Are silicone foul-release coatings a viable and environmentally sustainable alternative to biocidal antifouling coatings in the Baltic Sea region?

To combat unwanted fouling on immersed hulls, biocidal antifouling coatings are commonly applied to vessels trafficking the Baltic Sea. Here, the efficacy, environmental sustainability and market barriers of silicone foul-release coatings (FRCs) was assessed for this region to evaluate their viability as replacements for biocidal coatings. Coated panels were exposed statically over a 1 year period at three locations in the Baltic Sea region to assess the long-term performance of a biocide-free FRC and two copper coatings. The FRC was found to perform equally well or significantly better than the copper coatings. Even though most silicone FRCs on the market are biocide-free, a review of the literature regarding toxic effects and the identity and environmental fate of leachables shows that they may not be completely environmentally benign, simply for the lack of biocides. Nonetheless, FRCs are substantially less toxic compared to biocidal antifouling coatings and their use should be promoted.

Ship hull in-water cleaning and its effects on fouling-control coatings.

Today, ship hull fouling is managed through fouling-control coatings, complemented with in-water cleaning. During cleaning, coating damage and wear must be avoided, for maximum coating lifetime and reduced antifoulant release. When possible, cleaning should target early stages of fouling, using minimal forces. However, such forces, and their effects on coatings, have not yet been fully quantified. In this one-year study, minimal cleaning forces were determined using a newly-designed immersed waterjet. The results show that bi-monthly/monthly cleaning, with maximum wall shear stress up to ∼1.3 kPa and jet stagnation pressure ∼0.17 MPa, did not appear to cause damage or wear on either the biocidal antifouling (AF) or the biocide-free foul-release (FR) coatings. The AF coating required bi-monthly cleanings to keep fouling to incipient slime (time-averaged results), while the FR coating had a similar fouling level even without cleaning. The reported forces may be used in matching cleaning parameters to the adhesion strength of the early stages of fouling.

Towards an absolute scale for adhesion strength of ship hull microfouling.

In-water ships' hull cleaning enables significant fuel savings through removal of marine fouling from surfaces. However, cleaning may also shorten the lifetime of hull coatings, with a subsequent increase in the colonization and growth rate of fouling organisms. Deleterious effects of cleaning would be minimized by matching cleaning forces to the adhesion strength of the early stages of fouling, or microfouling. Calibrated waterjets are routinely used to compare different coatings in terms of the adhesion strength of microfouling. However, an absolute scale is lacking for translating such results into cleaning forces, which are of interest for the design and operation of hull cleaning devices. This paper discusses how such forces can be determined using computational fluid dynamics. Semi-empirical formulae are derived for forces under immersed waterjets, where the normal and tangential components of wall forces are given as functions of different flow parameters. Nozzle translation speed is identified as a parameter for future research, as this may affect cleaning efficacy.

Effect of ship hull form on the resistance penalty from biofouling.

Hull biofouling is a well-known problem for the shipping industry, leading to increased resistance and fuel consumption. Considering that the effects of hull form on resistance are known to be higher for a less slender hull, it is hypothesised in this paper that the effect of biofouling roughness on resistance is also dependent on the hull form. To test this hypothesis, previously reported full-scale numerical results on a containership are re-analysed. Form effects on roughness penalties, corresponding to KΔCT = 0.058 ± 0.025, are observed at a low speed (19 knots, Res = 2.29 × 109), which are however cancelled out by traditionally neglected roughness effects on wave-making resistance at a higher speed (24 knots, Res = 2.89 × 109). It is concluded that hull form effects on biofouling penalties can be significant at low speeds, though not generalisable for higher speeds, namely when wave-making resistance corresponds to ≥ 29% of total resistance.

Psychometry and Pescatori projective test in coloproctological patients.

BACKGROUND: Psychological assessment is not commonly performed nor easily accepted by coloproctological patients. Our aim was to evaluate the psychological component of coloproctological disorders using uncommon tools. METHODS: The 21-Item Depression Anxiety and Stress Scale and the Pescatori projective test were applied to coloproctological outpatients of the Gastroenterology Department of our hospital as well as to healthy volunteers. RESULTS: Seventy patients (median age 47 years, 22 male) divided in 4 groups (functional constipation, constipated irritable bowel syndrome, benign anorectal disease and perianal Crohn's disease) and 52 healthy volunteers (age 45 years, 18 male) completed the tests. Proctological patients showed higher scores of depression (P<0.001), anxiety (P<0.001), and stress (P<0.001) compared to healthy participants. Compared to the control group, patients with functional constipation, irritable bowel syndrome and perianal Crohn's disease maintained the highest scores in all subscales (P<0.05), while patients with benign anorectal disease only had higher anxiety and stress (P<0.001) scores. The patients' also showed lower scores in the Pescatori projective test (P=0.012). A weak association between the projective test and the depression subscale was found (P=0.05). CONCLUSION: Proctological patients had higher scores of depression, anxiety and stress and lower scores in the Pescatori projective test compared to healthy controls.