Training for "Recreational Trimix"?

[Slamfire]

One more thing on the doubles, Guy. A 130(43lbs)+ a 40 (15lbs) = 58 lbs. Two Al 80s = 62 lbs. None of these figures includes valves. And carrying two securely stable tanks on my back is more comfortable than carrying a lopsided load of a big tank with a stage, IMHO.

 

[danvolker]

One more thing on the doubles, Guy. A 130(43lbs)+ a 40 (15lbs) = 58 lbs. Two Al 80s = 62 lbs. None of these figures includes valves. And carrying two securely stable tanks on my back is more comfortable than carrying a lopsided load of a big tank with a stage, IMHO.

This point is not to argue...as both Sandra and I have doubles, and obviously I have used doubles for decades.....
The BUT...
But it is very hard to utilize charter boats, with the way charter boats are configured, and the way trips are run, with doubles:

1. Charter boats ARE the only option worth discussing... the private boat concept is foolish to discuss here....and with charter boats, they are rigged for divers storing either 2 single tanks, or 3 single tanks....If you have one set of doubles, you still need another set of doubles for your second dive, or third if it is a 3 tank and lunch dive. Going out to do just one dive, is something I don't do, and I will always make fun of it as a marketable practice for charter boats.
2. Unless the charter boat is a huge 46 foot Newton, with only 6 divers on board, there will not be enough room for 6 doubles divers ( two or three buddy teams) to store their 2nd and third sets of tanks for the other dives. Making a boat to be rigged for this, would be horrible for it's profitabilty, and a charter captain wanting this, is going to have a screw loose.
3. So Boats are set up for single tank diving. Doubles divers can get by if there are only one or 2 doubles divers on board, if the boat is not to crowded, but nothing is set up for doubles to be easy, and it never will be.
4. Special Doubles charter trips for tech divers can happen, but this introduces the worst form of single dive scenarios and deco weenie nonsense, that it is not something I would usually find desirable....on most of the tech trips that get run. They loose all the spontaneity and fun of a normal recreational trip, and you waste the whole day waiting for other people....and not diving that much.
5. Yes doubles are better by far in technical situations than a 120 or a 130....there is no contest. I love the way doubles feel in trim and balance--though they are slow in the current, and this can be a big negative in some places like the Hole in the Wall, where a 4 mph current can blow a doubles diver all over, but a low pressure 120 diver, with it jacked to being a 170, could be slick enough to have a better diving experience here. So while for the standard wreck penetration, that so many tech divers waste their time with, seeing almost nothing of any interest inside the wreck--while the doubles are far superior to the big single tanks in this environment....if you want to be outside of the shipwreck, on the deck, around the structure, all the places the larger masses of marine life and interest is found, then being slick in the current is more important than being stable in a dead stop hover in a place without currents.
6. Where is it said that tech diving is about penetrating? It should be about the best sights underwater in my book. So it will differ from site to site, whether this is a penetration mission, or a cruising around without penetrating mission, or just a deep reef cruise.
7. While I can carry doubles easily enough, many people get beyond the "critical threshold" they can carry with doubles, and can injure their backs. If boats and shops were set up properly for doubles users, and it was always easy to put them on your back and move them from one platform to the next, then it would be better...but this is the rare boat or shop, and most doubles divers have many awkward lifting angles and needs they get stuck with, and often their backs get involved in ways they should not, for the weight of the rig...and the result is the potential for a LIFE CHANGING INJURY that may be even worse for your future quality of life.
8. Having to buy 2 sets of doubles with manifolds, or 3 sets of these, so that you can enjoy diving with your friends that actually enjoy diving on 2 tank or 3 tank and lunch dives....is very expensive, and also means you need to buy a van or a truck to carry all these huge setups with....So a lot of this doubles stuff is really stupid for most divers.....Really it is stupid for me, but when has that ever stopped me

 

[TSandM]

You do add about ten pounds or so for the bands, manifold, and second regulator . . . There is no question in my mind that walking on a tossing dive boat in doubles is harder than doing it in a single tank, if you weigh about what the gear does. On the other hand, double Al80's dive like a dream. Some of the most delightful diving I've done anywhere was cruising around the Red Sea, doing recreational dives in double 80's and a dry suit. And someone diving wet wouldn't even have to wear as much weight as I did!

And they were pretty fun off West Palm, too . . .

I'm 5'4", 120 lbs, and couldn't climb out of the swimming pool in a single Al50 when I started diving

Edited because Dan posted while I was typing . . . There is no reason not to be able to get two recreational dives off a single set of Al80 doubles, IF you can get those two dives off two SINGLE Al80's. It just takes some simple planning. You can use a whole 80 cf on the first dive (which leaves you with 80 cf on the second, out of which you DO have to reserve rock bottom.) I've done two dives in Monterey off a set of 72s, although the second one had to be cut a little bit short to maintain rock bottom, because it was deeper than would have been ideal.

