hood and gloves, but between the relatively low visibility, the cold, and the menacing face of the wall, I was breathing hard. By now I know that I do not fall when I cannot see the bottom, but it is still a weird feeling. I did not want for it to overcome me, and so when I saw the wall slowly came into view, I swallowed hard and decided to swim along the sheer and near vertical face of the wall. Last time I had gone over it from the top, following Carol. This time, Carol had gone up to the top and peeked over it, feeling "like the Lion King" as she later told me. I swam along the face, breathing hard and hoping I'd soon come to something other than the sheer face. During those two or three minutes it instantly became clear to me why "blue holes" that often have walls that recede as you go down are considered so dangerous. It's easy to freak when there is nothing below you and rock above. Also, at just 65 feet I didn't feel what I suppose was the calming (to me) influence of a bit of narcosis that I probably had felt at 110 feet. In any case, I am very glad I went back to Rubicon Wall. I love those rock faces and giant boulders, but I'd like them that much better in clearer, warmer water.

Nitrox worked well for me, but then again I'd never had a problem with just air. So for now I know that Nitrox doesn't make me feel weird or anything. There's psychology in that. You need to find out for yourself how something makes you feel.

After a two-hour surface interval on the beautiful beach of the cove we did a second dive. This one was just for fun, poking around the rocks and boulders along the shallow shore. It rarely got to be more than 15 feet deep. We took movies with the SeaLife (once in its case, you cannot switch between still pictures and movies, so you need to decide what mode to use beforehand), watched whole colonies of feisty crawdads do their thing, marveled at how warm the fine sand at the bottom was when you stick your hands in it, and just played around.

This second dive was also a lecture in what an impact different types of tanks can have, and how even the same tank can behave differently when it gets empty. On the first dive I had used the high-pressure steel-80 tank and used 16 pounds of weight in the two pockets of my Scubapro Knighthawk BC. For the second dive I switched to my electric-blue Aluminum-80 tank, this time using 18 pounds to make up for the aluminum tank's higher buoyancy. Carol, who generally barely uses any weights at all, had on her new 7mm wetsuit and was on her second dive with the same tank. She doesn't like a lot of weight and dropped two pounds for this dive. As a result of the different buoyancy she now had trouble going down with eight pounds instead of the ten she'd used on the first dive, and so we switched things around again. Having less weight came back to haunt me after I'd used up about 900 psi of air. As we were returning to the beach and I found myself increasingly unable to stay at the shallow depths as my aluminum bottle was getting more and more buoyant, until I signaled it was no use and I had to surface, and so I did. Note to self: tanks that switch from negative to positive buoyancy are a pain.

I listed dogs in the title of this entry. Where do they come in? Well, we had fun watching some Retrievers and Labs play in the water during our dives. But that wasn't why I mentioned it. Like everyone else, I had learned to look up before surfacing so as not to collide with a boat. I did that and none were in sight. But when I came up I bumped into .... a dog. It was a chocolate Lab, and he'd probably been investigating my bubbles. He was just as surprised as I was and quickly doggie-paddled off. Me, I couldn't stop laughing.

Posted by conradb212 at August 11, 2008 04:07 PM