快猫短视频

鈥淚 WAS always fascinated by flight,鈥� says Richard Dryden. 鈥淲ings, how things
fly, aerodynamics and aircraft.鈥� So why are we perched precariously in a small
dinghy on the Teign estuary in Devon?

The answer is the sail that鈥檚 propelling us over the water. Bruce Wayne would
be proud of Dryden, because there鈥檚 no mistaking its shape: it鈥檚 a bat wing.
Dryden has taken one of nature鈥檚 best flying machines, turned it on its side,
and launched it onto the water.

鈥淚t takes a bit of a leap of faith, I suppose,鈥� he says, 鈥渂ut the more I work
with these things, the more I feel that a sail is simply a vertical wing,
experiencing all the usual forces a wing does, plus a few others.鈥� He calls his
sail and mast the 鈥渢ransition rig鈥� because not only is it shaped like a wing, it
folds up like a wing too. That makes it uniquely responsive to changing
conditions, and certainly far easier to adjust than a conventional sail.

Designing sails began as a hobby for Dryden, a University of Plymouth
biologist turned inventor. But now he is working on the rig full-time, courtesy
of a year鈥檚 grant from the National Endowment for Science, Technology and the
Arts, a lottery-funded organisation that backs 鈥渁dventurous innovators鈥�. He has
made sails for windsurfers and dinghies and even canoes and kayaks. Perhaps most
ambitious, his drawing board is covered in plans to put bat-wing sails on
gigantic ocean-going ships.

Dryden鈥檚 interest in sails began when he became hooked on windsurfing in the
rather warmer waters of Papua New Guinea in the early 1980s. In those early days
of the windsurfing craze, sails were triangular, a bit baggy and floppy, and
difficult to control in a strong wind. Dryden reckoned he could do better, so he
started making his own, cutting them more oval in shape, and gradually moving
towards designs that were more and more wing-like.

鈥淔rom aircraft I knew that some shapes were better than others,鈥� he says. 鈥淥n
aircraft, you don鈥檛 make triangular wings with the leading edge sticking out,
like you see in a sail with the mast as its leading edge. It doesn鈥檛 work. So I
began to take shapes that I was more familiar with in aircraft and make them
into sails.鈥�

As his windsurfing skills improved, so did his designs. He could soon make a
sail that would work efficiently at a given wind strength, learning how each
modification affected the sail鈥檚 performance. But then, of course, the wind
would change. Dryden began to ask himself the question that would eventually
lead to the transition rig. How could he make a sail that adapted spontaneously
to changing conditions?

In the late 1980s, he shifted his thoughts from aircraft wings to biological
ones. He remembers standing on a cliff top near his parents鈥� home in Devon
watching birds gliding on the rising air currents, noticing how they would keep
their wings close to their bodies during stronger gusts and stretch them out in
lighter winds. 鈥淚 think that鈥檚 what I had in my mind when I thought about how I
could make a mast and a sail that changed shape,鈥� says Dryden.

The mast of the transition rig is arranged like the bones in a wing
(see Diagram),
with two joints that allow it to fold into a Z shape. The middle
section has two parallel 鈥渂ones鈥�, just like a forearm, allowing the whole
structure to flex. The upper section is like a bat鈥檚 outstretched hand, with
鈥渇ingers鈥� forming the leading edge and a series of three battens to support the
membranous fabric of the sail.

Joints might have been Dryden鈥檚 first preoccupation, but sailcloth has turned
out to be a bigger headache. To be compatible with the mast it had to be
stretchy鈥攏ot a property that鈥檚 usually recommended for sails. 鈥淲hen I
mention that I鈥檓 making a sail from stretchy material, most sailmakers look at
me with a mixture of horror and sadness,鈥� says Dryden.

Early on, he used Lycra and spandex but they soaked up too much water and let
too much of the wind through their loose weave. So he tried a knitted nylon
fabric coated on one side with polyurethane. It was better, but still a bit too
absorbent. He鈥檚 just tracked down a material that has a polyurethane coating on
both sides. That鈥檚 what we鈥檙e testing out on the Teign estuary. It seems to work
pretty well, stretchy enough to stay taut and waterproof as well. And it goes
like the proverbial bat.

The only downside is its colour鈥攁 sickly shade of blue. 鈥淚 think it was
made for coating hospital inspection tables, which is why it鈥檚 this rather
unpleasant shade,鈥� says Dryden. The colour isn鈥檛 just a matter of aesthetics:
it鈥檚 less than ideal for a windsurfer because sails need to be
see-through鈥攐r at least to have a clear panel鈥攕o you can see where
you鈥檙e going. 鈥淚 just sail where there are not too many people at the moment,鈥�
Dryden confesses. If anyone knows of a transparent, stretchy and waterproof
material, he would love to hear from them.

