Horizontal Position Problem

[O2BBubbleFree]

Fact: A Ranger LTD is not more than 1 lbs inherently buoyant. I've tested it personally.

I e-mailed Zeagle about the Ranger. Their response is 3 lbs positively buoyant.

I don't want to fuel a fire here or anything, but find these two remarks interesting. I personally have the older style ranger, which I don't think is much different than the LTD, and have tested it.

I found it to be 3# positive in fresh water, which means more than 3# in salt water, and definetly more than 1#.

But that's all irrelevant to the OP's point. Pardon the divergence.

 

[O2BBubbleFree]

Try sucking the air out of the inflator to be sure.

If you don't keep your BC bladder disinfected (beyond just cleaning ), that's a real good way to get a pulmonary infection.

It's real easy to have lots of nasties growing inside a BC...

 

[gt3073b]

Since an AL80 is already 1.5lbs positive at half full, it would seem that moving the tank up would make you go MORE head-up for most of the dive. With a steel tank that is always negative, moving the tank up will lower your head since you replace lead with steel closer to your head. But with the 80, at the end of the dive you have 3.5lbs of lead on your hips to counter 3.5lbs of buoyancy closer to your head. Your trim will start off good, but your hips will end up under the middle of the tank 1/3 of the way into your dive. Moving lead up to trim pockets is a much better idea.

Imagine this from the side, with the diver's head to the right. (REMEMBER, THIS IS AN ALUMINUM TANK!)

..Tank
......BC
Lead

In this case, the tank starts off negative, the bc positive, so the feet go down to get the center of mass under the bc. It gets a little better as the tank gets lighter.

Now, the tank has been slid up...

.....Tank
......BC
Lead

So now the trim is constant as the center of buoyancy only moves away from your back, but still feet down.

Now even more extreme...

.........Tank
......BC
Lead

The dive will start off fine since the tank is negative and the bc is positive. The tank counteracts the weight belt. As the tank gets lighter (and more positive), the bc gets less positive. Center of buoyancy moves toward your head and you go even more head up throughout the dive. You'll actually end up more head-up than with the tank down low!

Now with a trim weight as many have suggested or with a BP/W

.....Tank Lead
......BC
Lead

or

......Tank
......Wing
......Backplate
Lead

In this case, as the tank gets lighter, the bc gets less positive but the center of buoyancy only moves away from your back, not toward your head or feet. The lead near the top of the tank helps balance against the lead on the belt or front pockets. The backplate simply replaces some of the lead on your belt and puts it right under the tank like a keel. Moving 8lbs off your belt to a backplate/STA is the same as moving 4lbs off your belt to the neck of your tank.

In the end, the backplate suggestion wasn't wrong, its just 30x more expensive than a trim pocket for similar results.

 

[Hapiguy314]

WoW ... Thanks so much for the advice guys. I'll definitely try it over the weekend (if anything at a pool).

I'll also really try to keep my camera in the dive bag until i master this horizontal position first :blinking: It's just that it's such a good tool for me and also serves as a semi - log book But I can always do the camera thing at later dives

 

[scubafool]

Since an AL80 is already 1.5lbs positive at half full, it would seem that moving the tank up would make you go MORE head-up for most of the dive. With a steel tank that is always negative, moving the tank up will lower your head since you replace lead with steel closer to your head. But with the 80, at the end of the dive you have 3.5lbs of lead on your hips to counter 3.5lbs of buoyancy closer to your head. Your trim will start off good, but your hips will end up under the middle of the tank 1/3 of the way into your dive. Moving lead up to trim pockets is a much better idea.

I can't speak for all Al 80's, but mine floats "butt up" when it start to get lower in pressure, so the positive bouyancy of the tank will actually be a plus in that situation. Also consider that the valve and the regulator are at the very top of the tank, and are always negative. Moving those two "weights" upward helps also.

Bottom line, for me, when I was trying to get trimmed out with my Al tanks, moving them up in the tank bands was a major help.

And as far as the regulator beating your head up, well, let's just say that it is your head hitting the regulator, not vice versa. About the third or fourth time that you do that, you will stop doing it. And it makes it easier to reach your valve.

 

[divad]

Is your camera housing buoyant?

 

[gt3073b]

Also consider that the valve and the regulator are at the very top of the tank, and are always negative. Moving those two "weights" upward helps also.

Good point about the valve and regulator. My original comment still stands that you need to keep buoyancy over mass, but I incorrectly treated the tank as a buoyant force acting through a point rather than both a positive and negative force acting through two different points.

Now I'm curious. Does a first stage sink the top of the nearly empty tank or does the tank and first stage float horizontal on the surface? If it floats valve-down, then I would have to agree that moving the tank up would create a net head-down force throughout the dive.

Darn, now I wanna go to the pool and play with this stuff!

 

[beach89]

I dive with a Ranger LTD BCD, use 20 lbs on the front weight pockets, 6 lbs, on the back pockets, and just rent the tank (usually AL80s). I currently weigh at 165-170 lbs (depending on how much I ate )

26lbs?!? I dive with eighteen in a new 7mm wetsuit. I weigh the same as you too. When I took my open water dives, I wore 24lbs and had the same problem as you. I couldn't get at a horizontal position no matter how hard I tried. I dumped six pounds and have no trouble anymore.

 

[Rainer]

I don't want to fuel a fire here or anything, but find these two remarks interesting. I personally have the older style ranger, which I don't think is much different than the LTD, and have tested it.

I found it to be 3# positive in fresh water, which means more than 3# in salt water, and definetly more than 1#.

But that's all irrelevant to the OP's point. Pardon the divergence.

That's about right. When I e-mailed them it was about the Ranger, not the Ranger LTD. I assume that lumbar pad alone is another one pound buoyant.

 

[Pook-60]

Howdy All

I've been working to adjust my trim on my Zeagle Ranger with a recent equipment addition but your discussions on the location of the rear trim pockets sparked an idea.

I couldn't get past floating with my feet lower than I wanted them so...I've now moved the trim pockets up by reversing them. Although I haven't tested them in the pool yet I can see two "bad" things...(1) I won't be able to easily use the emergency dump feature on the pockets and (2) I won't minimize my drag in this configuration.

What I will have is a weight momentum extended roughly 5 inches higher on the body line fulcrum point. Who knows...I might even be able to keep that first stage from beaning me again! Since I’ll have minimum weight in the rear…I see this as minimum risk for an emergency ascent.

BTW...it didn't take any tailoring...just removed the tank straps and took advantage of Zeagle's velcro based modular design.

Thanks for sparking the train of thought...

Pook