alternative ship hull coating system

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Alternative ship hull

coating systemANTIFOULING The cost of in-water cleaning of ship hulls is dwarfed by the resulting fuel sav-ings. David Phillips from Hydrex Group explains why a combination of hull protection and foul-ing control requires the fewest economic and environmental compromises.

The problem with under-water cleaning of hullsto remove slime (micro-

fouling) and hard fouling liesnot in the cleaning itself but inthe type of hull coating beingcleaned.The majority of coatings onship hulls as part of foulingcontrol systems deteriorate asa result of underwater clean-ing. Underwater cleaning ofbiocidal antifouling coatingsconstitutes a hazard to theenvironment due to the pulsedischarge of biocides producedby the cleaning. In many portsand states, in-water cleaning ofhulls bearing biocidal coatingsis therefore justifiably prohibit-ed. Some ports and states have

gone as far as to prohibit in-water hull cleaning altogether.

Problems with hull coatingsystemsThere are three main problemswith ship hulls and hull coat-ing systems:

Corrosion The hull of a shipmust be adequately protectedfrom the effects of the oceans.

This is a matter of protect-ing investment, of remainingoperational and of safety. Aparticular form of corrosion iscavitation damage, which es-

pecially affects propellers andrudders as well as adjacentareas. There are also opera-tional conditions that can be

extremely challenging to theprotection of the ships hull,such as ice and other harshenvironments.

Fuel efficiency Any devia-tion from a hydrodynamicallysmooth hull carries a fuelpenalty. This includes rough-ness due to poor constructionor finish, poor choice of paintor substandard paint applica-tion, a deteriorated coatingand a hull with microfouling(biofilm or slime) or both mi-cro- and macrofouling. Thepenalty can be anywhere from

1-3% for unfouled paint asapplied, to 80% or more fora heavily fouled, badly de-teriorated hull coating. This

greatly increases a ships fuelconsumption and consequentatmospheric emissions. Thehull coating system that isused can therefore play a hugerole positive or negative inthe cost of running the ship.

At current fuel prices, this canbe the make-break point ofprofit or loss for a ship.

Environmental concernsPollution or contaminationof oceans and waterways fromheavy metals and variouschemicals used as biocides inantifouling paints, and from

silicone oils and other sub-stances used in foul-releasepaints, can have disastrouseffects on the marine environ-ment, contaminating both the

water column and the sedi-ment. The harmful effects canpersist for years or decades,rendering ports, harbours,marinas and estuaries so con-taminated that they cannot bedredged by the usual proce-dures without the risk of veryserious pollution through re-

suspension of the chemicals.Furthermore, invasive aquaticfauna (and to a lesser degreeflora) are carried as ship hullfouling from one environ-mental zone to another, wherethey can be destructive. Thethreat of the spread of aquaticinvasive species has escalatedto a point where California,for example, is consideringlegislation to prevent shipsfrom entering state waters ifany macrofouling is present.

The IMO is also consider-ing this issue in depth andrecently instituted voluntarymeasures to combat the threatposed by ship hull foulingto ecosystems. This has greatFuel penalties graph

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economic significance sinceimported species can destroylocal species and upset entirelocal economies.

The fuel penalty incurred from

a rough, fouled hull has nega-tive ramifications for the envi-ronment as well. The more fuela ship burns to travel from Ato B, the more CO

2, NOx, SOx

and particulate matter it emits.Volatile organic compounds(VOCs) from hull coating ap-plication can be added to thislist. Hazardous waste from thedisposal of old paint when aship is prepared for a new hullcoating is also an issue.

Almost all traditional shiphull coating systems have beena compromise in which one ormore of the above factors havebeen sacrificed for the sake ofothers.

The problems surroundingship hull protection and foul-ing control centre on two fac-tors: economics and the envi-ronment. A solution must beeconomically viable so thatships can operate at a profit.

And for obvious reasons itmust be environmentally sus-tainable.

Existing solutionsThe main coating systems inuse today are of two generaltypes:

The first and by far mostprevalent consists of biocidalantifouling coatings. Copperis the most common biocidein use. Others include zincand a variety of pesticides andherbicides sold under names

such as Diuron and Irgarol.These coatings come in vari-ous forms but follow the samebasic principle: They attemptto kill the fouling organismsbefore or after the organismsattach themselves to the hull.

The main environmentalproblem is that these poisonsare indiscriminate in whatthey kill or affect. They tend toremain in the water and sedi-ment, harm non-target organ-isms, work their way up the

food chain and can endangerhuman health. They are alsoineffective in preventing thespread of aquatic invasive spe-cies that attach to niche ar-eas below the waterline.

