NEDERLANDS SCHEEPS-STUDIECENTRUM TNO
NETHERLANDS SHIP RESEARCH CENTRE TNOCORROSION AND 'ANTIFOULING DEPARTMENT LEEGHWATERSTRAAT 5, DELFT
COST RELATIONS OF THE TREATMENTS OF SHIP HULLS
AND THE FUELCONSUMPTION OF SHIPS
(VER13AND TUSSEN KOSTEN VAN BEHANDELING VAN DE SCHEEPSHUID
EN HET BRANDSTOFVERBRUIK VAN SCHEPEN)
by
Mrs. Drs. H. J. LAGEVEEN-VAN KUYK
(Economic Technical Department TNO)Dr. R. BULT
Jr. T. T. DEKKER
Dipl. Chem. H. F. M. FROHN
Ir. H. A. VAN DER HOEVEN Dr., H. J. HUECKIr. J. N. JOUSTRA
A. M. VAN LONDEN, Ing.
Jr. 0. R. METZLAR
Dr. W. J. NIJVELD Jr. J. PEREBOOM Drs. W. J. PFEIFFER J. W. UITTENBOGAART Drs. P. DE WOLFIr. H. C. EA
Verfinstituut TNO.
H. Vettewink.el & Zonen.
Ministerie van Defensie (Marine).
N.V. Kon. Mu. ,,De Schelde".
Centraal Laboratorium TNO.
Van Nievelt, Goudriaan en Co's Stoomvaart Mij N.V.
Verfinstituut TNO.
Kon. Ned. Stoomboot Mij. N.V.
Pieter Schoen & Zoon N.V.
Shell Tankers N.V.
Metaalinstituut TNO.
Dok- en Werf Mij. Wilton-Fijenoord N.V.
Centraal Laboratorium TNO.
Nederlands Scheepsstudiecentrum TNO.
De mogelijkheden voor de bestrijding van corrosie en van
aangroei van de scheepshuid hebben zich de laatste jaren
g unstig on twikkeld.
Verbeterde roestwerende verfsystemen, aangebracht op door stralen gereinigde ondergrond, verbeterde
aangroei-werende verven en de toepassing van kathodische
bescher-ming hebben de toestand van de scheepshuid aanzienlijk
verbeterd zodat thans de periode tussen twee opeenvolgende
dokkingen van het schip vaak meer dan 18 maanden is.
(Een tiental jaren geleden was dit slechts een maand of 9). De vraag rijst of de toepassing van de genoemde mogelijk-heden economisch aantrekkelijk is. In dit rapport worden de verschillende posten beschreven die bij de beoordeling van
de economic van belang zijn. Hierbij wordt gebruik
ge-maakt van gegevens die door deskundigen van enige rede-rijen, werven en verffabrieken ter beschikking zijn gesteld.
De kosten van enige methoden orn staal te ontdoen van
walshuid en roest, de kosten van enige oudere en moderne verfsystemen zijn geanaliseerd aLsmede de kosten van
onder-houd van het schip in dok. Het blijkt dat bij gebruik van
betere, (eventueel) duurdere oppervlaktebehandelingen en verfsystemen dusdanige besparingen worden verkregen op
dokkosten en onderhoudskosten dat dergelijke betere
be-handelingen zichzelf betalen.
Een voordeel is dat de toestand van de scheepshuid bij die betere behandeling aanzienlijk beter blijft dan met de oudere methoden bereikbaar is. De scheepshuid blijft gladder
waar-door de wrijvingscoefficient niet alleen van dokking tot dokking maar ook op lange termijn gezien slechts weinig
toeneemt. In principe zijn voortdurende besparingen op de brandstofrekening verkregen.
De grootte van de te verkrijgen besparingen kan ook wor-den vastgesteld. Aan de hand van gegevens uit de logboeken van enige vrachtschepen in lijndienst, passagiersschepen en
tankers zijn de veranderingen Van het brandstofverbruik geanalyseerd. Uit de verkregen resultaten is afgeleid dat voor de Nederlandse koopvaardijvloot een besparing van f 18.000.000, per jaa.r bereikbaar is met de thans ter
be-schikking staande middelen.
Het blijkt ook mogelijk te zijn uit de logboeken een indruk te verkrijgen van de toestand van de scheepshuid ; een
op-tredende verruwing wordt merkbaar en kan aanwijzingen geven voor de wenselijkheid van een dokking voor een
huidbehandeling.
De grootte van de te verkrijgen besparingen alsmede de
steeds kleiner wordende noodzaak schepen in dok op te
nernen voor werkzaamheden aan schroeven en roeren, wijzen crop dat verdere ontwikkeling van roestwerende en
aangroei-werende middelen en alles wat daarmede samenhangt
ge-boden is.
HET NEDERLANDS SCHEEPS-STUDIECENTRUM TNO
Means to prevent corrosion and fouling of ships' hulls have developed favourably.
Better anti-corrosive paint systems applied on blast
cleaned steel, better anti-fouling paints and the use of
cathodic protection have improved the condition of theships' hull. As a result, the period between two successive
dry-dockings of the ship has increased from 9 months, some ten years ago, to more than 18 months nowadays.
The question arises whether use of these technical means will be attractive economically.
The present report describes the factors relating to cost of pre-treatment of steel and coating, and cost of dry-docking, which have to be taken into account.
Information supplied
by experts from ship-owners,
ship-yards and paint-manufacturers has been condensedinto tables and diagrams, which are analysed. It has thus be-come evident that, in the long run, costs of better pre-treat-ment of the steel and better paint systems, are earned back through savings thanks to less dry-docking and lower main-tenance costs.
Application of better protection schemes moreover makes for a smoother hull; this has the advantage of a lower
fric-tional resistance, not only between two successive dry-dockings but also continuously. Thus an overall saving in
costs of fuel consumption will be obtained. The level of these savings are estimated by studying the pertinent information of the ship's log-books.
At the same time, indications are found in relation to the moment that a dry-docking for maintenance will be profi-table.
The level of the savings, as well as the present control of propeller and rudder-gear, are indicative of still longer pe-riods out of dry-dock; further development of anti-corrosive and anti-fouling agents is, therefore, a must.
page Glossary of terms
. ...
. ...
4Summary . 5
1 Introduction . .
. ... .
. . .. ... .
5Brief historical survey .
Surface roughness 6
2 3
4 Costs of pre-treatment of ship plates
5 Costs of bituminous paint systems . .
6 7 8 9 10 11 12 13
Costs of modern paint systems based on chlorinated rubber . . 8
Costs of mechanised shot blasting and the use of a zinc rich pre-construction primer 9
Costs of epoxy resin/coal tar based paint systems 10
Comparison of costs of older and modern paint systems 10
Fuelconsumption .
..
. ... .
