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• Another use for that tank that failed hydro?
• Some myths about getting a plus/+ rating on a low pressure (LP) steel tank
• Follow-up on my REE adventure
• Get college credit for PADI certifications
• If you are buying a used tank, look for a REE number
• Changing modes on your dive computer
• Tactical SCUBA boots
• Dry suit pros and cons, part 1
• Resources for Monterey shore diving
• Clean your first stage and BC thoroughly
• Moved the SCUBA blog from Blogger to my own URL
• Tips on buying a SCUBA tank
• Holy shark bait!
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If you are buying a used tank, look for a REE number

October 23rd, 2007   Filed Under Uncategorized  

If you are buying a used tank, especially a low pressure (LP) tank, look around the top of the tank where the serial number is for “REE” and then a number.  This Rejection Elastic Expansion (REE) number is what is used to give the LP tank the “+” rating so it can be filled to 10% over the service volume stamped on the tank.  Without the REE number, a hydrostatic test facility will only rate the tank to the service pressure stamped on the tank.  Unfortunately, LP tanks are marketed according to their “+” volumes, so if you have a LP 95 that cannot get its rating, then you really have a LP 85.

It may be possible to get the REE number for the tank from the manufacturer if you send them the tank serial number.

Changing modes on your dive computer

October 23rd, 2007   Filed Under Tips  

If your computer supports air, nitrox and gauge mode, there are some behaviors it may have when attempting to switch modes that you’ll want to keep in mind. If you change from air mode to either gauge or nitrox mode, you cannot switch it out of those modes for 48 hours or so. In nitrox mode, the computer is tracking your oxygen loading, and on m computer (Suunto Cobra) this O2 tracking does not carry over to air mode. As far as the computer is concerned it cannot accurately calculate your remaining bottom time if you switch modes since you are not coming in to the new mode “clean.” Being clean requires about 48 hours for everything to work its way out of your system. You can still dive air within the 48 hour window; with my computer I just leave it in nitrox mode and set the O2 percentage to 21%.

A similar case is true when switching to gauge mode. Once in gauge mode, the computer doesn’t know what you are doing…you could be in a swimming pool or doing a multilevel decompression dive. When you try to switch back to air or nitrox mode in less than 48 hours from a dive, the computer does not know where you are in terms of nitrogen loading. So if you intend to switch your computer to gauge mode to use in the pool, think first about when is the next time you want to use it in air or nitrox mode for a dive. If that is less than 48 hours away, then do something else (either leave it in air mode if it is a console computer, or leave it in your dive bag if it is a quick disconnect or wrist mount computer).

Tactical SCUBA boots

October 11th, 2007   Filed Under Tips  

I stumbled across some hefty looking tactical style dive boots. These are made by OTB (http://www.otbboots.com/)…as in over-the-beach which is apparently a Navy term when Navy Seals come out of the water and go over the beach and fight on land.

What is nifty about these boots is they have holes in the sole for water to drain out. If you go to the OTB site you can see a little animated demo of it. You can buy OTB footwear through online stores that sell tactical gear, like navyseals.com. These boots are in the $100 price range.

Dry suit pros and cons, part 1

October 10th, 2007   Filed Under Article  

Considering going dry? Here are some factors I was looking at when I made my decision to go dry.  I will split it up into multiple posts.

Pros:

User-variable compression
A wetsuit compresses the deeper you go. The more compression, the less thermal insulation. I have noticed that with a particular wetsuit setup I can be fine at 30 feet but then feel cold past 70 feet with similar water temperatures. So, that means that in order to be warm at 70 feet I need to layer up more neoprene before the dive. There are some disadvantages to this; more neoprene means wearing more lead in order to sink. Once the suit compresses some, buoyancy decreases, but I still have all that lead that required to initially get me down and keep me at 15 feet at the end of the dive. Now I am essentially overweighted for the rest of the dive. The deeper I go, the more overweighted I am since the wetsuit continues to compress more, and the deeper I go the less insulation I have.

A dry suit has a low pressure inflater hose connected to is so the diver can add air to compensate for the compression in the insulation layer caused by changes in depth. This allows the diver to maintain the same level of insulation regardless of the depth as the diver can add or release air to maintain the same volume of the air “bubble” in the suit as the diver ascends or descends. The other advantage of controlling the compression is all air in the suit can be vented in order to “vacuum pack” the suit. This reduces the volume of the suit, which reduces the amount of water the diver displaces, which makes the diver less buoyant. This is useful in managing the surface to 15 foot depth range - less weight is required to descend at the beginning of the dive along with maintaining a safety stop and slow ascent to the surface at the end of a dive (when the tank will weigh less since there is less compressed air in it). So with a dry suit you don’t have to pack extra lead for the shallower depths where there is less compressing force than at depth. Weighting for a wetsuit is pretty much what is required to keep you at 15 feet at the end of the dive, whereas weighting for a dry suit is more like the weight required to be neutrally buoyant during the dive with the desired amount of air in the suit. User preference and undergarment materials can affect the size of the bubble in the suit. So a dry suit isn’t so much about keeping the water out as it is about keeping the air bubble in.

