Going from singles to doubles

[zackalack8999]

Several Questions:
First, what size tanks do you recommend if I am diving singles now, but may pursue doubles in the future? I am definitely leaning towards steel, but I do not know the advantages of LP v. HP, so if anyone could clarify that as well that would be awesome. I'm a young guy(18), so air consumption is not all that big of a deal, but of course i'd like to maximize my BT. Second, how many dives would recommend doing before beginning to dive doubles/ getting into the technical aspect of diving? What are some courses that would help this transition?

 

[Dive-aholic]

What exactly are your plans with doubles? What's your body size - height/weight? What's your current experience level?

LP tanks came about due in part to shops not being able to fill HP tanks to the required pressure. An LP95 is the same as an HP119 and an LP108 is the same as an HP 133 if the respective tanks are filled to the same pressures. Fill a 95 to 3600 and you have a 119.

Steel tanks come in different heights and with different buoyancy characteristics. So you're body build will dictate which tank is best for you. You might be better off trying a few different sizes out to see which gives you the best trim.

Number of dives isn't as important as your trim and buoyancy. Make sure your dead on with buoyancy in a single tank. When you go to doubles, it will be all new. Start off with an Advanced Nitrox/Deco Procedures course after you've had about 3-4 dozen dives in doubles. And don't touch the manifold underwater until you're trained on it.

 

[DA Aquamaster]

Advanced Open Water and Rescue courses are common requirements before taking technical training. Some instructors may require 100 dives below 100 feet before accepting divers into some tech classes.

I am an advocate of starting your rec diving in gear similar to what you plan to use in technical diving. (BP/wing, long hose primary, etc). The bad news is that there are not many (if any) wings that work well for both singles and doubles so you either need two wings or will need to compromise a bit when single or double tank diving. For example the Dive Rite Rec wing works ok for both doubles and singles but excels at neither.

Most entry level tech courses start with gear configuration for doubles but if you wait that long to start diving doubles you are adjusting to using doubles at the same time you should be focusing on the more advanced and more critical skills in the course and that strikes me as pretty stupid. Consequently I am an advocate of getting familiar with doubles configuration and use prior to taking your first tech course.

Doubles themselves are not that hard to master with most of the learning centering on proper equipment configuration. Out of the water they are heavier and in the water they have more swing weight and have different weight requirements. Along with this trim issues will be more critical. But none of it is hard to master if you have access to someone with doubles and technical diving experience who is willing to mentor you a bit and help you get started.

Precise bouyancy control and proper weighting are essential. Due to the larger swing weight from the greater air capacity, you will be much more negative at the start of the dive and will be carrying more gas in the wing than you would with a single tank, so bouyancy control is a bit more difficult if you are not already proficient. Over weighting just amplifies the problem.

Tank wise, I like the E7-100. It is more or less AL 80 in size (2" shorter) and weight (1.7 lbs heavier) but offers 100 cu ft at 3442 psi and still offers about about 90 cu ft if you can only find 3000 psi air. It also has better boyancy traits than the AL80 but is not so negative as to cause major problems if you dive doubles with a thin wet suit or shorty. But it still is -1.3 lbs empty and -8.8 lbs full, per tank so you need to be aware of and avoid situations where you could eb over weighted. In general though it works well for most average sized people.

AL80's are also a good choice for entry level doubles and they offer the advantages of being cheap and readily available. Due to their bouyancy traits it's harder to over weight yourself and they are rock solid stable in the last half of the dive as they become slightly positive and it is much like floating around under a blimp. Trim issues are usually a bit less critical as well. And they offer 154 cu ft of gas which is more than enough to get you into 150' deco dives with run times in the 45-60 minute range if you are not a hoover.

 

[TSandM]

You've gotten good tank advice, and I'll chime in with a class recommendation. No matter what kind of technical diving you think you might want to do in the future, taking DIR-F is a good foundation. Even if you go on to do further training with another agency, the basic skills of good buoyancy control, correct trim, non-silting propulsion, and composure under task-loading are good to learn.

If you like, PM Rick Inman about what his technical (IANTD, if I recall correctly) instructor said about what Rick learned in Fundies.

You can get more information about the classes by going to the GUE website at gue.com.

 

[crpntr133]

Good job DA Aquamaster!
I just started diving doubles. I can say that diving doubles isn't hard but it is for sure different. I have the buoyancy under control but the trim is waaaayy off. With 4 dives I fell pretty comfortable.
I did a weight check and dropped 2 lbs. Of course this helped the trim and I could tell it with how much easier I went through the water. Never knew how much difference 2 lbs could make.

I choose to go with lp-77's since they are about the same characteristics of an AL-80 but no buoyancy. Also the whole hp fill problem. If you can borrow a set of doubles and dive them, do it. The biggest problem I had was with carrying the tanks to the water.

 

[zackalack8999]

I'm about 5'11- 6' and 160 pounds. I just recieved my AOW and nitrox training a few weeks ago, and am going to continue to dive as much as possible over the summer. I'm hoping to bulk up a bit over the summer though (don't know how well that one is going to work out). I understand that I will need a different wing when I eventually do switch to doubles. I've heard a lot of people pushing steel tanks, so when I do buy my own tanks and stop using the AL80s at my LDS then I will probably end up going with the E7-100. Thanks for the advice.

 

[Dive-aholic]

With your height, I would try the 26" tanks. They should trim you out nicely.

 

[jswensva]

I'm about your size (I'm an inch shorter and am about 160 now, but usually drop to about 150 or a touch less in summer once I start running). I've found the E8-119s are great and easy to don on boat/land, etc. Short notice, but The Dive Shop on Broad St. is doing a wreck diving seminar this evening from 7-9pm. I'll be there filling my tanks for a Morehead trip this weekend and hooking up the Haskel . Feel free to drop by and see how the tanks fit you.

Jason

 

[pickens_46929]

Also don't forget you can typically rent tanks to try various sizes too... went down to Northern Florida cave country and spent 2 days diving doubles before settling on LP-85s... dove LP-85s and LP-95s

Talked extensively with my technical instructor about pros and cons of LP vs. HP... ended up going with the LP tanks because they trimmed out so nicely and was buying at the right time (eg. they were on sale).