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Heavy calcareous fouling may results in powering penalties of more than 85%. Moreover even slime films can lead to significant increases in resistance and powering approximately 20%

Journal of Ocean Technology 9(4):19-28 · December 2014 Research by Christine Bressy and Marlène Noblet Lejars

AQUACLEAN.TECH will help you to reduce costs

Removal of biofouling will significantly improve the dynamic characteristics of your vessel

Thesis on the impact of biofouling on the economic component of ship ownership

Biofouling significantly increases fuel consumption and operating costs

1 year fouling on the hull 100%
Full cleaned underwater surface 71%

The cost of fuel is the main cost of operating the vessel. Any reduction in fuel consumption will result in a direct and proportional reduction in operating costs. Since up to 70% of a vessel’s propulsive energy is needed to overcome hydrodynamic resistance (friction).

Periodic cleaning of the ship hull and propellers from biofouling will significantly increase the distance that a ship can cover on the same amount of fuel. As the frontal resistance decreases, the speed of the vessel will also increase. And the lower the fuel consumption – the less polluting emissions will be, the more environmentally friendly your route will be.

Underwater cleaning of the hull from biofouling helps:

  • Reduces fuel consumption
  • Minimizes direct operating costs
  • Supports lengthened drydock intervals, phased maintenance, and repair programs
  • Improves effective lifetime of anti-foulant and anti-corrosive paint systems

Therefore, biofouling management can be an effective tool in enhancing energy efficiency and reducing air emissions from ships. This has been recognized by the IMO and is reflected in the 2016 Guidelines for the development of a Ship Energy Efficiency Management Plan (SEEMP) (resolution MEPC.282(70))

Underwater cleaning has other economic advantages besides those associated with propulsion efficiency. Unclogging fouled suction grates improves the flow of water to internal machinery and reduces pump wear. Cleaning the hull regularly prevents biofouling buildup, thereby lengthening the effective life of the anti-foulant coating and sustaining the anti-corrosive coating system for longer dry-dock intervals. Removing calcareous growth at its first appearance reduces the likelihood of external hull corrosion and pitting. During every cleaning, we see and carefully inspect each portion of the hull.


Removing lime build-up when it first appears reduces the likelihood of external corrosion of the hull and pitting. During each cleaning, our industrial divers carefully inspect each part of the hull and make a checklist, the results of which give you a detailed planned report.

Detailed research on the impact of biofouling on the cost of ownership of the ship

biofouling fuel increase
Below we show excerpts from a large research study conducted by the US Navy in relation to several large ships that have been observed for 15 years. The main objective of this research is to show the level of dependence of fuel consumption on the degree of biofouling.

“Economic impact of biofouling on a naval surface ship”

M. P. Schultz; J. A. Bendick; E. R. Holm; W. M. Hertel
a Department of Naval Architecture and Ocean Engineering, United States Naval Academy, Annapolis, MD, USA

We divided the level of biofouling on the category

Table 1

A range of representative coating and fouling conditions. Similar rating of a fouling index used by the US Navy based on Naval Ships’ Technical Manual Chapter 081 (NSTM 2006).
Description of condition Fouling rating
Hydraulically smooth surface
Deteriorated coating or light slime
Heavy slime
Small calcareous fouling or weed
Medium calcareous fouling
Heavy calcareous fouling

In order to estimate costs associated with water-borne hull cleaning, the frequency of full, partial, and interim cleanings carried out on the Arleigh Burke-class destroyers was quantified over a 3-year period from 1 January 2004 to 31 December 2006 Data were obtained from the database of ships’ hull inspections. 

Table 2

Dimensions of the test vessel
Dimensions Value
Waterline length
142 m
18 m
6.4 m
Wetted hull area
3001 m2
8768 metric tons
Heavy calcareous fouling
90 - 100

Due to their very low frequency, partial cleanings were pooled with full hull cleanings before analysis. Over the reporting period, 46 DDG-51 class vessels underwent 28 full/partial hull cleanings and 282 interim cleanings. The average frequency of full hull cleanings over the study period was 0.21/year, while the average frequency of interim cleanings was 2.4/year. 