Resources for Monterey shore diving

October 10th, 2007   Filed Under Tips  

I found the following resources to help find out more about Monterey beach dive sites and logistics to get to them:

http://www.divemonterey.info/Sites/divesite.html - This seems to be the most definitive of the online resources I found so far.

The book A Diver’s Guide to Monterey County by Bruce Watkins is available online from California Diving News or from many dive shops in the Bay area.

Clean your first stage and BC thoroughly

October 5th, 2007   Filed Under Tips  

Reading the book Diver Down and talking with a local dive shop owner reminded me of how important it is to thoroughly clean your first stage and the inside of the BC after a dive. The reason is that salt water leaves salt crystals behind when it dries, and those crystals cause problems when they jam up stuff.

Most first stages have a little hole in them that lets water enter in order to use the water pressure to as part of the function of how the unit works. Crystals deposited in there can interfere with the functioning of the unit. As recommended in both Diver Down and by the LDS owner, a quick dunk in fresh water is not sufficient to get all the crusties out. A first stage needs some soaking and vigorous swishing around to leave it clean. Yet another reason to own your own gear rather than rent…you know all that rental gear just gets a quick dunk when cleaned by the people renting it.

As for BC, the LDS owner said one time he saw a BC that got punctured by a salt crystal stalactitie that formed inside the air bladder and punched through as a result of not being rinsed out.

Moved the SCUBA blog from Blogger to my own URL

October 4th, 2007   Filed Under Uncategorized  

I moved my blog from Blogger to my own URL with WordPress as my blogging tool. My reasons for this are:

- Ownership and control of my content - my domain = my content

- More control over the blog interface. Blogger is limits and WordPress is rich with plug-ins and administrative control

- Google doesn’t index Blogger entries

- Ability to have more control over potential future Adsense and other marketing

- I want to start working on page rankings for this URL as a potential future site for a team blogging initiative on SCUBA

I had trouble importing the Blogger posts to here. The delivered import tool with Wordpress didn’t work, so I created a hosted wordpress blog (wordpress.com), imported the Blogger entries (it worked there) , then exported them to a file and imported here. Then I deleted the hosted blog.

Tips on buying a SCUBA tank

October 1st, 2007   Filed Under Article  

Making a purchase decision on your own SCUBA tank can be a confusing one. Aluminum or steel? High pressure or low pressure? What size? Here is what I learned in doing research for a purchase decision:

Aluminum versus steel:
As a primary/back cylinder, the common aluminum tank (AL - the Dept of Transportation code for an aluminum constructed compressed gas cylinder) is the 80 cu.ft. A 100 cu.ft. can also be found. There is one primary advantage of AL tanks - they cost less than steel tanks. Other than that, most people go steel over AL as a tank they wear on their back (a stage bottle or pony is a different story). In terms of buoyancy, AL tanks are not very negative when full and are positively buoyant by about 4 pounds when at 500 PSI. That means packing more lead in order to sink. One case where an AL can be beneficial is in the case of warm water diving where large capacity steel tank will have enough negative buoyancy that a diver in a thin wetsuit could still be negative even after dumping their weights. That is not a concern for me since I am a big guy and get cold easy, so I have more neoprene than most people and all that foam requires more weight to sink me; Plus where I live I will only be doing cold water diving with the tank. There are neutrally buoyant 80 cu.ft. AL tanks on the market, but they are more expensive than regular AL tanks. AL tanks have very poor resale value, and they tend to fail hydro long before a steel tank will. Most AL tanks are rated (will be full at) 3000 psi, with some rater at 3300 psi.

Steel (AA - the Dept of Transportation code for a steel constructed compressed gas cylinder) tanks have a thinner wall than AL tanks. Most AA tanks are more negative (for a given volume) at the beginning of the dive than AL tanks, and AA tanks end the dive still negative while weighing similar to an AL tank of same compressed volume on land. AA tanks come in a wider range of volumes and sizes than AL tanks do. AA tanks have good resale value because they last a long time and therefore hold their value well. It isn’t unheard of to buy a new one, dive it for a bit and sell it for 80% of what was paid for it. AA tanks cost anywhere from 2 to 3 times the cost of an AL tank.

High pressure or low pressure?
AA tanks pretty much come in two flavors, low pressure and high pressure. Low pressure (LP) is defined as 2400 psi. LP tanks on the market today have a plus (+) rating, which means they can be filled 10% over the 2400 psi, or to 2640 psi. High pressure (HP) tanks are rated to 3442 psi. HP tanks are relatively new to diving; they have been around since 2003 or so. Here are some fundamentals on LP or HP tanks before we move on:

• An advantage of a LP fill is that you know you will get a complete fill no matter where you go since all fill stations can fill to LP. Also, the tank doesn’t get as hot as a HP tank so there is less settling (lowing of tank pressure from drop in pressure) after a fill.

