Posted by ScubaGlenn on October 13, 2000 at 19:21:33:
In Reply to: Tanks: Buy vs. Rent posted by JRM on October 13, 2000 at 14:21:51:
As for the pros and cons of renting and buying:
Logistics:
Rent: When you rent you have to arrange to have the tank before you go. Some boats (e.g. SunDiver) provide tanks for you, others (e.g. Explorer) will arrange with the local scuba shop to have a tank on the boat for you. There is also the return of the tank you need to work out.
Own: When you own your own tank you don't have the deal with the logistics of getting a rental before you go. Provided the boat you are going on has a compressor, there is no need to visit the dive shop before leaving.
If beach diving it really doesn't matter either way since you will need to visit the shop to get a fill (unless you own a compre$$or) or a rental tank. However, with your own tank at least you can get it filled days before you leave. Most dive shops want their tank back within 24-48 hours.
Cost:
Rent: The recurring cost of renting tanks (I've seen from $2 to $10/day) can add up quick or slow depending on how much diving you do.
Own: Aside from the initial purchse, once a year you need to get your tank visually inspected where they open the bottle, shine a light inside and look for corrosion, cracks, and other things that lead to bad things for the tank. The corrosion is of high concern for the steel, and cracks for the aluminum tanks. Every 5 years you need to get the tank hydrotested. Basically, this tests the overall strength of the tank, that the metal hasn't fatigued. TIP: If you purchase a tank, have it visually inspected and stickered when you purchase it if the shop will do this for free.
Familiarity:
Rent: With different tanks you may wind up weighting yourself with x pounds one day, and with another tank y pounds the next. Keep a good log of your weighting with different tank types as different types have different bouyancy characteristics.
Own: You can generally run the same weighting (all other things being equal) day after day after day.
Comfort:
Rent: If you aren't comfortable with the standard rental tank (the AL80) then it adds another stessor to the dive. You should use gear you are comfortable with, including your tank. Some places do have steel tanks or AL63 tanks for rent to accomidate people of differnet sizes.
Own: When you own the tank you are comfortable with you don't need to worry about it not being available for rent you when you need it. There are dozens of different sizes of tanks available for purchase leading to a good possibility of finding one that is comfortable. Many dive shops will be happy to let you try diving with a tank before you purchase it.
As to the bouyancy you brought up, different tanks will have different bouyancy characterics. aluminums usually wind up positively boyant by the end of your dive whereas steel tanks tend to be negative to slightly positive depending on the type. Basically, the more negatively bouyant the tank is at the end of the dive, the less weight you need on the belt to compensate for. As an example, with an AL80 with my cold saltwater configuration I wear 26 pounds on the belt, with my steel 95, I wear 20 pounds. The less weight on your belt/bcd the more comfortable the dive will be.
As to HP vs. LP:
This depends on the availability of HP fills in your area and if you want to configure your reg for HP use. Most regs have adaptors made by the manufacturer to convert from LP to HP and vice-versa. In North America most tanks are LP. As a result, you can get a complete fill most likely anywhere. Only a few places offer HP fills. So that fancy HP120 is going to be much less with a LP fill. Something else to keep in mind: If you wind up needing to use a rental or boat provided tank you need to be able to turn your HP reg back to LP. One thing to look out for on the HP-LP conversion kits is that they keep the reg positioned out of the way of your head.
The aluminum tank manufacturers did a nice little rounding game in that their AL80 actually is 77 or so ft^3. Steel tanks do their own thing. The "plus" rating. This comes from a little "+" that is appeneded to the hydro test date. Basically this means you can fill the bottle 10% over its operating capacity, meaning that a 2400 psi bottle can operate to 2640 psi. Here is where manufacturer literature will get gamey. For example, my ScubaPro Steel "95" isn't so much a 95 ft^3 tank as it is an 86 ft^3 tank that for the first 5 years after its intial hydro date can be filled to effectively 95 ft^3. After 5 years, its operating pressure is back to 2400. There are hydro tests that can be done that will extend the + rating another 5 years, but you will need to shop around for shops that have access to this service. And to make things even more confusing supposedly there are DOT regulation changes that allow tanks to retain the + rating through the life of the tank.
But when it comes to tank makers, there really aren't that many manufacturers. For steel there is Faber and Pressed Steel that come to mind. The ScubaPro of mine is Faber made I believe. Luxfer and Catalina are in the aluminum tank business. There are also a couple of other tank makers, Seagate I believe is one, or maybe they are just a distributer.
Find a tank size and weight you are comfortable with and start there. Then look at who the manufacturers are and what they offer on their product. The Steel 95 has become a popular tank as it is shorter than an AL80 but bigger around and a little heavier.
For more info on tanks check out: http://diverlink.com/gear/ and page down to the tank links.
http://diverlink.com/gear/tanks.htm is pretty good, down near the bottom you can see what a difference some tanks, that are essentially the same, are.
But again, the most important thing is your overall comfort with the equipment you are diving with. While it might be nice to HP120, that bottle also weighs over 50 pounds and has about a 9 pound shift in bouancy from full to empty. I like the weight and fit of my 95, my girlfriend likes the AL63s. Although lately she took a liking to my bottle when I let her use it once. Wonder if I'll be in the market for another ;)
-Glenn