Power in VersaTackle

General Discussion
21

Keep in mind the words and examples with which these systems have been
presented/promoted–the “freeing bogged-down vehicles”, the “high MA”, the
“close to 3-to-1” assertions. There is a stark contrast of reality with that!
And such claims get increasingly (via WWWeb) bandied about at a rate greatly
exceeding any critical examination of them. Again, as PvdG wrote in his
Letter to Lester, that people propagate initial falsehoods sufficiently often
enough to establish them as truths. At least with much to do with knotting.

To the remark I made above, that “the Versatackle’s self-locking mechanics
can be replaced with the Dbl. Spanish Burton’s ones,” I’ve just done a test with
the 7/16"? nylon solid braid previously used and found 25# to readily raise 50#,
though one can then draw the haul line into untensioned state and HOLD,
by friction alone!! --thinner 'biner high, thicker low; almost no movement
through the low 'biner, btw.
The arrangement, in specifics, is:
rope tied w/end loopknot positioned just through upper 'biner,
rope reeved through 'biner down through lower 'biner attached to weight;
then mid-line eye tied immediately at 'biner, line run up through upper eye,
then mid-line eye tied immediately at 1st eye, line run down through lower eye,
and up through upper 2nd eye (no double reevings in this set-up), and then
down as haul line.

The cost is lack of movement distance! In contrast, a Versatackle can collapse
its multi-reevings to draw the initial two eyes together, moving the load half
of the span between the eyes at start; the Dble. Spanish Burton’d one moves
it much less (given the holding, one might try a short Prusik sling to make
a sliding final/haul eye). But, if one needed power, say to free up some
well-stuck snarl of flotsam-jetsam rope half buried in beach sand (amazing how
little sand can resist efforts to free it, even w/'biner sheaves!), this might do.

Now, I’ve just revised above to be a single Span.B. set-up:
Clove-Plus hitch to lower (& alas thicker) 'biner, shorter line run up through
top 'biner & into immed. loopknot; longer line run up through LK eye into
haul line. And … ? --one can hang 40# against the 50# load w/no hint of
movement! With 50-50, it moves well; but 50 hauling 55 moves a little, with
momentum, then self-arrests. Theo.MA (TMA) = 4:1 ; Act.MA (AMA) = 1.08 : 1 ?!
Replacing the upper eye w/'biner sees 50# move 60# slowly, continually,
bit by bit. AMA = 1.2 : 1
Replacing the lower CloveH. to 'biner with pure 'biner brought no improvement
–no rope movement through this “sheave”!
Replacing the older solid braid with a new, slick 8mm nylon kernmantle (fairly
supple/flexible), improved the performance to 50# moving 65# slowly, upping
AMA to 1.3x : 1 .

In fairness, the solid braid is NOT slick rope–has an aged though not worn
feel to it. But in practice, is a new rope going to be employed–or that long stuff
you’ve had around for years waiting for a purpose? YMMV. Using some kind of
metal for sheaves should help, but there is still a good gap between TMA/AMA.

–dl*

22

The Spanish Burton strategies are to me an exapmple of 2Handing; in that the inner/ first system pulled inputs from both ends/ the equal and opposites of the forces generated, into the larger/ outer system. Increased power from the pulls at both ends of the inner/first pulled system able to input distance multiplier from each end into the larger/ outer system.

Definite loss of travel for reason you say, distance limited to half the shorter leg.

Lockings coming from friction, and in multiple lines running through an eye crossing each other as crossed turns on pulls, then keeping that position to kinda be like hitches; whne the load pull becomes the greater pull than hand pull(when hand lets go); weight of line etc.

23

“way tighter” is subjective, and as you’ve seen in this thread there are
some ways to quantify things. Although there are many factors that
come into play, notably cordage qualities. In a frictionless system
you would not be able to tie anything down, in theory; but in less
than perfect frictionlessness, you do have MA alone working on
your behalf, which you needn’t overcome to gain tension.

Now, I revisited this topic on seeing Roo’s Notable notes on this structure
still persisting in claiming a “high” MA for it. He says that he tested some
PP cordage tied as he shows and got 2.6:1 MA, which is well higher than
what I saw in my testing. So, I got out some gear and tried a few things.

Roo claimed a 2.6:1 MA with PP rope. I’ve just tried to achieve this,
using carabiners/krabs for sheaves with 3/8" soft-laid PP rope:
structure vertically oriented, with the anchoring (V’tackle-material-feeding)
end (Roo’s “B”) end low; feed runs up through top sheave 3 times and down
to haul weight(s), passing 2 times through bottom, anchor sheave.
12.5# doesn’t budge;
14.5# doesn’t budge;
17.5# slowly raises 25#.
Even guessing favorably that 16# is break-even, that works out to MA <1.6:1,
and with metal vs. cordage, and apparently an extra half pass (i.e., extra in 1 sheave)
over Roo’s system. (Note that he didn’t provide details of this; his NKIndex shows
two configurations. I’m likening mine to the one on the left, not the tie-down one.)

