Marine Antifouling

SeaLite Engineering, Inc., is a 34 year-old R&D company that has focused on new ways of oceanographic sensing that minimize the ocean’s natural and aggressive tendency to foul instrumentation. Long deployments of sensors and instruments and the use of autonomous underwater vehicles (AUVs) have increased the importance of protection from fouling, now often the limiting factor in deployment durations.

SeaLite’s Chlorine Microshield has been developed to provide that protection.

Figure 1. Buzzards Bay estuary fouling of external instrument housing after 21 days in July.
Figure 2. Clam Bayou, Gulf of Mexica sensor fouling after 21 days in July.

The Technology
SeaLite has developed patented technology* for preventing the fouling shown above. It uses: 
(1) selective halogen electrolysis of seawater*, 
(2) density-driven boundary layer flow*, 
(3) early stage biofilm intervention*, 
(4) conformable, stable electrodes*.
(5) microshield driver electronics that provide a fixed cycle, are controllable
from on- board biofilm sensors or remotely*,
(6) unmeasurable toxic residue.

This technology has undergone extensive testing and at-sea deployments since 2015, first in a Buzzards Bay, Massachusetts estuary and, independently, in a University of South Florida station in a Gulf Coast Bayou. These both involved year-long deployments, and intercomparisons with other techniques of antifouling.

A prototype Chlorine Microshield was installed in the sensor guard of a YSI 5-sensor instrument (the EX01). This instrument was then deployed in Clam Bayou, Florida, in May 2015; the sensors are shown in figures 4, 5, and 6 after 2, 3 and 5 months. The thin, planar and formable electrodes have also been adapted to protect mooring lines and a transmissometer.

The improvements that the Chlorine Microshield provides over other antifouling methods are: durability over long deployments (> 1 year), low power consumption, large area and full-instrument protection.

Chlorine Microshield Operation
The protection can be turned on locally, or remotely, to balance energy consumption with the level of protection needed in seasonal or variable fouling environments. To further save power, an on-board controller can set the frequency and duration of the electrolysis, for example, once-a-day for 10 minutes in northern latitudes and twice-a-day at a higher current in the tropics. Figure 3 provides a schematic and circuit diagram for both density-driven and forced convective boundary layer shields.

Figure 3. Chlorine Microshield schematic and electrical circuit for forced and natural boundary layer shield operation.

Experimental Results at-Sea

Figure 4. Chlorine Microshield YSI sensor protection after 2 months in Clam Bayou, Gulf of Mexico. This compares with Figure 2 of the same YSI sensors in Clam Bayou after only 21 days, but unprotected.
Figure 5. Chlorine Microshield YSI instrument protection after 3 months in Clam Bayou, Gulf of Mexico, one end protected, one not.
Figure 6. Chlorine Microshield instrument sensors protection at the bulkhead after 5 months in Clam Bayou, Florida.

Ongoing Development
To further conserve power, an internal fluorescent biofilm sensor system is being developed directed at the surface to be protected. It will turn on the electrolysis when the surface biofilm reaches the EPS growth point.

Custom Design: SeaLite Engineering offers custom configuration of electrodes to specific applications for customers who desire fouling protection for sensors, instrument housing and AUV control surfaces.

Sealite Engineering
508 564 4404,
19 Mystery Lane, Box 401
Cataumet, MA. 02534
*U.S. Patent No. 9,090,492 of June 19, 2015
*U.S. Patent No. 9,371,243 of June 21, 2016 
*U.S. Patent No. 10,407,323 of September 10, 2019 One U.S. Patents Pending.

Publications: Seaver, G. and D. Butler, 2021: Antifouling with Chloride Ion Electrolytic Recycling through a Momentum Boundary Layer. Journal of Atmospheric and Marine Technology, 38(10), October 2021, Vol. 38 (10).