• HP tanks are great in that you get a lot of air in a compact cylinder, but they need to be filled slowly and preferably submerged in water to control heat so there will be minimal settling. There are probably some fill stations out there that cannot go higher than 3000 psi, but all that I have seen recently can give a HP fill. The problem is if you get a quick fill, like on a dive boat or in a shop at a dive location where the tank is not going to be in water during the fill, then you will end up with a short fill. I was talking to someone who recently went on a live-aboard where his fills would consistently settle to around 3100 psi.

• In the past many people would over fill their LP tanks to 3000 psi and above. The nickname for this is a “cave fill” since cave divers want the maximum amount of gas volume in the minimal amount of space. I think it is also because HP tanks haven’t been around very long, so what they were essentially doing was creating HP tanks from LP tanks. To do this they would need to add another burst disk to the tank. Over filling is a practice you can’t count on getting. Everyone is so safety paranoid today that even though there is a past record of the practice working, tank manufacturers and many fill stations will not condone it.

• Buoyancy characteristics of LP and HP tanks are about the same

• The price between LP and HP tanks are about the same for a given volume

• A HP tank does not need to be filled at HP all the time. It can be filled “short” to mid or low pressure, but the volume will be less. For example, according to a steel tank information page on the DiveRiteExpress.com web site, a HP 100 will be an 80 at 2640 psi, and an 89 cu.ft tank at 3000 psi.

• I read one belief that HP tanks strain equipment in the upper psi range of the fill, and that it is better to fill HP tanks to about 3000 psi.

Since a HP tank can also become a LP tank (with smaller volume), I decided to choose a HP tank of appropriate size so that the LP volume would meet my needs. That way I would always get enough of a fill that I need for most dives. My plan is to have it filled to around 3000 psi the majority of the time, and then occasionally take it up to 3442 psi if I need the extra volume.

One disadvantage of a larger tank is if the volume in it is more than you need (i.e. you come up with a bunch of air left) then you are lugging around the extra weight of that air in the water. For example, a 130 tank when full is about 11 pounds heavier than when at 500 psi. If a diver consistently only uses 5 pounds of that air, then they are carrying around an extra 6 pounds that has to be compensated by having more air in their BC…and the more air in the BC the more buoyancy is hard to control. Why not just drop 6 pounds off the weight belt in that scenario? Proper weighting means the diver can hold a safety stop with 500 psi, so if you don’t breath the air in the tank, then it is just extra weight. So….the biggest tank on the market is not necessarily the best for everyone. It is more like – get the tank that has physical dimensions that fit you and that has a LP volume that will work for you, and then choose the fill based on what you will probably need for the dive. This is why a diver may choose to short fill a high capacity tank and turn it in to a LP tank.

See the Variable Capacity of Cylinders section on this page from Dive Rite Express: http://www.diveriteexpress.com/gas/steel.shtml

Tank dimensions:
Different capacity tanks have different dimensions. Some are close in volume but different in shape. The diameter of the tank will be either approximately 7.25 or 8 inches, and the length varies by tank. As an example of two similar volumes with different sizes, the XS SCUBA 120 cu.ft. is 7.25 inches by 28 inches long. Their 119 tank is 8 inches by 24 inches long. For comparison, an AL tank is 7.25 by 26 inches. Length can play a part in comfort and trim. A shorter, fatter tank will put more weight high up on the diver’s torso. A tall diver probably wants to get a longer tank since they have a longer torso, and a shorter diver probably wants a shorter tank so they don’t feel like is it hanging between their legs in the water. I am 6’4”, but I chose not to get the 120 as I believe anything longer than an AL 80 will feel a tad long on me.

Which size did I choose? I dived a LP 95 and a HP 100 and felt those volumes were the minimum I want to be able to do the slow ascents that I want to do. In terms of volume, a 119 is perfect but it is a bit short for a tall person. I was torn between the 120 and 130 cu.ft. tanks as far as a purchase decision. I decided to go for the 130 since I was a little concerned about the length of the 120. So the 130 is three volumes in one tank – according to the Dive Rite Express web site regarding tank selection, a 130 is also a low pressure 104 and mid pressure 117. It all depends on how much air you put in it.

Additional reading:
Dive Rite Express page about choosing a tank
http://www.diveriteexpress.com/library/tanks.shtml

Dive Rite Express page about tank volumes
http://www.diveriteexpress.com/gas/steel.shtml

XS SCUBA specs page for their tanks
http://www.xsscuba.com/tank_steel_specs.html