Doubles setup recommendation

[EireDiver606]

Twin 15s are shorter then 12s. Not sure you see 15s as twins, 18s is the next step I guess. You have to be crazy to use those to

My 15l is shorter than my 12l tank.

12l tanks come in two types. The long 12 and the fat 12.

Long 12 is the most used. All 15l I seen is shorter than a long 12 but with bigger diameter.

Sorry I meant d18. Brainfart...

 

[formernuke]

I have similar issues and I'm going into tech. Back and knee injuries. At one point I had hp120s doubled up. In the water I was fine, but picking them up to get into or out of the car etc was not going to happen. I talked to my potential new instructor and they recommend asking around and seeing what size people had doubled up. Pick up and manhandle the different ones (80 foot minimum capacity each tank) and go from there.

 

[Marie13]

I have similar issues and I'm going into tech. Back and knee injuries. At one point I had hp120s doubled up. In the water I was fine, but picking them up to get into or out of the car etc was not going to happen. I talked to my potential new instructor and they recommend asking around and seeing what size people had doubled up. Pick up and manhandle the different ones (80 foot minimum capacity each tank) and go from there.

I have knee/sciatica issues which is why I’m doing HP80 doubles, admittedly an uncommon size. In my case, I’ve found that moving them on my back is the much safer route.

HP80 doubles are so short they probably won’t work for most people, can be head heavy, and difficult to trim out. However, I’m 5’5” and they work well for my height.

I believe my HP80s are roughly equivalent to 10L tanks for those outside North America.

 

[formernuke]

I have knee/sciatica issues which is why I’m doing HP80 doubles, admittedly an uncommon size. In my case, I’ve found that moving them on my back is the much safer route.

HP80 doubles are so short they probably won’t work for most people, can be head heavy, and difficult to trim out. However, I’m 5’5” and they work well for my height.

I believe my HP80s are roughly equivalent to 10L tanks for those outside North America.

That was my problem with HP steel 80's (I'm 6 foot 2 inches)

I found I can manage HP100s they are just enough lighter for me. If those didn't work I was going to have to go AL80s, which is adding a lot of lead to the belt.

OP as you can see 2 people with injury issues found 2 different solutions to fit our individual needs. It is just a matter of figuring out what fits yours.

 

[Deep South Divers]

6.8L at 300Bar = 1824Liter or ~60CF. Double up is equal to a HP120, which is like 39lb dry but -4lb empty. Double Canbondive 6.8L is 27.5lb. The question its empy buoyancy. If it is +8lb, then they are really equal in term of total weight a driver has to carry.

How do you figure? 6.8L x 300 bar = 2040L = 72.04 cuft. Twin 6.8's at 4500 psi = 144 cuft of gas. The twins weigh under 28 pounds, but will require something like 6 pounds of lead to offset their buoyancy. Total weight, therefore, is something like 34 pounds, which is less than an aluminum 80 with the lead it needs... But have 144 cuft of gas in lower profile, flatter configuration that includes redundant first stages and a manifold.

 

[RyanT]

Apparently I missed some of the early discussion regarding the possibility of double HP 80s. They don't work well for most people, but...if you can get them to work for you, they are a really great set of doubles. I had a set and they dove great. Because they put more of their mass near your head, they can be hard to trim out. I'm 5'10" and I got them to trim nicely for me. One possible reason for this is I have relatively long, heavy legs, so that extra mass cantilevered out behind me probably worked to my advantage to trim them. I also wore a set of Hollis F1 fins which are quite heavy. I eventually gave them up in favor of HP 100s, mostly because they were too short for me to sit comfortably on the bench. I made a block of wood to support them, but then sometimes I'd forget it. Then I'd be stuck slouched down on the bench sweating my a## off, waiting for the boat to tie in. That was really stressful. On a positive note, they hold a nice amount of gas and they are about 20 lbs lighter than my HP 100s. Getting on and off the boat with them was a joy compared to the 100s. As others have said, if you can try some different sets, that's the way to go.

 

[Marie13]

Apparently I missed some of the early discussion regarding the possibility of double HP 80s. They don't work well for most people, but...if you can get them to work for you, they are a really great set of doubles. I had a set and they dove great. Because they put more of their mass near your head, they can be hard to trim out. I'm 5'10" and I got them to trim nicely for me. One possible reason for this is I have relatively long, heavy legs, so that extra mass cantilevered out behind me probably worked to my advantage to trim them. I also wore a set of Hollis F1 fins which are quite heavy. I eventually gave them up in favor of HP 100s, mostly because they were too short for me to sit comfortably on the bench. I made a block of wood to support them, but then sometimes I'd forget it. Then I'd be stuck slouched down on the bench sweating my a## off, waiting for the boat to tie in. That was really stressful. On a positive note, they hold a nice amount of gas and they are about 20 lbs lighter than my HP 100s. Getting on and off the boat with them was a joy compared to the 100s. As others have said, if you can try some different sets, that's the way to go.

A number of people have poo-pooed HP80 doubles to me for reasons that make no sense. Usually about the amount of gas. My arguments start off with if people are diving AL80 doubles, what’s wrong with my HP80 doubles that actually hold a bit more gas than AL80 doubles? No one has a good response for that. Some people like their older 72 doubles. Nothing wrong with that. They’re longer which may be better for a lot of people. I saw my first set of 72 doubles in the wild about 6’ weeks ago. I couldn’t believe how long they were.

I have the slouch thing going on when I’m at the quarry on a picnic table. They get taken on the boat Sunday!

 

[RyanT]

Usually about the amount of gas. My arguments start off with if people are diving AL80 doubles, what’s wrong with my HP80 doubles that actually hold a bit more gas than AL80 doubles?

Ding, ding! If AL80s are sufficient, then HP80s are a smidge better. Sure, doing 200'+ dives in a set of 80s is not a great idea, but if all your diving is north of 165' or so (50m for our European friends), then they are an appropriate tool for the job!

Good diving Marie!

 

[Marie13]

Ding, ding! If AL80s are sufficient, then HP80s are a smidge better. Sure, doing 200'+ dives in a set of 80s is not a great idea, but if all your diving is north of 165' or so (50m for our European friends), then they are an appropriate tool for the job!

Good diving Marie!

@RyanT

Just curious - what made you go with HP80s in the first place? I only did them as they were what I already had for single tank. They had worked for me for SM, so figured might as well! Besides the knee/sciatica issues, of course.

 

[Deep South Divers]

I'm 6' 1" tall and prefer my HP80s... Which are new Faber FX80's. I get how some people don't like the shortness of them (they're 6" shorter than an AL80), but it doesn't bother me a bit, and they dive really well. Very balanced. -1.74 lbs empty.