Chapter 23: Anchor Rode
astern in heavy seas to aid in directional sta-
bility underway: “trailing a warp.”)
The Problem of Rope Chafe
Rope is lighter and considerably less expen-
sive than chain, but it chafes, abrades, and
wears out. It’s not well known that sand, salt,
and other grit routinely work their way be-
tween the strands of rope anchor rodes
(warps) and cause internal abrasion, which
can lead to failure of the warp. Nylon also
absorbs water, and when saturated it loses
roughly half its strength.
Figure 23-9 shows the nylon mooring
pendant with a polyester chafe jacket that
failed in a typical 40-knot nor’easter. Note
that the rope was stretched under load, so
when it failed, it broke even farther from the
chock and the deck edge than it appears in
the picture. The surveyor concluded that
interfiber abrasion from salt grit was a con-
tributing factor. The combination of inter-
fiber abrasion and loss of strength due to
water saturation is usually not taken into ac-
count properly. Rope is most definitely good
for anchor warps, but keep its weaknesses
in mind and check the rope carefully.
Proper Chocks Are Critical
Protection from chafe is paramount. To this
end, large, strong, exceptionally well-
rounded and strongly fastened chocks are an
absolute must. It’s an unfortunate thing to
note, but many boats have inadequate chocks
that are inadequately fastened. There are also
many manufacturers of chocks and cleats
that seem to make them as angular and sharp
as practical (Figure 23-11)! This appears most
frequently from some European manufactur-
ers. A few make cleats and chocks that are
apparently designed to look “sharp.” Possible
this is a styling thing (racy?) and possibly it’s
a cost-saving measure; perhaps it’s both. In
any case, there are too many inadequatelyTABLE 23-11. THREE-STRAND NYLON ROPE
Diameter Weight Breaking Strength
inches mm lb./100 ft. kg/m lb. kg(^3) / 16 5 1.0 0.015 1,200 544
(^1) / 4 6 1.5 0.022 2,000 907
(^5) / 16 8 2.5 0.037 3,000 1,361
(^3) / 8 9 3.5 0.052 4,400 1,996
(^7) / 16 11 5.0 0.074 5,900 2,677
(^1) / 2 12 6.5 0.097 7,500 3,403
(^9) / 16 14 8.2 0.122 9,400 4,265
(^5) / 8 16 10.5 0.156 12,200 5,535
(^3) / 4 18 14.5 0.216 16,700 7,577
(^7) / 8 22 20.0 0.298 23,500 10,662
1 24 26.4 0.393 29,400 13,339
TABLE 23-12. DOUBLE-BRAID NYLON ROPE
Diameter Weight Breaking Strength
inches mm lb./100 ft. kg/m lb. kg
(^3) / 16 5 0.9 0.013 1,200 544
(^1) / 4 6 1.6 0.024 2,200 998
(^5) / 16 8 2.5 0.037 3,400 1,543
(^3) / 8 9 3.6 0.054 4,900 2,223
(^7) / 16 11 4.9 0.073 6,600 2,995
(^1) / 2 12 6.3 0.094 8,500 3,857
(^9) / 16 14 8 0.119 10,800 4,900
(^5) / 8 16 10 0.149 13,500 6,125
(^3) / 4 18 14.3 0.213 19,400 8,802
(^13) / 16 18 16.5 0.246 24,400 11,071
(^7) / 8 22 19.4 0.289 26,300 11,933
1 24 25.4 0.378 34,000 15,426
11 / 8 28 35 0.521 46,000 20,871
11 / 4 30 40 0.595 52,000 23,593
15 / 16 32 45 0.670 58,000 26,316
11 / 2 36 58 0.863 74,000 33,575
15 / 8 40 71 1.057 90,000 40,835
13 / 4 42 85 1.265 106,000 48,094
2 48 102 1.518 126,000 57,169