Chapter 23: Anchor Rode
systems. For example, ACCO makes a moor-
ing chain (stamped MC) with higher strength
than standard proof coil and BBB. The links
on a mooring chain are too long to wrap well
around a windlass chain wildcat. It is for use
in permanent-mooring systems, not for boat
anchoring systems. There are also marine
chains for lashing deck cargo and for fishing
applications such as trawl-door chain and
tuna-net chain. None of these are suitable for
anchor rodes.
When purchasing or inspecting chain,
look for the identifier stamp marks on the
chain. If they are not visible in a size of
(^5) / 16 inch (8.4 mm) or over, or do not match the
previously recommended chain types, you
have a potential problem. Note that some
manufacturers stamp every link, while others
stamp a link every foot (30 cm) or so.
Meaning of the Chain-Grade
Number
Chain-grade numbers roughly relate to the
tensile strength of the chain alloy and are
nominally one-tenth of the actual strength.
Thus grade 40 is actually 400—that is,
400 MPa or N/mm^2. (Newtons per square
millimeter are the same as megapascals.) If
you know the chainsize, this allows you to
approximately calculate the ultimate break-
ing strength of the chain. Say you had a
(^3) / 8 - inch (10 mm) grade 40 (high test) chain.
The ultimate breaking strength would be
approximately as follows:
(^3) / 8 in.= 0. 375 in.= 9 .525 mm dia.
Radius= 9 .525 mm ÷ 2 = 4 .7625 mm
Area of a cross section of the chain link is
found from:
A=pr^2 = p (4.7625 mm)^2 = 71 .25 mm^2
71 .25 mm^2 × 400 N/mm^2 = 28,500 newtons
per side
28,500 newtons per side× 2 sides of a chain
link= 57,000 newtons
57,000 newtons× 0 .2248 lb./newton= 12,800 lb.
ultimate strength
or
57,000 newtons ÷ 9 .80665 newtons/kg=
5,812 kg ultimate strength
This is good basic information, but you will
find that manufacturers’ chain tables don’t
usually match the preceding calculations.
Part of the reason for this is that the length
of the chain’s links and the chain welds also
affect the chain’s strength.
TABLE 23-3. GRADE 40 OR 43—"HIGH TEST" CHAIN SPECIFICATIONS
Trade Wire Wire Inside Inside Inside Inside Working Working Wgt. per
Size Diameter Diameter Length Length Width Width Load Load 100 ft. Wgt.
inches mm inches inches mm inches mm Limit, lb. Limit, kg lbs. kg/m
(^1) / 4 † 7.0 0.276 0.84 21.34 0.41 10.41 2,600 1,180 73.3 1.1
(^1) / 4 7.0 0.276 1.19 30.23 0.50 12.70 2,600 1,180 62.5 0.9
(^5) / 16 † 8.4 0.329 1.03 26.16 0.51 12.95 3,900 1,770 103.0 1.5
(^5) / 16 8.4 0.329 1.24 31.50 0.46 11.68 3,900 1,770 94.0 1.4
(^3) / 8 † 10.0 0.394 1.22 30.99 0.59 14.99 5,400 2,450 147.8 2.2
(^3) / 8 10.0 0.394 1.33 33.78 0.57 14.48 5,400 2,450 142.6 2.1
(^7) / 16 † 11.8 0.464 1.40 35.56 0.65 16.51 7,200 3,270 205.6 3.1
(^1) / 2 † 13.2 0.519 1.59 40.39 0.76 19.30 9,200 4,170 256.8 3.8
(^1) / 2 13.2 0.519 1.72 43.69 0.75 19.05 9,200 4,170 255.6 3.8
(^5) / 8 † 16.0 0.630 1.79 45.47 0.90 22.86 13,000 5,900 421.2 6.3
(^5) / 8 16.0 0.630 2.12 53.85 0.82 20.83 13,000 5,900 382.4 5.7
(^3) / 4 † 19.8 0.781 2.20 55.88 1.09 27.69 20,200 9,160 591.4 8.8
(^3) / 4 19.8 0.781 2.60 66.04 1.02 25.91 20,200 9,160 552.1 8.2
(^7) / 8 23.0 0.906 2.66 67.56 1.25 31.75 24,500 11,100 804.6 12.0
1 26.2 1.031 2.88 73.15 1.40 35.56 34,000 15,400 1,044.0 15.5
†=to ISO Specifications