1. Ship and Hull Maintenance and Repair
30 April 2010
Allan Larsen

2. Optimum Intervals for Hull Maintenance
Hull Planned Maintenance PMS-H

3. Optimum Intervals for Hull Maintenance
Maintenance may be defined as
“The act of keeping, or the expenditure required to keep, an asset in condition to perform efficiently the service for which it is required. ”
Optimum may be defined as ………..
“A condition, degree, amount or compromise that produces the best possible result.”
“Repairs & Maintenance is generally the second largest cost category for all vessel types, typically accounting for % of total operating costs” Ocean Shipping Consultants Ltd.
“The impact of ship age is obvious. Operational costs of ships aged years exceed those of the units aged years by 32% - 60%” HSH Nordbank 3

4. Optimum Intervals for Hull Maintenance
Efficient planning of hull maintenance and repairs to ensure that these are carried out at optimal time intervals has considerable advantages.
“Hull planned maintenance improves asset management by reducing operating and maintenance costs.”
Bureau Veritas
“Owner’s hull inspection and maintenance schemes are to be encouraged as a means for maintaining compliance with classification and statutory requirements between surveys” IACS PR33 4

5. Optimum Intervals for Hull Maintenance
So what are the optimal time intervals for hull maintenance?
The most cost efficient method of hull maintenance is to undertake the main work in alignment with those periods where the ship is required by Class rules and Statutory requirements to enter into a dry-dock.
This answer is ship type and age dependent. 5

6. Optimum Intervals for Hull Maintenance
TYPES OF HULL MAINTENANCE
PREVENTIVE
PREDICTIVE
CORRECTIVE
REACTIVE
Coatings
Fatigue Studies
Coatings Repairs
Coatings Repairs
Anodes
Anodes Renewal
Steelwork Repairs
Steelwork Repairs
Inspections
Coatings Renewal
Hull Cleaning
Hull Cleaning
Propeller Cleaning
Propeller Cleaning
Propeller Cleaning
Planned
Unplanned
Cost
Inefficient
Cost
Efficient 6

7. Optimum Intervals for Hull Maintenance
Planned Maintenance System for Hull (PMS-H)
Advantages
Reduced operational downtime by closely aligning surveys with the ship staff’s annual inspections.
Reduced operating costs by pre-planning and maximizing resources for the annual scheduled surveys and inspections. 7

8. Optimum Intervals for Hull Maintenance
Planned Maintenance System for Hull (PMS-H)
Advantages
Improved vessel staff inspection routines and defects identification, leading to early identification of repair needs and hence reduced risk during vessel’s operation.
Reduced maintenance costs by improved pre-planning for repairs during periods where resources can be maximised either in operation, or at planned dockings. 8

9. Optimum Intervals for Hull Maintenance
Planned Maintenance System for Hull (PMS-H)
With continuing innovations on inspection techniques, condition monitoring, planned maintenance systems and advances in coatings this has allowed Flag Administrations, Classification Societies and Ship Owners to discuss and review the time intervals between Dockings with the view to extend these intervals for certain vessel types. Various test cases are ongoing.
Bureau Veritas are amongst the societies who are actively involved in these reviews. 9

10. Fouling and its Effect on Ship Performance
Hull and Propeller Cleaning Intervals 10

11. Fouling and its Effect on Ship Performance
Fouling of the hull and propeller by marine growth increases the roughness of the hull which causes a reduction in hull speed through the water for a given shaft power output.
As the fouling increases with time the drag on the hull increases, the propeller efficiency reduces and the hull speed decreases.
An increase in engine power output is then required to maintain the desired speed.
Akzo Nobel 2004 11

12. Fouling and its Effect on Ship Performance
The more power required to maintain speed the more fuel is required to be burned and the amount of CO2 released into the air increases.
Akzo Nobel 2003
Costs go up and so does the vessel’s carbon footprint.
As the hull and propeller get even dirtier the engine will at some point become incapable of producing enough power to make the designed speed and this will affect charterability. 12

