Size of Doubles

[JS1scuba]

I'm just getting into Tech. Are the twin Faber LP85s I just purchased going to be enough for begining DECO? Too much? Should I go bigger? Smaller? My air consumption, I have found is below avarage for sport divers. Is there a baseline for air consumption that will help figure this all out. Have also purchased DR/Transpac with SS back plate. Do I go ditchable or non-ditchable weights. Thanks

Ron,

I have been diving with the Faber 85s since 1995 when they were first introduced. I own 4 sets of them. For most of my diving in the 200 fsw and shallower range in open ocean I use these cylinders. They have perfect buoyancy specs and will allow you to be very lightweight in the water. They are easy to "swim out" meaning when they are empty they are neutral and you can swim them up if you have lost your lift from some faliure.

As to how much gas you need to carry? I have found in my years at this you only need to carry what you need plus a 1/3 so do the math for the dive before jumping in.

At 2640 psi you have 170 cuft of gas. If you are going to have a 1/3 left over net of deco you have 113 cuft of usable gas. If you are average you will use .7 cuft per minute of gas, factor that to depth and you can calculate max time for these tanks.

It kinda looks like this.

FSW Minutes
33 81
66 54
99 40
132 32
165 27
198 23

If you breathe better than .7 cuft per minute you can pull more time. If you are new to deco then you really want to make sure that you don't get yourself in to more than a 3 stage (10,20,30 fsw) stops plus some deep stops too soon. Most of the dives can be accompllished in the shallow ranges with EAN and you can accelerate decompression with a simple 40 cuft stage bottle which give you upwards of 50 mimutes of deco gas when managed.

Sure there are bigger tanks, but bigger may not be better. Use the correct tank for the dive. For dives deeper than 200 fsw or where the on-the-bottom time needs to be more than illustrated above I shift to larger cylinders, 108s' and 131's (yeah i have a bunch of those too). Must past a 300 fsw dive and scuba is not efficient for effective bottom time, at that point it's rebreather time.

Hope this helps you.

 

[Captain Ron]

WOW! Lots of Info. I will be reading this thread a couple more times.
My dive buddy is using a pair of PST HP 80's and has a similar air consumption rate.
I ordered a Dive Rite Transplate harness (SS back plate) with 51lb. rec wings and an 8lb V weight. I also picked up a pair of nonditchable weight pockets that hold 5lb ea. I will be going non-ditchable weights.
It seems that the 85's will be good for what I plan to do. I also have a Pair of Faber Lp 65's that I plan on using for stage bottles and a AL 40 for 100%.
The best I can figure by my log book is a breathing rate of .7cfmin. Mondy I will be making dives to get it on the mark.
Thank You very much for the info.
Captain Ron

 

[JS1scuba]

Ron,

at 6'1 248 lbs in a dry suit or semi dry 9 mill wet suit I use a 6 lbs plate and an 8 lbs weight belt with the 85s in salt water, in fresh water no weights. Be careful with the non ditch weights or "v-weight" the V on these tanks may make them to heavy to swim out (though you should be able to) I would start out with the tanks with a weight belt for tests.

On the deco bottles --- the 66 will have you a bit tilted to the side -- its a steel bottle and has some heft to it. At 25 lbs dry neg 5.15 lbs full and neg 1.67 lbs empty this surely is a bit of a pig for a deco tank. Start off with the Alum 40 for a while. For most of the shallow stuff -- 150 and less for the most part you will only need a single deco bottle with a 50/50 nitrox mix in it.

Regards,

 

[Caver95]

But how do you guys go deeper than 130ft? couldn't you die?

 

[South Pacific Diver]

IMHO it has been wisely said "no one has ever died from having too much air". I have found it best to tailor my setup to the paticular dive. If I am diving 150' or less then I generally use a BFT(big &%@# tank) with a H-valve. 200' or less double 80s serve me just fine. Over 200' then 100s or 108s are the norm. The bottom line is know your RMV and constantly re-evaluate it. Never lose focus on gas management and never, never violate the rule of thirds. Be good at shutting down loose air quickly and take slow baby steps learning the deco world.

 

[JS1scuba]

But how do you guys go deeper than 130ft? couldn't you die?

Typically we find dive sites that have a bottom that is deeper than 130 fsw

 

[Scuba_Vixen]

Two things to keep in mind that I didn't see anyone mention yet:

The nice thing about the LP 85's over the hp counterpart, is that you get a lot more than 170cft (typically ~220) with reasonable (~3200#) overfills. So they are not nearly as small (effectively) as they may seem at first.

The other point is that "Dive the San Juans" sounds kinda tropical, so we may be talking wetsuit here. *Some* ditchable weight may be advisable in such case ... as well as redundant sources of bouyancy .... redundant bladder wings come to mind.

Safe dives and welcome to the world of overhead, where what used to be just an "ooops", is now a Big "OH Sh*t !"


Darlene

 

[kramynot2000]

The nice thing about the LP 85's over the hp counterpart, is that you get a lot more than 170cft (typically ~220) with reasonable (~3200#) overfills. So they are not nearly as small (effectively) as they may seem at first.

Darlene, this is a very good point. With my HP80's, as others have mentioned on this board, I never get a full fill. Usually I hit the water right at 3200-3300 psi after the fill has cooled down. Let's see if I can remember this:

160 cu' / 3500 psi = 0.046 * 3200 psi = 147.2 cu' of actual gas.

If I had the choice, I would take the LP85's over my HP80's but at the time I put my doubles together, I was moving up to my first set of doubles, I had two single HP80's in the garage and my LDS had a sale on a manifold and bands so I decided to do it. I've considered selling them and purchasing some LP85's but I guess I'm sentimentally attached to them now.

 

[DEEPLOU]

Typically we find dive sites that have a bottom that is deeper than 130 fsw

I think he was being a WA.

 

[scubaputz]

The other point is that "Dive the San Juans" sounds kinda tropical, so we may be talking wetsuit here.

I think he's referring to the San Juan Islands in north western Washington State...

It may sound tropical, but I certainly don't consider 48F to be warm.