Heavy with doubles

[adamd]

yes my 10 pounds is negative at the end of the dive they are 3500 psi aluminum 80s

 

[scubafool]

3500 psi aluminum 80's?

 

[nereas]

Okay I have figured out I have the Faber FX-100. They are -8.41 full, and -.59 empty. I will test with them around 500 psi and see what I have for bouyancy using my neoprene suit. These cylinders are considerably lighter than my single HP100's. The difference is the HP100 singles i have are rated to 3180+10% and the FX-100's are rated for 3442.

I have determined my buoyancy in tech gear to be affected as follows:

Regs -4.0 lbs
Bands -2.0 lbs
Manifold -4.0 lbs
Tanks -4.0 lbs
nitrox/trimix/O2 -20 lbs

Total starting (excluding backplate) -34 lbs
Total finishing (excluding backplate) -14 lbs


So you see that the main factor in the nonditchable weight issue is the gas (nitrox or trimix or O2).

The choice of an aluminum or steel backplate is then determined by the cold or warm water environment. For warm water, I would normally require aluminum. For cold, steel.

That may be what is giving you trouble, early into your dives.

For warm water, if buoyancy is indeed an issue, Oxycheq offers double-bladder wings, if you need them for backup (in other words, you are indeed negative and you absolutely do not want to swap out your steel tanks for aluminum).

 

[DeepSeaExplorer]

The choice of an aluminum or steel backplate is then determined by the cold or warm water environment. For warm water, I would normally require aluminum. For cold, steel.

You have the right plate, since the steel tanks are already heavy enough. Rule of thumb: if the tanks are heavy, like steel tanks, you need a light AL plate to avoid making the rig even heavier. If the tanks are light, like AL 80s, then you need a steel plate to compensate for the lighter tank's buoyancy.

The problem is that double steels don't go with a light wetsuit. If you dive that setup, you will always be negative - no way around it. Normally, a light wetsuit calls for aluminium 80s. Steel tanks are used with either a dry suit or a very thick wetsuit. Not to say that setup isn't diveable, you'll just have to accept the limitations.

 

[nereas]

You have the right plate, since the steel tanks are already heavy enough. Rule of thumb: if the tanks are heavy, like steel tanks, you need a light AL plate to avoid making the rig even heavier. If the tanks are light, like AL 80s, then you need a steel plate to compensate for the lighter tank's buoyancy.

The problem is that double steels don't go with a light wetsuit. If you dive that setup, you will always be negative - no way around it. Normally, a light wetsuit calls for aluminium 80s. Steel tanks are used with either a dry suit or a very thick wetsuit. Not to say that setup isn't diveable, you'll just have to accept the limitations.

I completely agree. However nobody seems to want to own twin aluminum tanks. Everyone seems to prefer steel. That is why I would simply go with a twin bladder wing, or else simply wear my shell drysuit into the warm waters without insulation.

 

[SparticleBrane]

A couple years ago I did the uncontrolled ascent thing from 100 feet the very first time I dove doubles; can't remember what kind of tanks (they were 100's) but it was an AL backplate and I had 16 pounds of lead in my harness when my drysuit refused to dump and things went to hell fast. That instilled in me a bit of an aversion to being light
Ber :lilbunny:

I'm surprised it didn't instill an aversion to testing something new (especially doubles) in a deep environment. Only test something major like that in a shallow controlled environment...
Being light wasn't your problem -- doing your first dive in doubles to 100ft was.

 

[Ber Rabbit]

I'm surprised it didn't instill an aversion to testing something new (especially doubles) in a deep environment. Only test something major like that in a shallow controlled environment...
Being light wasn't your problem -- doing your first dive in doubles to 100ft was.

We actually started the dive shallow and all went well there once I got my body position right and stopped doing somersaults. The plan was to move deeper when I was comfortable and that's what we did, after cruising around in the shallows and swimming through the attractions we moved to 60 feet and cruised there for a while. My instructor gave the "go/no go" signal for deeper and I felt comfortable enough with the tanks to make the "go" choice. It wasn't the doubles that were the problem it was the drysuit valve and I had sent that back to be checked by the factory when I had a problem before and they said it was fine. I learned the hard way never to trust that drysuit, that's why I had put 16 pounds of lead in my harness with the doubles. The whole point of that dive was to get me over my irrational fear of the deep end of Gilboa and my instructor's desire to make sure I did the dive while properly equipped was well-intentioned. He's in the "don't dive deep without redundant air" camp and felt since I'm an instructor it shouldn't be a big deal to make the switch to doubles and execute a straightforward dive once I demonstrated I was comfortable in the gear. Our max depth was 135' and other than being narced and chasing "wispies" on the bottom (diving 27%) until my buddy had to pull me by the hand to start our trip up the road everything went fine. I felt the drysuit starting to expand at about 100 feet and tried to dump it but nothing would come out of the valve. I signalled my buddy to abort and turned for the wall as planned. Evidently he had been asking if I was ok but I was so narced I never answered him and he thought something was wrong so he grabbed my harness. That's when things got ugly, communication completely broke down and the drysuit took off with both of us. My suit refused to dump until we were about 10 feet from the surface, then the valve finally started venting.

Ber :lilbunny:

 

[rjack321]

yes my 10 pounds is negative at the end of the dive they are 3500 psi aluminum 80s

You mean 3300 psi neutral bouyancy AL80s?

 

[Doc Intrepid]

I believe that is what he is referring to. I have a set of the same tanks.

 

[piikki]

He's in the "don't dive deep without redundant air" camp and felt since I'm an instructor it shouldn't be a big deal to make the switch to doubles and execute a straightforward dive once I demonstrated I was comfortable in the gear. Our max depth was 135' and other than being narced and chasing "wispies" on the bottom (diving 27%) until my buddy had to pull me by the hand to start our trip up the road everything went fine.

It’s funny how many principles sound so funny when reflected against other actions one is willing to hop into – like being OK doing first doubles dive to anywhere into a depth where any kind of narciness is a remote possibility, for example

You instructors you!