13. Fouling and its Effect on Ship Performance
A speed reduction of 10% due to fouling would roughly correspond to an increase in fuel consumption of 30%.
Even Slime and algae can cost a ship an additional 10% in fuel consumption to achieve design speed.
It has been observed that speed reductions of 5 to 10% are typical between hull renewals when the hull renewal period is three to five years.
According to Chris Geater blogging on the Sustainable Shipping web site. April 2010
Hull fouling costs ship owners $8 billion in extra fuel consumed and produces an additional 70 million tons of CO2 in order to achieve design speed.
The marine industry spends $6 billion a year in the prevention or treatment of biofouling. 13

14. Fouling and its Effect on Ship Performance
In April 2006 during the Motorship Propulsion Conference Torben Munk M.Sc. presented a paper on “Fuel Conservation through Managing Hull Resistance”
The below graph has been reproduced from that paper (with thanks). The graph shows curves of actual performance due to added hull resistance (fouling & coatings treatment) for a fleet of 7 vessels of similar design.
From the graph it is shown that at 22 knots the fuel consumption, of the vessel with 19% added resistance, increased by approximately 11.29% from the sea trials, or putting this another way an increase above the designed fuel consumption of an additional 14 tonnes per day.
Equating to an additional 42 mt of CO2 and +1 mt SOx.

15. Fouling and its Effect on Ship Performance
It is difficult to accurately calculate the actual Ship performance drop-off due to hull and propeller fouling because ships tend to operate on a worldwide basis and such factors as wind resistance, waves, ocean currents and engine efficiency are variable.
Analysis of the increase in slip (i.e. the difference between the distance the hull should have travelled through the water compared with the distance the hull actually travelled) and the increase in fuel consumption to propel the hull through the water at a given speed are the usual methods to assess any deterioration in the hull and propeller efficiency.
Solutions such as CASPER® Computerised Analysis of Ship’s Performance and SeaTrend® amongst others, are designed to assist the vessel operator in onboard Ship performance analysis.
However no matter the methodology used, the determination of just when it is time to clean the propeller and the hull is dependent on what performance drop off the ship operator or Charterer is prepared to accept. i.e. There is no fixed time parameters for cleaning. 15

16. Fouling and its Effect on Ship Performance
Hull Cleaning Intervals
Propeller Cleaning Intervals
Obviously the ideal and easiest time to clean (Superpolish) the propeller is in drydock.
However onboard Slip and fuel consumption calculations have shown that in-water propeller cleaning periods should be scheduled more frequently than at drydock in order to maintain the propeller efficiency.
Propeller cleaning intervals of between 4 and 8 months would appear to be prudent and intervals of 6 months have been set by some companies as standard for their fleet planning. 16

17. Fouling and its Effect on Ship Performance
Hull Cleaning Intervals
As removal and disposal of hull marine growth is banned in some countries and only allowed in controlled conditions (such as at drydock) in some others; the optimum time to clean the hull would appear to be when the vessel is in dry-dock.
Which means that hull coatings preparation, application and the choice of type of coating, as a preventive maintenance solution to fit in line with the desired frequency between docking intervals, takes on even greater importance. 17

18. Coatings and Hull Protection
IACS Unified Requirements vis-à-vis Downtime for Surveys 18

19. Coatings and Hull Protection
The application and maintenance of hull coatings, both internal to the hull and on the external hull, are regulated by International conventions, state requirements and class rules.
In this part of the presentation we will discuss the IACS unified requirements as they apply to coatings and their survey, and how these requirements can be used to reduce the downtime required for periodical surveys and by doing so help to reduce operating costs. 19

20. Coatings and Hull Protection
Z3.1.2
There is to be a minimum of two examinations of the outside of the ship’s bottom and related items during each five-year special survey period. One such examination is to be carried out in conjunction with the special survey. In all cases the interval between any two such examinations is not to exceed 36 months. An extension of examination of the ship’s bottom of 3 months beyond the due date can be granted in exceptional circumstances.
Z3.1.3
Examinations of the outside of the ship’s bottom ….. may be given to alternate examination ………… as an In-water Survey, ……… Special consideration is to be given to ships of 15 years or over before being permitted to have such examinations. 20

