Travel BCs

Scott wrote:
> "-hh" <recscuba_google@huntzinger.com> wrote in message
> news:1154139192.140818.26140@i3g2000cwc.googlegrou ps.com...
>
>
>
>>Actually, it sounds very much like "one of those things" that works
>>fine in coldwater that doesn't necessarily does as well in warmwater.
>
>
> You mean like the Florida divers always trying to dictate diving, gear and
> methods to people who dont dive warm?
>
>
>
People who dive in cold water are, by definition, just a little
wacko...

In article <1154139192.140818.26140@i3g2000cwc.googlegroups.c om>, -hh
<recscuba_google@huntzinger.com> wrote:

€ Star wrote:
€ > ...[snip]...
€ > Have you ever dove cold water?
€ > ...[snip]...
€ > It's not an argument and its not weak. Its diver education.
€
€ Actually, it sounds very much like "one of those things" that works
€ fine in coldwater that doesn't necessarily does as well in warmwater.
€
€ Especially when its a warmwater dive trip to a resort with AL80's.
€

It works fine in warm water. You just need a smaller wing with less
lift.

Sure, a large wing fully inflated on the surface will tend to push you
forward. Likewise, an improperly fitted jacket will squeeze your chest
and cut off your breathing if you fully inflate it on the surface.
Neither argument is valid because it assumes improper usage of the
equipment. A properly sized wing, on a *properly weighted diver,*
inflated just enough to keep the diver floating on the surface, will
not have enough of a moment to strongly push the diver face forward.



€
€ > ...[snip]...
€ > I'd be happy to help you work that out if you like.
€
€ Try the gear workup for a generic warmwater vacation diver: AL80
€ rental tank, no weighted BP in his luggage, and no wetsuit.
€
€ Oh, and here's some prefabricated illustrations that might be useful:
€
€ http://www.huntzinger.com/dive/sb/BC_physics1.jpg
€ http://www.huntzinger.com/dive/sb/BC_physics2a.jpg
€
€

I see the point you're trying to make, but I have a suspicion that you
pulled the CG and CB points out of thin air



€
€ -hh
€

Scott wrote:
> I dont know,

We'll just figure it's less than 10 then.

That's just one more reason not to have a BP. Statisically speaking,
their owners don't dive very much. How could they? They spend all their
time trying to sell BPs.

>I am not petty enough to count or try to use them as a podium.

Sure you are. Don't sell yourself short Scotty.

Scott wrote:
> No one here is talking absolutes, except you and all the other BP haters.

Where are the BP-Haters?
Where did anyone say that they hate BP's?

Alan Street wrote:
> -hh wrote:
> € ...it sounds very much like "one of those things" that works
> € fine in coldwater that doesn't necessarily does as well in warmwater.
> €
> € Especially when its a warmwater dive trip to a resort with AL80's.
>
> It works fine in warm water. You just need a smaller wing with less
> lift.
>
> Sure, a large wing fully inflated on the surface will tend to push you
> forward. Likewise, an improperly fitted jacket will squeeze your chest
> and cut off your breathing if you fully inflate it on the surface.

> Neither argument is valid because it assumes improper usage of the
> equipment. A properly sized wing, on a *properly weighted diver,*
> inflated just enough to keep the diver floating on the surface, will
> not have enough of a moment to strongly push the diver face forward.

Please define "inflated just enough to keep the diver floating on the
surface".

For example, since there's often many claims heard here about leaving
the snorkel on a nail back in the car garage, that would suggest that
the amount of required surface lift needs to be enough to lift the
mouth clear of the water. Call it an extra inch for the chin and
you're getting close to vertebra C3 - this means that the whole head is
being lifted clear, which is roughly 10lbs.

So your BC needs to be inflated to provide at least 10lbs of buoyancy.
I say "at least" because the valve stem and regulator might also be
starting to lift clear of the water too.


> € Oh, and here's some prefabricated illustrations that might be useful:
> €
> € http://www.huntzinger.com/dive/sb/BC_physics1.jpg
> € http://www.huntzinger.com/dive/sb/BC_physics2a.jpg
> €
> €
>
> I see the point you're trying to make, but I have a suspicion that you
> pulled the CG and CB points out of thin air

These are merely dimensionless illustrations of the appropriate
coordinate system to help people visualize the proper context.


-hh

"bullshark" <bullshark@gmail.com> wrote in message
news:1154195845.180381.316640@h48g2000cwc.googlegr oups.com...
> Scott wrote:
> > I dont know,
>
> We'll just figure it's less than 10 then.

Figure what you want to, asshole.

