Assembling first doubles rig: Looking for a starting point

[Rainer]

Easily. It means you don't have to do what Captain said and get the largest possible doubles you can handle. Instead, get reasonably sized doubles now (e.g. HP100s, LP85s, Al80s) and *then* if you need more gas in the future for longer/deeper dives, just add a stage bottle. That lets you dive more reasonably sized cylinders now and still allows you to do bigger dives later, without having to buy a bunch of different sets of doubles (though Lord knows that usually happens anyway).

Make sense?

Sorry I'm having trouble following. what do you mean by learning to dive stages? As in diving stage bottles? How would that influence the choice of back gas tanks?

 

[Colliam7]

I simply don't have the opportunity to check out what's out there myself. In assembling my first set of doubles, I will have to make do with online research and mail order. . . .

Everybody has to start somewhere, and despite all the 'research' that many of us do, we ultimately select an initial set of tanks that meets most of our needs, maybe not all. And, many of us find that 'one (set) is not enough'. But, acquiring multiple sets of doubles is a topic for another time. much further down the road.

At this point, I don't really know where to start. Should I sit down and go into V-Planner and start calculating simulated dives to figure out what capacity tanks I need?

Probably not. Your choices seem almost endless but they actually boil down to several factors which have as much to do with diving environment, buoyancy and trim characteristics, and personal preference, as capacity.

Personally, I feel that if I make the move into doubles, I might as well get as much capacity as possible, but I noticed that LP 85s seem to be very popular. This strikes me - from a noob perspective - as kind of small?

Not necessarily, if you overfill the tank. Your choices involve AL vs steel, and LP steel vs HP steel, and then size. For me, manufacturer never has made a lot of difference, although I have limited exposure beyoind Luxfer for most of my AL tanks and PST and Worthington for most of my HP steels. The drawback to HP steel you have already mentioned - some fill stations don't have the ability to fill to ~3500 PSI. I am somewhat surprised that you wouldn't find a 3500PSI fill when you dive on the CA coast, I must admit. But, the other steel issue is whether you can find a station that will overfill LP steels. In the SE, particularly FL, that is common practice, but I would defer to others who dive the west coast to comment on that.

Here is what I'm planning on diving: Sea of Cortez (drysuit in winter, wetsuit in summer); Southern California (year-round drysuit); local lakes (mostly drysuit). Most diving will be from boats.

So, most of your diving is salt water, and drysuit, BUT you want to be able to dive wet at times, presumably with the same rig. That tends to favor AL80s, or HP100s, but does not absolutely exclude other tanks.

Currently, I am thinking steel HP100's, since a lot of people seem to like them and they are a compromise in terms of weight, but no dive shop in this area will be able to fill them, I'd dive them under-filled, which would equal something like 80 cu ft times 2.

Great tanks, very popular, trim out nicely for most people, work well with wetsuit or drysuit diving, and give you plenty of gas for two recreational dives in the 80-100' range, or one deeper, and one shallower dive.

Is that enough?

And, as you can imagine, the answer to that depends very much on you - how much gas you use, and are the majority of dives you reference above in the a) 60-80', b) 80-100' or c) 100-130' range? If a., possibly b., then the answer is 'probably'. If you are routinely doing two dives to 120', or you are a self-confessed 'air hog', I would favor bigger tanks myself.

Also, would it be considered insane to dive those with a wetsuit? (In the summer, you simply cannot dive in the Sea of Cortez in a drysuit.)

You can dive virtually any set of double steels in a wetsuit. You will probably be (quite) negative, you will probably want to use an AL BP with bigger steels, and possibly go with a dual bladder wing - there are quite a few SB threads on the issue of not having ditchable weight which I will leave you to interpret as you choose. My personal preference for NC coastal, recreational, wetsuit, doubles diving - HP100s, followed by AL80s. Since we can only take two tanks on a recreational charter, which means one set of doubles, I prefer the 100s. But, in a drysuit, my AL80s actually trim out VERY nicely and are my personal favorite for fresh water, winter fun diving. I have also dove my 120s and 130s off the coast in a 3mm westuit with a single bladder wing without problem. That is not a usual practice though.

My suggestions reflect my personal preferences, and experiences:
1. HP100s
2. AL80s
3. HP130s
4. HP119s

I don't dive LP steels so, I leave it to others to promote them.