Costs for full/partial and interim hull cleanings vary across ports. Costs used in the model were unweighted averages across the ports. The model estimated current costs by correcting the 2001 contract cost for 8 years of inflation at a rate of 3%. The estimated 2009 cost for a full hull cleaning was $26,808, and for an interim cleaning $18,735. Due to variation in actual annual prices, the actual costs in 2009 and moving into the future may be slightly different. For example, under the current (2010) contract, costs range from $26,200 to $34,200 for a full cleaning and $15,000 to $21,500 for an interim cleaning. 

Prediction of the hydrodynamic impact of hull fouling 

In order to predict the impact of hull fouling on the total resistance and powering of the DDG-51, the procedure was employed. In the present work, towing tank test results for a 1:36 scale model of a mid-sized naval surface combatant taken at the US Naval Academy Hydromechanics.

Laboratory were used to obtain the baseline resistance and powering requirements for the hydrodynamically smooth condition. The model tested was similar to the DDG-51, the dimensions of which are shown in Table 2 Estimates of the change in total resistance (DRTs) for an Arleigh Burke-class destroyer (DDG-51) as result of hull condition at speeds of 7.7 m/s and 15.4 m/s (15 knots and 30 knots) are shown in Tables 3 and 4, respectively. The resulting change in required shaft power (DSP) as result of hull condition at speeds of 7.7 m/s and 15.4 m/s (15 knots and 30 knots) are also shown in Tables 3 and 4, respectively.

Table 3

SPEED of 7.7 m/s (15 knots).
Predictions of the change in total resistance (DRTs) and required shaft power (DSP) for a test vessel with a range of coating and fouling conditions
Description of condition Change in total resistance (kN) % Required shaft power (kW) %
Hydraulically smooth surface
Typical as applied Anti Fouling coating
Deteriorated coating or light slime
Heavy slime
Small calcareous fouling or weed
Medium calcareous fouling
Heavy calcareous fouling

Table 4

SPEED of 15.4 m/s (30 knots)
Predictions of the change in total resistance (DRTs) and required shaft power (DSP) for a test vessel with a range of coating and fouling conditions
Description of condition Change in total resistance (kN) % Required shaft power (kW) %
Hydraulically smooth surface
Typical as applied Anti Fouling coating
Deteriorated coating or light slime
Heavy slime
Small calcareous fouling or weed
Medium calcareous fouling
Heavy calcareous fouling

Calculation of fuel consumption and fuel costs

In order to relate the required shaft power predictions to ship fuel consumption, further discussion of the Arleigh Burke-class destroyer (DDG-51) and its operation is required. The DDG-51 is a twin-screw ship powered by four General Electric LM2500 gas-turbine engines. Together these engines produce in excess of 80,000 kW in shaft power. When the ship is underway, there are three common plant operation modes. The first is the trail-shaft mode in which only one of the gas turbines is operational. In this mode, a single engine powers a single shaft while the other shaft remains idle. This is the most fuel efficient operation mode at cruising speed. The second mode of operation is termed the split-plant mode. In this mode, two engines are online with each powering a separate shaft. The last operational mode is the full-power mode. In this case, all four engines are used with two powering each shaft.

This mode is used for high speed operations. For the analysis presented here, it was assumed that the ship operated in trail-shaft mode while cruising at 7.7 m/s (15 knots) and in full-power mode while steaming at 15.4 m/s (30 knots). In the full-power mode, it was also assumed that the power supplied by the four engines was equal.

The relationship between the output shaft power of the engine and its fuel consumption can be obtained from the engine’s specific fuel consumption (SFC) curve. Figure 3, adapted from Guimond et al. (2006), gives the SFC curve for the General Electric LM2500 gas-turbine engines. By entering Figure 1 with the required shaft power for an engine, the specific fuel consumption (SFC) can be obtained. The SFC is mass of fuel consumed per kW-h. This along with ship operational data can then be used to calculate the mass of fuel consumed.

