Diving Doubles

[kanonfodr]

Yea we thought about other tanks But like the Size/Weight of the 100's. but if we did go bigger it would have been either the 119's or 130 but at that point rather just go with 2 100's

I'd much rather have a single HP130 over any doubles any day of the week, if the dive doesn't explicitly require double tanks (overhead, COOLD water, etc) and especially if you are slinging an AL40 as a pony. Easier on the back, both above and below the water; easier to transport, but still plenty of gas. The only reason I use my AL40 with my HP120 is so I have about 80 cf of gas for 2 dives by staging the 40 on the first dive, the second dive I leave it in the Jeep.

Peace,
Greg

 

[Sas]

I'd do more dives in a single tank if your dive count is accurate especially if you are not needing it for any diving you are doing now. Maybe in another 50 dives or so when you are most likely much more comfortable with trim and buoyancy in your single tank, start borrowing different types of doubles off friends to find out what you like. Then get your own set. You might hate diving with them or lose interest in the type of diving that requires them in the mean time.

Get someone to explain valve drills and how a manifold works if you plan to get manifolded doubles. You don't need a class, it is easy stuff. I mean a doubles clinic won't hurt but it's something that can be self taught.

Personally I avoid using doubles wherever I can though I have 100cf manifolded twins and am soon going to set up sidemounts. Single tank + wetsuit is the most simple, pleasant diving for me but got a twinset for overhead diving (primarily redundancy reasons) as I am doing a lot of that these days. Otherwise I would not bother with twins for dives less than 100'... I'd probably just sling an AL40 for dives down to 130' or solo dives if they were NDL no overhead dives.

Oh and my SAC rate more than halved in my first 80 dives so I am sure you'll find amount of gas less and less of an issue even with a single tank.

 

[Mayor]

Started with a set of steel HP 100's that I found to cause me all kinds of problems with trim. They are long gone and replaced with a few sets of alum 80's. Of course I found this out the first day of GUE-F. My point is sign up for a class like this one, pass or fail it will give you the skills needed and in the long run save you some green. They really don't charge enough for a class like this. The information and skills will last a life time.

You will never find what your looking for online...

 

[keithdiver]

Started with a set of steel HP 100's that I found to cause me all kinds of problems with trim. They are long gone and replaced with a few sets of alum 80's. Of course I found this out the first day of GUE-F. My point is sign up for a class like this one, pass or fail it will give you the skills needed and in the long run save you some green. They really don't charge enough for a class like this. The information and skills will last a life time.

You will never find what your looking for online...

Jim, did you just feel the 100's were to heavy top or bottom for trim purposes?

 

[DevonDiver]

You will never find what your looking for online...

​

 

[halocline]

Oh, this is SO true! When Peter first started diving his doubles, he did what most of us did -- ended up in strongly head-up trim. He kept moving weight UP his body, despite me telling him over and over again that he needed to add weight LOW. When he finally did start moving weight down, he was amazed at how his trim corrected itself.

Joe Talavera used to have a LOVELY essay on this on the defunct 5thD-X forum, talking about how too much weight high makes you rear up to shorten the effective lever arm through which the excess weight can act.

You can waste a lot of time trying to solve weight, trim and gear adjustment issues on your own, when a good mentor can fix problems in a few minutes.

I don't really understand this. Are you saying that when someone starts with doubles, they typically have too much weight up high (that makes sense) so in order to counteract the head-down tendency, they dive with head up?

I guess....for me it was simple. First time out, I went head-down, so I moved some weight down, problem solved. In my case I was able to move the tanks down to a lower set of holes in the BP and the wing up a bit.

I'm also a big believer in using doubles in OW for training, if it's your intention to eventually dive in overhead environments. I use my doubles to assist with OW cert classes in 15 ft of water. It's great practice hovering and just moving around with doubles.

 

[rjack321]

I don't really understand this. Are you saying that when someone starts with doubles, they typically have too much weight up high (that makes sense) so in order to counteract the head-down tendency, they dive with head up?

Yes its called "popping a wheelie". If you have too much weight up high you'll drop your knees and rear your torso back towards vertical in an effort to shorten the torso "lever" and have some semblance of a center of gravity (CG) near your waist/hips. Your CG will be near your waist, but you will be far from flat & level.

 

[Tortuga68]

I've never seen that problem with AL80 doubles

You will never find what your looking for online...

What he's looking for online is advice on whether a formal doubles course is required; I'd say he's found that already

if the dive doesn't explicitly require double tanks (... COOLD water etc)

Why does cold water explicitly require doubles?


I've done quite a few rec dives with doubles; the best thing about diving recreational doubles is the feeling of freedom (on land) when you put a single on But given the OPs plans I don't think it's a bad thing at all

 

[Mayor]

Jim, did you just feel the 100's were to heavy top or bottom for trim purposes?

Tanks were not long enough for my frame. I did like them but as I became more skilled, the SAC was reduced the 100's were not worth the trouble.

 

[keithdiver]

Tanks were not long enough for my frame. I did like them but as I became more skilled, the SAC was reduced the 100's were not worth the trouble.

Thank you Jim.