Educate yourself on SAC, RMV, and Minimum Gas / Rock Bottom. Then you'll realize they are full of BS.
Which tanks to choose
- Thread starter Ross19966
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GiraffeMarineSalvage
Contributor
I got a ton of use out of HP steel 120's (but I'm 6' tall 220 lbs, so it's clearly not the right choice for someone 5' tall 110 lbs...). There is so much which goes into tank selection I would highly recommend finding a way to dive the type of tanks you are considering before purchasing...
Also, depending on your diving logistics and frequency of diving renting all the tanks you need generally is the same price as having your own tanks filled so the big value of owning your own tanks is being ready and able to dive whenever you want (an ability which is absolutely worth it in my opinion, but I would differentiate having enough tanks to do the spontaneous diving you might want to do from owning enough tanks to do the most diving you could possibly ever want to do at one time when $50 of tank rentals would cover that need). With that said spending 3k+ on dive tanks would be better than buying your own compressor (with all the noise and maintenance that entails..).
Personally a galvanized steel tank's buoyancy characteristics and long life in a diameter which fits in a standard boat tank rack are the factors I would consider in addition to tank true capacity.
Side note: I also think it's really lame when dive shops don't provide a full fill and it's very likely dive shop you spoke to is drawing off their banked air to fill your tank and there is nothing at all to prevent them from fully filling a high pressure tank if they wanted to... But with that said proper etiquette in my opinion would be picking up a full high pressure fill when they will be running their compressor instead of expecting the compressor to be fired up just to fill a tank or two... Also a HP120 filled quick from 500psi to 3500psi will have warm air so the pressure will naturally drop when it's cool..)
Also, depending on your diving logistics and frequency of diving renting all the tanks you need generally is the same price as having your own tanks filled so the big value of owning your own tanks is being ready and able to dive whenever you want (an ability which is absolutely worth it in my opinion, but I would differentiate having enough tanks to do the spontaneous diving you might want to do from owning enough tanks to do the most diving you could possibly ever want to do at one time when $50 of tank rentals would cover that need). With that said spending 3k+ on dive tanks would be better than buying your own compressor (with all the noise and maintenance that entails..).
Personally a galvanized steel tank's buoyancy characteristics and long life in a diameter which fits in a standard boat tank rack are the factors I would consider in addition to tank true capacity.
Side note: I also think it's really lame when dive shops don't provide a full fill and it's very likely dive shop you spoke to is drawing off their banked air to fill your tank and there is nothing at all to prevent them from fully filling a high pressure tank if they wanted to... But with that said proper etiquette in my opinion would be picking up a full high pressure fill when they will be running their compressor instead of expecting the compressor to be fired up just to fill a tank or two... Also a HP120 filled quick from 500psi to 3500psi will have warm air so the pressure will naturally drop when it's cool..)
Be careful, as the capacity numbers can be confusing. For example, an HP100 and a LP85 are very nearly the same internal volume (about 1% difference). Fill either one to 2640 psi (the LP rated pressure) and it holds about 81 cuft. Fill either one to 3442 psi (the HP rated pressure) and it holds about 100 cuft.
If the purchase cost is comparable, buy the HP version. At the shop, pointing out a short fill on your HP is likely to gain more traction than begging for an overfill of the LP.
Those are huge and heavy tanks. Out of the water, an LP108 at 45 lb is 11 lbs heavier than an LP85/HP100. The LP120 is 49 lbs and probably infeasible to back mount for anyone shorter than about 6'5". (Those weights include enough ballast to be neutral when empty. You'll also need additional ballast/lead to offset any exposure suit buoyancy.)
Before you buy a bunch of tanks, I would urge you to figure out your consumption and see just how much air you need for the dives you typically do (incl. reserves). Don't forget you will also be limited by your buddy's choice of tank. Or if you're going solo, it's better to have 2 smaller than 1 larger.
gmerick
Contributor
What kind of diving do you do? If the usual weekend dive crowd you hang out with does max 1 hour, max 50 ft, it's nice to have a couple AL80s like so many casual divers have. They're easy to handle, and socially friendly. The HP 120's are nice to have also. Deeper longer dive without worries. No rule says they have to be pumped up to 230 bar every time. Treat them like LP95's except when the weekend's plan calls for more air. Also consider getting the 120's cleaned and labeled for Nitrox. If you have the capacity for longer dives, it's discouraging to run up against NDL. Again, just because it's Nitrox ready, it doesn't have to be 32 or 36. A good shop will blend at 28 or even fill as EAN21. Yes the shop charges a bunch more for EAN21 vice air. One of my favorite weekend dives is to sidemount a pair of Faber 117's at 3442psi and EAN32, then disappear into the lake for all morning, gives the navigation skills a workout, but man is it a great stress relief. No I'm not concerned about equipment weight - I'm 6'++ and 240lbs, an extra hundred lbs of equipment is meaningless at neutral buoyancy, and when I'm idling along for 3 hours I'm not doing quick depth changes. Recommendation 2, possibly 4 AL80s for air, 2 possibly 4 HP120s for Nitrox.
A helpful resource for considering tank options is the PDF/spreadheet attached to post #1 of the Updated SCUBA tank specifications list thread.
Following
+1
I use a 4lb weight on a camband near the bottom of my AL80s.
And what's this bollocks about a 10 min bottom time, are you going to 40m?
If you're having issues with gas then an HP100 would be the better choice of tank, but in general an AL80 will work fine.
It would be helpful to know what your normal local diving is like, as wetsuit/drysuit diving as well as depth are key factors in making a decision on this purchase.
The HP100 is just 23% more capacity than the AL80 (77cf actual). I'd look at it more for ideal buoyancy characteristics than I would the extra gas. Me, I prefer the size of the LP95/HP117 (15 liters) tanks. But if you were looking at purchasing a number of tanks, the cost of the AL80s is appealing--especially on the used market.
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