Marine Maintenance Technology International - April 2016

HULL COATINGS (^) ⠿
MARINE MAINTENANCE TECHNOLOGY INTERNATIONAL | APRIL 2016 ⠿ 37
been done, the roughness of the coating may
actually be the root of the problem.
Coatings can be compared against a
baseline ship performance, starting when
it is freshly refloated after dry dock and
continuing during the service period before
recoating the hull. It has been suggested that
a vessel will on average lose 5% of its speed
(even with a clean propeller) over a five-year
period. Such a loss could roughly translate
to a fuel increase of 15%.
The starting point – JHPMM
The Jotun Hull Performance Measurement
Method (JHPMM) is used by the company
for performance-based contracting, and
was adopted as the starting point by the
ISO working group.
Jotun is now using data supplied by
DNV GL to process hull and propeller
performance computations based on
computational fluid dynamics models. Dr
Torsten Büssow, DNV GL’s head of fleet
performance management, says, “This
approach generates a much greater amount
of baseline data than a conventional
model tank test could deliver and provides
customers with the information they
need to prove that they reduced both fuel
consumption and emissions.”
Measurement noise is filtered out by
using long-term trends. Data inputs (every
10 to 15 seconds) include deviation from
the vessel’s specific speed-power curve
normalized for the vessel’s draft.
Information recorded at that rate
generates upward of several million
datapoints per year, which need to be filtered
to compensate for bad weather and extreme
readings (such as would occur when
navigating shallow waters).
GPS coordinates, forward and aft draft,
a Doppler speed log, shaft power, fuel
consumption and anemometer readings
are among the additional measurements
assessed in the efficiency calculations.
Dr Andreas Krapp, of Jotun’s hull
performance solutions, says, “ISO 19030
focuses on the measurement of changes
in hull and propeller performance. It will
always be the combined effect of hull
and propeller performance changes that
is measured by applying the ISO 19030
standard and also in our approach.
“The troubleshooting wisdom of changing
one parameter at a time applies to isolating
the interactions between hull fouling and
propeller condition,” Krapp says. “If you
make a change to one component at a time,
you can evaluate the effect by applying ISO

19030. If you makes changes to two things
       together, say the hull and the propeller, you
       cannot evaluate the combined effect.”

Roughness

Hull roughness measurements are not part

of ISO 19030. Krapp explains, “This standard

focuses on in-service measurements that

are taken continuously over a complete

docking interval [usually five years] and

also over several docking intervals. ISO

19030 implicitly takes hull roughness into

It takes a 3% increase

in fuel to compensate

for 1% loss of speed

FAR LEFT: Smooth undercoating

layers are important to achieve

long-lasting results for hull coatings

LEFT: Some ships need coatings

tough enough to resist abrasion

from winter ice in the Baltic

BELOW: Shell’s Prelude floating

liquid natural gas vessel needs a

highly corrosion-resistant coating

as it will be processing gas while

anchored off the coast of Australia