Size of Doubles

[Captain Ron]

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

 

[TX101]

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

The best way is for you to work it out yourself. Estimate your max depth and desired time, add some contingency - whether it be 1/3rds, rock bottom, etc then multiply by your SAC and thats your gas requirements. Also remember that you will usually be carrying deco gas seperately so you can calculate that and size your deco cylinder(s) accordingly (note to pendants: let's just forget about lost deco gas for now, okay?)

My SAC is a little above average (around 20L/min and I plan for 25L/min). I wear twin 12's, so for a 40m dive (for example), I'll be lucky to get 35-40min bottom time on a square profile.

As far as ditchable weight.. well that debate could go for pages. My personal preference is a weightbelt because thats what I'm used to - but I do my crotch strap up over my weightbelt so if it comes loose I don't have a rapid ascent. My head says there's no reason to ditch weights while diving as it can cause more problems than it solves, so I probably should go for v/p/etc weights on the backplate. But then again it makes passing up the rig to people on a RIB a pain in the *** - the twinset is heavy enough as it is without adding another 6kg.

 

[goatboy_k]

85's might be a bit small, but it all depends on what kind of dives you want to do. Most people i dive with dive 104's or 108's doubled up. But we can usually do 2 dives on one fill (200 foot range for 10 to 20 min decent and bottom time apeice square profile). If you plan your gas you will know what your going to need and how much reserve you'll have to play with. Your class should go into the quite a bit. I also have a set of e7-80's that are really nice, i can do the same dives but i get only one dive with alot left over, or a couple shallower ones. It really dosn't matter how big your tanks are as long as you are responsible planning your gas. If you got 85's do dives with depth's and times that are reasonable for 85's. The only time it's really mattered to me is in class where everyone else had 108's. Gas matching, planning turn pressures, and blending, is quite a bit easier when everyone is on the same size of tanks. I was using 104's so the difference was pretty much nill, but had i used 80's or something else the math just to figure turn pressure vs. volume would of been a pain. Also we were also just walking into the lake or quarry so the big tanks really don't matter as much as if we were in the ocean or on a boat. Overall i would be proud that you own your own set of 85's. Once you start planning your dives and gas in class you'll figure out if your next set should be bigger or smaller.

good luck

kurt

 

[goatboy_k]

forgot about the weight part

i use a fred T 12lbs backplate for all my weight. It's the 1/4 inch stainless regular length model. this is the setup i use for all my diving. Even with the big doubles, drysuit with 400g undies, 2 alum stages, and halcyon 13.5 can light i am weighted perfect, if the doubles get down to about 500, and the stages are starting to get low, i am weighted perfect at 20 feet or so.

most of the guys i dive with just use their plate for all the weight. Some like me have to use thick plates, one guy i know only has to use an alum plate and he's perfect at the last stop. really depends on you.

the reason i choose to use only the backplate for weight is you don't have to fumble with a weightbelt or have anything other the the harness on. And more importantly even at the entry level of deco diving there really isn't an option to ditch weight and make a run for it. if you do loose weight your prob not going to stop, and if you have a deco obligation thats bad times. All probs have to be worked out at depth. Rely on your wing, as well as your drysuit for backup. In a last ditch you could winch yourself up with a liftbag, but that's a long shot.

One other weighting option i have seen alot of guys do is with the weights on their doubles. The use a standard backplate, and then use a camband with a weight on it. The weight is cinched between the tanks somewhere. One good thing about this system is that you can change the amount of weight, (unlike my thick plate). So if you move up your drysuit insulation you can add a bit more or whatever. The other really good thing about this way is you can move the weight up and down the tanks to dial in trim. This is especially nice when your first starting with doubles or if your having probs with floaty feet or something.

Lots of different options. Pick whats best for you and that will be what works best for you

good luck
kurt

 

[kramynot2000]

I think for the initial tech dives you'll be doing, the 85's are sweet. I dove a set on a trip to B.C. and loved those tanks. For me they seemed to trim out really well. Plus they are relatively light so they are easier to haul around for shore dives, recreational boat trips, etc. I have a small set of HP80's that are great for the small stuff. For the <165' dives they are all I need and its a lot easier to move them around than my buddy's 130's. He's actually gonna get a set of 80's or 85's because he's tired of lugging around those big tanks. For the deeper dives though he'll use his 130's and I'll go up to my LP95's and just pump them up a bit.

As for weight, I think some of this decision will depend upon your trim. Many people, myself included, find that they are head heavy in doubles, particularly smaller ones. So, you may need to move your weight lower to counteract this, such as going with an AL BP and using a weightbelt. Personally I like the AL BP/weightbelt combo instead of a heavy BP because it makes moving your gear around topside easier, particularly on a small boat.

Just my $0.02.

Tony

 

[Doc Intrepid]

Captain Ron,

What are your buddies diving?

The team turns when the guy with the lowest supply (ratio of volume and consumption rate) hits turn pressure first.

This is because even if you have a low consumption rate, but your buddy has a high consumption rate, and he runs out of gas at the deepest point of penetration, you have to bring both of you back.

So, your tanks become assets of the team - not just you. It is wise to have most members of the team equipped with the same amount of gas.

So.....what are your buddies diving?

Doc

P.S. on the weight issue, many find that twin steels + a 6lb bp don't require much more weight. If you do, a V-weight works best IMHO.

 

[matt_unique]

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

I'm doing entry level tech (<160) and my double (aluminum) 80's are plenty. For example I can do two 150' dives (dive one for 20 min bottom time and dive two for 15 min bottom time) and surface after dive two with 1/3 of my back gas remaining. This of course assumes you are using a stage bottle(s) for deco. There are other contingencies that would reduce or limit the dive 2 ability of course - failed stage systems, buddy air share, higher than planned air consumption, etc.

Tank weight is also a factor to consider. Lighter is obviously easier in terms of lugging things around.

I personally prefer ditchable weight worn on my harness rather than a weight belt in terms of comfort. Steels require less and in some cases no lead.


--Matt

 

[Hyper-limits]

I'm doing entry level tech (<160) and my double (aluminum) 80's are plenty. For example I can do two 150' dives (dive one for 20 min bottom time and dive two for 15 min bottom time) and surface after dive two with 1/3 of my back gas remaining.


--Matt

I love my 85's, When I did my deco course I used twin 72 that I borrow from a friend and they were good enough for that course. Because I do a lot of shore dives the 85's
are the best choice for me. I done dives to 200+fsw(using stages for deco) and I finish with 1/3 or more gas remaining. I also done 2 deco dives with a profile similar to the one Matt described above and I had over a 1000psi remaining. So depending of your SAC/RMV they should be perfect.

 

[Epinephelus]

I prefer diving my 85's (rather than 104's) whenever the gas plan allows it, which is most of the time. In fact I plan to get another set when I can afford to.
E.

 

[scubaputz]

I'm using twin 85s in my helitrox class and love them. They're perfect (for my RMV) for dives in the 150' range. My buddy with the twin 130s was cursing me all day!