. 11Fuelconsumption of cargo vessels. 12
Fuelcon.surnption of passenger vessels . 1,5
Fuelconsumption of tankers 116
14 Estimation of economics in fuelconsumption for the Dutch Merchant Navy 18
15 Conclusions . . . . 18 Acknowledgement 19 19 20
GLOSSARY OF TERMS
References . . . Tables Figures . . .Surface preparation
The Method to remove rust and mill scale from steel
surfaces.
Weathering
The exposure to sun and rain which causes the break-down of mill scale. The resulting rust can be removed by steel wire brushing.
Pickling
A process in which a solution of chemicals in water
removes mill scale and rust.
Blast cleaning
All methods to remove mill scale and rust from steel
surfaces by blasting with grit. These techniques are done with steel shot (round), cut pianowire (round when in
use), ground copperslag (coarse), etc.
Steel wire brushing
The method to remove loose particles of rust and of mill kale by rotating steel wire brushes.
Pre-construction primer
A special kind of paint which is applied in a Very thin layer to protect the prepared steel surface from rusting during construction.
Paint
Anticorrosive or antifouling compostion as delivered by the paint manufacturer.
Anticorrosive paint
A paint to protect the steel surface from corrosion.
Antifouling paint
A paint to protect the underwater part of the ship's
hull from fouling by algae, barnacles, molluscs, etc.
Paint system
A number of Coats of anticorrosive and antifouling
paint applied on the ship's hull.
Paint coat
One layer of either anticorrosive or antifouling paint.
Application costs
The costs of application by rolling, brushing or spraying of paint.
Period of service
The time in which the ship is able to sail between two successive drydockings.
Touching up
Making repairs in the damaged paint syStern, restricted to rather small areas.
COST RELATIONS OF THE TREATMENTS OF SHIP HULLS AND THE
FUEL CONSUMPTION OF SHIPS
by
Mrs. Drs. H. J. LAGEVEEN-VAN KUYK
Summary
An analysis has been made to the costs of different methods of surface preparation of ships' hulls, the costs of application of paints and the costs of different paint systems.
By comparing the total costs of several painting schemes with the costs of drydocking over four years, it has been found that the use of better paint systems has economic advantages.
Investigations have been made for cargo vessels, passenger vessels and tankers concerning the condition of the ship's hull as a result of the difference in protecting properties of the paint systems, and changes in fuelconsumption for the voyages in several periods of service.
An economy on fuel costs of 10% may be obtained by using the best available products. This means an economy of approx.
Dfl. 18,000,000. per year for the Dutch Merchant Navy.
1
Introduction
The development of new paint systems, of modern
ways of pre-treatment and of application methods
has led to a great divergency in the treatment of
schip's hulls to protect these against corrosion and
fouling.
To make a choice out of all the possible schemes
the financial aspects as well as the protection
prospects should be considered.
An economic evaluation will be made about
costs of pre-treatment of the steel, the costs of
application of paint systems, costs of paints and
costs of maintenance in drydock.
The requisite information came from
ship-owners, shipyards and paintmanufacturers which
gave helpful collaboration. Valuable data about
changes in fuel consumption were collected from
ships' logbooks.
Most of the informations and considerations are
based on new ships and on 1963 prices.
2
Brief historical survey
Corrosion and fouling roughen a ship's hull and
thus a higher frictional resistance occurs, which
results in lower speed at equal power. All
ship-owners and other interesties are familiar with this
effect. For cargo vessels the normal frictional
resis-tance may be about 80% of the total resisresis-tance and
for large passenger vessels and men-of-war, which
move faster than cargo vessels it is never lower than
50%.
Before World War II, the British Admiralty and
the United States Navy paid attention to this
matter, finding an increase in frictional resistance
for each day after the ship has left drydock. The
percentage depends on the type of ship under
consideration and the area of operation. More
details are given in Marine Fouling and its
Pre-vention [I] and by KEMPF [2].
After World War II, considerable attention has
been paid to trials with the Lucy Ashton" by
CONN e.a.[3]. A comparison has been made of the
frictional resistance of different pigmented paints,
viz, iron oxide and aluminium. By simply selecting
an aluminium bituminous paint a 5-10% decrease
in frictional resistance has been observed.
TODD investigated also the effect of different
types of paint on surface roughness [4]. He found
that plates. coated with a zinc chromate
anticorro-sive paint with a cold-plastic antifouling paint on
top yield a slightly increased resistance in
compa-rison to the resistance obtained when normal paint
systems are used, and that plates with an
anti-corrosive
paint and a
hot-plastic
antifouling
composition show a distinctly greater increased
resistance. The latter coating feels rough and
sandy. However, ships painted with a hot-plastic
antifouling composition remain free from
corro-sion and fouling for a longer period of service,
whereas ships painted with other types of paint are
fouled and corroded sooner, which results in a
great increase in roughness.
It is possible to carry out investigations into
the relation of roughness of the ship's hull and an
increase of the ship's resistance by making runs
along
the
measured
mileduring favourable
weather conditions. This can be done for warships
quite conveniently, but in the case of
merchant-men this cannot be arranged practically.
How-ever, by comparing many observations on fuel
consumption per covered mile, a picture can be
obtained of the economic significance of the
rough-ness of a ship's hull.
Prior to 1940, ships were usually built with
steel plates from which the mill scale had largely
disappeared by weathering. Just before launching
rust and remaining mill scale parts were removed
partially using steel wire brushes. Rust and mill
scale often remained in the plate's pores, causing
rust and blistering after painting.
After World War II, ships were built under a
system of prefabrication, which took less time. It
often happened that large parts of mill scale had
not yet been weathered from the plates. Since
steel wire brushing is a time-consuming operation
it is not easy to be done in a proper way to remove
all mill scale and rust. The remaining mill scale
is then covered by paint, which is undesirable from
a corrosion point of view.
Sand-blasting has been done to a large extent,
though pickling has been used also. Some years
ago, however, in the Netherlands blasting
tech-niques with sand were forbidden because of
silico-sis' danger. Other types of blasting materials have
found their way for cleaning purposes. Steel shot,
cut piano wire and ground copperslag are
exam-ples of different types nowadays in use to remove
mill scale and rust.
At present the application of paints is generally
done either by brushing, rolling or by the more
modern way of airless spraying. Brushing is
prac-tically restricted to the application of the first
coat of the anticorrosive part of the paint system.
Rolling is done mostly for maintenance in
dry-dock. However, airless spraying has found its way
for the application of all anticorrosive and
anti-fouling paints, during construction of the ship as
well as during drydocking.
For a long time a main constituent of
anticor-rosive paints has been some kind Of bitumen or
coaltar. The cheapest paints were and are still
based on this product. Bituminous paints,
pig-mented with iron oxides became very popular and
are still in use for older ships and coasters.
The pigmentation of bituminous paints with
aluminium flakes improved the performance. This
type of paint is in use to a very large extent, though
the commercially available products vary
consid-erably.
