⠿ HULL COATINGS
(^38) ⠿ MARINE MAINTENANCE TECHNOLOGY INTERNATIONAL | APRIL 2016
account as it will result in a change in the
performance indicator used in the standard.”
Hull roughness is particularly tricky
to measure as so much depends on the
quality of the work done in the dry dock.
“The hull roughness concept is well suited
to evaluating the quality of the work done
in the shipyard, especially the pretreatment
before the coating application,” he says.
It is difficult to reliably translate a
measured hull roughness into a resistance
term. This is due to the difficulty of
measuring hull roughness and in translating
any changes into a resistance factor for a
specific vessel. Hull roughness is not enough
to quantify the changes of the coating
surface to real ship performance.
However, Krapp says, “Hull roughness
measurements still relevant, as they are a
very good tool for evaluating the quality
work done in dock.”
Tolerant measurements
Hempel’s marine and strategic technology
director, Diego Meseguer Yebra, says of
the methodologies, “Several suppliers of
hull monitoring services have proprietary
methodologies to separate hull and propeller
contributions, even without reliable thrust
meters. However, we tend to agree that such
algorithms are not reliable enough.
“The methodologies suggested under
ISO 19030 only measure the outcome of the
‘added roughness’ together with the other
factors that can contribute to increased
powering demand. The ISO methodologies
filter out some of the external factors when
possible (e.g. rough weather), while the rest
will just contribute to the scatter. The degree
of data correction for some of these external
factors is minimal in the ISO methodologies,
but substantial in other, more advanced,
proprietary methodologies.”
In comparison
Comparison figures will be popular with
shipowners, even if there are flaws. Jeppe
Skovbakke Juhl, senior marine technical
officer for BIMCO, says, “In general, hull
and propeller performance refers to the
relationship between the condition of a
ship’s underwater hull and its propeller, and
the power required to move the ship through
the water. Measurements of changes in hull
and propeller performance over time make it
possible to determine the impact of hull- and
propeller-related maintenance, repair and
retrofit activities on the fuel efficiency of the
ship in question.
“Estimating the ship’s overall
performance is a very challenging task that
includes hull and propeller performance,
‘above the water’ hull wind resistance,
engine performance, as well as other
sources of energy use. And these elements
are not exactly what ISO was aiming at when
it started to develop the standard.”
All hull surfaces degrade over time
regardless of the coating, how applied,
what kind and where the ship operates.
“The scope of ISO 19030 is limited to
hull and propeller performance only,
and by measuring the performance in a
consistent way you may find how much the
performance is reduced compared with
when the coating was brand new,” says Juhl.
This monitoring may show when a ship
needs some remedial work – hull cleaning
and propeller polishing – to reduce fuel
consumption due to fouling. ISO 19030 may
bring benefits by simply standardizing a
method for accurately isolating hull and
propeller performance from the other
drivers of ship efficiency.
Juhl continues, “In general, an ISO
standard is voluntary, developed for and
by the industry. This one is no different. It
makes use of commonly available methods
for measuring changes in a ship’s specific
hull and propeller performance based on
data provided by the owner or operator
and related to the ship’s operation. The
Cleaning propellers
alone can reduce fuel
consumption by 5%
ABOVE: A vessel
ready for hull
recoating – most of
the original coating
has been lost
RIGHT: Regular
hull cleaning can
improve efficiency,
but it is best to do
so before barnacles
build up