Preventing Marine Fouling

This invention relates to alleviating fouling of boats and ships from marine creatures such as barnacles.

A persistent problem with boats and ships has long been marine fouling. Various attempts have been made to alleviate such fouling from such creatures as barnacles.

An attempt to that end by ultrasonic vibration of ship hulls, with oscillators coupled inside the hulls, was disclosed in a Russian publication: "Transactions. Technical Operations of the Maritime Fleet. Thermochemical Studies. Control of Corrosion and Fouling. Central Scientific Research Institute of the Maritime Fleet No. 160, 1972."

Piezofilm, so called polymer sheet producing mechanical deformation in both lengthwise and thickness (and widthwise) directions when subjected to voltages therethrough, is disclosed in Murayama et al. U.S. Pat. No. 3,792,204, "Acoustic Transducer Using a Piezoelectric Polyvinylidene Fluoride Resin Film as the Oscillator", granted Feb. 12, 1974, and in a brochure "Kureha KF Piezofilm", published by Kureha Chemical Industry Co., Ltd.

Other attempts at antifouling devices are disclosed in Taylor U.S. Pat. No. 2,435,986, "Antifouling Device", granted Feb. 17, 1948.

It has been discovered that a highly effective, practical, relatively inexpensive antifouling result using relatively little energy can be achieved by energizing piezofilm carried on the outside of a vessel. In preferred embodiments the piezofilm is secured in upwardly extending spaced strips therealong.

The structure and operation of a presently preferred embodiment of the invention are as follows.

The drawings show the preferred embodiment, then described.

FIG. 1 is a perspective view of a boat hull embodying the invention;

FIG. 2 is an enlarged, perspective view, partially in section, of the portion of the hull indicated in dotted lines in FIG. 1, with circuitry indicated; and

FIG. 3 is a cross-sectional view of a portion of the hull and a portion of one strip assembly of FIG. 2.

A yacht indicated generally at 10 (FIG. 1) has secured to it a multiplicity of strip assemblies indicated generally at 12. Each strip assembly 12 includes a length 14 of piezofilm (FIG. 3) formed of polarized polyvinylidene fluoride, 30 cm. wide and 30 microns in thickness; the piezoelectric coefficients of the piezofilm length are 20 picocoulombs per Newton, in both longitudinal and thickness directions. The strip assemblies 12 are secured to the hull of the yacht with double-sided adhesive silicone tape (Densil brand) strip members 16; and over each piezofilm length is another length of adhesive silicone tape strip 18. On the inside and outside of the piezofilm layer, except along a 1 mm border therearound for insulation, is a thin corrosion resistant electrode layer of sputtered Monel 15, 17. Strip assemblies 12 extend generally transversely of the hull, spaced on 30 cm centers, thus overlying less than half the area of the hull. Conventional epoxy paint 19 is then applied over the whole.

Wires 20 and 22 (FIG. 2) running along the top of the hull are connected respectively to leads 24 and 26 connected through conductive, flexible adhesive (CHO-Bond 1038) respectively to front and back strip assembly electrodes, and to 20 volt a.c. power supply 28. Power capacity is 30 to 100 watts, for yachts of 8 to 25 meters. Sinusoidal voltage output frequency is 5 KHz, although other frequencies may be used, as to avoid audio interference.

In operation, when vessel speed is anything less than 3 knots, energization of the power supply produces longitudinal, transverse, and thickness-wise mechanical vibration of the piezofilm and hull which turns out to be highly effective in discouraging fouling through deposit of marine life such as barnacles, bryozoan, marine worms, and mussels.

Other embodiments within the scope of the invention will occur to those skilled in the art.