After World War II new types of anticorrosive
paints came up. The difference with the older
types was the use of unsaponifiable vehicles. The
vinyl type is well known. In the present report
only attention will be paid to the chlorinated
rubber based red lead paints and an epoxy resin/
coaltar based paint system.
The antifouling paints are based on special
, I
matrixes, the
toxic agent
ismostly
Fuprous-oxide. The amount of copper differs in relation to
different qualities.
Special antifouling paints have been developed
for application on the modern types of
unsaponi-fiable anticorrosive paint systems.
A recent development is the use of
pre-construc-tion primers.
In the case that mill scale and rust are removed
before construction which can economically be
done fully mechanized, a protection is needed to
prevent rusting during the
construction' period.
This is done by using pre-construction primers,
among which the zinc rich primers are very
successful [5].
3
Surface roughness
Three types of surface roughness can be
distin-guished for a ship's hull:
worsening of the surfaces due to corrosion of
the plates and the desintegration of the
paint-system in the course of years,
fouling by encrusting organisms, and
fouling by algae.
When proper antifouling paints are used regularly,
surface roughness caused by barnacles etc. need
not occur any longer.
Smooth surface of a very good paint system after of service, before overcoating
The surface roughness is then caused by corrosion
and desintegration of the paintsystem or by a
combination of this roughness and fouling by
algae.
However, because on many ships
particularly
the smaller types and old vessels
the correct paint
systems are not used generally, all types of surface
roughness will occur. It is practically impossible
to determine the economic consequences of each
type of surface roughness separately for each vessel.
In the majority of ships that will be discussed in
the present report, corrosion occurs in combination
with fouling by algae and sometimes with fouling
by barnacles. In some cases the increase in fuel
consumption is due to algae fouling only.
For other vessels, the consequences of corrosion
(and deterioration of the paint system) have
be-come economically observable because the fuel
consumption was determined before and after
cleaning the ship's hull by blasting with copper
slag and repainting.
4 Cost of pre-treatment of ship plates
As has been indicated in the brief historical survey,
all mill scale and rust have to be removed from
the ship plates. The most common methods of
surface preparation are.:
weathering followed by steel wire brushing,
blast cleaning with steelshot, cut piano wire,
or copperslag,
fully
mechanized
blasting techniques with
steelshot, or cut piano wire.
Method (a) will not lead to a perfectly cleaned
substrate, but for small ships it is still done.
Method (b) can be done by hand in which case
compressed air is used to accelerate the grit.
Method (c) can only be done for plates (and
sections)before construction. In most
circum-stances the surface preparation by method (b) and
by method (c) has to be followed by the application
of some pre-construction primer as this will prevent
corrosion of the perfectly cleaned substrate. In the
present
report
only zinc rich pre-construction
primers were taken into account, either based on a
polystyrene binder or on an epoxy resin based
binder.
It must be remembered that these
pre-tion primers will be damaged during the
construc-tion of the sub-assemblies.
The damage locations have to be touched
up
before the sub-assembly leaves the workshop. In
Table 1 a comparison is given of the costs of the
mentioned methods.
Table 1. Comparison of costs of surface preparation
The costs of the pre-construction primer and the
touching-up will be considered together with the
completion of the paint systems in following
chap-ters.5
Costs of bituminous paint systems
For protecting the ship's hull against corrosion,
the anticorrosive paints based on bitumen
are
pigmented with iron oxides. However, the
protec-tion will only last for a very short time. For better
performance, the bituminous anticorrosive paints
have been pigmented with aluminium flakes.
Some remarkably good paints are still
on the
market now.
For preventing the ship from fouling antifouling
paints are used which are pigmented with fillers
e.g. iron oxide, and in particular cuprous oxide as
a toxic agent. The antifouling action depends
among others on the content of cuprous oxide.
The price of the paints increases if more
cuprous
oxide is used in the paints. See Table 2. The North
Atlantic qualfty has the lowest amount of toxic
followed by the tropical and supertropical quality.
Table 2. Comparison of costs of antifouling paintsFour paint manufacturers have given valuable data
about painting schemes of different qualities,
as canbe seen in Tables 3, 4 and 5.
Table 3. Costs of bituminous paint systems (anticorrosive paint with iron oxide as a pigment)
pre-treatment method 1963 price Dfl./m2
(a) (b) (c)
steel wire brushing blast cleaning
fully mechanized shot blasting
approx. 2.50 approx. 6.70 approx. 0.75
antifouling paint 1963 price Dfl./rn2
North Atlantic quality, type II tropical quality, type III
supertropical quality, type IV
approx. 0.30 approx. 0.45 approx. 0.60
part of the treatment
1963
price Dfl./m 2 paint manufacturer
A B C
steel wire brushing 2.50 2.50 2.50 anticorrosive paint, 3 coats to
100 p.m 0.75 0.60 0.40
antifouling paint III, 1 coat 0.60 0.45 0.46 application (4 coats brushed or
rolled; overheads included) 1.50 2.00 2.00
Paint manufaturers B and C estimated the costs of
wages at approx. Dfl. 0.50 per m2. Manufacturer A
quoted a slightly lower figure. However, according
to data given by a shipyard, 3 to 4 minutes are
required per m2 per coat; at a wage level of
Dfl. 8.- to 8.50 per hour, this results in Dfl.0.42
to 0.56 per m2 per coat.
Table 4. Costs of bituminous paint systems (anticorrosive
paint with aluminium flakes as a pigment)
) 4 coats.
) 3 coats of a top quality product. ) 1st layer.
) 2nd, 3rd, 4th layer.
An improvement of these older procedures has been
obtained by using a zinc rich polystyrene based
primer immediately after the removal of rust and
mill scale although this system is not in use
nowa-dags. The higher costs of this system are given in
Table 5.
Table 5. Costs of an improved paint system (zinc rich primer followed by an anticorrosive paint with aluminium flakes as a pigment)
Discussion
It will be noted that there is very little difference
among the prices quoted by the
paint
manufac-turers, both as regards the iron
oxide and the
aluminium pigmented bituminous anticorrosive
paints. Whereas the difference between the
anti-fouling paints of type III and type IV is only
Dfl. 0.12 to 0.15 per m2, which is approx. 3% o
the total costs per m2, it is recommendable to use
only the best antifouling paints.
6
Costs of modern paint systems based on
chlorinated rubber
On big freighters, passenger vessels and tankers, a
high quality paintsystem is often used, for example
built up with paints based on chlorinated rubber.
The anticorrosive paints are usually pigmented
with red lead.
For antifouling purposes the tropical and the
supertropical types are generally used. Application
is mostly done by airless spraying.
Since it has no sense to apply these better and
more expensive paints on a ship's hull that has not
been pre-treated properly, the hull has to be
cleaned as good as possible, the best method being
blast cleaning. The costs of such treatment are
summarized in Table 6.
