US NAVY'S - Incat

A Smoother, Cleaner Bottom!
Captain Mike Jackson
The value of having a clean ship’s bottom would
be known to most people involved in maritime
operations. A fouled bottom increases hull resistance
and generally results in a loss of speed. Where this
happens it will either involve an increase in power
and therefore fuel consumption or increased passage
times and the inability to maintain schedules. Or a
combination of both.
Recent experience with one Incat vessel where the
operator reported an unexplained loss of speed
resulted in much head scratching at Incat Head
Office and in the end a team was sent to investigate.
The craft in question was operating for long periods in
tropical waters including extended periods alongside.
The craft was experiencing a speed loss of five knots
and was unable to attain maximum engine RPM.
When the investigating team boarded the craft the first
thing they noted was quite a luxuriant growth of weed
on the underwater surfaces. They also determined that
there was a problem with the engine control system.
The engine control system was quickly resolved and
once corrected allowed for an immediate two knot
increase in speed. Thus it was estimated that the hull
growth was slowing the craft by up to three knots.
At the first opportunity divers performed a complete
hull clean and the craft’s speed was reinstated.
This experience demonstrates the need to keep the
hull clean but perhaps also the need to use anti
fouling appropriate to the nature of the operations it is
undertaking. Anti fouling is anti fouling I hear you say,
but is it
An examination of different manufacturer’s
specifications indicates a varied number of different
anti fouling schemes for different applications and also
different hull materials. They are all Tributyl Tin (TBT) free
of course, but they include different properties from
silicone to self-polishing, conventional and long life.
Given that craft only have to complete in water
bottom surveys every two years, then the opportunity
to renew and/or repair anti fouling coatings also comes
along once every two years. If the scheme is damaged
or unable to last this distance for some reason then the
possibility for hull growth is increased and with it the
spectre of increased fuel costs.
What can be done If operators are happy with their
anti fouling schemes but find the craft is suffering
hull growth between dockings, then hull cleaning
by divers may seem to be the appropriate solution
to the problem. Regular cleaning by divers may
prove more effective than an expensive change
of antifouling schemes, but of course that is up to the
operator.
12 Incat THE Magazine Issue 36