 

[japan-diver]

If you are looking at diving wet I would stick with the aluminum 80's. If you can not get the HP tanks filled getting them would be kind of a waste. Start with the 80's normally the least expensive and you can grow from there.

 

[AbyssalPlains]

Thanks to everyone for your comments and the really helpful insights! It looks like it may boil down to Al80s vs. HP100s. i just talked to a friend and dive buddy who has been using HP100s and found them extremely heavy and negative to dive in a wetsuit in warm water. Given that the Sea of Cortez gets too warm even for a 5mm in the summer and that I have dived a pair of Al80s in a drysuit before with no problem, I'm starting to think that the Al80s might be my best bet at this point. Conceptually, I still prefer the HP100s, but I'd rather have a doubles rig that is great in warm water and slightly suboptimal in cold water, than a rig that is optimal in cold water but unusable in warm water. If that's the case, then Al80s are a no-brainer. However, if HP100s are ok for diving in a 5mm or 3mm wetsuit, I'd rather have those. I guess I'll have to sit down and play around with buoyancy calculations a little bit. ;-))

 

[Doc Harry]

If you will diving from a boat, also consider whether or not you can climb the ladder with what's on your back.

 

[AbyssalPlains]

Alright, after sitting down and doing the math, I think I'm going with Al 80s. Even though I like the concept of the HP100s better, I don't think it would be a smart thing to do in my situation. Here is why: I do want to be able to use my doubles with a 5mm wetsuit. Experience tells me that with a single Al80 tank and an aluminum BP, I carry about 5 Lbs of non-ditchable weight (BP and tank) and 13 Lbs of ditchable weight. In the case of a wing failure, I can easily swim up 5 Lbs.

Double HP100s incl. BP, manifold and regs, on the other hand would leave me with at least 25 Lbs of non-ditchable(!) weight. Even though I haven't tried it, I'm pretty darn sure there is no way I could swim that up, especially in a life-or-death situation.

None of the options for redundant buoyancy in a wetsuit configuration appeal to me. I don't trust double-bladder wings, because I'd be pretty sure that whatever was enough to puncture one bladder, could easily puncture the other, too. Lift bag? I don't think so. If I'm in 1000 feet of water, sinking fast, there is no way in hell I'll be able to deploy that device fast enough. Plus, Even if I were to deploy it in time, then what? I'd do an uncontrolled ascent to the surface. I simply don't like the idea of depending on some sort of crutch to get me up from depth.

In contrast, the drawbacks of diving Al80s in a drysuit all seem manageable. In fact, I went back to my logbook and it turns out that on those few occasions where I dove double Al80s in my drysuit, I carried 14 Lbs of extra weight. I think that's not bad and I remember being trimmed out reasonably well, too.

And if double Al80s turn out too small in terms of gas quantity, I figure I can always sling another 40 or another 80 with bottom gas in addition to my deco bottle.

 

[Captain12Pk]

If you find yourself in 1000 fsw, I venture to say that deploying a lift bag is the least of your worries.

 

[DwayneJ]

I went with Steel HP100's. Also modular valves (Thermo or Diverite) so I can reassemble as singles.

Since you need valves/manifold, may want to go with DIN300... Hopefully your existing 1st stages are already DIN.

Also purchase a Transfill Whip. My LDS expects there to be air in the tank when I get a fill else they demand a VIP. When assembling or breaking your tanks, you likely will need to empty both of them and as such, the transfill whip will help you refill your tank/s from a third tank.

Dwayne

 

[LenC]

I personally prefer the HP 100's. I've used AL 80's, HP 130's, LP 95's and HP 120's and the HP 100's just worked out better all around. If you are going to go with the AL 80's, and there is absolutely nothing wrong with that decision, you want to make sure you use a manifold which will allow you to transition to HP's in the future.

 

[Elvistheking]

I've dived steel twin 12's (are they the same as HP 100s?)in a 3mm shorty with a SS BP, needed sod all lead as you would imagine but not really that much of a problem. It sounds like the vast majority of you diving will be dry so why compromise for the small amount of wet diving? As to the comment about getting up a ladder Ali80's will need probably weigh more than Steel's of the same capacity out of the water AND need more lead to sink them.

Probably a better compromise is get Steel cylinders and an Ali BP for when diving wet.