Table 6. Costs of chlorinated rubber based paint systems
Permanent roughness due to overcoating rust, rests of fouling and partly desintegrated paint system
e-"-
"7 --..e
part of the treatment
1963
price Dfl./m2 paint manufacturer
B C D
steel wire brushing 2.50 2.50 2.50 anticorrosive paint, 3 coats 1.20 1.202) 1.532)
intermediate coat, 1 coat 0.18
antifouling paint III, 1 coat 0.45 0.45 0.43
application of total paint system
(overheads inculded) 2.50 2.50 0.843) 1.26°)
total 6.83 6.65 6.56
part of the treatment
1963
price Dfl./m2 paint manufacturer
A B C
blast cleaning of the hull under
construction, manually 6.70 6.70 6.70 anticorrosive paint, 4 coats 2.80 2.00 2.60 antifouling paint, tropical, 2 coats 1.65 1.30 1.36
application of total paint system
(overheads included) 2.50 3.60 3.60
total 13.65 13.60 14.26
part of the treatment 1963 price Dfl./m2 steel wire brushing 2.50
zinc rich polystyrene based primer,
1 coat, thickness 35 t.ern 1.20
application of the zinc rich primer
(overheads included) 1.00
anticorrosive paint, 3 coats 0.90
antifouling paint III, 1 coat 0.45 application of the anticorrosive
and the antifouling paint
(over-heads included) 2.00
Paint manufacturer B has specified the use of a
zinc rich pre-construction primer based on
poly-styrene giving still better protection; the costs are
given in Table 7.
Table 7.
Costs of an improved paint system (zinc rich
primer followed by a system based on chlorinated rubberDiscussion
Also in this case it will be noted that there is
little difference among the prices quoted by the
paint manufacurers.
The costs of pre-treatment are the major part
of the total price and constitute about 45%. The
price of the antifouling paint is about 9% of the
total price and practically equal to the percentage
in older systems. Accordingly there is little point
to economize by using a cheaper antifouling paint.
As -a-result of the higher coat thicknesses and
higher quality of the paints a better protection
against corrosion and fouling can be expected.
Close-up of permanent roughness
7
Costs of fully mechanized shotblasting
and the use of a zinc rich pre-construction
primer
One of the shipyards has specified the costs of the
removal of all rust and mill scale by using an
im-peller type of shotblasting installation.
Immediate-ly after cleaning a zincrich epoxy resin based
pre-construction primer is sprayed on all plates and
sections. This is done fully mechanized. After
construction of the sub-assembly the damages in
the primer coat are touched up by steel wire
brushing and the application of a coat of the
zinc
rich epoxy resin
based pre-construction
primer locally. After that the whole sub-assembly is
coated with a second coat of this primer.
On the stocks the anticorrosive coats are applied
and finally the antifouling paint. Good results have
been obtained with a chlorinated rubber based
paint system properly applied. Using this system
the periods between dockings could be extended
from about 9 months to about 14 months, because
of the better quality of the antifouling paint and
the good condition of the anticorrosive part of the
paintsystern. The costs of this system are given in
Table 8.
Table 8. Costs of a modern treatment of the hull of a new ship
The fully mechanized surface preparation and
use of a pre-construction primer has led to
con-siderable savings in costs of treatment, see also
Table 7. Investments are rather expensive and
might be prohibitive for smaller shipyards.
However, at the moment, steel can be ordered
in a blastcleaned condition and protected by a
pre-construction primer.
part of the treatment 1963 price Dfl./m 2blast cleaning of the hull under
construction, manually 6.70 zinc rich polystyrene based primer,
1 coat of 35 p.M 1.10
anticorrosive paint, 4 coats to
100 ilm 2.00
antifouling paint, supertropical,
2 coats to 50 p.m 1.30
application of total paint system
(overheads included) 4.60
total 15.70
part of the treatment
1963
price Dfl./m2 shot blasting, fully mechanized (wages and
overheads included) 0.70
zinc rich epoxy resin based primer, 1 coat
thickness 10 p.m 0.35
touching up 0.20
zinc rich epoxy resin based primer, 1 coat
thickness 15 p.m 0.50
application of the second coat of the zinc
rich primer (overheads included) 1.35
intermediate coating, based on chlorinated
rubber 0.68
anticorrosive paint, 2 coats of chlorinated
rubber red lead paint thickness 200 p.m 5.22 antifouling paint, 1 coat, supertropkal quality 2.28 application of the last 4 coats of the paint
system (overheads included) 1.50
8
Costs of epoxy resin/coal tar based paint
systems
Epoxy resin/coaltar based paints have the
advan-tage of the possibility to apply a coat of about
200-250 p.m in one operation.
A particular good protection against corrosion
is possible.
Usually an intermediate coating is necessary,
between the epoxy resin/coal tar based paints and
the antigouling paint to obtain a good adhesion of
the antifouling paint. The costs of this system are
given in Table 9. During the obligatory annual
dockings the anticorrosive part of this paint system
will only need to be touched up to repair the
mechanical damages. The estimated life of this
anticorrosive paint system is about 10 years. It
must be remembered that the antifouling paint
has to be renewed every one or two..years.
In maintenance jobs it can be difficult to use
epoxy resin/coal tar based paints because of
ad-hesion troubles*).
Table 9. Costs of an epoxy resin/coal tar based paint system
The prices mentioned in Table 9 have been given
by paintmanufacturer B. Other prices are
men-tioned also, specially for the epoxy resin/coal tar
paint. As the epoxy resin part of the paint is
rather expensive and the coal tar part cheap, the
price will depend very much on the ratio of these
two parts.
However, an average price of this painting
scheme (manual,
blast
cleaning included)
of
Dfl. 16.00/m2 can be considered as reasonable.
This price can be reduced to Dfl. 10.00/m2 if
fully mechanized shotblasting is used.
1) At the moment some practical solutions are available.
9 Comparaison of costs of older and
mod-ern paint systems
Comparing the costs of a modern paint system with
the costs of the older paint systems, the modern
systems are twice as expensive as the older ones.
FAMY [6] has come to the same conclusion,
com-municating that an older paint system
costsNfr. 12.92 per m2 (Dfl. 9.50 per m2) and a modern
system Nfr. 26.02 per m2 (Dfl. 19.00 per m2).
Naturally the question arises whether there are
distinct advantages justifying the greater expense
when a modern paint system is
used. So also
maintenance and repair costs have to be considered.
Moreover the advantages of a smoother ship's
hull might lead to savings in fuelconsumption.
