There But For
The Right Storm Line
Why do some nylon anchor lines
hold and others break in a storm?
There are five critical factors that
predict how rope fares in a storm.
s sometimes happens in early
spring, a line of dark clouds suddenly appeared on the horizon
and Dan Arsenault got caught in
an especially violent April thunderstorm.
He had been bringing his 37-foot sailboat
from its winter storage yard to its summer
home near Saginaw Bay, Michigan, when
the wind built to near hurricane force and
seas grew to nine feet. Dan’s boat was
bounced off the bottom several times,
damaging the rudder. After a brief attempt
to work his way into the marina, Dan
crawled up to the bow, set the anchor and
went below to wait for the wind to subside.
Moments later, amid the horrific noise of
the storm, he heard a loud “explosion.”
The anchor line had parted.
In less trying conditions, nylon’s ability to stretch makes it an almost perfect
choice for an anchor line. The stretch
absorbs shock, which means less strain on
the anchor, less jerking and a more comfortable night’s sleep. Members of the BoatU.S.
Hurricane Cat Team, however, have found
that the same nylon rodes that are fine for
everyday use have proven to be woefully
inadequate in a violent storm. In Florida
hurricanes, hundreds of boats have been
driven ashore because their nylon anchor
rodes, usually more than one, parted.
After a storm, it’s easy to look at the
frayed remains of the line and conclude
that it had chafed. The solution has typically been to recommend more and better
chafe protection. However, the “chafed”
line could have broken — even exploded
— under the tremendous load because
it lacked strength, or failed because it
lacked elasticity or failed internally, actually
melted, by the tremendous heat generated
by friction; or it could be a combination of
these. There have also been at least as many
examples of anchor lines that survived,
despite being tested for many hours by the
same high winds and seas.
Consider these five critical factors that
predict how rope will fare in a storm:
1. Breaking strength is determined by
wrapping new rope around two large-diam-
eter capstans and slowly tensioning the line
until it breaks. All things being equal, a
braid-on-braid line has the most breaking
strength, followed by plait and then three-
strand (see box). While breaking strength
(tensile strength) seems like the obvious
criteria for selecting anchor line, the forces
on a rope in a hurricane are not applied
slowly on large-diameter drums; it takes
more than breaking strength for a rope
to survive something as violent as a hur-