Page 58 - Practical Design Ships and Floating Structures

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Inspections are generally made at periodical survey and intermediate survey in accordance with ship
classification rules. In some ships self inspections are made by ship owners and crews. By utilizing this
information the scopes and costs of repairs are estimated. Also necessary materials and manpower can
be previously prepared in ship yards.
It is almost impossible to make close up mey in all the holds and tanks at every inspection, so close
up survey is divided into several times to concentrate on a few tanks. Maintenance costs include these
inspections but comparatively small to the maintenance costs.
3.2 Repair

Repair cost is divided into general repair cost, which is periodical expenditure and special repair cost,
which is required for a big failure at every few years.

In case of hull stmcimal part, the number of failures suddenly increases after 10 years, as shown in
Figure 3 (Nippon Kaiji Kyoukai, 1995). This is due to the influence of corrosion. Figure 4 indicates the
same tendencies in general ships and VLCC but the average numbers of failures of VLCC are bigger
than in general ships(Nippon Kaiji Kyoukai, 1995). Old aged ships have 10 failures per a year in
average.
Consequently general repair cost is estimated to be 0.1 - 0.5 % of building cost per one repair. Special
repair cost is not necessarily required for every ship but it rises to a big amount, once a big failure
OCCUTS.
Special repair cost is covered by insurance, if it is due to natural disaster.

A
'-

-1'

Figure 3: Frequency of failure per ship-year Figure 4: Frequency of failure due to fatigue
v.s.ship's age(for all ships) and corrosion of VLCC per ship-year

3.3 Corrosion protectwn

Corrosion protection is very important. Paint films of ballast tanks are generally damaged after about
10 years and corrosion of steel structures starts. Plates are generally renewed one after another, if their