Figure 1.
Specific fuel consumption (SFC)

In order to translate results into annual rates of fuel consumption and fuel costs, data on steaming time, the proportion of steaming time spent in various powering modes, and fuel costs (per barrel) are required. Analysis of the Navy VAMOSC (Visibility and Management of Operating and Support Costs) database of steaming hours showed that the average steaming time for an Arleigh Burke class-destroyer (DDG-51) was 2835 hours per 1 year. Guimond et al. (2006) reported a typical operational tempo for DDG-51 class vessels as *90% of steaming time at cruising speed (15 knots or 7.7 m/s) and approximately 10% of steaming time at high speed (30 knots or 15.4 m/s). For the purposes of the economic model, the direct cost of fuel (distillate fuel marine – DFM) was assumed to be $104.16 per barrel based on guidance from the Naval Sea Systems Command (NAVSEA) released in December 2008 The indirect cost, or burden, for DFM was taken to be $59.93 per barrel, based on similar NAVSEA guidance. Note that the direct cost of fuel can vary greatly over time. For example, the NAVSEA guidance for July 2008 was $170.52 per barrel and for February 2009 was $69.30 per barrel. Significant changes in fuel prices outside of those due to inflation will affect the performance of the model.

The economic impact of hull roughness and fouling

Hull roughness due either to the presence of a coating or to hull fouling incurs an operational cost to the vessel due to increases in shaft power to reach a given speed and associated increases in fuel consumption.

US Navy cumulative costs per ship over 15 years for four hull roughness conditions were calculated (Table 5). These include:
1) ideal hydraulically-smooth paint (Case 1),
2) newly applied ablative AF coating with no fouling (Case 2),
3) typical hull roughness given the Navy’s present practices including qualified ablative AF coatings and regular interim and full hull cleanings (Case 3), a
4) scenario featuring an upper bound for hull fouling (Case 4).

Scenario Coating description Fouling level Interim cleaning Full cleaning Increase in fuel costs
Case 1
Hypothetical hydraulically-smooth
Case 2
Typically applied antifouling coat (standard roughness)
Case 3
Typically applied antifouling coat (standard roughness)
FR-30 (Heavy slime)
every 4 month
1 time in 3 year
$ 1'510'000
Case 4
Typically applied antifouling coat (standard roughness)
FR-60 (Small calcareous fouling or weed)
every 4 month
1 time in 3 year

$ 2'320'000

The hydraulically-smooth hull scenario (Case 1) served as the baseline for all other cases and the scenarios. In this scenario, the baseline cost for propulsive fuel is approximately $11.1M per ship per year.

Despite the vessel remaining free of fouling, the typical paint roughness of as-applied AF coatings leads to an increase in fuel consumption of 1.4% per year, or about $0.15M per ship per year.

Cases 3 and 4 demonstrate the enormous effect of fouling on fuel consumption and subsequent operating costs. The 15 year cumulative cost (over baseline) for operations under current Navy hull maintenance practices is approximately $22.7M per ship. The largest source of this cost is increased fuel consumption due to hull fouling. Based on the data obtained in the research, the annual loss on the cost of fuel associated with the power loss due to biofouling is $ 1.51 million dollars per year.

Based on the present analysis, FR-30 level of fouling generates an increase of 10.3% in fuel consumption relative to the hydraulically-smooth condition of Case 1. This increase equates to a cost of approximately $1.2M per ship per year.

For the worst-case scenario (Case 4), representing a ship operating with a mixed community of relatively small hard fouling organisms (FR-60), the cumulative cost over 1 year from coating roughness and fouling is approximately $2,32M per ship.

Hull fouling of FR-60 causes an increase of 20.4% in fuel consumption compared to the hydraulically-smooth condition. This equates to a present-day cost of approximately $3.3M per ship per year.

Waterborne underwater hull cleaning

Waterborne underwater hull cleaning allows for the removal of fouling accumulations on hulls and propellers without drydocking. Appropriate use of these cleanings increases the availability of the ship to the fleet and extends the life of the hull coating system while minimizing maintenance costs associated with drydocking. Waterborne hull cleaning also recovers performance or operating efficiency (in terms of fuel expenditures) lost due to fouling accumulation, to a condition similar to that of a clean hull.

