IF THERE鈥橲 one thing James Bond didn鈥檛 have, it was some decent amphibious
clothing. Just think of all the times he clambered out of water clad in diving
gear, only for the bad guys to get a head start while he struggled to get into
dry clothes. Now a US military lab has come up with an answer: a diving suit you
can wear comfortably out of the water. Their amphibious suit is designed so
divers from the US Navy鈥檚 Sea-Air-Land (SEAL) division can get out of the water
ready for action in lightweight garb.
In the water, the amphibious diving suit performs like any other dry suit,
keeping the wearer warm by preventing water from reaching the skin. But once out
of the water, the structure of its novel three-layer membrane changes to let
perspiration escape, so the wearer doesn鈥檛 overheat. Normally, dry suits would
become unbearably hot and SEALs would have to change into dry clothes they have
dragged along with them.
The suit was designed by the US Army鈥檚 Soldier and Biological Chemical
Command lab in Natick, Massachusetts. Next month Navy SEALS and a submersible
sensor-packed mannequin will test out the suit for general comfort and warmth in
a range of water temperatures and pressures.
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It will be at least a couple of years before the suit is ready for use, says
Quoc Truong, programme manager at the Natick lab, but after that it won鈥檛 be
long before it finds its way into civilian life. 鈥淭here are plenty of civilian
applications,鈥� says Truong. Wind surfers, divers, air-sea rescuers and even kelp
farmers could all use it. 鈥淎nyone who needs to get in and out of the water will
definitely find very good uses for this technology,鈥� he predicts.
鈥淐ompared to a dry suit, it will be a little bit heavier because we wanted to
use a durable fabric,鈥� says Truong. 鈥淏ut it鈥檚 still very light.鈥� And SEALs won鈥檛
have to lug around an extra set of dry clothes.
So how does it work? The suit consists of a polyurethane-based shape-memory
polymer layer, sandwiched between a laminated low-drag stretchable outer fabric
and a heat reflective insulation layer on the inside
(see Diagram). The
transition temperature of the polymer membrane is predetermined, which means
that between 13 and 18 掳C it has a dense molecular structure that stops
water molecules from passing through it.
When the temperature rises above this, between 18 and 27 掳C, the material
softens and becomes more amorphous, so sweat molecules can pass through it. This
range of temperatures is ideal for the wide range of water conditions that dry
suits are typically worn in, says Truong.
Depending upon how cold the water is, you can wear additional layers of
fleece-like insulation under the suit, whereas you would need a different dry
suits for different temperature conditions.
The suit is also impervious to urine, says Truong. On land, wearers will be
able to relieve themselves by way of a zipped opening that reaches from the
shoulder to the groin, but in the water SEALs would have no alternative but to
pee in their suit. Truong is confident that the acid in urine will not rot the
new suit鈥檚 material and hamper the diver鈥檚 activities.