When
designing and making sails, there are
several variables to keep in mind:
-
the outline and camber (aerofoil shape)
of the sail
-
the required area
-
the materials to make it from
-
the method of construction.
In the
context of the Transition Rig, sail-making
is complicated by the way that the mast
extends and folds - the sail has to be able
to accept these changes. The sail has to be
able to give in certain regions, for example
around the upper joints during folding,
rather like the skin over the elbow as it
bends. If
modern inextensible sail cloth is used in
those locations it will resist folding and
be in danger of tearing - an elastic
material is required.
If the
variable geometry nature of the Transition
Rig is to be used while sailing to alter the
profile of the sail in different wind
strengths then the whole sail membrane
must be elastic. However, the sail must have the capacity to
maintain a good aerodynamic shape during
shape changes. This is a difficult balancing
act - if the sail is too stretchy, it will
blow out of shape in stronger winds. If it
is not stretchy enough, the trailing edge
will go slack as the rig flexes.
Over
the years, I have tried many different
approaches to sail making with different
degrees of success. Some sails have been
made over a 3-dimensional curving surface in
order to build in the right amount of
camber, and I have experimented with many
different types of fabric to find the right
balance of elasticity, strength, weight, and
UV-resistance.
Summarised below is the way that I make
sails now. This approach applies mainly to
rigs for kayaks, canoes, and dinghies in
which the mast is extended and locked into
place for sailing and then unlocked and
lowered when not required, ie: the variable
geometry feature is not used while sailing.
(I shall describe variable-geometry sails on
another page.) I have simplified the construction as much
as possible and the sails can be cut and
assembled on a flat surface such as the
floor. Useful tip: use double-sided
tape to stick panels and other materials
together before passing them through the
sewing machine. This will ensure that the
components remain correctly aligned during
sewing.