The objective of this project is to design a cleaning tool test device that can support a future effort centered on:
- Quantification of cleaning tool impact on antifouling paint systems in terms of coating damage/service life and environmental inputs including biocide release. The method will include both a test device (design of cleaning tool test device funded separately) and a standardized process.
- Using the new test method, apply cleaning tools currently used by the US Navy to both legacy and emerging coating systems and evaluate the associated impacts.
- Relate results of newly developed method to already established test methods or field observations for evaluation of coating thickness and biocide release.
- Publish a standard method based on the new test device and processes.
- Quantify the effect of hull cleaning tools to coatings at ship scale. Compare results to those obtained with the new test device and method.
- Revise coating performance specifications (for example, MIL-PRF-24647E) to reflect the new evaluation capability.
- Institutionalize findings and procedures across all Department of Defense (DoD) services.
Naval Surface Warfare Center Carderock Division (NSWCCD) will work with the Space and Naval Warfare Systems Command (SPAWAR) to establish a contract with a company with suitable design skills. Note that in a follow-on effort, a contract will be established with a suitable company to build to the final design.
The first step in the design process will include quantification of operating characteristics of SCAMPTM and the hand-held cleaning tool, for the suite of brushes to be used in the evaluation device. Working with Seaward Marine Services, Inc., and using their test facilities, the research team will determine clamping forces and brush compression, rate of rotation of brushes, and transit speeds or residence times, typical of use of SCAMPTM and hand-held cleaning tools. Tools will be operated by professional, experienced divers. Operating characteristics will be employed in the design of the test device, and formulation of the test methodology, for quantifying the impact of cleaning on antifouling coatings (see Task-2 below). Based on previous work and experience with hull cleaning and hull cleaning tools, the researchers have identified general requirements for the design that enable collection of the appropriate data:
- Brushes must be compressed to the same extent as observed during operation of actual cleaning tool in the field, thus generating comparable shear and normal forces on the sample.
- Brushes must rotate, and transit the sample, at the same rate as observed during operation of the actual cleaning tool in the field.
- Brushes must be easily removed and replaced.
- The test device should allow the operator to easily collect water samples before and after completion of the test in order to quantify biocide release or other environmental inputs. The entire test device should be designed such that it can be easily drained and refilled between evaluations.
- Materials used in the construction of the device must be corrosion resistant and should not introduce any chemicals into the sample water that might interfere with measurement of biocides, repellents, or other compounds or inputs associated with the paint systems being evaluated.
The initial design concept (see Figure 2) features a raceway incorporating the rotating brush and a rolling dolly holding the test sample (18” x 18” coated steel panel). By raising or lowering the height of the dolly the rotating brush can be compressed to the degree observed during operation of SCAMPTM or hand-held single brush cleaning tools, thus generating the appropriate shear and normal forces on the test sample. The device may be equipped with a sensor for measuring these forces directly. The brushes to be used will be those actually used on the cleaning tools of interest (Figure 1, Table 1). Wheels at the center of the raceway drive the dolly across the brush surface, at a rate of translation matching SCAMPTM . The raceway is constructed such that it can be easily drained and water samples collected for analysis of solids/particulates and biocide concentration.
Devices similar to this one have previously been designed, built, and operated for use in research programs on brush design for hull cleaning vehicles (Myers et al. 1999, Fig. 3). The suggested device, however, incorporates features that allow realistic transit of the test surface and complete capture of all cleaning effluent.
In order to improve control of biofouling and thus reduce the deleterious impacts of biofouling on ship operating efficiency, the DoD continues to explore advanced or novel control technologies, including alternative coatings and maintenance practices. Experience and data suggest that for most DoD vessels, all types of advanced paint systems, including copper-free ablative, self-polishing, and fouling-release coatings, will at some point in their service life require in-water cleaning to remove biofouling. Despite the potential for significant impacts of cleaning tools and practices on coating system performance or service life, there is no requirement in the current US Navy antifouling coating performance specification (MIL-PRF-24647E, 2013) to evaluate the effects of cleaning tools. The current specification requires only that a vendor estimate the frequency with which a paint might be cleaned, and suggest a process for cleaning when hulls are fouled with hard-shelled organisms.
There are no standardized tests, for paints applied to civilian or DoD vessels, or published methodologies for the development of such information. Without standardized methods to assess the impact of cleaning on underwater hull coatings, the DoD will remain unable to accurately predict coating system service life, determine if increasing the frequency of hull cleaning represents a viable strategy for improving fleetwide fuel efficiency, predict environmental inputs associated with any reduced coating service life, or respond to ever-tightening environmental regulations addressing biofouling control.