Since the effects of fouling on performance vary among ship classes, and the intensity of fouling differs with type of hull coating, operational profile and area of operations of the vessel, the Management companies does not specify intervals for the conduct of hull cleanings. Instead, the decision on whether to clean is based on the results of regular inspections. Performance criteria can also be used to indicate the need for a hull cleaning, including a 1 knot reduction in speed at constant shaft revolutions, an increase in fuel use of 5% to maintain a specified rate of revolution of the shaft, and an increase in shaft revolution rate of 5% to maintain a particular speed.

Several types of waterborne cleaning are available to restore performance. In a Full Cleaning, fouling is removed from the entire underwater hull, propellers, shafts, struts and rudders, and all openings. Interim Cleaning refers to removal of fouling from propellers, shafts, struts and rudders. Partial Cleaning covers removal of fouling from particular sections of the ship hull, and can be performed in combination with an Interim Cleaning.

The economic impact of a proactive hull cleaning

Waterborne hull cleaning is typically a response to increased hull fouling with hulls being cleaned once they reach a condition where efficient ship operation is compromised. AQUACLEAN.TECH propose a proactive approach to waterborne hull cleaning where in the hull is cleaned at high frequency (for example, once every month) using less aggressive tools than those usually employed, with the goal of maintaining the hull at a very low fouling rating.

Results of initial trials suggested that light cleaning of the ablative AF coatings every 30 to 40 days allowed only a light biofilm (FR-10 to FR-20). This form on the painted surface may generate cost savings if ships can be maintained at lower than typical fouling ratings without greatly increasing cleaning expenses or decreasing the coating lifespan.