The chief economic problemswith these antifouling paintsare that they generally are in-effective against microfouling,cannot be cleaned and need

repair and recoating every fewyears, resulting in a badly de-teriorated coating with the ac-companying rise in fuel con-sumption.The second coating, which isgaining market share, is thefoul-release, non-biocidal type.It provides a slick surface thatis hard for fouling organisms toadhere to and easy to removefrom. These coatings are mostsuited to ships that travel fastand frequently and are not laidup for extended periods. They,too, do not prevent a slimelayer from building up. Theymust be cleaned very gently atthe microfouling stage and, ifallowed to acquire macrofoul-ing, cannot be cleaned withoutdamaging the coating. There isevidence that while they do notcontain biocides as such, theyare not free from toxicants.More research on their toxic ef-fects is definitely needed.

A third, far less prevalent typeof coating is hard and inert.It is non-biocidal, non-toxicand has been mainly used inzones where fouling is muchslower to accumulate, such asin arctic regions or very cold

waters. While these coatingscan be cleaned in the water,many of them, such as epox-ies, tend to deteriorate with in-

water cleaning and thus causemounting fuel consumption.

Surface-treated coatingAn alternative type of hardhull coating system seems torequire the fewest compro-mises of all. Known as surface-treated coating (STC), it is es-sentially a whole system forhull protection and foulingcontrol.STC consists of a glass flake vi-nyl ester resin coating, whichprovides the best possible hullprotection when combinedwith routine in-water clean-

ing to remove fouling in itsearly stages and optimise fuelconsumption. Ecospeed, pro-duced by Antwerp-based Hy-drex Group, is an example ofan STC. X

A niche area of a hull coated with biocidal antifouling paint

Ecospeed coated hull being cleaned of slime using a Hydrexmedium-sized, self-propelling in-water cleaning tool

STC after several years of service cleans back to pristinecondition

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The coating is applied once ona properly prepared hull andlasts the lifetime of the ship.Only very minor repairs areneeded during routine dry-docking. This coating improveshydrodynamically with everyin-water cleaning, becomingsmoother and thus less likelyto foul. It can be cleaned asoften as needed without anyharmful effects on the environ-ment or coating. It even solvesthe problem of cavitation dam-age to rudders.How does an STC such asEcospeed fare when judgedagainst the points coveredabove?

Corrosion Because it is

mainly glass, is designed to

last the life of the hull withoutreplacement and is not subjectto cavitation damage, an STC,if correctly applied, is a hullsbest protection against corro-sion. The use of the coatingreduces or even entirely elimi-nates the need for impressedcurrent systems.

Fuel efficiency In the long run(the life of the ship), an STCcan save a shipowner/operatorupwards of 25% in fuel costswhen compared with a conven-tional hull coating. The coatingdoes not deteriorate over timeas others do. In fact, it becomessmoother and creates less fric-tion with routine cleaning. Aproper cleaning routine can

keep fouling down to at most

a light slime, thus reducing thefuel penalty to near zero.

Environmental concerns AnSTC is completely non-toxic.After in-water cleaning of thehull using a high pressure jet, aship can leave any environmen-tal zone entirely free of foulingand thus not translocate inva-sive aquatic species to other en-vironmental zones. This is theultimate solution to the prob-lem of the spread of invasivespecies via hull fouling. Atmos-pheric pollution will decreasein proportion to lower fuelconsumption. An added bonusis that Ecospeed is very low onVOCs and is only applied once,thereby eliminating pollution

from repeated applications.

Ecospeed is in use by an en-tire national navy, a leadingcruise line, a number of ice-going vessels and icebreakers,and cargo vessels of all types.It is also being applied to thehull of the Sea Launch Odysseyrocket-launching vessel.

ConclusionAt a time when answers to thehull coating system problemare being sought, STCs suchas Ecospeed present a solu-tion immediately availableto shipowners/operators. Ap-plied and maintained correct-ly, an STC is the hull protec-tion and antifouling systemthat requires the fewest eco-nomic and environmental

compromises.

Same ship (Interscan MV Patriot) after 18 months with a conventional coating (left) and again after 18 months trading in ice withEcospeed STC (right)

SEKISUI CHEMICAL GmbH

phone: +49-(0)211-36977-0

fax: +49-(0)211-36977-31

[email protected]

www.calmmoon.de

Self-adhesive composite sheet only 1.3 mm thick

Cabin Wall

Cabin Floor

Excellent

Noise reducing-technology

12 Ship & Offshore | 2012 | No 1

SHIPBUILDING & EQUIPMENT | CORROSION PROTECTION & SURFACE COATING TECHNOLOGY

alternative ship hull coating system

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