Cruising Helmsman – June 2017

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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