The Design and Build of a Stratis Sail

Doyle Sails has become one of the leading
manufacturers of laminated sails worldwide. One of our
particular fields of expertise is superyacht sails, and
Doyle Sails Head of Design Richard Bouzaid explains
the process for developing a STRATIS™ superyacht sail
from design, through engineering and manufacturing to
final finishing.

 

“As with any sail, the first stage in the process is the sizing
of the sail. This is especially important on large yachts as
errors are costly and can require cranes to take sails on and
off a yacht for changes to be made. Very accurate
measurements are required for all the parameters of the boat
to ensure that the design can proceed correctly.

Three dimensional design

"Our first stage in the process is to build a precise 3 dimensional
model of the yacht within our design software. These models are
accurate to millimetres and include all of the relevant detailing that
can affect the fit and performance of the sails. Details of the sail
attachment points, furling units, head swivels, mast detail with
halyard positions, spreaders and other potential conflicts with the
sail are included. We even take into account possible interference
from radars scanners, communications equipment and stanchions
as well as calculating possible positions for headsail cars.

This allows us to then fit a sail to the model with the certainty that, in
real life, the sail will not only fit correctly to the 3 attachment points,
namely head, tack and clew, but also where and if the sail will have
other stress or chafe points due to fittings on the boat. The sails can
then be suitably reinforced or the geometry altered to avoid
these conflicts.

"The accuracy of this type of modelling has been one of the biggest
steps forward with sail design software in the last 10 years.

MODEL OF
KOKOMO BLADE

The model is of the 57 metre Dubois design Kokomo built at Alloy Yachts in New Zealand and launched in 2010.

The blade is accurately modelled in 3D to ensure precise fit first time without interference from spreaders and deck gear.

The high level of detail in the model to include anything that can influence the sail is crucial to the success of the sail design.

FIBRE MAPPING

This diagram shows the mapping of fibres to address the load paths on a sail. By directly addressing the load paths, superfluous fibre which adds unnecessary weight to the sail, is avoided. Stretching of the sail is eliminated as the fibres are oriented to counter the tensile pressures the sail will experience.

SAIL STRETCH ANALYSIS

This diagram shows an analysis model of elongation in a sail. The colours highlight areas that are experiencing more stretch than is desired - with the light green area showing the area of maximum elongation.

Shape optimisation and fibre mapping

Shape optimisation is the next stage in the sail design process. Base
sail shape moulds are used for certain geometries and applications and
then adjusted for the requirements of the actual sail that is being
designed. For example a cruising genoa will have more shape towards
the back of the sail to be more effective when the sheet is eased.
During this process the sails will be accurately aligned to the actual
attachment points on the model so that mast bend and headstay sags
can be incorporated into the sail design.

Once the parameters of shape have been worked out, the orientation
and density of the fibres that address the load paths of the sail can be
established. We engineer ours sails to stretch by a certain amount,
rather than to a % of their ultimate breaking strength. For a high
performing sail we would be typically be looking for a maximum
elongation anywhere in the membrane in the region of 0.15-0.2 per
cent; and it is important that this elongation (stretch) is as uniform as
possible throughout the membrane.

During the process of establishing the correct fibre alignment and
density, different combinations of fibres may be used to get the best
balance between weight and overall durability. There are various fibres
that we use in a STRATIS™ sail depending on the application.
Performance cruising boats will typically use Vectran or a combination
of Vectran and carbon fibre. Performance racing boats will use twaron
(Kevlar), carbon fibre or a combination of the two fibres.

Lamination and consolidation

Once the orientation and density of the fibres has been finalised, the
fibre map for the sail will be programmed into the 12m wide x-y
plotters that will lay the fibres onto the surface. This base surface will
become one of the sides of the finished sail. These fibres are all laid
under tension to exact paths determined by the earlier studies.  

The final process in the membrane manufacture is the application of
the top surface. This top surface is also a film sheet, often pre-coated
with adhesive with  a polyester taffeta on the outside. The laminated
membrane is finally vacuum bagged to the table and then the
laminator, using infrared heat lamps and 12000KG of downward
pressure makes computer controlled passes over the membrane to
activate the glue and expel any remaining air in the laminate. The
STRATIS™ factory operates with two of these laminators.

The membrane is left to cure for several days before being moved to
the Doyle New Zealand 30,000 square foot sail loft floor for finishing
or shipping to one of the many Doyle Lofts worldwide for completion.

1.3 million metres of fibre are laid per week
85,000sqm of Stratis membrane was produced in 2012
The cad fibre laying machines travel an average of 150,000 metres a week

Finishing

The completed membrane is then sent to the
finishing floor to have hardware attached and
any other finshing tasks completed.

Doyle Sails New Zealand's finishing
floor:
large enough to take care of the
world's largest sails.

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STRATIS™ sails are made exclusively for the Doyle Group of Sailmakers and
supplied from Doyle Sails New Zealand's custom STRATIS™ facility in Auckland