Tough to do good "science" when nature won't cooperate!  8^)

8^)

I find almost every dive interesting, even if it's only because of some
unusual situation like you experienced. Today, looking up from 50' and
seeing whitecaps from below was different. Looked like a river rapids
up there. Vis was 30' horizontally at that depth, but the surface was
easily seen in the bright sun.

By the way, I've been describing my typical dive activity level as
"low", but it may be similar to your recent dives. I'm finning almost
the whole time, too, but slowly, like one kick every 2 seconds.

Also, my activity level is raised a little by my dragging a "tuna ball"
around, especially when heading up-wind on such a windy day as today. I
know I use more air as a result.

I figure my weighting a bit differently by using the greatest positive
buoyancy of the equipment (when the tank is empty) because my goal is
to always be able to get neutral.

I've got some HP steel 100's by Pressed Steel, which I assume is what
you have. Their buoyancy _when empty_ is listed as -1.0 lb, so if I was
switching from my HP steel 120's, which are listed as neutral when
empty, to the 100, I might add a pound of lead to keep my buoyancy
about the same (if I cared to tweak to that degree, which I don't).

As far as your SS plate being 5 lbs negative, I'd count that certainly,
too.

Regarding first stages, it's probably close enough to use the weight of
the first stage in the calculation, since the weight of the other
fittings will help with the fudge factor of the displacement of the
gear.

Unless you've actually got a HP 100 that is 14 lbs negative when empty,
I would have described your weighting as 28 lbs of lead, 5 lbs of back
plate, 2 lbs for the regulator and I would have omitted the weight of
air, since it will be gone possibly at some point. Again, my goal is to
still be neutral with an empty tank, not including the extra wieight I
want for warmth.

For your recent dive, I'd say your total weight that affects buoyancy
is 35 lbs. Or I'd say you wore 30 lbs with that gear configuration of
steel backplate.

 I used 1,726# of air but the tank wasn't full when I

I don't think chasing the changing weight of air is going to help
achieve the result of fine-tuned buoyancy, since the empty tank's
increased positive buoyancy is the most important consideration.

Here's the link to Cabela's for the first layer I use, which I estimate
to be 100 weight polypropylene fleece:

http://makeashorterlink.com/?I1112352E

Here's a link to their Polartec product that I use as the 2nd layer,
which is 300 weight:

http://makeashorterlink.com/?R2315252E

I use the same type garments for the legs, too.

The fleece pads on my chest are simply 100 weight fleece blanket
material from WalMart that I've cut or folded to create 4 layers to
cover about 12x18" of my chest.

I have some nice Polartec 300 material that I got from a yard sale last
year that I will eventually use for custom pads or garments, when I get
the time to sew something up. I got lucky and picked up about 3 yards
by 60 inches wide for $5! Gotta love yard sales!

Actually, the greater displacement made my HP 120 neutral when empty,
so yours is more negative by a pound, when empty.

The point we should be heading toward is that the fine-tuning needs to
be done in-water with the tank empty, or, if full, made with some
calculation of the added weight of it's air, to make sure to have
enough weight to be neutral with an empty tank.

I think half my cramping problem is simply being out of shape, not
walking enough, etc. The steady, slow finning I do, even with gentle,
flexible Mares Quattros, still gives me occasional cramps late in the
dive.

Well, just to bring something to the discussion, I did a little
experimenting at the end of today's 92-minute dive in 48 degree fresh
water.

First let me just add a little color to this story by saying I had
forgotten how this lake is always windy as a bastard when a high is
coming from the northwest, and it was ripping a steady 25 miles per
hour, I'd guess, and the 50 degree air temp felt absolutely wintry in
that wind! Chilled me more than the water did! Needless to say, I
didn't do my usual "dubbing around" while gearing up! It felt very nice
to finally get into the suit and into the water!

I had only reduced my saltwater weighting by 3 pounds, instead of the
usual 4, because I thought there would be colder water especially below
the thermocline. The recent winds have apparently "turned the water
over" and there was no thermocline, even down to 60'. It was 48 degrees
throughout.

My total lead weight was 41 lbs.

Now, about the experimenting.

At the end of the dive, with about 200 psi left in the 120, I took my
BCD off and checked the buoyancy of everything: BCD, HP 120, al 30 and
Highland steel pony bracket. It was about 5 lbs negative as determined
by tying a 1-gallon plastic milk jug to it with just enough air inside
the jug to get the whole rig neutral. A little more than half a gallon
of air, so about 5 lbs of buoyancy.

I detached the 120 and its regulator and the empty tank alone was
essentially neutral, barely bobbing on the surface.

The BCD was essentially neutral, so that leaves the full 30 cubic foot
aluminum pony, bracket and two first stages, etc, to account for the 5
lbs of negative buoyancy. No surprise there.

The 41 lbs of lead I still had on me was just about perfect for being
neutral with the suit vented as much as possible at the surface.

Being inquisite, I later checked the volume of the insulation I wore.
That insulation was the same as last week: 100 weight polypropylene
fleech shirt and pants, 300 weight Polartec jacket and pants, 4 layers
of fleece chest pads, 2 pairs of socks. The volume of that insulation
in a 5-gallon bucket, when pressed down moderately to firmly was just
above the 4-gallon point. Again, the rough estimate method probably has
another confirming data point perhaps, since the buoyancy of the hoods
and gloves wasn't taken into account yet, and those are easy enough to
measure.

This tells me it's a useful method to find a starting point to find the
right weighting with different undergarments. Sounds like you're a
believer, too.

If we get back to how much extra weight and therefore air we have, I
say I have my extra 5 lbs of lead and am warmer as a result.

Again, it will be very interesting to hear what you find is your actual
minimum of weight required to be just at the neutral point with an
empty tank.

How about checking that out?

Just for the sake of discussion, at the beginning of the dive, the
additional weight of the tank's air means even more air in the suit is
required to achieve neutral. Unless, of course, one wants to complicate
things by adding some air to the BCD, which I don't usually like to do.

Sometimes, it might be desirable to have some of the needed air in the
BCD instead of the drysuit, such as if one was overheating and wanted
to lose some loft of insulation. Another case might be if the air
shifting in the suit became a problem. My suit fits snugly around my
insulation, so that isn't a problem at my current level of excess air.
In the summer, when I have very little insulation, if I use too much
weight, the air can really shift rapidly within the suit.

Any thoughts?

--
Dave C

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