To set the sail up, you haul it upright with an elastic tensioner running
from the top of the mast, around the outer edge of the joints and down to the
base. This tensioner keeps the mast fully extended, but its elasticity also
allows the rig to compress down into a more compact Z shape. It even folds up
altogether, so when you鈥檝e finished for the day you don鈥檛 have to remove the
sails or cart a full-length mast home.

But the main point of the transition rig is that it changes shape while
you鈥檙e on the water. You don鈥檛 have to swap your sail or reef it in when the
wind changes. When windsurfing, this shape change happens almost
automatically.

As the wind gets stronger, you intuitively lean back more to counteract the
pull on the sail, so you don鈥檛 fall in. Doing this creates a downward force
which compresses the sail slightly, reducing its height by 15 to 20 per cent and
giving it a more swept-back shape鈥攁 better shape for stronger winds. The
鈥渃entre of effort鈥� of the sail鈥攖he point where its driving force seems to
be focused鈥攊s lowered, making the board easier to control. If the wind
slackens you lean back less and the sail opens out again.

On the dinghy, you have to control the extension with a rope attached to the
elastic tensioner. But it鈥檚 still a lot quicker than reefing a traditional sail,
and a good deal easier than swapping sails.

Dryden鈥檚 ideas put him at odds with conventional sail designers, at least of
boat sails. Their aim is to make rock-solid sails with as little give in them as
possible, and masts that are held rigid by stays and shrouds. That鈥檚 an
unbeatable strategy鈥攊f you don鈥檛 mind swapping sails every time conditions
change.

On a windsurfer, where the sailor plays the part of stays and rigging, a bit
of flexibility is normal. But exactly how flexible the sail should be is an open
question. 鈥淎nything too stiff and inflexible, while perhaps being more
aerodynamic on paper, will actually be considerably slower and more difficult to
use than something 鈥榮ofter鈥�,鈥� says Bill Dawes, editor of Boards
magazine. 鈥淗aving said that, it can鈥檛 be too soft鈥攁 good sail needs to
transfer gusts into extra power and drive.鈥�

So maybe the transition rig isn鈥檛 the best thing if you鈥檙e a competitive
windsurfer trying to be faster than everyone else. Dawes doesn鈥檛 think it will
ever replace the modern sails developed for stronger winds and more competent
sailors. These already spill a little of the power of a gust by twisting, so you
get a smooth increase in speed. But he thinks there might be a place for the
transition rig in lighter winds, or for beginners. 鈥淚t鈥檚 an interesting idea,鈥�
says Dawes. 鈥淚f nothing else, the idea of a rig that is so portable and so
easily erected is wonderful.鈥�

Dryden agrees he鈥檚 aiming at less experienced, recreational sailors who, he
says, have different needs from skilled windsurfers. He hopes novices will be
attracted by a forgiving rig that can be used comfortably in winds up to force
4. 鈥淵ou鈥檙e not going to be overpowered so quickly by a sudden gust,鈥� says
Dryden. 鈥淭he sail absorbs some of that energy.鈥�

The wing shape is still evolving. Dryden wants to improve its speed, and for
this he鈥檚 planning a sail based on a swallow鈥檚 wing. It鈥檚 narrower and sleeker,
and he hopes it will make a faster rig.

As for designs for other vessels, Dryden has no shortage of ideas. 鈥淢y
feeling is that this approach could be used on any sailing vessel,鈥� he says.
He鈥檚 already looking at yachts, including sand yachts, ice yachts and land
yachts. Perhaps the first to go to market will be a small, simplified version of
the transition rig for canoes and kayaks. Dryden has already had a lot of
interest from canoeists who tour with a small foldaway sail.

At the other end of the scale, he鈥檚 even thought about oil tankers. A naval
architect colleague did a few calculations for him and concluded that five or
six transition rigs, each about 40 metres high, would deliver significant fuel
savings on big vessels. When not needed, or in stormy weather, they would just
fold away. And, just for a change, he鈥檚 designed a set of sails for a windmill
that are completely self-regulating and can automatically adapt to different
wind conditions.

But an interest in wings still occupies his thoughts. He often wonders
whether the behaviour of variable-geometry sails in unsteady wind conditions
could reveal more of the mystery of flight鈥攅specially of a flapping wing.
But he doesn鈥檛 think he鈥檚 ready to move over from sail to wing design quite yet.
鈥淲ith sails, especially when you鈥檙e windsurfing, you can hold them, be part of
the structure and feel the shifting forces,鈥� he says. 鈥淢ore importantly, it鈥檚 a
lot safer to fall off a windsurfing board than it is to jump off a church tower,
like people used to do to test out wings.鈥