If I dove the same shitty reef every weekend, I wouldnt be bragging.

> That's just one more reason not to have a BP. Statisically speaking,
> their owners don't dive very much. How could they? They spend all their
> time trying to sell BPs.

Since I havent sold one for months, I guess you would be full of shit,
again.

> Sure you are. Don't sell yourself short Scotty.

No, I am not. But hey, define others as you define yourself makes you comfy,
doesnt it?

Got two in today, and at least one tomorrow, you?

rec.scuba's resident pussy "Scott" <pugetsounddiver@gmail.com>:

> If I dove the same shitty reef every weekend, I wouldnt be
> bragging.

You don't dive, Scotty. You post on rec.scuba every weekend, all
weekend.

--
Posted via a free Usenet account from http://www.teranews.com

-hh wrote:
> Star wrote:
> > ...[snip]...
> > Have you ever dove cold water?
> > ...[snip]...
> > It's not an argument and its not weak. Its diver education.
>
> Actually, it sounds very much like "one of those things" that works
> fine in coldwater that doesn't necessarily does as well in warmwater.
>
> Especially when its a warmwater dive trip to a resort with AL80's.

All the more reason I might want some weight on my back. In fresh
water, I don't wear any lead unless I have an Al80 and a drysuit and a
BC. With the plate, no lead.

>
>
> > ...[snip]...
> > I'd be happy to help you work that out if you like.
>
> Try the gear workup for a generic warmwater vacation diver: AL80
> rental tank, no weighted BP in his luggage, and no wetsuit.

No wetsuit does not happen for me.

>
> Oh, and here's some prefabricated illustrations that might be useful:
>
> http://www.huntzinger.com/dive/sb/BC_physics1.jpg

Remove lead from hips and place on back. Orange arrow changes
magnitude in proportion to amount of lead moved x distance. Note that
fat woman will have different placement of CG than will skinny man. I
would like to see some actual data to verify this diagram.

> http://www.huntzinger.com/dive/sb/BC_physics2a.jpg

.....and would like to know how the points for CG and CP (what is this,
btw?) were determined. And are you defining moment arm as the
horizontal (WRT the diagram) distance between CG and CP?

*

Star wrote:
> -hh wrote:
>
> > Actually, it sounds very much like "one of those things" that works
> > fine in coldwater that doesn't necessarily does as well in warmwater.
> >
> > Especially when its a warmwater dive trip to a resort with AL80's.
>
> All the more reason I might want some weight on my back. In fresh
> water, I don't wear any lead unless I have an Al80 and a drysuit and a
> BC. With the plate, no lead.

Understood, but that is not generally applicable here: the weighted
plate / STA is generally going to be expected to be left at home
because of airline baggage weight limits. As such, the majority of the
diver's need for ballast is not going to be transported with him, but
obtained locally at the tropical resort (usually in the form of
traditional weightbelt ingots).


> >
> > Try the gear workup for a generic warmwater vacation diver: AL80
> > rental tank, no weighted BP in his luggage, and no wetsuit.
>
> No wetsuit does not happen for me.

Exactly my point. Changing thermal protection for cold/warm -water
typically results in a change of ballast required. For example, my
difference is roughly 20lbs. That's why I suggested that perhaps this
miscommunication is a cold/warm -water thing: what works fine in one
is no assurance that it will work fine in the other ...

... particularly when we have obvious basic physics contributors that
are telling us to be wary of our assumptions!


The general question of shifting around one's ballast to obtain desired
trim is such that "the more you have", the more options you have.
Plus, it will tend to overwhelm secondary contributing variables.

In other words, as you go from coldwater to warmwater weighting
configurations, since you'll have less ballast to work with, getting
the rig trimmed out becomes less easy.


> > Oh, and here's some prefabricated illustrations that might be useful:
> >
> > http://www.huntzinger.com/dive/sb/BC_physics1.jpg
>
> Remove lead from hips and place on back. Orange arrow changes
> magnitude in proportion to amount of lead moved x distance.


My apologies: this was a poor illustration. Please allow me to
explain and expand.

First, the top half of that JPG was an original; the bottom half and
the other illustration were the derivatives. The top half is obviously
wrong, because centroids generally have to originate from within the
object in question.


To that end, two new illustrations. First, get rid of the confusing
half:

http://www.huntzinger.com/dive/sb/BC_physics1a.jpg

This is looking simplistically at just the centroids for CG and CP
(bouyancy). Its intent is to show that any horizontal misallignment
between the two creates a moment arm that will affect the trim of the
diver.

FWIW, for the illustration as shown, this diver would go "legs down".