Moving to pure cordage, my full set of haul weights (12.5 + 5 + 2 = 19.5#)
doesn’t budge the 25# load; with some helpful surging of the haul line,
one gets a very slight follow-on haul then arrest. So, granting 19# as the
break-even point, even, that’s an MA of <1.3:1, for the cordage. Yet Roo
got double this !? Again, how, in what orientation?

Well, I decided to remove a reeving and use a pully wheel for re-direction
and so my haul weights now would be pulling UPwards into the lower
sheeve, directly towards the task of raising the 25# weight (instead
of hauling downwards into the Versatackle with the goal of simply contracting
it however it cared to achieve that (top sheave moving downwards, or lower
upwards, or a bit of both together). The result was dramatic!
Ultimately, using rope sheaves BUT for the ones the Verstackle
itself runs through, I saw breakeven move towards half of the load,
so ~= 2:1, conceivably better.
NB: Only the lower VersaTackle sheave moved – upwards-- ; the top eye
knot stayed snug against the top metal ('biner) sheave. !?

Then I considered the tie-down structure and realized that this revised
structure was overly easy on MA, with metal and extra TMA. So, I
changed the structure to match the tie-down, with upwards haul line
redirected through the pulley. (I.e., my "tie-down" was a "tie-up",
with the haul line redirected downwards for gravity’s hauling.)
Another dramatic change: here, it seems that 14.5# is somewhere near
the “breaking point”, as I’ve called it --some manual assistance getting
some follow-on movement-- ; 17.5# raises the 25#. And both sheaves
move – that of tied-down fixed-position eye knot coming towards the
anchorage point, and that going around the anchor moving to meet
the other. So, this is an MA of about 1.75:1.

To be clear, my structure, oriented in terms of a truck-top tie-down,
has the line (to be tightened) coming down to form the upper eyeknot,
continuing down around a lower anchor sheave, and --on turning
upwards-- forming another directional eyeknot, the tail running up
through the top knot, down once through the lower, then finishing
through the upper one, to be hauled (and nipped by its first passage,
upon release). (VersaTackle bunching-in-a-sheave only occurs in
the top eyeknot.)

Adding one further course to the structure (one more down-through
& up-through, in tie-down orientation) doesn’t change the MA; it
just leads to some ugly bit of loose reeving protuding after tightening.

I’ll wager that supple solid-braid (commonly nylon, but elasticity isn’t
a plus) will perform better; the ruts of this laid rope could be felt.

–dl*

24

Trying to decipher what you’re doing, I think, maybe, I understand your problem. You’re not using the mechanical advantage to its fullest. If you are lifting weights with an input weight traveling downward, you are not utilizing the input weight’s full effect and are measuring the weaker output.

Try putting a scale at the top, a restraint bar at the bottom, and let your input weight hang without bounce.

If 16 raises (or is the break even point for) 25, then the top scale should see 16+25=41.

41/16=2.5625

25

::slight_smile:

I’ll hope that you have already had a good chuckle at your sophistry here
(but just didn’t edit the post). By this reasoning, a pure block has an MA
of 2 (as X mass will break-even with itself); or let’s just figure out what
happens with 17# hoisting 16# via the ceiling-mounted pulley, and call
33/16= 1.94 : 1 ?! Of course, a simple pulley such as this is 1:1
(and we could check this with rope_movement / object_movement).

–dl*

26

Are you kidding me? A single pulley DOES have a maximum mechanical advantage of 2. See center diagram below:

http://hyperphysics.phy-astr.gsu.edu/Hbase/mechanics/imgmech/pulley.gif

Notice that the input force is going in the same direction as the output motion, which is what you’ve been failing to do. All this time I assumed you knew how to measure mechanical advantage.

You have your output measurement where your restraint should be, and you have a restraint where your output measurement should be. You’ve been measuring what should have been the restraint reaction force instead of measuring the output force!

27

:smiley:

Okay, I’ve ignored/misinterpreted your “restraint” and focused
on your “raised” (where one might’ve said “would raise” – were
things oriented otherwise), and gone topsy-turvy thus.

I used pulley#1 to redirect force into my structure for, yes, raising
the various weights, in my latest structures; prior ones essentially
were getting the re-direct within the VersaTackle, and so paying
a great price in efficiency (but one not apparent in that such a pull
can be seen as working to pull down the upper VersaTackle-eye
sheave and collapse the structure around the fixed upper pin).

And what is being measured is the effect of certain structures,
as oriented – how they might be better oriented is another issue.

Now, maybe with stuff still about, I’ll find some different cordage
to play.

–dl*

28

Further follow-up: I used a flexible, thin (3/16"-ish), nylon or maybe
multifilament PP solid-braid cord. Despite its smoother surface, the
results were much the same as for the laid PP rope. Moreover, even
putting in another course in the VersaTackle (which would affect the
Theoretical MA) had little or no beneficial effect (!) for MA.

–dl*

29

Super old thread, but…

I just used a Verstackle outside on a REAL application. I got the line WAY tighter than I could have without using the Verstackle. I also got the line tighter than a regular Trucker’s hitch.

On one hand, friction does reduce the mechanical advantage in a Versatackle. One the other hand, friction allows the person to tie down the final knot. In a frictionless system, I would have had trouble tying down the rope by myself. The friction acts as a third hand in the final turn of the Versatackle.