ship handling

Home page|| Tanker Notes || Container Ship Operations || Ocean Navigation ||



Ship resistance and hull roughness measures - Energy Efficiency considerations

The ship resistances due to wetted surface areas are composed of frictional and wave making resistance. Frictional resistance, in particular for slower speed ships, is the primary component of total resistance. A tanker at its design speed will use the majority of its fuel overcoming frictional resistance when sailing in calm water.

When the hull moves through the water, water will be dragged along, creating a body of water following the ship and forming what is referred to as a “boundary layer”. In the forward part of the ship this boundary layer will be comparatively thin, but it grows in thickness along the sides of the hull. A boundary layer will form even on completely smooth hull surfaces. Increasing the roughness of the hull surface tends to increase the boundary layer, consequently increasing the frictional drag of the hull.

green-weed
Fig:Types of under water fouling: green-weed

In ship resistance, another major player is the ship speed relative to water close to hull surface. The effect of surface roughness on the resistance depends on the effective speed of the water relative to the hull, and this varies over the hull surface. For example increased surface roughness in the bow area will cause greater resistance than in the aft areas or under the hull bottom because the effective speed of the water will be less. So in reducing the roughness, different part of the ship will have different level of impacts even if their original roughness is the same.

The smother the hull, the less resistance the ship will have and thus the faster it will go for the same power output, saving fuel and reducing Green House Gas GHG emissions. Fouling will reduce the smoothness (increase roughness) of the hull and even may add weight to the vessel reducing the cargo carrying capacity. These impacts make the hull roughness and fouling a major issue of control for energy efficiency.

It is not uncommon for a new ship to be delivered with surface roughness as low as 75 µm and later in life enter dry-dock with a roughness of 250 µm. Historical records have shown that even with good maintenance practices average hull roughness can increase by 10 to 25 µm per year, depending on the hull coating system, even when fouling is not included [ABS 2013].



Causes of surface roughness

Hull surface roughness comes in many forms and from many sources which can be broadly categorized as physical or biological. These sources are further grouped based on size as either micro roughness (less than 1 mm) or macro-roughness (greater than 1 mm). The physical micro-roughness can be increased in service by mechanical damage, failure of the applied coating and even improper preparation of the surface and/or improper application of a new coating. Biological roughness (fouling) also has a significant impact on resistance, even at the micro level (slime, algae, etc.). See Figure for some types of fouling.

Predictions based on model tests of a light displacement fineform ship indicate that a light slime covering the entire wetted surface can increase total resistance by 7 to 9 percent. A heavy slime results in a total increase on the order of 15 to 18 percent. Small barnacles and weeds push this up to a 20 to 30 percent increase in total resistance [ABS 2013].

burnacles-&-mussels
Fig:Types of under water fouling: burnacles & mussels

Figure - Example of fouling [International Paint]

Biological fouling is a very complex process that depends on factors such as the ship’s loading condition, its operating zones, the effectiveness of anti-fouling paint and environmental conditions. If a ship is constantly moving it will not gather as much marine growth as one that spends long periods in port or at anchor. If a vessel is left static for extended periods it will allow the marine growth, that cause fouling, to attach itself to the hull and propeller which will reduce the speed of the ship and increase the fuel consumption. Hull cathodic protection also tends to work better when the ship is moving. The main factors that influence hull fouling rates are: During the operation of the ship, surface roughness can increase due to cracking and damage to the coating as well as due to corrosion which can also attract marine growth. The growth of organic species will include slime, weed fouling, and barnacles as examples shown in Figure . Current antifouling paints tend to last for a maximum period of 3–5 years when the self-polishing coating must be renewed however its performance is reduced gradually over time as explained later. The hull will also require cleaning / brushing that can either be performed by divers or automatically with either the whole hull or just critical parts being targeted. Having a shorter interval between the applications of coatings may therefore reduce energy consumption but there are some problems as the ship will require an additional dry-docking that is very costly.



Read more on

Pollution by oil [Marpol Annex I ]

What is toxic releases onboard and associated hazards? ....

How to report in case of an oil spillage onboard

Oil disaster prevention

Handling guideline for oil cargo

Oil pollution prevention method



Read more on

Energy efficiency measures -Trim optimization

Energy efficiency measures- Ballast water management

Energy efficiency measures- Causes of Hull roughness and preventive measures

Energy efficiency measures- hull roughness reduction

Energy efficiency measures- propeller maintenance

Energy efficiency measures- engine load management

Energy efficiency measures- fuel management

Energy efficiency measures - ship maintenance requirement


Related articles

Oil spillage prevention procedure

Pollution by other harmful substances & harmful packaged goods

Pollution by garbage [ Marpol annex V ]

Pollution by sewage [ Marpol annex IV ]

Pollution of air [ Marpol annex VI ]

Prohibition on use of harmful (TBT) anti-fouling paints

Pollution by ballast water

Prevention of pollution while carryiung out overboard maintenance

Environment friendly purchasing

Decommissioning / ship recycling

Environmental awareness






Other info pages !

Ships Charterparties Related terms & guideline
Stevedores injury How to prevent injury onboard
Environmental issues How to prevent marine pollution
Cargo & Ballast Handling Safety Guideline
Reefer cargo handling Troubleshoot and countermeasures
DG cargo handling Procedures & Guidelines
Safety in engine room Standard procedures
Questions from user and feedback Read our knowledgebase
Home page




ShipsBusiness.com is merely an informational site about various aspects of ships operation,maintenance procedure, prevention of pollution and many safety guideline. The procedures explained here are only indicative, not exhaustive in nature and one must always be guided by practices of good seamanship.

User feedback is important to update our database. For any comment or suggestions please Contact us
Site Use and Privacy - Read our privacy policy and site use information.
//Home //Terms and conditions of use

Copyright © 2015 www.shipsbusiness.com All rights reserved.