As importantly, it is now consistent with the second illustration,
http://www.huntzinger.com/dive/sb/BC_physics2a.jpg


Next, the length (magnitude) of an orange vector isn't changed by
moving ballast. It is changed by the addition (or elimination) of
ballast. Moving existing ballance around merely shifts where this sum
total vector applies to the larger body.

This is because the single orange vector (ditto the green) is a
mathmatical summary of multiple descrete sources. Again, in
illustrative form, it would look something like this:

http://www.huntzinger.com/dive/sb/BC...s-centroid.jpg


FWIW, note that I've included locations for things like ankle weights,
etc. These may or may not be present in a specific case, plus I've
generalized the vector magnitudes..ie, a 5lb weightbelt ingot is a
longer vector than a regulator 2nd stage (which could be zero), etc.

Note carefully that the mathematical formula is not a simple "add up
and divide" average: this is leading to a classical physics "see-saw"
problem, so it factors in both the magnitude and its distance from some
reference datum, since neither the CG nor CP are fixed.

Once we figure out each one relative to the datum, we can then do a bit
more math to see if they "see-saw" balance against each other, which
way its off and by how much.


FWIW, while this may sound confusing, the basics are straightforward
"Sophomore Year" Math & Engineering...this is vector addition in a
constrained space. While normally that would entail at least 3 degrees
of freedom (left, right, rotation), we're only looking at one degree of
freedom (rotation).


> Note that fat woman will have different placement of CG than will skinny man.

Not necessarily. First off, the whole point of this exercise is to
show how one can move substystems around on the diver so as to alter
the net CG location. Second, the human body is fairly close to being
neutral in water, so the magnitude of the contribution of "naked" human
within the larger system is fairly small. If you look at the
'centroid' URL, you'll see that there's an orange dot with a short
vector in the belly of the diver (it is indexed by the topmost
horizontal black arrow below the diver): this vector is very sort
because we're really talking about net buoyancy in water, not the dry
(air) weight of the diver.


> I would like to see some actual data to verify this diagram.

Yes, that's what I effectively asked you for. Please do keep in mind
that these diagrams are simply intended to be illustrations to help us
articulate exactly what we're talking about.


> > http://www.huntzinger.com/dive/sb/BC_physics2a.jpg
>
> ....and would like to know how the points for CG and CP (what is this,
> btw?) were determined.

CP = Center of Pressure. Here, its the same as our net effective
("center") location of buoyancy.

And as I just said above, this is merely a "process" diagram to
illustrate the methodology of the analysis. The specific points for CG
and CP are placed here intuitively, in the absence of hard data.


> And are you defining moment arm as the
> horizontal (WRT the diagram) distance between CG and CP?

Good catch. This was a key point for why I originally made up these
illustrations: the moment arm is always horizontal ... or to be more
precise, it is always perpendicular to the CG and CP vectors, which
allign themselves with/opposite the Earth's Gravity vector.


The general implications of this are that since an ideal diver would
want to have effortlessly perfect trim regardless of his orientation,
the ideal configuration ("design objective") would want to minimize the
torque between the CG & CP. Which either means to minimize the CG/CP
values, and/or to put the CG and CP as closely together as possible ...
in all dimensions.


What I've seen with the Wing is that it is a very easy system to put
the CP directly above the CG for the horizontal orientation that a
diver's in for ~90% of his dive, which nearly zero's out the Moment
Arm.

For novices, this also adds comfort because its like adding dihedral to
an aircraft wing: it is self-centering.

However, for an advanced diver who wants *total* positional freedom in
the water, this makes it harder to roll onto one's side, or to do a
complete roll onto one's back.

Plus, when the diver goes to a vertical orientation, unless the diver's
using a weighted BP / STA, the odds are that there's now a potentially
very nasty moment arm between the CG and CP introduced, because a
Wing's CP is located completely behind the diver.


-hh

Star wrote:
> Have you ever dove cold water?

Not really. 62F in Galapagos is about the low-end.

> Dive what you like; I'm sorry that your experience with a BP was less than satisfactory.

Why would you be sorry? It was a try-out. You asked:

> "SO, who here has actually dove a properly adjusted BP/wing, and not
> liked it, and why? Or are the doubters just giving lip service to this
> set-up?"

I answered. Lip service? no. There isn't any doubt. There's nothing too
wrong with it.
It just wasn't anything special, certainly no better than my current
backwing, which was presented to me as a gift a couple of years ago.

You can dive fine in a BP, so can I, but that doesn't preclude diving
well in anything else. It's a matter of experience and effort.

>I'd be happy to help you work that out if you like.

Likewise, I'm sure. (c: