Switching to doubles - Am I in a rush?

[Searcaigh]

I recently switched to doubles as an alternative to slinging a pony, took me a couple of dives to perfect my buoyancy especially as I always carry a camera with HP7.9L doubles.

Just picked up a new set today of two of my old S50s, which I am assuming will be slightly more buoyant than my other HP set, so some check out dives will be needed to sort that out, but I don't expect too many issues.

 

[Colliam7]

I have around 30 logged dives, since I've started logging them . . . I am comfortable diving in cold water and less than ideal conditions. . . . I want to get an idea if switching to doubles is in anyway rushing myself. I thought that my initial foray into diving was sort of rushed and I don't want to get ahead of myself, mastering the mental and physical skills of diving is more important to me than some new gear.

I agree with the general consensus, that you are not necessarily 'rushing' it in considering a switch to doubles. I also think TSandM makes a very good point, about gaining experience and a level of mastery of buoyancy and trim using a single cylinder configuration. If you feel that your B & T control is reasonably well-developed, then doubles are something to consider. You will have a new learning curve. Depending on the doubles set you use, you may find the initial experience to be a bit frustrating - most of us who dive BM or SM doubles have gone through that. Adding to your gas supply has the potential to put you into a challenging situation if you don't pay attention to NDLs. You mention that you did not get encouragement to log dives, even the ones done to complete your OW certification. I have to wonder - did you get encouragement to PLAN your dives based on NDLs and gas supply? I am not criticizing your training, merely pointing out that moving to doubles should encourage you to move to a new level of dive planning. Assuming your profile is accurate, you are already in a drysuit, which is good, if you are comfortable with it. Going to doubles as a drysuit diver was, for me, a real asset - I could take a lot of weight off my waist (and put it on my back). You will be well-served to change your BCD (to a BP/W), you will have the expense (not trivial) of cylinders, rigging, regs, etc. And, I agree, that getting some initial training / mentoring is a good idea. I put together a set of doubles, and started diving them years ago, with advice, but without formal training. And, that worked. When I then took tec, I learned a lot more, possibly because I had already worked through the more common initial issues of strapping myself to 100 lbs of weight and jumping in the water.

I think you are the best one to answer the question, because you know how comfortable you currently are with your B & T. If you feel you are still early in the curve of developing control of B & T, I would stick with a single cylinder configuration for a while. If you feel you have reached a reasonable level of control, then stepping up to the next level of learning in a set of doubles is not 'rushing' it.

 

[elan]

Haha, no my SAC rate is rather average....
My point was that if a diver is totally reckless not monitoring their gauges and timing they can have problems far worse than hitting an NDL.

Some single tanks are actually bigger than doubles.

It doesn't have "nothing to do with it" at all, not sure if you read my post. A diver who is not paying attention to NDLs can rack up a much bigger deco obligation with
doubles than the same diver with a single tank.

But congratulations on your low SAC rate, if that was the point of your comment.

 

[kylehorn]

I have to wonder - did you get encouragement to PLAN your dives based on NDLs and gas supply?

I did, but it didn't seem very thorough. My OW check outs were in Cape Anne in April so we were in 46f water - needless to say our checkouts were short. I don't think we went passed 20 feet and the dives themselves didn't last more than 15 minutes. Only thing we could plan on was being cold, really. It was quite the first experience.

While I haven't done dives that have required extensive planning I am always monitoring my NDL and gas in reference to the dive I'm doing - I'm very conscious of what my limiting factor is likely going to be on the dive. I've been on a couple dives where things have not gone to plan and I've had to adapt and react to correct whatever the situation called for.

 

[doctormike]

Haha, no my SAC rate is rather average....
My point was that if a diver is totally reckless not monitoring their gauges and timing they can have problems far worse than hitting an NDL.

Some single tanks are actually bigger than doubles.

True dat! Point well taken...

But with most things, the devil is in the details. Yes, you can certainly set up a set of double 50s (as fdarden posted) which gives you redundancy without extra gas, but the vast majority of people diving doubles will have more gas than a single tank diver. Even double 72s give you more gas than the biggest commonly available single tank.

So while it's true that a person with absolutely no situational awareness is at more risk for OOG than a deco obligation, most people (especially those diving in cold water with doubles) aren't like that. But bringing extra gas does put you at risk for a greater deco obligation if you are not used to tracking that - and believe it or not, many new OW divers are simply not aware of this at all.

I have seen it several times in warm water where people are diving without a basic understanding of decompression theory or NDLs, despite having passed their OW exam. I just saw this last week, in Cozumel with a club dive, when a friend of mine was asking what was the point of a dive computer, what was it actually measuring. While it doesn't look like the OP is in this category, we didn't really know that when all we saw was 30 logged dives.

A lot of new divers (like my friend from Coz) follow the "follow the leader and ascend at 700 psi" rule that Caribbean divemasters promote. So if you took that person and put a set of doubles on her, she might well rack up a good bit of deco. Yes, you can easily blow past your NDL with a single tank too if you SAC is decent, but it's a matter of degree.

 

[kylehorn]

This happened to my girlfriend - she went into a short deco on a 70 ft dive we were doing in the Bahamas. Luckily for her, she's not like me and could probably breath an AL80 for the next 400 years and not get low on gas, so she was OK. She just wasn't aware of how to read the computer and utilize the information it gives you. Her OW dives were in Cozumel and she was simply lead around by an instructor or DM who acted as their 'computer'. The problem was easily remedied by going over the different information displayed on the computer during our surface interval.