 

[danvolker]

I'm 5'4", 120 lbs, and couldn't climb out of the swimming pool in a single Al50 when I started diving

Edited because Dan posted while I was typing . . . There is no reason not to be able to get two recreational dives off a single set of Al80 doubles, IF you can get those two dives off two SINGLE Al80's. It just takes some simple planning. You can use a whole 80 cf on the first dive (which leaves you with 80 cf on the second, out of which you DO have to reserve rock bottom.) I've done two dives in Monterey off a set of 72s, although the second one had to be cut a little bit short to maintain rock bottom, because it was deeper than would have been ideal.

Hi Lynn,
I am just putting this out because most of us in tech, treat this issue as Black and White, and it really is not, due to the lack of support for the doubles choice/direction by shops and boats and cars.

As to the 2 dives on one set of doubles, in Palm Beach, unless it is a very shallow baby dive like Breakers or Pauls, the dive will be 75 feet or deeper, and the norm is going to be hp 100's or more for this, among the advanced divers you are with....so you can't make half of your doubles, last long enough !!!

Every time I have tried the doubles thing on the normal rec dives north of the inlet( depths 75 to 100--not talking about deep dives), all the people I dive with are using hp 100's or bigger, and I end up having to work harder, dragging the slowest tank set up around, and end up with way less gas per dive than anyone else. It does not work, unless I want to bring a second set of doubles along..and none of the boats would like that

Best,
Dan

 

[TSandM]

Oh, Dan, for those dives off West Palm that we did, I totally agree with you . . . logistics for two deep dives like that are difficult with Al80s, and I would have been happier with two bigger singles. It would have made walking on the railing-less, steep and unstable ramp off the boat in Jupiter less frightening, too

Honestly, I don't know what the best answer for the OP's wife is. Single 130s are not light, and swapping them out on a tossing deck is not fun. But Al80's as doubles are only really going to give you one dive at the depths they're talking about, unless it's a very short dive indeed.

Cost/benefit and convenience factors just line up with narcosis issues, and that's why the vast majority of the dives I do nowadays are about 70 feet max depth.

 

[halocline]

Maybe sidemount is worth thinking about in charter boat cases, just gear up in the water and hand the tanks up one-at-a-time. I'm sure there will be lots of sidemount cheerleaders that would agree.

I didn't know about the sensitivity to ascent rates of trimix, so I learned something new on this thread!

 

[danvolker]

Maybe sidemount is worth thinking about in charter boat cases, just gear up in the water and hand the tanks up one-at-a-time. I'm sure there will be lots of sidemount cheerleaders that would agree.

I didn't know about the sensitivity to ascent rates of trimix, so I learned something new on this thread!

Except a diver that takes that long to get out of the water, is forcing everyone to wait for them...it is a behavior to be discouraged.

 

[dumpsterDiver]

The OP was asking about a non-deco dive in 100 to 130 feet. I do those kinds of dives in that area with a large single steel tank and a 13 cu-ft pony bottle. I also, was not aware that the Nodeco limit for helium mixes is less than nitrox. So if they are going to dive helium mix, then i guess their dives will be even shorter. And if they are doing repetative dives, then they have a 3-gas computer or tables? And then they need oxygen to do their no-deco stop too if it is on helium mix? Is that the recommendation?

 

[danvolker]

The OP was asking about a non-deco dive in 100 to 130 feet. I do those kinds of dives in that area with a large single steel tank and a 13 cu-ft pony bottle. I also, was not aware that the Nodeco limit for helium mixes is less than nitrox. So if they are going to dive helium mix, then i guess their dives will be even shorter. And if they are doing repetative dives, then they have a 3-gas computer or tables? And then they need oxygen to do their no-deco stop too if it is on helium mix? Is that the recommendation?

The difference in no deco is mostly that you just need little 1 minute stops on the way up, in a few places.....time to surfacing is just a little slower because helium comes out of your blood faster than nitrogen....the flip side is that after a 40 minute surface interval, the recreational trimix diver should be considerably better offgassed than the Nitrox diver that was on the same dive.

And no, If I did the Hole in the Wall on 25-35, I would not bother with an O2 bottle. If you and I did the same dive, same bottom time, you on Nitrox might intially ascend faster, but you would still be likely to do a good long safety stop, and I would be catching up at that point, and could get out of the water "almost" as soon as you would with your Nitrox.

 

[Scott L]

And no, If I did the Hole in the Wall on 25-35, I would not bother with an O2 bottle. If you and I did the same dive, same bottom time, you on Nitrox might intially ascend faster, but you would still be likely to do a good long safety stop, and I would be catching up at that point, and could get out of the water "almost" as soon as you would with your Nitrox.

When are we doing the dive again?