Home' Afloat : AFLOAT October 2018 Contents 54 AFLOAT.com.au October 2018
by Malcolm Riley*
*Malcolm Riley worked for the Bureau of
Meteorology for 34 years and gives marine
weather training to boating groups. He sails
on tall ships in various parts of the world and
skippers the Lady Nelson in Hobart.
Inearly got caught out kayaking recently.
I was not paying attention, paddling in
relatively calm conditions when off to
the port quarter I saw three large waves
(of about a metre) approaching. I had no
time to turn the bow into the waves but
managed to turn stern to the waves and had
a few exciting moments surfing the waves.
Once things had settled down, off
in the distance I saw the speck of a fast
catamaran heading away from me. Fast
catamarans can in certain conditions,
usually calm or low wind conditions and in
relatively shallow water, propagate waves
that can travel a long way from the vessel.
During the early years of the large fast
catamarans operating in Europe, these
ships occasionally generated large waves
on beaches and along the coastline. While
my wave was only about a metre as the
catamaran was small, the larger vessels
operating worldwide can be huge, 100
metres in length, over 10,000 tons and they
can travel in excess of 50 knots.
These large, powerful vessels can
generate waves that become huge once
shoaling occurs. There are instances
of waves up to five
and crashing onto
crowded beaches in
the early days of these
At certain speeds
the bow of these
vessels can generate
a strange wave called
a soliton or solitary
wave. Soliton waves
can travel through
the water faster than
the speed the vessel that generated them
was travelling at the time the wave was
A soliton is a wave that is stable and
moves quickly. They do not merge with
other waves which non-soliton waves
do. Soliton waves were first noticed on
the Union Canal in Scotland in 1834 by a
scientist named John Russel.
“I was observing the motion of a boat
which was rapidly drawn along a narrow
channel by a pair of horses,” John Russel
explained.” When the boat suddenly
stopped – not so the mass of water in the
channel which it had put in motion.
“It accumulated round the prow of
the vessel in a state of violent agitation,
then suddenly leaving it behind, rolled
forward with great velocity, assuming
the form of a large solitary elevation, a
rounded, smooth and well-defined heap
of water, which continued its course along
the channel apparently without change of
form or diminution of speed.
“ I followed it on horseback, and
overtook it still rolling on at a rate of some
eight or nine miles an hour preserving its
original figure some thirty feet long and a
foot to a foot and a half in height.”
John Russel followed this wave on
horseback for two and a half miles before
The fast catamaran needs a
combination of critical speed and shallow
water to generate a soliton wave. The
waves they generate may only be a few
centimetres but unlike a normal wave that
has a trough and a crest, these waves only
have a crest.
When these waves reach shallow water
they tend to shoal significantly, often
breaking with a plunging wave (dumper).
These waves also have longer run ups
(distance a wave travels up the beach)
than wind driven waves of a similar size.
In some respects a soliton wave acts a bit
like a tsunami wave at a beach.
Soliton waves from fast ferries have
led to swamping of vessels, danger for
small coastal craft (like kayaks), people
washed from beaches and even the case of
one wave that ran up the beach and broke
windows of a waterside cafe. Ferry wash
can also be a problem for divers working
in shallow water close to the shore.
Many of these wave problems in
Europe have largely been fixed by changing
the routes the ferries take and limiting
speeds in shallow water. However, if you
are in a kayak and a fast ferry is seen to
be operating in your area and moving at
speed, be aware of these types of waves
See AMC youtube video: https://www.
youtube.com /watch?v= D14QuUL8x60
The high speed ferry Francisco operates in South America is 99 metres long and can travel
at 58 knots.
Beach signs warn of
fast ferry waves.
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