Upon comparison of the maintenance costs of
three sister vessels, on which the same aluminium
bituminous paint system had been applied, but
the surface preparation had been different, it was
found once more that proper treatment of a ship's
hull is of major importance. One of the ships had
been blast cleaned, one chipped with a rotating
steel wire flail and one steel wire brushed. The
costs of chipping are in between blast cleaning
and steel wire brushing. After three years the
maintenance costs were lowest for the blast cleaned
ship, twice as high for the ship which has been
chipped and three times as high for the ship which
has been steel wire brushed. From the difference
in expenditures it can be calculated that there is
alma-,
rionamAik
mo_NE.41
-1.100c
Subassemblies, made of blast cleaned steel plates and fully
protected in the workshop by two coats of a zinc rich
epoxy resin based pre-construction primer. An epoxy resin/ coal tar based paint system is applied on the stocks resulting in a smooth surface.part of the treatment
1963
price Dfl./m2 blast cleaning of the hull under construction
(manually) 6.70
2 coats zinc rich epoxy resin based
pre-con-struction primer, 25 [Lai 1.10
application of the zinc rich primer
(over-heads included) 1.00
1 coat epoxy resin/coal tar based
anti-corrosive paint, 200-250 iim 2.00 application of the anticorrosive paint
(overheads included) 1.00
1 intermediary coating, 20 p.m 0.50 application of the intermediate coating
(overheads included) 0.60
2 coats antifouling paint 1.30
application of the antifouling paint
(overheads included) 1.20
an economy in costs of maintenance materials and
wages
of about Dfl. 2.00 per m2 of wet surface
per year for the blast cleaned ship compared
with these costs of the steel wire brushed ship.
A ship painted with an older system must be
re-painted every 9 to 12 months; during
drydock-ing one or more coats of anticorrosive paint have
to be applied and after that the usual antifouling
coat. When the ship is about 5 years old, the rust
must be removed by scraping and chipping to
make reasonable good painting possible. Due to
the heavy corrosion, repairs must be carried out
much sooner than is necessary for a ship properly
protected against corrosion.
A ship treated in the modern way needs only
touching up of the damages in the anticorrosive
part of the paint system and a new coat of
anti-fouling paint every 12 to 15 months. Dependent of
the system used, overcoating the entire ship's hull
with anticorrosive paint will only be necessary
every 2 to 4 years.
The following savings in maintenance costs can
be calculated :
A saving in wages of about Dfl. 1.00 per m2 of
wet surface per year as it is not necessary to
apply one or two coats of anticorrosive paint;
the application costs being Dfl. 0.35 to Dfl. 0.70
per m2. Moreover there is a saving in costs of
scraping and chipping.
Any savings in material costs of the
anticorro-sive paint are considered to be not important
as most of this saving is consumed by the more
expensive antifouling paint.
For touching up the anticorrosive part of the
paint system and the application of one new
coat of antifouling paint, drydocking will
normally require two days.
However, when there is much scraping to be
done and an entire new coat of anticorrosive
paint has to be applied (being the case for the
older
systems)the
drydocking time
willsoon cover three or even more days. Actually,
there is not only one day saved per drydocking,
but more days are saved because of the longer
periods between successive drydockings. These
periods may be such that over a period of four
to five years the ship will drydock 4 times or less
when modern paint systems are used, but will
have to drydock 6 times when older systems
are involved.
Drydocking costs depend on the size of the
ship, ranging from Dfl. 2.000. to
Dfl.5,000.--per day for the first and last day for vessels of
about 10,000 to 50,000 tons respectively. This
includes all costs of bringing the ship in and out
of drydock.
Extra drydocking days are cheaper. After
conversion to m2 of wet surface, the costs of
drydocking for a ship painted with a modern
paint-system are about Dfl. 0.50 per m2 per
year lower than for ships painted with an
older system.
During drydocking the permanent costs like
salaries of the crew, costs of insurance,
de-preciation, etc. have to be paid. These costs
differ very much for several types of ships, but
for drycargo-liners a loss in permanent costs
of about Dfl. 2.00 per day per m2 of wet
surface of the ship can be calculated. Due to
the low number of days at sea of these ships
about 140-180 per year
it may be assumed
that there is a fair chance that anyhow the
ship would not have been in operation that
extra day of drydocking which would imply
that no loss in permanent costs is sustained.
Assuming the chance of a loss would be 50%,
it can be taken into account that roughly
Dfl. 1.00 per m2 of wet surface per day would
be involved as regards permanent costs.
Recapitulating, the total savings will be in the
order of Dfl. 2.00 to 3.00 per year per m2 wet
surface for ship protected in the modern way. The
modern painting schemes are about Dfl. 6.00 to
9.00 per m2 wet surface more expensive than the
older ones.
This extra expenditure has to be earned back
within 2-4 years by lower costs of maintenance
for counter-balancing extra costs and savings,
which is actually the case. Further savings due
to a lower frictional resistance resulting from a
better condition of the ship's hull, can be
consid-ered a sheer profit.
10
Fue.lconsumption
The fuel consumption of three categories of ships
will be considered, viz, cargo vessels, passenger
vessels and tankers.
This classification is necessary because of
dif-ferences in service, especially difdif-ferences in actual
steaming days. Also differences in paint systems are
usual. For instance tankers are about 300 days per
year at sea and are usually protected by modern
paint systems.
Drycargo-liners only make some 140-180 days
at sea per year and most of them are protected by
the older paint systems, especially the smaller
On an average, there is an 'increase in
fuel-consumption per mile covered during each period
of service. This increase is accelerated for all
categories in the event of fouling. As indicated in
chapter 4, fouling by algae is the main type of
fouling met on ships nowaday. This type of
fouling particularly
occurs when the
ship
isoperated in warm waters, and fouling starts
usually within 6-8 months after the ship has left
drydock. The corresponding extra increase in
fuelconsumption in the last few months of each
period of service constitutes heavy extra costs.
From an economical point of view it is important
to calculate these extra costs as exactly as possible.
Accordingly, the mean fuel consumption of the
last voyages has been compared with the mean
fuel consumption of the first voyages for the same
period of service. The number of voyages taken
into account depends on the total number of
voyages in each period of service. Although
it
would be possible to compare the mean
fuel-consumption of some voyages immediately before
and after drydocking, one cannot be sure that
any decrease of fuelconsurnption is only attributed
to the re-smoothing of the hull. Normally during
drydocking repairs are carried out or changes are
made at the propeller and main engine.
A study of the fuel consumption of a ship can be
made by calculating the average fuel consumption
per mile covered for each voyage. However, it is
necessary to make corrections to an assumed rate
of
speed which is close to the average rate of speed
for all voyages.
It was found from data out of the ships'
log-books that the displacement of a ship for different
voyages along the same routes did not
differ very
much. As can be seen from the formula this factor
Fig. 1. Fuel consumption of ship I
o drydocking
does not affect the fuel consumption so much as
does the rate of speed. For sake of simplicity no
pertinent corrections for differences in
displace-ment have been applied.
For correcting the fuel consumption because of
differences in speed, the formula given by the
British Admiralty has been used:
x va
E.H.P.
Cad
E.H.P. = effective horsepower
D=
displacement of the ship in tons,
v=
speed in knots, and
Cad =
Admiralty Constant.
No corrections have been made for the fuel
con-sumption of auxiliary engines.
