THINK about this : substitute "sheet" for "Lapp"!!
After centuries of use, has anyone reported testing
as you ask for this venerable knot,
noting sizes and which side --they're different-- breaks
!
(I know of none, including even myself, say, using
cheaply got mason-/fish-line. .:. lazy me!)
Well, I am not aware of load tests, but how these knots function best has certainly been passed down through the years. How much is anecdotal I don't know, but the old salts from years gone by were a canny lot and would have worked out pretty quickly what worked and what didn't.
Perhaps, in some cases, and for some situations
(which might've changed, in time). Whether the
popular literature captures this knot knowledge
is an entirely separate question --mostly, knot
books seem to copy other knot books, even errors!
For example, if the lines are of a significantly different diameter, sailors don't use a single sheet bend.
If lines are of a thick diameter, neither the sheet bend nor double sheet bend is preferred, instead a Carrick is used.
Really?
I've never found a
carrick bend tied anywhere
in the Wild ! I've heard, well, seen on t.v., that
it is used by the Alaskan crabbers. The
zeppelinwould be good one for them, too, though they might
want to bind the tails (tape) and the former makes
that easier.
I generally tie an Alpine Butterfly Bend
if I need to join two ropes of roughly the same size.
In the last few days I have practiced the Zeppelin
until I am super comfortable with it and will make that
the knot of choice now.
And you'd use these *fashionable* knots instead
of Ashley's bend #1452 (or 1425!) because ... fad?
Nope, because I have read that the Ashley and Hunter
could not be untied after a load had been applied, so I never
bothered even glancing at them. Sailors generally prefer to learn
how to tie the minimum number of knots they can get away with 
.
I have never come across anyone using the Ashley bend on
board a boat and simply dismissed it as an option.
!!
Pity what misinformation can do --and that you
gave up so easily, rather than testing assertions
(which must've come from the Net). #1452 can
be dressed to jam or not to jam; Ashley doesn't
illustrate the knot well, and might not have known
it so well, either. You want to orient the tails so
that they
start being rotated against each other
in a locking manner and are further so rotated by
the draw of the SParts. (Unlike the
butterfly bend,
#1452, #1408, & zeppelin have SParts rotating in
the same direction --the b.'s go opposite.)
(The jamming state might be beneficial when working,
e.g., with polypropylene rope in some light-load situation;
w/o heavy loading, you will easily be able to untie.)
Ashley's #1408 & the
zeppelin have similar shapes
of their
overhands, with the former interlocking
them more fully, but the latter giving more of a
sharp bend to the tail at its tuck, which I think
helps it resist *flowing* loose --material doesn't
move through the right-angle bend well, whereas
#1408 has a smoother bend here.
So, my question remains.
Is #1434 or #488 going to perform better under load,
particularly when the diameter of the lines is different?
If so, 1434 should be banished from sailors' repertoires .
You shouldn't be so narrowly
Index-to-exact-knot-minded,
but understanding of how the knots work so that
you can make adjustments per situation.
E.g., Roo warns of snagging of the bight-side tail
with the
sheet bend-like knots : this vulnerability
can be redressed by essentially seizing the tail to
the SPart with the end of the hitching line,
using a multiple
strangle knot (or, if you want
to keep to *fad*, a less-well-oriented vis-a-vis tails
alignment,
constrictor 
); the first-formed
will do the heavy work, the seizing knot just will
keep things in place, and be no tighter than it
was set, roughly --and thus, loosenable.
[Here I'll remark at how "untiable" is an ambiguous
term --can we NOT tie it, or can we UN-tie it?!]
Frankly, the two previous knot alternatives I suggested
--those using overwraps of either hitching SPart and
one leg of the bight side, or both legs but then
with a more or less normal
sheet bend front end,
will provide some *seizing-like* security vs. snagging.
(Of course, the
zeppelin is woefully awkward with much
line-diameter difference, and will please only the most
pedantic & z.-zealous of mariners.
)
Btw, FYI Dave Richards of the Cordage Institute (or of
a member firm --but I believe he was on the board ...)
did testing of kernmantle ropes (rockclimbing, caving,
SAR), and found that sometimes the
dbl.S.B. slipped
but not the single (& also the
fisherman's knot(!),
sometimes both (resp. 12.5mm & 7mm low-elongation),
and once only the single (dynamic). So, that was eye-opening!
(No photos to show details, et cetera, so much must be
presumed or left to question.)
((This report was taken off-line, sadly, for some minor
discrepancies --which should've been redressed quickly
and simply (and there were even offers to assist!)--,
and appears to be yet NA, unless maybe by something
called the Internet WayBack Machine or whatever ... !?))
--dl*
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