Cruising Helmsman – June 2017

(Sean Pound) #1

46


Cruising Helmsman June 2017

ESSENTIAL KIT


CRUISING SAIL


TECHNOLOGY UPGRADES
As with most things in life, choosing new
cruising sails involves compromise.
You can opt for the longer life and lower cost
of woven polyester sails and accept that, within
a season, they will begin to stretch. You will
lose full control when you cannot flatten the
sail, which means more heeling, more weather
helm, more leeway. This leads to more stress
on autopilots and crew.
There are sailcloths available that weave in
stretch-resistant fibres, but the very fact that
they are woven means they will still stretch as
the fibres straighten under load. They remain
popular because of the comparatively low cost,
higher ultraviolet resistance and higher flex
resistance, which means they can take a lot of
punishment.
In the early 1980s, another option became
available: the panelled laminate sail. It is
lighter aloft, holds its shape very well and
will deliver better sail control. But costs
more, is prone to mildew and is more fragile.

For cruising purposes, this is then covered
on both sides with tafetta to protect the film
and scrim. The scrim is built with straight
fibres so stretch is greatly reduced compared
to a woven cloth. However, once the Mylar
film or the scrim is damaged, the sail loses
its strength and sooner or later it will fail in a
spectacular and expensive way.

Third wave
Now there is a third option. In the search
for performance advantage, racers demand
innovation from sail lofts, sail designers
and scientists.
Since time immemorial, sails have been
made from panels of cloth sewn together.
That was still the case in 1955 when DuPont
released Dacron, a woven polyester sailcloth
that replaced cotton canvas as the cloth
of choice. The cloth is still cut into panels
and sewn together in the time-honoured
fashion but, compared to cotton, Dacron was
stronger, lighter and had better UV resistance.
In 1992 North Sails introduced 3DL sails
for racing yachts. The big breakthrough was

having the sail laid up on a mould, built in
three dimensions rather than two, so its shape
could be controlled perfectly. Also, it enabled
the use of continuous fibres along the entire
loadpaths, rather than the discontinuous
fibres you get if you stitch panels together.
The result was perfect shape, hardly any
stretch and light weight.
The only drawback was that 3DL was a
laminate sail, hence fragile. The challenge
was: can we build a moulded sail without
using Mylar film?
The breakthrough came when Swiss
engineers working for Alinghi’s 2007
America’s Cup challenge laid out fibres and
pre-impregnated them with a thermoset resin
glue, creating featherweight filament spread
tapes of pure fibre.
By building these into sail sections,
adding extra layers of tape in high stress
areas where strengthening is needed, then
vacuuming these onto the mould, essentially
heat-treating to activate the resin glue, a one-
piece sail was created that was pure fibre
and, crucially, no film.
In the end Alinghi did not use the shiny, jet
black sails but North Sails understood the
potential of the technology, then known as
Amalgam, bought it and used it to launch its
3Di range of sails.
If you follow ocean racing, you will be
familiar with 3Di sails. They are used by
most of the boats in the Vendée Globe and all
of the boats in the Volvo Ocean Race. They
were also used by Thomas Coville aboard his
31 metre trimaran Sodebo Ultim when he
sailed solo around the world in under 50 days
plus on the 31.5m trimaran Idec Sport when
Francis Joyon and his crew of five sailed
around the world in under 41 days.
Reliability is not an issue for 3Di. The
technology is well proven.
North Sails is now adapting this technology
to process polyester fibres. The result is 3Di
Nordac, a sail that is 100 per cent polyester, the
fibres and the resin, which has all the durability
characteristics of a polyester sail: high UV
resistance and high flex resistance, but holds
its shape because it is built with tapes made
from straight fibres, not woven ones.
Also, because it is polyester, it’s low cost.
Surely this is too good to be true?
While the old Dacron sails involved a 14
step production process, these new Nordac
sails take only nine. This is from the fibres
being created to the finished sail delivered to
the yacht owner.
http://www.au.northsails.com
Free download pdf