As usually, it has been assumed that the E.H.P.
is proportional to the fuel consumption per unit
of time for alle rates of speed concerned. Thus, the
fuel consumption per mile covered will be
pro-portional to the square of the ship's speed.
11
Fuel consumption of cargo vessels
The fuelconsumption of 5 ships has been
consid-ered:
Ship I of 4,750 G.R.T.,
Ship II of 10,900 G.R.T.,
Ship III of 10,950 G.R.T,
Ship IV of 500 G.R.T. and
Ship V of 2,700 T.D.W.
ship I
Ship I has been making regular services from the
Netherlands to African coasts and back, each
voyage covering about 10,000 miles.
0 0.05 a. 2 0. 0.04 1 0.03 15 10 1_1 :1 35 40 45 SO number of voyage I I 30 250.10
0.05 1
fouling by algae could be observed.
The ships bottom was scraped and scrubbed.
After touching up with anticorrosive paint an
entire coat of anticorrosive paint was applied and
after that an antifouling coat, tropical quality.
Since 1960 an antifouling paint
supertropical
quality has been used.
As to the fuelconsumption the corrections have
been made as mentioned in chapter 10.
The
average speed was 12.5 knots.
The resulting data are given in Table 10 and
plotted in Fig. 1.
In the twelve periods of service, there is a
dis-tinct
increase
in fuelconsumption during ten
periods. The two remaining periods are not
comparable, because only a very small number of
voyages were made. For the first periods, from
1953 to 1957, the average fuelconsumption during
the second half year is 20% more than the mean
value in the first half year. Voyage no. 24
indi-cates a low fuelconsumption after the ship was
overhauled in 1958.
The mean fuelconsumption rises considerably
during the next voyage and then remains
con-stant for the other voyages of that period of service.
From 1959 to 1964, the average fuelconsumption
for the second parts of the periods of service was
again higher than the mean value for the first
parts. For the individual periods of service, the
increases were.
1959+16.4%
1960+12.5%
1961±11.5%
1962+ 8.0%
1963+ 7.0%
This effect might be attributed to the use of
an iniproved paint system during the latter years,
resulting in less corrosion and fouling, the ship's
hull being kept in a better condition as to surface
roughness. It must be admitted that in 1961 and
1962, the increase was greater, but it occured only
at the last voyages.
Ship II and Ship III
Ships II and III have been making regular
ser-vices, each voyage covering about 13,500 miles,
composed of several short and a few long distances.
The periods of service of both ships were often
shorter than 12 months. In respect of the mean
fuelconsumptiern, corrections have been made to
an average speed of 16.5 knots.
During drydocking the hulls were touched
up
with an aluminium bituminous
anticorrosive
paint, whereafter one entire coat of the
anticorro-sive paint and one coat of an antifouling paint were
applied.
However, in 1962 Ship III was blast cleaned
after which an epoxy resin/coal tar based paint
system was applied. During subsequent drydockings
only touching up by anticorrosive paint and the
application of a new coat of antifouling paint has
found to be adequate.
As to the fuelconsumption, the corrections have
been made as mentioned in chapter 10. The
avera-ge speed was 163 knots for both ships. The
resul-ting data are given in Tables 11 and 12 and plotted
in Fig. 2.
and A = drydocking
I
10 15 20 25
number of voyage
For ship II the decrease in fuelconsumption
after each drydocking was considerable, e.g.:
from voyage:
3 to
4 from 0.089 to 0.073 ton per mile
5 to
6 from 0.083 to 0.071 ton per mile
11 to 12 from 0.088 to 0.077 ton per mile
19 to 20 from 0.083 to 0.080 ton per mile
25 to 26 from 0.088 to 0.065 ton per mile
In 1959, there was an increase of about 12% for
fuelconsumption during two short periods of
ser-vice averaging 6 months. The next two periods
each lasting approximately 11 months show an
increase of 13%.
Then a period came in which only the last
voyage shows a distinct increase, being 10%. In
the last period of service during the last three
voyages 10% more fuel was used.-than in the first
three voyages. After the ship had been shotblasted
in 1963, the fuelconsumption was very low, viz.
0.065.
During all periods of service after 1960, Ship III
showed an increase in fuelconsumption. This
in-crease amounted to approximately 10% after
about 5 months of operation, after which the
fuelconsumption remained constant for one or two
voyages. During the sixth voyage, it showed again
a steep increase. After three out of four drydockings,
a considerable drop in fuelconsumption was
ob-servable (see Table 12).
Reviewing the figures for Ships II and III,
being vessels of the same class, it can be observed
that after nine out of eleven drydockings there was
a considerable drop in fuelconsumption and after
the other two drydockings the fuelconsumption
re-mained on the same level. There is a marked,
nearly equal, drop in fuelconsurnption for either
ship after its hull had been blast cleaned, viz. from
0.088 to 0.065 and from 0.086 to 0.069 tons per
nautical mile.
This means a decrease of about 25%.
-o 11 o_ I 10 9 -.1 I - I 1 I I 5 10
Fig. 3. Speed of ships IV
15 20 25
Ship IV
This ship, a small coaster of 500 G.R.T, is making
regular voyages from Amsterdam to the ,Baltic
Sea usually covering 1,388 miles in 7 to 8 days.
For protection against corrosion ordinary
coal-tar is applied every year. No antifouling paint is
used.
The main engine was adjusted to its specific
power. The increase of the frictional resistance
was caused by fouling of algae in summer,
re-ducing the rate of speed considerably. For
examp-ple, in 1963 the average speed was about 11.5
knots in May, dropping to 10.5 in July and even
9.5 to 9.7 in August. Later in the year the average
speed increased gradually.
Owing to the lower rate of speed, the voyages
take about one day more and the fuelconsumption
thus rises 10 to 20%. Further informations are
given in Table 13 and Fig. 3.
Ship V
This ship of 2,700 tons D.W., on which a very
good paint system is used, is known to be hindered
by algae fouling.
In June 1962 a very good antifouling paint ivas
applied. After 12 months no fouling by barnacles
could be observed, though a minor "beard" of
algae was present along the waterline. This beard
has been removed but a new coat of the antifouling
paint was not applied. Immediately after
dry-docking fouling by algae occurred again after
which the speed dropped about 0.5 knots at a speed
of 10 knots and about 2 knots at a speed of 20
knots.Estimated Economies for cargo vessels I, II, III, IV and V
Although Ships IV and V give interesting pictures,
comparison of profits and losses cannot be ma.de
due to insufficient information. With ships I, II
and III, the increase in fuel consumption for the
last few years, after 1960, is not so great in any
o = drydocking I 1 1 I 30 35 40 45 50 55 number of voyage 4 12 August '63 August '62
period of service as in the years before 1960. Very
probably this may be attributed to better
pre-treatment of the ship's hull and improvement of
the quality of the paints.
When for cargo vessels a changeover is made to
improved products,
e.g. aluminium pigmented
bituminous anticorrosive paints of good quality
and antifouling paints of the supertropical type,
which are about Dfl. 1. more expensive per m2
of wet surface, the increase in fuelconsumption
will be approximately 10% less for the second
half of a period of service.
