Single vs. double tanks

[Dryglove]

The point being, twin 72s are way too much gas for anything but really shallow diving. You would exceed your NDLs with twin 72s at any depth deeper than about 50 ft, OR ELSE be hauling around a lot of spare gas that you do not need.

They work great if use the rule of thirds . Its give you plenty of gas for your dive and still have enough gas in reserve for your buddy if the need arises. I also like to have plenty of gas in reserve for rough shore entries or if i misnavigate and need to go back under the kelp rather than crawl across it.

Therefore, depending on your planned depth, for NDL diving, twin 40s would make a lot more sense than twin 72s, if you really want to wear twin tanks, and gain the advantage of the redundancy and trim.

You have to also realise that i purchased two older steel 72's, had one set O2 cleaned, hydro'd and had a VIP done for way less than the price of one single 40. I bought a sea elite isolation manifold from divers supply for 130.00 and a set of GUTS bands for something like 80.00.

Although i did see a nice set of double 45's at the dive shop last week. The only drawback was they wanted over 650.00 for them. That is well over double the price of what i paid for one set of my double 72's.

Twin 40s are going to weigh a lot less on the shore or boat than the twin 72s as well.

Very true but i can easily handle my double 72's in all but the worst shorediving conditions. I have even used them for kayak diving although they can be a bear to drag back on my fish n dive.

 

[newdiverAZ]

What about the buddy you are diving with? You need enough gas to get him and yourself back the surface making any stops that you may need. And in the oog situation his rmv and yours for that matter are gonna be higher.

Karl_in_Calif once bubbled...
Based on the NAUI dive tables for reference (no particular reference is sacred), here is what I get for ideal tank sizes (based on total air consumption) given the following planned depths and assuming a 0.75 surface RMV:


100 ft

Air21 = 76 cu ft
EAN32 = 100 cu ft
EAN36 = 130 cu ft (note your ppO2 at 100 ft will be in the high range)

pony = 13 cu ft (or add this to the above amounts for your buddy if no pony is being brought)


50 ft

Air21 = 160 cu ft
EAN32 & EAN36 = off the scale / the NDL is over 3 hours

pony = 7 cu ft (or add this to the above for your buddy if no pony is being brought)


The point being, twin 72s are way too much gas for anything but really shallow diving. You would exceed your NDLs with twin 72s at any depth deeper than about 50 ft, OR ELSE be hauling around a lot of spare gas that you do not need.

Therefore, depending on your planned depth, for NDL diving, twin 40s would make a lot more sense than twin 72s, if you really want to wear twin tanks, and gain the advantage of the redundancy and trim.

Twin 40s are going to weigh a lot less on the shore or boat than the twin 72s as well.

 

[Uncle Pug]

Somebody PM'd me and asked if I would make a post to this thread since I dive double 72s (as well as double 104s, single 104s, single 72s, ect.)

But I didn't want to have to read the whole thread so could you please sum it up for me in one succinct sentence?

Thanks.

 

[Karl_in_Calif]

lal7176 once bubbled...

Although i did see a nice set of double 45's at the dive shop last week.

Twin 45s are probably the perfect size tanks, for air21 or EAN32 diving within NDL limits. I mean perfect.

Anything larger than this is probably oriented more towards decompression diving. In which case, twin 72s are probably great. There are still a lot of good 72s around. Therefore the deals on them is almost irresistible.

Anything larger than twin 72s depends on how deep you are going and how long you plan to say, plus the rule of thirds margin.

Unless you are penitrating something, and do not have access to immediate ascent and the beginning of decompression, the rule of thirds is probably not warranted. Its a cave convention, adapted to shipwrecks as well.

 

[Don Burke]

Karl_in_Calif once bubbled... Based on the NAUI dive tables for reference (no particular reference is sacred), here is what I get for ideal tank sizes (based on total air consumption) given the following planned depths and assuming a 0.75 surface RMV:


100 ft

Air21 = 76 cu ft
EAN32 = 100 cu ft
EAN36 = 130 cu ft (note your ppO2 at 100 ft will be in the high range)

pony = 13 cu ft (or add this to the above amounts for your buddy if no pony is being brought)


50 ft

Air21 = 160 cu ft
EAN32 & EAN36 = off the scale / the NDL is over 3 hours

pony = 7 cu ft (or add this to the above for your buddy if no pony is being brought)


The point being, twin 72s are way too much gas for anything but really shallow diving. You would exceed your NDLs with twin 72s at any depth deeper than about 50 ft, OR ELSE be hauling around a lot of spare gas that you do not need.

Therefore, depending on your planned depth, for NDL diving, twin 40s would make a lot more sense than twin 72s, if you really want to wear twin tanks, and gain the advantage of the redundancy and trim.

Twin 40s are going to weigh a lot less on the shore or boat than the twin 72s as well.

By your own figures, 40s aren't going to hack it for 100ft dives on EAN32.

Just eyeballing it, they look about optimum at 80 with EAN36, which is where a heck of a lot of my no-stop diving is done.

Then assume that next week I'm going to do some staged deco diving.

 

[Karl_in_Calif]

Don Burke once bubbled...
By your own figures, 40s aren't going to hack it for 100ft dives on EAN32.

Agreed. I should have added, that for EAN32 dives, twin 50s would be the most appropriate.

That is also one more reason why the twin 45s are so perfect overall for NDL diving.

 

[Karl_in_Calif]

Don Burke once bubbled...
Then assume that next week I'm going to do some staged deco diving.

NOW you are in the realm of the twin 72s !!!

 

[Dryglove]

Uncle Pug once bubbled...
Somebody PM'd me and asked if I would make a post to this thread since I dive double 72s (as well as double 104s, single 104s, single 72s, ect.)

But I didn't want to have to read the whole thread so could you please sum it up for me in one succinct sentence?

Thanks.

I'll give it a shot.

One time at bandcamp..........ahh never mind

 

[Don Burke]

Karl_in_Calif once bubbled... Agreed. I should have added, that for EAN32 dives, twin 50s would be the most appropriate.

That is also one more reason why the twin 45s are so perfect overall for NDL diving.

My figures show that running a set of 50s to the EAN32 no-stop limit at 100 feet puts a diver pretty close to an OOA ascent. I'll carry the extra gas instead.

I wish I could afford to have as many sets of doubles sitting around as you think I should.

 

[newdiverAZ]

I'll give it a shot too.
Gas management and proper planning.

lal7176 once bubbled...


I'll give it a shot.

One time at bandcamp..........ahh never mind