Why does an LDS push newbies away from BP/WINGS?

[-hh]

MikeFerrara once bubbled...


the only thing I don't understand is if all the weight is behind you and you're body/suit is (buoyant?) then why would the wing push you foreward? Is it the weight of the camera? You're experiment might be worth doing.

The camera is the biggest obvious culpret. Its a Nikonos V with dual SS200 strobes, which means its ~15lbs in air, although only -2lbs (negative) underwater.

Just for reference, when my doubles are full, I'm pulled backwards because all the weight is in the tanks (behind the wing).

Understood. As I said before, my concern is surfacing after the dive and the pickup is nowhere to be seen...that's where we need to be concerned about the potential fatigue that comes with surface orientation problems, and that will be with empty tanks. Afterall, if our tanks are full, the odds are that we've just gotten into the water, so the diveboat hasn't had a chance to get itself lost yet


-hh

 

[Rick Murchison]

Forward pitch is a problem for single aluminum tanks. Weighting is on the body, buoyancy is on the back, so with the additional weight of the head out of water (also forward of the wing) the pitch moment is forward and uncomfortable, especially for newbies. With steel tanks the center of weight is aft of the center of lift, so the forward pitch tendency from the head out of water is counterbalanced by the steel tanks. To attain balance with a single AL tank, the diver must pitch way back, until the center of weight is over the center of lift, and then learn to balance there. Once learned this is nearly an unconscious activity requiring minimal finning, but for a newbie it can be a real problem.
Rick

 

[grouchyturtle]

Mike 14lbs. is still a lot less than I use in a 2 piece 7mm with an AL 80! I think I had 20 - 22lbs. last dive. And I'm a pretty small guy.

Although I've only used the new rig a few times and I'm still adjusting things, and I was overweighted on that dive.

Is that just another one of those things, the more experience you get the less weight you'll need?

Although now that I think of it, the first dive I did with it was a shore dive, and with just a little less weight I couldn't even break the surface.

 

[MikeFerrara]

grunzster once bubbled...
Mike 14lbs. is still a lot less than I use in a 2 piece 7mm with an AL 80! I think I had 20 - 22lbs. last dive. And I'm a pretty small guy.

Although I've only used the new rig a few times and I'm still adjusting things, and I was overweighted on that dive.

Is that just another one of those things, the more experience you get the less weight you'll need?

Although now that I think of it, the first dive I did with it was a shore dive, and with just a little less weight I couldn't even break the surface.

It's hard to say. Different suits have different buoyancy. Don't worry about it though. If you're weighted right you're ok.

Oh, I have an H valve and a second reg so that's a little extra also.

My point was the distribution not the anout and of course that the rig does not push me foreward at all .

The plate and the weight on cam bands balances everything perfectly because all the weight is generally in-line with the wing.

 

[MikeFerrara]

-hh once bubbled...


The camera is the biggest obvious culpret. Its a Nikonos V with dual SS200 strobes, which means its ~15lbs in air, although only -2lbs (negative) underwater.



Understood. As I said before, my concern is surfacing after the dive and the pickup is nowhere to be seen...that's where we need to be concerned about the potential fatigue that comes with surface orientation problems, and that will be with empty tanks. Afterall, if our tanks are full, the odds are that we've just gotten into the water, so the diveboat hasn't had a chance to get itself lost yet


-hh [/B]

I wouldn't expect two pounds to make that gig of a difference.

My doubles only pull be backwards when full. Once some gas is gone I'm balanced perfectly on the surface and with a single tank the balance is fine all the time.

the back plate and the weight on the cam bands balances everything well.

I don't find the back inflate bc's (or for that matter any bc) anywhere near as nice in the water (on the surface or at depth.

 

[-hh]

MikeFerrara once bubbled...


I wouldn't expect two pounds to make that gig of a difference.

It is a small weight, but what is likely making it significant is that it is working off of a relatively long moment arm.

Recall that Torque = mass * "leverage" (Moment Arm), so even a small -2lb mass can be significant because of its standoff distance. Here, if we assume the mass/buoyancy centerline to be approximated by the diver's spine, because a human is anthropometrically ~9.5" thick (plus wetsuit & gear), the center of mass of the camera is going to be more than a foot away from the centerline. In comparison, a weighted backplate is going to be ~3", which means that the camera's moment arm has a 4:1 advantage in effective leverage. So this -2lb mass is functionally as significant as an -8lb backplate because of their respective moment arm lengths' contribution to torque.

Since we've now applied the principles of Physics, this is now Engineering (FWIW, one of my professional expertises).

Overall, what I've found interesting is that I've been carrying this camera wearing a Jacket for more than a decade, and the "Overturning Moment" (Torque) from holding it in front of me while I'm at the surface simply hadn't even been noticable, let alone a recognized problem.

It just boils down to what trade-offs we need to make for our diving requirements. The conclusion that I'm coming to is that back-inflate doesn't work for me, which includes an UW camera and the need for lightweight WWW travel gear and single AL80 rental tanks.


-hh

 

[grouchyturtle]

Yeah I didn't think of all the little extra gear the some of us may or may not carry that ads weight.

As well as suits possibly havin different buoyancy, even thouh they're the same size.

Also now that I think about it, newbie or not, if with just a few less lbs., with an empty BC, sitting perfectly still, I can't even get my head below the water, then I guess my weighting is correct, regardless of the fact that I may be carrying more weight than some others.

 

[mgri]

When we are talking about pitching forward at the surface with a single 80, are you talking about using a BP/W or a back inflate BC?

I've dived a Halcyon 30#, a AUL 55# and my Qxyceq wing and have never had an issue with forward tilting on the surface.

I could understand that a back inflate BC would do this due to the lack of negative buoyancy behind your back but with a BP/W you have the back plate and STA helping to balance you out.

IMO a BP/w is better at the surface. I don't get my lungs squeezed like in a jacket on the surface and I can't slide out of it like a jacket which tends to be lose on me.

 

[Big-t-2538]

-hh once bubbled...

Recall that Torque = mass * "leverage" (Moment Arm), so even a small -2lb mass can be significant because of its standoff distance. Here, if we assume the mass/buoyancy centerline to be approximated by the diver's spine, because a human is anthropometrically ~9.5" thick (plus wetsuit & gear), the center of mass of the camera is going to be more than a foot away from the centerline. In comparison, a weighted backplate is going to be ~3", which means that the camera's moment arm has a 4:1 advantage in effective leverage. So this -2lb mass is functionally as significant as an -8lb backplate because of their respective moment arm lengths' contribution to torque.

Also recall from physics that hydrodynamics takes effect here since you are in the water and that the "moment arm" is shortened due to support on your body from the water...thus making a 2 pound weight not much of an issue as whatever you are using to support the camer (probably your arm) is also being suppored by the water....I would think supporting the camera below you would actually make the total effect worse because now you've taken that little 2 pounds that is distributed over your body through your arms and added a fixed point load onto your body.

I don't buy your argument that the camera is throwing your trim off at the surface...I think there's somethind else fundamentally wrong.

 

[IndigoBlue]

What store is going to do anything other than stock a bunch of Oceanic rental B/Cs for their new students?

Why would they even think of bothering with Halcyon or OMS gear??

Why would they even give shelf space to Halcyon or OMS gear unless they have an established tech clientele???

And if they are a tech store, why would their instructors veer from the norm so as to use anything but the Oceanic rental stuff for the basic students? Why? Is there some kind of crusade?

[Please do not answer these questions. They are rhetorical, intended to shed light on why the overwhelming majority of stores do not carry nor offer backplates let alone push them onto new students.]