Marine Technology Group

Galvanic Isolation Kits 

 
 

GALVANIC ISOLATION KITS 
 
 

The H/RI Galvanic Isolation kits are intended for use for aluminum vessels equipped with sacrificial anodes.  For vessels equipped with an impressed current galvanic control system contact H/RI with the details for assistance.  These kits are available for all models of the Arneson Surface Drive.

All of the H/RI Isolation Kits are intended to be used when mounting ASD units on aluminum vessels.  The purpose of the kit is to galvanically isolate the ASD units and cylinders from the transom of the vessel.

The most effective method of mounting the ASD system on an aluminum hull would be to have the ASD system totally isolated (electrically) from the hull and machinery.  The hull would then have its own sacrificial anodes and the ASD equipment would be tied into their own sacrificial anodes.

The method of total isolation is not always practical, having to electrically isolate the drivelines from the transmissions, isolate the feedback mechanisms from the cylinders, isolate the hydraulic hoses, etc.  Any electric contact would furnish a current path.  An alternative, although not as good, would be to isolate the ASD units from the hull and electrically bond the ASD system to the existing ships bonding system.  Additional sacrificial anodes should be mounted on the transom, in the proximity of the ASD units.  In this case, care should be taken to monitor the time and amount of deterioration on the sacrificial anodes, as well as detailed inspections of the aluminum structure immediately surrounding the ASD mounting locations, to insure that adequate protection is being provided.

Galvanic isolation is accomplished by mounting the ASD thrust socket and cylinders on a sheet of plastic to electrically isolate the ASD components from the hull.  In addition to isolating the ASD components, all penetrations from bolts, pipe penetrations and thru-hulls must also be isolated.  These components are galvanically isolated by using plastic bushings where these components come into contact with the transom.  For penetrations that are not structural, such as the lube and hydraulic oil pipe penetrations from the thrust socket and the cylinders, a clearance hole through the transom is sufficient to eliminate any electrical contact.  Reference H/RI drawing N^o: 2J2002-4 for a typical transom penetration.

Once the ASD units and cylinders are mounted on the vessel, electrical continuity should be checked between the thrust socket and the hull, trim cylinder and the hull and the steering cylinder and the hull using an ohmmeter.  There should be no connection.

Electrical connections from each ASD transom penetration such as the trim cylinder, steering cylinder and thrust socket must be individually bonded to the respective anode or ships bonding system.  Care should be taken in the installation of the bonding wire and end connectors to insure that all connections are performed with minimal resistance.  The current flowing through this circuit is quite low, with any resistance at the connections reducing the voltage between the ASD system and the zinc anodes, with a corresponding reduction in protection..

It is recommended that the ASD units (if bronze) be painted with an electrical barrier paint such as an epoxide or vinyl resin base to keep the exposed area [of the most noble metal] to a minimum, reducing the surface area of the galvanic cell.  Thickness of the coating should be based on recommendation from the manufacturer, but approximate thickness of 150-200µm can be used as a guideline.