A novel indicator for ship hull and propeller performance: Examples from two shipping segments. (1st June 2020)

• Record Type: Journal Article
• Authors: Oliveira, Dinis Reis; Granhag, Lena; Larsson, Lars
• Is Part Of: Ocean engineering. Volume 205(2020)
• Publication Date: 2020-06-01
• Subjects: Hull roughness -- Hull biofouling -- Energy efficiency -- ISO 19030 -- Fouling-control coatings -- In-water hull cleaning; Ocean engineering -- Periodicals; Ocean engineering; Periodicals; 620.4162
• DOI: 10.1016/j.oceaneng.2020.107229
• Languages: English
• ISSNs: 0029-8018

Abstract

Abstract: Ship hulls and propellers suffer from both mechanical defects and marine growth, which increase surface roughness and thus lead to significant power/speed penalties. A recent standard, ISO 19030:2016, aimed at establishing a transparent and accurate method to compare a vessel's performance to itself over time. However, the standard performance value, percentage speed difference V diff, is both vessel-specific and sensitive to operation point, most importantly vessel speed. The current paper thus proposes a new performance indicator, based on the concept of equivalent sand-grain roughness height k s, which would enable comparisons between vessels, increased accuracy for comparison of a vessel to itself over time, and calculation of penalties under operating conditions differing from past data (e.g. slow steaming). Sand-grain height k s is determined iteratively, through modelling roughness penalties on propulsive power (Granville's similarity law scaling), comparing modelled and measured penalties, and stopping the iterative process at a given tolerance on power penalty. This new performance indicator is applied to onboard-collected data from a Panamax tanker and two Roll-on/Roll-off sister vessels, yielding qualitative agreement with hull condition reported from diving inspections. Comparative advantages and limitations of k s are discussed in relation to the ISO 19030 performance value. Highlights: A new indicator for hull and propeller performance based on equivalent sand-grain roughness height is proposed. Sand-grain roughness height is determined iteratively for each onboard-measured power penalty. Results using this novel indicator show qualitative agreement with diver inspections of hull condition. The new indicator enables calculation of performance for different loading conditions and speed.