As an example the economy thus obtained can
be calculated as follows: The wet surface of
Ships II and III is about 4,200 m2. The extra
costs for
paints
amount
4,200 x Dfl. 1. =
Dfl. 4,200.. Covering 60,000 miles per year at
0.08 tons of fuel per mile, the fuelcosts will be
Dfl. 50. per ton x 60,000 x 0.08 = Dfl. 240,000.
When in the second -half year 10% less fuel is
used, then the economy will be Dfl. 12,000.
Dfl. 4,200. = Dfl. 7,800..
In relation to the wet surface this means an
economy of about Dfl. 2. per m2 of wet surface
per period of service (approximately I year).
However, changing from an older system of
good quality to a modern system, another profit
of 10% in fuelconsumption may be attained, viz.
for the first half of the period of service. This
in-volves blast cleaning of the hull; but this extra
expenditure will be earned back in 2-4 years by
lower costs in maintenance (chapter 10).
For Ships II and III the advantage in costs of
fuelconsumption would be Dfl. 24.000. per year,
which means Dfl. 6. per m2 of wet surface.
12
Fuel consumption of passenger vessels
The fuelconsumption of two passenger liners will
be considered:
Liner I of 23,114 G.R.T. and
Liner II of 15,000 G.R.T.
Liner I
Liner I made its maiden trip in 1947. The voyages
from 1959 will be considered.
Each year 5 voyages were made of about 26,500
miles each with an average speed of 20.5 knots.
These voyages often took the ship to tropical
waters.
About half a year after the ship had left
dry-dock considerable fouling by algae was observed.
The frictional resistance increased, thus
neces-sitating more fuel in order to stick to the time
schedule.
Consequently the ship was drydocked every half
year (after 2 to 3 voyages). After removal of the
algae fouling the ship was touched up with
corrosive paint after which a new coat of
anti-fouling paint was applied.
As to the fuelconsumption corrections were
made to the average rate of speed of 20.5 knots,
although these corrections were very small. No
corrections were made in way of changes of
dis-placement as these are only very small for passenger
liners. The resulting data are given in Table 14.
In the period of service from 1959-1960 five
voyages were made.
Comparing the last two voyages with the first
two, a raise in fuel consumption of 15.6% can be
calculated. The extra fuekonsumption has cost
2 x 26,500 x (0.218
0.189) x Dfl. 50. =
Dfl. 78,175..
If the ship had drydocked after voyage 5, then
the fuelconsumption during voyages 6-and 7 would
have been as low as that for voyages 3 and 4. This
means a saving of Dfl. 48,000. being the
dif-ference between Dfl. 78,000. and Dfl. 30,000.,
the costs of drydocking, touching-up with
anti-corrosive paint and one coat of antifouling paint.
In fact the shipowners realized this point and,
accordingly, in the subsequent periods of service
the ship was drydocked after the third voyage
(No. 10).
Actually, during voyage No. 10 the
fuelcon-sumption went up by 18% over against that for
voyages 8 and 9; this involved Dfl. 45,000,
more for fuel, so that it would have been even
more advantageous - to drydock the ship after
two voyages. This point is hard to judge; only if
at the end of the second voyage there is a clearly
observable beard of algae and an increase of
fuelconsumption, a drydocking after the second
voyage has to be considered.
It should not be overlooked that the ship, when
drydocking, lies idle for one day, which costs
ap-proximately Dfl. 25,000.. However, when the
schedule of voyages is arranged that anyhow a few
idle days are avaible these costs should not be
considered, or only partly, whenever a decision
is to be taken with regard to drydocking.
Liner II
This passenger vessel was built in 1950. The
The ship crosses the Atlantic regularly, making
voyages of about 2,800 miles at an average speed
of 16 knots.
During drydocking at the end of 1960, the
ship's hull has been blast cleaned after which the
paint system was renewed entirely. An economy
in fuelconsumption was obtained of
approxi-mately 12%.
Whereas the fuelconsumption is affected rather
considerably by such factors as heavy seas, wind,
etc. only the outward bound voyages were
com-pared, the same was done with the homeward
bound voyages in as much as they were made in
the same season.
Of 10 voyages, the average fuelconsumption per
mile has been calculated at an average speed.
Thereafter the fuel consumption has been
correct-ed to an average specorrect-ed of 16 knots. The resulting
data are given in Table 15.
A comparison was made of the voyages that
were made immediately before and after blast
cleaning of the ship's hull. A distinct economy in
fuel of approximately 12% was noted for outward
as well as for homeward voyages.
Upon comparison
of the
voyages92-101
(Table 15), which were made in 1959 before
blast cleaning with the voyages 130-139 (Table
15), which were made after blast cleaning, it is
noted that only the outward voyages show a
considerable saving. This may be I incidental in
that either the weather was bad during the
out-ward voyages in 1959 or during the homeout-ward
voyages in 1962. However, the average economy
isstill 16%.
According to the shipowner the extra
expen-diture for blast cleaning and painting, amounting
to Dfl. 76,056. has been earned back in about
18 months. The shipowner compared 20 voyages
before blast cleaning (92-111, Table 15) and 20
after blast cleaning (114-123,and 130-139, Table
15) and found that 1,868 tons more fuel were
used in the period prior to blast cleaning. At a
price per ton of Dfl. 50. this means an economy
of Dfl. 76,800., moreover, as an extra advantage
the average speed was 0.29 knots higher.
Two years after blast cleaning the
fuelconsump-tion in respect of the voyages 130-139 is about
8% higher than that for the voyages 114-123,
which were made immediately after blast cleaning.
It has been stated by AERTSSEN [7] that in the
case that older ships showing heavy
corrosion are
blast cleaned, the advantage of lower
fuelcon-sumption is less spectacular than when a ship with
less heavy corrosion is blast cleaned. Blast cleaning
the hull of rather new ships, the original condition
can be regained. Ships having a badly corroded
hull, the original smoothness cannot be regained,
thus introducing a more rapid desintegration of
the paintsystem.
13 Fuelconsumption of tankers
The fuelconsumption of two tankers will be
con-sidered:
Tanker I of 32,000 tons D.W. and
Tanker II of 50,000 tons D.W.
Tankers habitually move to places all over the
world, covering distances of less than 2,000 to
more than 8,000 miles per voyage.
As the fuelconsumption of tankers in ballast
conditions is much lower than when fully loaded,
these two conditions will be dealt with separately.
For cleaning, drydocking and overhauling the
engineroom, tankers are taken out of service for
10 or more days per year. They are in ports for
only about 30 days per year. Tankers generlly
experience little inconvenience from fouling dining
the first 6 to 8 months after drydocking, so that he
fuelconsumption does not rise very much during
that time. Thereafter, fouling by algae is often
Observed, which causes a rapid increase in
fuel-consumption.