 

[Rooster In Ohio]

The problem was easily remedied by going over the different information displayed on the computer during our surface interval.

IMHO (and it really is humble), a dive computer is generally not a planing device; rather, it provides a historical record of a dive's execution based on depth and time and associated inferences based on whatever algorithm is programmed into it. The quoted statement appears to be exactly what the post suggesting that anyone moving to doubles needs to be up on his or her planning skills because gas will now be sufficiently abundant to allow the uncautious or unaware to exceed NDLs was cautioning against. Someone told me long ago that hope is not a plan, and I don't think that waiting for some computer to start flashing is much of a plan, either. Planning allows one to anticipate and either avoid or otherwise account for foreseeable consequences of actions; noticing that one's computer is announcing that one has exceeded NDLs calls for a reaction within the scope of available options, one of which may or may not be making an appropriate deco stop (again, based on the computer since there was no plan in the first place) based on remaining gas. I plan because I don't ever want to be in the position of having to decide between deco and drowning.

Sorry to be preachy, the comment just really scares me.

R/S,

db

 

[Lorenzoid]

I've been reading this thread with interest, and this seems like a good place to chime in with a question.

Assuming one is diving from a dive op's charter boat, how do dive ops generally feel about people using doubles on no-deco dives, and how do the mechanics of stowing the rig, switching tanks, etc. typically work on board?

I can imagine that some boats in the Northeast and other wreck diving locations routinely have people diving doubles and make accommodations for them with appropriate tank holders and sufficient space between seats/holders. But what about dive ops and boats that don't see many customers with doubles? Do they roll their eyes and wish the guy with the doubles would just dive a single tank like everyone else? If he looks out of place, do they worry that maybe he's likely to get himself into unplanned deco (or worse yet, that he secretly plans to do a little deco when the boat forbids deco diving)?

As for the mechanics of handling doubles on a boat, are two standard single-tank holders typically spaced apart by the same width as two tanks rigged as doubles? Or does the diver with doubles necessarily take up extra spaces on the boat that would otherwise be used by single-tank divers? If so, I'm sure the dive ops just love that.

If one is doing a 2-dive (no-deco) charter, is it typical to switch out tanks between dives? It occurs to me that unless the diver switches out tanks, he is starting the second dive without the ample reserve that presumably prompted him to use doubles in the first place. Switching out tanks on a doubles rig is obviously not a quick thing to do like it is with a single tank. I imagine it requires tools.

It has occurred to me that doubles might be a better way to provide redundancy and an ample reserve than a pony bottle (as Searcaigh mentions he did). But perhaps being the guy with the doubles on a boat full of people diving singles presents some additional challenges?

 

[kylehorn]

Rooster Im not sure I follow your reply. My last post was in reference to someone diving a single
tank who was unaware of how to use the information displayed on a computer. By showing her what information she could monitor while diving, she could avoid surpassing her NDL on future dives. This happened while we were diving in the bahamas, with a large group who all knew one another so our dive briefing from the guide was our general plan...we werent left with much time to plan the dives ourselves before we splashed. We got to a site and were told basic info; landscape, currents, depth etc...and then we splashed.



Lorenzoid,

On my trip one of my group members was diving sidemount. While I cant speak to someone diving doubles the charter simply gave him the two tanks he would have dove individually which he outfitted with his bands and clips. He kept them that way for the week we were there, no problems. Doubles on the other hand seem much more cumbersome on a boat that is doing single tank dives. It doesnt seem feasible, especially switching tanks.

 

[Rooster In Ohio]

Rooster Im not sure I follow your reply. My last post was in reference to someone diving a single
tank who was unaware of how to use the information displayed on a computer. By showing her what information she could monitor while diving, she could avoid surpassing her NDL on future dives. This happened while we were diving in the bahamas, with a large group who all knew one another so our dive briefing from the guide was our general plan...we werent left with much time to plan the dives ourselves before we splashed. We got to a site and were told basic info; landscape, currents, depth etc...and then we splashed.

I don't want to beat a dead horse or hijack your thread (which I think is a good one), but my point is directed at exactly what you describe - I won't simply splash and follow the leader, relying on my computer (or the DM's computer or anyone else) to tell me if and when I've exceeded NDLs, PO2, or anything else as I go. I have made an absolute commitment that I will plan and execute each dive and make sure that my buddy understands and is committed to the plan (planning is commensurate with the conditions - and may be as brief as establishing a max dept, max bottom time, and max run time for a simple recreational drift dive on air) and I am not shy about asking to DM to be more specific in his briefing. As a tangent, my commitment includes a commitment that I will not enter any unplanned environment during a dive just because that is where the leader goes - I will only enter if I determine it to be appropriate (think overhead, swim through, etc.).

I think the post to which I referred was directed at this same issue - the greater the volume of gas carried, the longer the diver can remain at any given depth such that a diver that is used to splashing and going until reaching 500 PSI on a HP80 may find him or her self way past NDL (or PO2 limits) long before 500 PSI comes around when carrying more gas (steel 120, twins, etc.) - thus emphasizing to the need to plan before the dive and not just follow the leader and/or react to the historical data your computer may be giving you.

R/S,

db