HANSA 05-2019

Schiffstechnik | Ship Technology
Performance tests for antifouling coatings
Current performance testing of antifouling products is mainly based on static raft exposure
tests (according to ASTM D3623/ D6990) or polishing tests in seawater (ASTM D4938).
Such methods give only indirect measurement of friction drag properties of hull coatings
Major function of antifouling coatings
is to keep added friction drag due to
biofouling accumulation on a ship hull at
a minimum. There are three test methods
that do give direct data on friction drag
properties of coatings (with and without
fouling) and as such can be used in product
comparison and selection of suitable
products. Whereas for registration of antifouling
products manufacturers need
to provide efficacy data from (simulated)
field tests, a short description of this
standardised method is given as well.
Efficacy tests for registration
of antifouling products
Endures has long lasting experience in
static raft exposure tests of antifouling
paints. These tests are carried out according
to the BPR Guidance Document
Vol. II – Efficacy (version 3, ECHA, April
2018).
As an independent contract laboratory
Endures can make direct comparison of
the performance of paint products from
different suppliers under the same exposure
conditions. Our exposure site in the
harbour of Den Helder, the major naval
base in The Netherlands, is representative
for North Sea coastal water with high
fouling pressure during a fouling season
lasting from March till November.
Seawater parameters such as temperature,
pH, salinity and oxygen concentration
are continuously monitored at
the lab. The methodology to evaluate
the efficacy of antifouling paints is based
on methods described in ASTM D3623/
D6990. Regular inspections and photographs
are made during the fouling season,
percentage coverage of fouling on
panels is estimated and from these data
a Fouling Resistance (FR) rate is derived:
FR 100 means no fouling and with F 0 a
panel is fully covered. Product performance
is evaluated on pass/fail criteria
described in the BPR Guidance document.
This test will only show the ability
of a coating to resist or prevent the settlement
of fouling organisms.
Endures raft in the harbour of Den Helder and raft exposure rack with different hull coatings
Drag performance testing
of ship hull coatings
The principle of this test is to carry out
comparative measurements of friction
resistance of coated disks with and
without fouling. In addition to static
raft exposure tests this test gives relevant
information on fouling adherence
and release properties of hull coatings.
This test is carried out with the Friction
Disk Machine available at the laboratory.
Paints under investigation need to
be applied on circular disks. The coated
disks are first measured in clean
condition, then exposed for a specific
time period in the harbour of Den
Helder where they get fouled and then
retrieved to the laboratory for a second
drag measurement.
The difference in friction drag between
fouled and clean condition gives
quantitative data on the drag penalty
that a certain fouling pattern may give.
This way different paint products can
be compared on friction drag properties.
The test method is suitable for both
self-polishing paints (SPC) as well as for
fouling release coatings (FRC).
Minimal speed foul release
test for hull coatings
The purpose of this test is to establish the
minimal speed for self-cleaning of hull
coatings with marine fouling. The test
protocol involves two different steps:
Static exposure of coated panels to marine
fouling for periods of 1 – 4 months,
followed by rotating drum testing in seawater
at increasing speed (4 – 30 knots)
for several rotation times. After static exposure
the panels are inspected on fouling
condition, mounted onto the rotor
drum and subjected to a rotation protocol
with incremental speed steps of two
knots up to the speed where all fouling
is removed. At each speed several rota-
Friction Disk machine for drag measurements on coated disks with and without marine fouling
© Endures
52 HANSA International Maritime Journal 05 | 2019