Tanker I
This tanker was built in 1955. The voyages as
from 1960 to 1964 will be considered. The fuel
consumption per mile covered has been corrrected
to an average speed of 15.5 knots for ballasted
and for loaded voyages.
Tanker I is drydocked every year, the hull is
touched up with an aluminium bituminous
corrosive paint after which a coat of an
anti-fouling paint is applied with a thickness of 80-100
m.The fuelconsumption after drydocking is
con-siderable less than just before drydocking, as can
be seen by comparing the last three voyages before
drydocking with the first three after drydocking.
See Tables 16a and 16b.
A comparison is made of the increase in
fuel-consumption for the loaded voyages for the last
voyages over against the first voyages for
each
period of service. For the three periods of service
each of one year, the increases are 10%, 31%,
18%, averaging 20%.
After drydocking the fuelconsumption is much
lower (Table 16a) e.g. in:
1960 drop from
0.228 (voyage 11) to 0.193 (voyage 13)
1961 drop from
0.212 (voyage 34) to 0.151 (voyage 37)
1962 drop from
0.216 (voyage 60) to 0.183 (voyage 62)
1963 drop from
0.227 (voyage 79) to 0.189 (voyage 82)
For the ballasted voyages the same has been done.
The increase in fuelconsumption of the last voyages
over against the first voyages in the three periods
of service of one year are; 24%, 17%, 24%,
avera-ging 22%.
Here again the fuelconsumption is
distinctly
lower after drydocking (Table 16b) in:
1960 drop from
0.185 (voyage 10) to 0.163 (voyage 12)
1961 drop from
0.203 (voyage 35) to 0.161 (voyage 36)
1962 drop from
0.173 (voyage 61) to 0.156 (voyage 63)
1963 drop from
0.194 (voyage 80) to 0.140 (voyage 81)
Tanker II
This tanker was built in 1961. The voyages as from
1961 to 1964 will be considered. For the majority
of voyages, the distance covered was about 6,300
miles. The fuelconsumption per mile covered has
been corrected to an average speed of 16.5 knots.
Before construction all steel plates were blast
cleaned and protected by a zinc rich epoxy based
paint coat.
eu 0.30 a, 2 7,"' 0.25 0.20The anti-corrosive system, consisting of another
coat of the same zinc rich paint and but a very
thin coat of an epoxy resin based anticorrosive
paint pigmented with micaceous iron
oxide,
failed badly by severe blistering. This phenomenon
has been understood later. The ship was clrydocked
and blast cleaned again after which an epoxy resin/
coal tar based anticorrosive paint system was
ap-plied. After this drydocking the fuelconsurnption
was found to be much lower than original, see
Tables 17a and 17b. After about seven months'
service fouling by algae increased the frictional
resistance, leading to a rise in fuelconsumption of
37% (compare voyage 28 and voyage 10 in loaded
condition).
At the next drydocking (1963) only fouling of
algae was observed. A new coat of antifouling
paint was applied. In the next period of service the
fuelconsumption was considerably lower (voyages
29 and 30). During the first seven months after the
1963 drydocking, no fouling has been reported and
no substancial rise in fuelconsumption was
observ-ed (voyages 39 and 40).
The extra costs due to higher fuelconsumption
at the end of the 1962-1963 period of service, can
be calculated on a basis of 6,000 miles per voyage
and fuelcosts of Dfl. 50. per ton.
Comparing loaded voyages 24, 26 and 28 with
voyages 10,
11 and 13 (Table 17a) has shown
Dfl. 62,700. extra fuelcosts and comparing
bal-lasted voyages 23, 25 and 27 with voyages 9, 12
and 16 (Table 17b) has shown extra costs of
Dfl. 44,700.. The total of Dfl. 107,400. extra
expenditure was probably only caused by the
o= drydocking
/ ballasted
/..
Fig. 4. Fuelconsumption of tanker II
//
A/\
\
/
loaded 20 25 30 1 35 40 number of 'voyage 5 10 15algae fouling which has been observed at the
1963 drydocking.
Assuming that algae fouling has to be expected
after 8 months, it could be considered profitable
to drydock the ship just to remove this fouling and
apply a new coat of an ordinary antifouling paint.
In that case the extra drydocking can be of short
duration and will cost about Dfl. 30,000.. The
advantage would be that algae fouling will cause
no troubles in two years. An economy of about
Dfl. 90,000. per year seems to be possible
(2 x Dfl. 107,000. extra costs of fuelconsumption,
minus Dfl. 30,000.
extra drydocking, in 2 years).
14
Estimation of economies in
fuelcon-sumption for Dutch merchant navy
On January 1st, 1963 the total number of sea
going vessels sailing under the Dutch flag was
1,525 and their
total
tonnage amounted to
5,037,000 G.R.T. In these figures fishing craft,
warships and lifeboats are not included [8].
It can be demonstrated that per 10,000 G.R.T.
per mile covered the fuelconsumption is 0.1 ton.
The price at that time was approximately
Dfl.50.--per ton, which means that Dfl.50.--per mile covered
Dfl. 5. is necessary for each 10,000 G.R.T.
It is considered to be possible to decrease the
average frictional resistance of the ship's hulls by
better protection against fouling and corrosion,
using better paint systems so that about 10% less
fuel is consumed. However, the ships considered in
the present report have already been treated in a
better way than usually is done for the larger part
of the Dutch Merchant Navy. This means that
the attainable economies will
bebetter than
given here for the following three categories of
vessels:420 Cargo vessels
of 500 G.R.T. and more
about 3,000,000 G.R.T.
898 Cargo vesselsof less than 500 G.R.T.
For 140 days of service at an average speed of
15 knots the mileage covered per ship will be
50,000 per year.
For 3,000,000 G.R.T. the fuelcosts are
approxi-mately
300 x 50,000 x Dfl. 5. = Dfl. 75,000,000..
The saving of 10% on these costs leads
approxi-mately to an economy of Dfl. 7,500,000..
57 Passenger vessels, totaling 610,000 G.R.T.
For approximately 200 days of service at an
average speed of 17.5 knots the mileage covered
per ship will be 84,000 per year.
For 610,000 G.R.T. the fuel costs are
approxima-tely 61 x 84,000 x Dfl. 5. = Dfl. 25,000,000..
The saving of 10% on these costs leads
approxi-mately to an economy of Dfl. 2,500,000..
121 Tankers, totaling 1,609,000 G.R.T.
For 300 days of service at an average speed of
15 knots the total mileage covered per ship will be
108,000 per year.
For 1,600,000 G.R.T. the fuelcosts are
approxima-tely
160 x 108,000 x Dfl. 5. = Dfl. 86,000,000..
The saving of 10% on these costs leads
approxi-mately to an economy of Dfl. 8,600,000..
The total economy for the larger part of the
Dutch merchant fleet would thus be more than
approximately Dfl. 18,000,000..
15
