Skin-friction results are presented for fouling-release (FR) hull coatings in the unexposed, clean condition and after dynamic exposure to diatomaceous biofilms for 3 and 6 months. The experiments were conducted in a fully developed turbulent channel flow facility spanning a wide Reynolds number range. The results show that the clean FR coatings tested were hydraulically smooth over much of the Reynolds number range. Biofilms, however, resulted in an increase in skin-friction of up to 70%. The roughness functions for the biofilm-covered surfaces did not display universal behavior, but instead varied with the percentage coverage by the biofilm. The effect of the biofilm was observed to scale with its mean thickness and the square root of the percentage coverage. A new effective roughness length scale (k_eff) for biofilms based on these parameters is proposed. Boundary layer similarity-law scaling is used to predict the impact of these biofilms on the required shaft power for a mid-sized naval surface combatant at cruising speed. The increase in power is estimated to be between 1.5% and 10.1% depending on the biofilm thickness and percentage coverage.

Item Type:	Refereed Article
Keywords:	drag, powering, biofilms, biofouling, roughness, fouling-release coatings
Research Division:	Engineering
Research Group:	Maritime engineering
Research Field:	Ship and platform structures (incl. maritime hydrodynamics)
Objective Division:	Energy
Objective Group:	Energy efficiency
Objective Field:	Transport energy efficiency
UTAS Author:	Walker, JM (Dr Jessica Walker)
ID Code:	106800
Year Published:	2015
Web of Science® Times Cited:	71
Deposited By:	NC Maritime Engineering and Hydrodynamics
Deposited On:	2016-02-22
Last Modified:	2017-11-03
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