Section 1 Introduction
Clasification Society 2024 - Version 9.40
Clasifications Register Guidance Information - Guidance Notes for Air Lubrication System Guidance Notes, January 2020 - Chapter 1 Air Lubrication System Guidance Notes - Section 1 Introduction

Section 1 Introduction

Parent topic: Chapter 1 Air Lubrication System Guidance Notes

1.1 General

1.1.1 This document provides guidelines for the integration of an Air Lubrication System (ALS), either during new construction or in-service operation. These guidelines do not introduce any new Classification Rule requirements, they provide guidance on existing Classification Rules that would need to be considered when installing an ALS.

1.1.2 The Energy Efficiency Design Index (EEDI) was made mandatory for new ships in July 2011 – it has the intention to promote the use of more energy efficient equipment and engines. New ship design needs to meet the reference level for the ship type. It is expected that this will stimulate the continued innovation and technical development of the components affecting fuel efficiency. ALS is a documented technology for the increase of efficiency and, as such, a decrease in the assigned EEDI value.

1.1.3 It is recognised that designers, shipyards and Owners may need support during the design, construction, installation, and testing of an ALS to demonstrate compliance with the (Clasifications Register) Rules and Regulations for the Classification of Ships, July 2022. Relevant statutory conventions and their associated publications have been identified in Ch 1, 11 Notes on statutory compliance to Ch 1, 14 Statutory in service: survey, however these references are not considered exhaustive due to possible specific regulatory requirements of individual Flag State Administrations.

1.2 Background

1.2.1 Many factors contribute towards the total resistance of a ship, including friction and viscous effects which act on the wetted hull. The viscous seawater interacts with the vessel’s hull creating a turbulent boundary layer. The thickness of this boundary layer depends on the sea-state, the vessel’s speed and the hull frictional resistance coefficient.

1.2.2 Over the years, several methods have been proposed to reduce the hull frictional resistance coefficient:
  • Create large cavities within the bottom structure that are occupied with air;
  • Create a thin layer of air by using a water-repellent paint (hydrophobic paint); and
  • Create a thin layer of bubbles between the hull surface and the water.
This guidance only considers the latter.

1.2.3 Reducing hull friction by expelling an air stream into the turbulent flow is expected to decrease the total fuel consumption for a given speed, or increase the speed for a specific shaft power, under certain conditions.

1.2.4 The concept relies on the reduction of hull frictional resistance through suspending air bubbles along the length. Optimum results are generally achieved with full hull forms and operation in calmer sea states.

1.3 Considerations for marine application

1.3.1 Prior to installing an ALS, the following factors should be considered:
  • hull form characteristics: the beam ratio, the extent of flat of bottom and block coefficient;
  • power availability from generators;
  • hazardous areas, e.g. tankers, LNG Carriers; and
  • vessel’s itinerary with specific speed and draught profile.
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