Page 200 - J. C. Turner - History and Science of Knots

Studies on the Behaviour of Knots 189

way the rope lies, how it packs when tightened, and the supposed likelihood
of working itself loose, but neither experimental data nor field experience are
cited. This point could do with further study. The Alpine Club [2] reported
on two knots of whose exact identity I am unsure, tied `with' and `against' the
lay; I am unsure of the sense in which they meant these terms. The `Swiss
Loop' had a strength efficiency of 57% against the lay, 71% with it, whereas
the `Openhanded Knot' had efficiencies of 53% and 55% respectively. The way
in which the parts of a knot are loaded may also be important. Are the loads
on the two legs of a loop equal? Is the load on hitches always at the same
angle to the object hitched? Is the Clove Hitch loaded on one end or two?
And so on.
Rope: Inspection of Table 2 failed to find any consistent differences in
knot efficiency that could be attributed to the kind of rope, except that the
thin flax of column 2 had higher efficiency values that any others. On the
other hand, Table 3 shows a marked effect, attributed to the differing inherent
rigidity of the different fibres and the internal frictional forces [20, p. 243].

Table 3. INFLUENCE OF ROPE TYPE ON KNOT STRENGTH EFFICIENCY
'Overhead Knot' tied in % inch diameter rope [20, p243]
Type of Rope Laid Braided
Dry Wet Dry Wet

Ramie 58% 94% 53% 84%
Cotton 50% 69% 77% 96%
Nylon 54% 40% 58% 75%
Manila 62% 60% - -
Changing the size of the rope changes the knot efficiency somewhat errat-
ically, with a tendency for knots tied in smaller ropes to have lower efficiencies
(Tables 4 to 6). The ranking order of knots may also be a bit different in dif-
ferent size ropes. Thus in Table 4, the Overhand Bend has a higher efficiency
than the Reef Knot in 4 inch and 1 inch diameter ropes, lower in a but equal
ins and a inch rope; in Table 5, a Clove Hitch had a higher efficiency than an
Overhand Loop in 4 mm and 5 mm rope, but lower in 7, 9 and 12 mm, while
the Overhand Loop was of substantially lower efficiency than the Bowline in 5
mm rope, slightly lower in 4 and 7 mm, and equal in 9 and 12 mm; in Table 6,
the Figure Nine End Loop has a higher efficiency than the Double Fisherman's
Knot in 9 mm rope, lower in 11 mm. In other work, Prohaska [32] found that
the ranking order of the strengths of some loop knots varied with the diameter
of the rope used; he did not express his results as efficiencies, so I have not
tabulated them. Different sizes of rope are not, of course, simple scale models