On Thu, 9 Jul 1998 08:50:19 -0400 (EDT), Mike Zimmerman wrote:

>Not to try to claim bondage wings are GOOD, but on this point
>I think there may be some (valid) alternate views.
>
>Ok, so bondage would keep wings close to body, even when inflated,
>more along the plane of the body, and you claim present a larger 
>forward swimming profile, equalling more resistance....
>
>Other wings will wrap up around the tank, providing (as you
>claim) less of a forward swimming profile.
>
>first I must say I am not convinced about the profile.
>As long as the air is disrtibuted within the wings, and
>doesn't tend to collect at the top (defined as closer to
>the diver's head) in one style more than the other I can't
>see how wrapping around a tank accomplishes the magic trick
>of providing the same bouyancy in less space.


	By less space I was referring not to the actual water displacement but rather
the effective 
profile of the diver with regard to snagging or entrapment hazard.  A
traditional wing pressed 
against the tanks seems better protected, or rather, less likely to present a
problem as a direct 
result of position than a bladder constrained to the plane through which it is
attached.  This was 
just an assumption of mine and should only be considered as mere conjecture. 
Regarding air 
distribution, I may be way off base here but I was under the assumption that
the OMS wing had a U 
shaped bladder with approximately circular cross section through its entire
length, including the 
top behind the diver's head.  The traditional wing systems that I have seen
were narrower in this 
section, although I do not know if this is isolated to certain manufacturers
only.  As regards the 
drag issue, perhaps my last post was too superficial in addressing this.  It is
imortant to 
consider three dimensions instead of merely the forward profile, since
intuitively we know that 
streamlining a cylinder into a sausage shape will result in less drag, even
though the cross 
sectional area is still the same.  Without actually getting my hands on an OMS
wing to comment on 
this objectively I am hesitant to get into this analysis, but you also need to
consider turbulent 
versus laminar flow, Venturi & Bernoulli effects and other considerations of
actual water flow over 
the diver system.  Your guess is as good as mine as to whether this analysis
has any real world 
significance.  The problem is akin to Rich Pyle's titanium doorstop analogy.



>Second, it would seem to me that as your wings wrap around your tank
>it moves the bouyancy moment (I use the term loosely) farther
>away from your own center... ie it would seem to me that the
>circumference of the diver as a resistive force in the way has now
>increased.  Just as you want your weights close to your body
>I would think you'd want your bouyancy close to your body.  
>We wouldn't put weights on the back of our tanks as they
>tend to want to flip us over... if we put bouyancy closer to
>the back of our tanks, it seems like that makes it harder
>to flip over when we want to, or to even turn sideways when
>going thru a restriction.
>
>Again, leave out the other arguments about bondage wings, 
>if you want to disagree, just lets discuss this one point?


	A valid question.  Consider how the force exerted by the buoyancy compensator
is 
distributed.  The buoyant force exerted on the diver is not located at the
actual center of 
buoyancy in the bladder but rather is distributed through the wing material to
the grommets, bolts, 
backplate and to some extent through the harness.  In the horizontal position
(prone) there is a 
small amount of force exerted through surface contact with the traditional wing
against the tank 
surface on both sides.  These torques are generally equivalent and cancel out. 
The effort put 
forth by the diver (a system in equilibrium), or more accurately the neccesary
torque when 
pivoting, such as to negotiate a restriction, need only be equivalent to the
sum torque exerted by 
the wing until it reaches zero or a positive value in the direction you are
trying to pivot.  When 
pivoting to a sideways orientation, the air within the bladder is
preferentially distributed to the 
upper wing, which is acting on the attachment point on the backplate. 
Intuitively (more 
conjecture), it would seem that the effort required to overcome inertia and
drag would be equal or 
greater than the torque factor, which drops out of the equation after about 30
degrees of roll (at 
an estimate).  What does this mean in the real world?  Probably nothing.  Back
to the titanium 
doorstop...


>
>Thanks,
>Mike


	A diver wearing an OMS wing will encounter slightly less resistance (to
torques acting 
about the diver's longditudinal axis) when pivoting from a prone position than
a diver wearing a 
traditional wing.  This can be seen as an advantage or a disadvantage, as a
diver wearing a 
tratitional wing may have slightly less tendency to roll from this position
when transiting or 
performing work.  It is important to note that this effect may be entirely
negligible when compared 
to other factors.

-Sean




--
Send mail for the `techdiver' mailing list to `techdiver@aquanaut.com'.
Send subscribe/unsubscribe requests to `techdiver-request@aquanaut.com'.

Navigate by Author: [Previous] [Next] [Author Search Index]
Navigate by Subject: [Previous] [Next] [Subject Search Index]

[Send Reply] [Send Message with New Topic]

[Search Selection] [Mailing List Home] [Home]