21. Coatings and Hull Protection
During each survey cycle, all items are to be surveyed (and tested, where required) in regular rotation, as far as practicable, with uniform annual share within the five-years class period.
The owner is entitled to fix the sequence in which the individual items of the hull are intended to be surveyed. ………The survey in dry-dock may be held at any time within the five-year class period………...
For ships more than 10 years of age, the ballast tanks are to be internally examined twice in each five year class period, ie. once within the scope of the intermediate survey and once within the scope of the continuous system for the hull special survey.
The agreement for surveys to be carried out on a Continuous Survey System basis may be withdrawn at discretion of the Society concerned.
Which is normally at 20 years but may be extended at Class Discretion 21

22. Coatings and Hull Protection
2.27
Where provided, the condition of corrosion prevention system of ballast tanks is to be examined. For tanks used for water ballast, excluding double bottom tanks, where a hard protective coating is found in POOR condition and it is not renewed, where soft coating has been applied, or where a hard protective coating was not applied from time of construction, the tanks in question are to be examined at annual intervals…….
When such breakdown of hard protective coating is found in water ballast double bottom tanks and it is not renewed, where a soft coating has been applied, or where a hard protective coating was not applied from the time of construction, the tanks in question may be examined at annual intervals……
2.28 22

23. Coatings and Hull Protection
At the time of new construction, all salt water ballast spaces having boundaries formed by the hull envelope shall have an efficient protective coating, epoxy or equivalent, applied in accordance with the manufacturer's recommendations. 23

24. Coatings and Hull Protection
At the time of new construction, all internal and external surfaces of hatch coamings and hatch covers, and all internal surfaces of the cargo holds, excluding the flat tank top areas and the hopper tanks sloping plating ………. are to have an efficient protective coating (epoxy coating or equivalent) applied ……….
For existing bulk carriers, where Owners may elect to coat or recoat cargo holds as noted above, consideration may be given to the extent of the close-up and thickness measurement surveys ………………. 24

25. Coatings and Hull Protection
Z7.1 Hull Surveys for General Dry Cargo Ships
Z7.2 Hull Surveys for Liquefied Gas Carriers
Z10.1 Hull Surveys of Oil Tankers
Z10.2 Hull Surveys of Bulk Carriers
Z10.3 Hull Surveys of Chemical Tankers
Z10.4 Hull Surveys of Double Hull Oil Tankers
Z10.5 Hull Surveys of Double Skin Bulk Carriers
Tank Protection
A Ballast Tank is to be examined at subsequent annual intervals where:
a. a hard protective coating has not been applied from the time of construction, or
b. a soft coating has been applied, or
c. substantial corrosion is found within the tank, or
d. the hard protective coating is found to be in less than GOOD condition and the
hard protective coating is not repaired to the satisfaction of the Surveyor. 25

26. Coatings and Hull Protection
URZ 7, 7.1, 7.2, 10.1, 10.2, 10.3, & 10.5
Extent of Overall and Close-up Survey
Where Overall Survey of tanks and spaces is to be carried out at Intermediate survey and or Special Survey………
For areas in tanks where hard coatings are found in GOOD condition:
The extent of Close-up surveys may be specially considered.
The extent of Thickness Measurements may be specially considered.
URS31
Renewal Criteria for Side Shell Frames and Brackets in Single Side Skin Bulk Carriers and Single Side Skin OBO Carriers not Built in accordance with UR S12 Rev.1 or subsequent revisions
When the measured frame webs thickness tM is such that
and the coating is in GOOD condition, sand blasting and coating may be waived even if not found in “as-new” condition, ……… provided that tripping brackets are fitted and the coating damaged in way of the tripping bracket welding is repaired. 26

27. Coatings and Hull Protection
And as discussed earlier in the presentation even Docking Intervals for some types of vessels may be extended depending on Maintenance of Coatings and Cathodic Protection Systems both external to the hull and internal to the tanks. 27

28. Coatings and Hull Protection
When planned maintenance goes well then the condition of the external hull may look like this when the vessel next enters a dock.

29. When Planned maintenance goes
Coatings and Hull Protection
When Planned maintenance goes
not so well.… 29