double 104's

[FIXXERVI6]

Considering double LP104's for wet suit diving.

My question is, with double LP104's, will 65# of lift be enough? I'm fairly negative, and would be looking to use an aluminum backplate.

I can dive a standard 80 with 6lbs of lead and a 3 mil wet suit, with my neutral 80 and no wet suit I can dive no lead, but I always put in 2lbs just in case.

 

[Boogie711]

You shouldn't dive steel doubles wet... at least not LP104's. With only a 3 mil to boot???

If your wing fails, you're going to make a very pretty boat anchor at the bottom.

 

[Big-t-2538]

I'm with the boogster here...consider a wing failure....that is one heavy load to be toting around and back to the surface.

 

[Don Burke]

FIXXERVI6 once bubbled... Considering double LP104's for wet suit diving.

That's not normally a good setup.

FIXXERVI6 once bubbled... My question is, with double LP104's, will 65# of lift be enough? I'm fairly negative, and would be looking to use an aluminum backplate.

The buoyancy swing on a set of 104s is something like 11 pounds and the buoyancy change due to depth on a 3 mm wetsuit would be somewhere around 8-12 pounds. That plus five pounds or so per sling bottle is all your wing really needs to do underwater. Add some capacity for dealing with things on the surface and 55# would probably be my choice.

My concern would be what you are going to do in the event of a wing failure.

The two scenarios to worry about would be:

1. You jump off the boat and catch on something, ripping your inflator hose to shreds. How much weight do you need to drop to stay on the surface?

2. You fix problem 1, get to the bottom and rip your inflator hose to shreds on something on the bottom. How much weight do you need to drop to get to the surface?

FIXXERVI6 once bubbled... I can dive a standard 80 with 6lbs of lead and a 3 mil wet suit, with my neutral 80 and no wet suit I can dive no lead, but I always put in 2lbs just in case.

Assuming the rest of your gear stays the same, with a siingle 104, you'll carry about one pound of lead. With double 104s, you'll carry no lead. That leaves you nothing to drop. You'll need about 20 pounds to get off the bottom with full tanks and you don't have it.

The 104s can get you killed since you have no margin for error.

I wear double 80s with my wetsuit and I get along just fine. I suggest you look into doubling standard 80s.

I'm intrigued by the "2lbs just in case". What good does that weight do you?

 

[Karl_in_Calif]

Double anything with a wetsuit seems like it would not be a good idea. Unless you stayed shallow all the time.

I dont see that much difference between double 72s, double steel 80s, or double 104s, in combination with a wetsuit. They are all a bad idea. Unless you stay really shallow, above 60 ft.

And do not plan on any future decompression diving with this setup and a wetsuit, because a wetsuit is simply too cold for deco stops. You lose too much heat with a wetsuit. Therefore you cannot dive deep with your doubles, if you are wearing a wetsuit, because you cannot comfortable perform deco stops. The increased cold and shivering is also a DCS risk.

An 80 or 90 cu ft tank with a stage tank backup is about all you need for deep NDL diving. That would also weigh a lot less and cost less than manifolded double tanks.

And a drysuit is what you need for staying longer at deep depths and performing deco stops than you could with an 80 or 90 cu ft single tank.

If you are planning to get twin tanks, you should get a drysuit first. You will love diving in a drysuit, and you will have a backup to your B/C in terms of buoyancy with a drysuit.

I can only think of two reasons to get a high lift capacity B/C:

1) you are a tech instructor
2) you carry a heavy tool bag underwater on salvage ops.

 

[Karl_in_Calif]

Don Burke once bubbled...
I wear double 80s with my wetsuit and I get along just fine. I suggest you look into doubling standard 80s.

You stay shallow, right?

 

[roakey]

Don Burke once bubbled...
The buoyancy swing on a set of 104s is something like 11 pounds...

Never a need to guess at swing, air weighs about 1 pound for every 13 cubic feet. So twin 104s (208cf) have 208/13 = 16 pounds of swing.

Let's add this up. If a neutral 80 is enough for you (0 empty) then every pound over that is overweighting. Let's look at empty dual 104s first. Each weighs about -5 empty. Add -2 for the manifold. We're up to –12 or so at the end of the dive IF your cylinders were completely empty and you were shallow so your suit wasn't compressed. This should make you seriously worried, that's a lot of weight to swim up.

But wait, now things get scary. Beginning of dive, deep so the suit is compressed. -16 more for air, -10 for wet suit buoyancy loss = -12 + -16 + -10 = 38 pounds negative with no ditchable weight!

If anything goes wrong with your wing the ONLY way you're going to get up will be to completely ditch the entire kit and make a truly free ascent. The more probable outcome will be that you'll be dead.

We throw about the saying “Don’t dive steels wet” quite often, but it’s just a rule of thumb, there are a few exceptions if you’re willing to run the numbers and understand what’s going on. However, this is an excellent example of some steels you absolutely, positively don’t want to dive wet with.

Roak

 

[Don Burke]

roakey once bubbled... Never a need to guess at swing, air weighs about 1 pound for every 13 cubic feet. So twin 104s (208cf) have 208/13 = 16 pounds of swing.

That assumes you are going to breathe them flat. I normally leave 400-500 pounds in the tanks.

2640/500 means you'll have about 20% of the capacity left when you get to your minimum pressure. That leaves about 12 pounds of swing when you dive the tanks.

 

[roakey]

Karl_in_Calif once bubbled...
Double anything with a wetsuit seems like it would not be a good idea.

Not true, in the case of cylinders that go positive, you can actually end up more positive at the end of the dive than with one cylinder (granted, you're more - at the start, but with cylinders that swing +, it's not much).

case in point, AL80s that swing -3 to +3. Double them, add two pounds for the manifold/bands and you have a kit that swings from -8 to +4, only 5 pounds more - at the start than a single cylinder, and (just barely) more positive at the end.

Roak

 

[Karl_in_Calif]

Don Burke once bubbled...
That assumes you are going to breathe them flat.

You probably would, too.

In a dire emergency.