working load limit (WLL) of the BBB and
refer to the high-test chain table (Table 23-3)
or the stainless chain table (Table 23-4) to
find the high-test chain size with the same or
slightly greater WLL.
Use the weight of the standard steel
bower anchor, not the weight of a lightweight
anchor (if you’ve gone that route). Returning
to Hold Fast, we would enter 36 pounds
(16.4 kg) as the anchor weight in Formula
24-2, and find that we need to outfit her with
0 .33-inch (8.4 mm) chain BBB or proof coil.
This falls between^5 / 16 inch and^3 / 8 inch (or is
closest to 8.73 mm wire dia. BBB). For a no-
compromise voyaging world-cruiser, I would
go with the^3 / 8 - inch diameter (10.32 mm wire
dia.), but most ordinary boats should round
down, so we’ll get^5 / 16 - inch (0. 3125 in. or
8 .73 mm wire dia. BBB) chain for Hold Fast.
Note that I prefer BBB because it functions
best of all on a windlass wildcat and is
slightly heavier for a more pronounced cate-
nary; however, BBB is not a metric-size
chain. Outside the United States and Canada,
you would use ISO proof coil or high test.
If saving weight were desirable, then we
would use high test. From Table 23-2, we see
that the WLL of^5 / 16 inch (8.73 mm wire dia.)
BBB is 1,900 pounds (862 kg). Per Table 23-3,
high-test of^1 / 4 inch (7 mm) has a WLL of
2,600 (1,180 kg). The BBB^5 / 16 inch weighs
72 pounds/100 feet (1.6 kg/m), while the high-
test^1 / 4 inch (7 mm) weighs 62.5 pounds/
100 feet (1.1 kg/m). On 300 feet (90 m) of
chain, this is a weight reduction of about
112 pounds (51 kg).
The rule of thumb is that you select high-
test chain one standard size smaller than the
equivalent BBB or proof coil, which gives
the same results here (as would referring to
the tables).
Shackle and Swivel Diameter
The galvanized anchor shackle table
(Table 23-5) indicates that^5 / 16 - inch (7.94 mm)
shackles are too weak, with a WLL of just
(^3) / 4 ton (1,500 lb., or 681 kg). Accordingly, we
need to specify^3 / 8 - inch (9.52 mm) galvanized
anchor shackles, with a working load limit of
1 ton (2,000 lb., or 907 kg). Note that the high-
test chain is actually over 1-ton working load
limit. Since we’ve gone to it to save weight
and it already exceeds the strength of the
BBB required, you don’t have to increase the
shackle size above^3 / 8 inch (9.52 mm). How-
ever, to use the full strength of the high test,
you would need to increase shackle size to
(^7) / 16 inch (11.11 mm), with a WLL of 1.5 tons
(3,000 lb., or 1,361 kg). Note that this will not
fit in^1 / 4 - inch (7 mm) high-test chain, which
has an inside width of just 0. 41 inch
(10.41 mm), while the^7 / 16 - inch (11.11 mm)
shackle has a pin diameter of^7 / 16 inch
(0. 4375 in., or 11.11 mm). This is the reason
that it is best to order anchor chain with over-
size end links built in by the manufacturer.
Swivels also need consideration. For our
(^5) / 16 - inch (8.73 mm wire dia.) BBB chain, we
need a swivel with a WLL of 1 ton. Table 23-8
shows that a^3 / 8 - inch (9.52 mm) galvanized
jaw-eye swivel will slightly exceed this at 1. 1
ton WLL. To match the full strength of^1 / 4 - inch
(7 mm) high test, again you would find that
the^1 / 2 - inch (12.7 mm) swivel would not fit a
standard link.
The stainless swivel would need to have a
breaking load of 4 times the WLL of the
(^5) / 16 - inch (8.73 mm wire dia.) BBB chain; so
1,900 lb.× 4 =7,600 lb., or 862 kg× 4 =3,448 kg.
This matches the swivel size recommended
for this size chain (Table 23-9). Remember
not only that high test would need the next
size swivel up to develop the full strength of
the high test, but also that this full strength
isn’t required in this application.
Rope Anchor Rode
(Warp) Diameter
Of course, most smaller boats and many light
performance and inshore boats don’t use an
all-chain rode, but some combination of
chain and rope. The rope rode or warp diam-
eter can be found by using the following
formula.
Formula 24-3. Rope Anchor Rode Size
Nylon Anchor Rope Rode (Warp) Diameter,
in. = 0. 2 +(anchor weight., lb. ÷185)
or
Nylon Anchor Rope Rode (Warp) Diameter,
mm = 5. 08 +(anchor weight., kg ÷ 3 .3)
Again, use the bower anchor weight from
the formula, not a lightweight anchor’s weight.
Chapter 24: Sizing the Anchor and Rode and Selecting Anchor-Handling Gear
Formula 24-3.