Types of commercial vessel and what all of they do

General cargo vessel
General cargo vessels are the most basic dry cargo carrying vessel; they are used to carry loose and irregular cargo which is not suitable for container, Ro-Ro, bulk or specialist heavy lift vessels. Stevedores will secure cargoes to these vessels using custom fittings often welded to the ships hold. General cargo vessels are often fitted with rigging for winches which are used to load and unload cargo to the vessel hold
Passenger Vessels
Passenger vessels range from small 10 person ferries to large cruise ships capable of carrying more than 6000 passengers. Passenger vessels such as cruise ships are fitted with hotel-like interiors and include facilities such as restaurants, shops, cinemas and swimming pools. The largest passenger vessel is the ‘Allure of the Seas’ which is 1187ft long and can comfortably accommodate 6296 passengers.
Tug Vessels
Tugs are highly manoeuvrable and powerful vessels which are used to assist larger and less manoeuvrable vessels. They can be used to assist ships in, out and around ports as well as during bad weather when they’re power and manoeuvrability can ensure the safe transit of large vessels. Tugs are also used for port to port transportation of barges and the movement of large structures such as offshore platforms and floating storage units.
Fishing vessels
A fishing vessel is a boat or ship used to catch fish in the sea, or on a lake or river. Many different kinds of vessels are used in commercial, artisanal and recreational fishing. According to the FAO, there are currently (2004) four million commercial fishing vessels. About 1.3 million of these are decked vessels with enclosed areas. Nearly all of these decked vessels are mechanised, and 40,000 of them are over 100 tons. At the other extreme, two-thirds (1.8 million) of the undecked boats are traditional craft of various types, powered only by sail and oars. These boats are used by artisan fishers.
Heavy Lift / Project Cargo Vessels
Heavy lift / project cargo vessels are specialist vessels built to transport extremely heavy or bulky cargoes including heavy industrial components and other vessels, such as yachts. There are two main types of heavy lift / project cargo vessels; semi-submergible (also known as flo-flo or float-on/float-off) which are used for the transportation of other vessels and augment unloading vessels which are fitted with specialist heavy lift equipment to make unloading at under-equipped ports possible. Semi-submergible vessels allow cargoes to be floated into position before the semi-submerged vessel de-ballasts to lift the cargo out of the water.
Livestock Vessels
Livestock vessels are usually converted from other types of cargo vessels and fitted with the necessary equipment to safely transport large numbers of animals. They are designed to provide adequate ventilation, food and water. There is two types of livestock vessels; open livestock carriers with animal pens installed on open decks, providing natural ventilation and avoiding the reliance on mechanical ventilation systems, and closed livestock carriers which have animal pens within holds and internal decks of the vessel. Closed carriers required mechanical ventilation systems but also allow for a more controlled environment which is sheltered during server weather.
Bulk Carriers
Bulk carriers are used to transport loose dry cargoes such as ore, grains and cement which often have a high weight to cost ratio making ocean transportation by other methods / vessel types inefficient. Bulk carriers are large vessels which are usually divided into separate cargo holds, covered by hatches. Bulk carriers are loaded by spouts, conveyors or by cranes fitted with grabs, some carriers have cranes fitted to allow the loading and unloading of cargo without the need for port equipment. Bulk carriers are usually unloaded using cranes fitted with grabs although some cargoes can be unloaded using specialist equipment to speed up the process. Bulk cargo is generally loaded from the vessel into hoppers which then use conveyor belts to transfer the cargo to open storage or silos.
Container Vessels
Container ships transport an estimated 52% of all global ocean trade and are specifically designed to transport ISO standardised shipping containers, these include 10, 20, 40 & 45ft standard containers, high-cube containers, open-top containers, flatrack and platform containers (these are used for oversized cargo), tank containers (for liquids / gasses) and refrigerated containers which require a power source to provide temperature control. Container ships are loaded / unloaded using gantry cranes which move the containers straight between the vessel and truck which removes the need for warehousing and improves efficiency. Container vessels come in many different sizes, the world’s largest is the Maersk Triple-E class which is 1306 ft long and has a capacity of 18,340 TEU.
Roll-on/Roll-off vessels
RO-RO or roll-on/roll-off vessels are ships designed to carry wheeled cargo, they come in different forms depending on the need, including vehicle ferries, cargo vessels (which are used for truck trailers, railroad cars etc) and car carriers which are the most prominent. Ro-Ro vessels are loaded/ unloaded using single or multiple loading ramps. The largest Ro-Ro vessel is the Mark V Class owned by Wilh. Wilhelmsen which is 869ft long and has three hoistable decks which provide 138,000 cubic metres of cargo space.
Tankers: Crude Carriers
Crude oil carriers are designed (as the name suggests) to transport crude oil to refineries where it can be processed. Very Large Crude Carriers (VLCCs) and Ultra Large Crude Carriers (ULCCs) are the largest ships in the world. Due to the size of these supertankers many cannot dock at ports so cargoes are unloaded at offshore pumping stations / terminals. Supertankers (VLCCs & ULCCs) can carry approximately 2,000,000 barrels of oil or 318,000 metric tons. The Knock Nevis is regarded as the largest ULCC supertanker ever built with a length of 1504ft although this vessel stopped operations in 2009.
Tankers: Product Carriers
Product carriers are much like crude carriers but generally smaller, they are used to transport refined products from larger terminals to smaller ports located worldwide. These vessels carry products such as petroleum, diesel, asphalt, jet fuel, tar and lubricating oil, the smaller of these product carriers are also used for non-petroleum bulk products such as palm oil.
Tankers: Liquefied Gas Carriers
Liquefied gas carriers are highly specialised vessels which are used to transport Liquefied Natural Gas (LGN) or Liquefied Petroleum Gas (LPG). The cargo is stored within spherical tanks under high pressure and often at low temperatures. Loading and unloading of these vessels require specialist terminals and handling equipment. LGNs are usually larger than LPGs, the largest type of liquefied gas vessel is the Q-Max which is a 1132ft long LGN vessel and has a capacity of 266,000 m3.
Tankers: Chemical Carriers
Chemical carriers are used for the transportation of a whole range of chemicals, which each have different properties, characteristics and inherit hazards. Chemical tankers generally have a number of separate cargo tanks which are either coated with specialized coatings such as zinc pait/ phenolic epoxy or they are made from stainless steel. The material used for the cargo tanks or the coating determines what types of cargo each tank can hold, epoxy coated tanks can hold cargoes such as vegetable oil whilst hazardous cargo such as aggressive acids (e.g. phosphoric and sulphuric acid) must be carried using stainless steel tanks.

More information about vessels types you may find here

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