7KH
ISSUE 138
NOVEMBER 2012
6XSHU\DFKW
TRUTH • OPINION
KNOWLEDGE • IDEAS
A N D E X P E R T I N D U S T R Y A N A LY S I S
5(3257
ILONA
THE VICEM VULCAN
BULBOUS BOWS
BUSINESS FOCUS
Her remarkable and extensive refit
by Amels, which surpassed even the
owner’s expectations.
Page 33
The Turkish boatbuilder confirms its
entry into the superyacht segment
with its new Vulcan line.
Page 45
Three recent hull designs developed
as more fuel-efficient alternatives to
conventional displacement yachts.
Page 58
An analysis of the business sector of
our industry – from taxation to law,
finance and insurance.
Page 74
Below the
Waterline
For 15 years the Canadian design studio
Bray Yacht Design & Research has been
looking into fuel-efficient hull forms and
appendages. As a continuation of this
ongoing development, they have been
running a new model test programme
focusing on an enhanced bulbous bow
tested to 20 knots. Patrick Bray explains
how, by innovating below the waterline,
it is possible to reduce fuel requirements
and the carbon footprint of a yacht.
T
oday’s superyachts may surprise you: in an industry
once known for its conservative attitudes, innovation
is now key. Transcending the purely aesthetic changes of
style, today’s changes penetrate deeply. The application
of scientific principles in new and more effective ways has
helped to transform the industry.
Modern superyachts are floating works of art, reflecting
the personal taste and expressions of their owners, but as a
marine machine, they must also be ergonomically correct
and operationally functional. A yacht that is a true blend
of these qualities is a masterpiece in every way. A vessel that
MODEL RUN AT 16 KNOTS (BELOW) & AT 20 KNOTS (OPPOSITE)
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THE SUPERYACHT REPORT | ISSUE 138
can move through the water with very little bow wave or
wake, for example, has almost a mystical quality about it
for a designer. Coincidentally, this also usually means lower
fuel consumption. Almost all of this is achieved below the
waterline, where it is out of sight and out of mind, leaving the
freedom to express the client’s style above the waterline.
Fuel-efficient hull technology combined with speed, safety
and seaworthiness are a great advantage in a motoryacht,
especially one designed for long-range passages, and are
the key elements in creating a modern superyacht design.
In achieving these elements, there are also significant side
benefits: a lower carbon footprint, lower wake profiles
creating fewer disturbances in the water, and even greater
interior space within the vessel since less space is taken up
with redundant tankage.
Technical advances in hull design have moved ahead in
leaps and bounds in the last 15 years, and we have taken
performance levels beyond previously accepted norms.
Model test evaluations of our new bow bulb on a 45m
hull provided a 25 per cent reduction in propulsion
requirements, much more than the previous typical
reduction of 15 per cent. The benefits of the bulb start
to take effect at nine knots (Froude number 0.235) and
continues on right up to 20 knots (Froude number 0.523).
This was achieved by a combination of changes to the bulb
Not only does this hull form give greater interior space,
it also allows for operation of the vessel at a higher
speed without paying a penalty in terms of fuel, while
at the same time maintaining a high level of comfort
in that higher speed range.
PATRICK BRAY
that makes the bow entrance angle appear narrower, thereby
reducing the bow wave. This same design studio has other
new hull technologies under development that will push
these savings a further 15 per cent, allowing even lower
wake profiles, smaller carbon footprints and greater interior
accommodation. These developing technologies include the
midship bulb, which has already netted an additional six per
cent reduction by flattening out the midship hollow; the bifoil-skeg, which is a fixed hydrofoil under each rudder giving
passive trim control and pitch dampening; and the stern
bulb, which has been shown to achieve a seven per cent
advantage by reducing the stern wave. All this adds up to a
superyacht that provides 50 per cent more fuel efficiency
than today’s standard vessels.
A fuel-efficient hull form obviously means lower fuel
consumption, but the interesting thing is that this means
it can also take smaller engines and smaller fuel tanks to
achieve the desired speed and range, less structure weight,
which means less overall weight, less power to move it, and
so on. This reflects favourably in the build cost and, with
lower tankage and mechanical space demands, greater space
for interior accommodations.
To give you an idea of the fuel savings, let’s look at the
results from our most recent test programme: a 45m
motoryacht that weighs in at a conservative 363 tonnes and
is powered by twin 745kW diesel engines for a top speed of
16 knots. It will take just under four litres per mile to run at
nine knots. At 12 knots, fuel burn will be 84 litres/hr, while
at 16 knots it will be 322 litres/hr. In order to achieve a 20knot top speed, the hull will require a scant 1,009 litres/hr
(2 x 2,080kW).
It is very difficult to get comparative performance figures
from other designer’s builds, but available published data
shows twin 1,117kW engines are typical for a vessel of this
size to reach 16 knots (50 per cent larger than the tested
hull). This represents a fuel burn of 483 litres/hr (50
per cent more fuel usage). Data was not available for a
comparison with other hulls at 20 knots.
In combination with these advantages, research shows
that these appendages are reducing the pitching motion,
allowing for a smoother ride and greater passenger comfort.
This has already been proven on several trans-Atlantic
crossings and very extensive cruise voyages. So, not only
does this hull form give greater interior space, it also
allows for operation of the vessel at a higher speed without
paying a penalty in terms of fuel, while at the same time
maintaining a high level of comfort in that higher speed
range. A win-win situation all round.
Follow this link to view a video of tank testing of the
Bray Yacht Design & Research’s development hull model:
http://bit.ly/PHUMDr
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