Advice for small doubles

[halocline]

i don't think TS&M is using the LP 72s that we are referring to, because she once posted that her 72s were 7.25" in diameter, the same as AL80s. The LP 72s I'm referring to are 6.9" in diameter, about 25" long, marked 3AA2250.

These tanks are very similar in size to LP85s, which are TS&M's favorite doubles.

 

[dl348]

I'm 5'9" myself and curious.

Did she manage a static equilibrium? Or does she needs to constantly adjust?
i.e. if she gets in trim and freeze, will she slowly rotate and end up with her head in the sand? Or stay in trim until she's bored.

To me, that's the difference between the HP100 and the MP72. The only way I could ever manage a stable trim with the 72s was with a tail weight of about half a ton AND ankle weights. (Not worth it for open water - I'll take the dynamic equilibrium).

She does not face plant, she is able to hover motionless in pretty good trim. She says that she does not have to "constantly" adjust, but she does have to some of the time.

 

[Akimbo]

… My girlfriend has only dove doubled aluminum 80s in the tropics and let me just say its a lot of weight for her. ....

... We have also looked at other options like the low pressure steel 72s which are awesome but have a slightly lower capacity than we want…

A set of old LP 72s might work out well. ....

My first though: What is the ratio between your and hers’ air consumption? It is not unusual for female air consumption to be around 60% of a male’s. Using that as an example, she could use twin 60s to your twin 100s unless you are planning decom or exit reserves that have to be shared.

As mentioned, don’t confuse circa pre-1990s, 6.9” OD, 2,250 PSI steel 72s with modern LP-72s. IMHO, they have much better weight and trim characteristics. I still have three that won’t die, all with ½” tapered CGA threads instead of O-ring neck seals. The oldest hydro is 1959 and they just passed again last year.

Note that most early 1960s and newer tanks are O-ring sealed and will be required to use a modern doubles isolation manifold.

 

[TSandM]

The LP72s we have date back to the 1970's. They're quite different from the LP 72s the shop uses, which have much shorter necks and fatter, rounder shoulders.

 

[David_57]

The LP72s we have date back to the 1970's. They're quite different from the LP 72s the shop uses, which have much shorter necks and fatter, rounder shoulders.

So what is Bobs and Your opinions of the HP 100's for trim? Just wondering as I am involved in another forum Ontario Divers where a GUE instructor states the HP 100's suck for trim and the aluminium 80's trim better; Which is not my experience I love the HP 100's for trim I'm 6'-0" if anything I keep a little air in my feet to keep them up without any effort.

 

[halocline]

The LP72s we have date back to the 1970's. They're quite different from the LP 72s the shop uses, which have much shorter necks and fatter, rounder shoulders.

Would you mind posting the markings that are on your LP72s, and measuring the diameter? Since they're set up as doubles, you should be able to put a couple of strait-edges on either side across both tanks and get a pretty good idea of the diameter, just measure the distance between the straight-edges.

I've never used LP85s, but if it turns out that the trim between them and LP72s (the 6.9" tanks) is really different, I'd be a little surprised due to the similarity of the tanks' sizes. I thought I had found a nice set of doubles here in San Antonio that looked to be about the size of faber LP85s, but they were european tanks and could not be hydroed in the U.S. Other than the 72s, the only doubles I've used (and these only a few times) are AL80s. On those I put a few pounds on bands near the bottom of the tanks to get them to trim like my 72s.

I am really curious about LP85 doubles again thanks to you....

 

[TSandM]

I have found the LP85s and HP100s trim out almost exactly the same, but the 100s are heavier to carry.

I'll measure the 72s in the morning. (I've been up more than 24 hours now, and I"m too tired to go out in the cold and do it!)

 

[David_57]

Depending on which manufacturer the LP 85 can be slightly heavier for example the Worthington LP 85 is 1LB heavier than their HP 100, same for the Aluminum 80 they can be slightly heavier than the HP 100's.

Check below link for different tank specs

http://www.rocketcitydivers.net/cgi-bin/st_html.pl

I also like my double HP 100's for the buoyancy characteristics -10 x 2 full -2.5 x 2 empty great for drysuit diving with thick underwear no need for a ton of additional weight, this is something that should be carefully considered when deciding which tanks to double up.

 

[airstream]

I think the best answer can be summed up in two words : SIDE MOUNT.

 

[Jim Lapenta]

I'd love to get my hands on another set of LP72's. I have no problem trimming them out wet or dry diving. I also have a set of LP 85's that are my favorite for deeper stuff.