bassemir wrote:Q1: what is the purpose of the disk on the transom on my 1991 OUTRAGE.
The purpose the metal disk (or disc) is to create an electrical connection to the sea. The disk is made of bronze. It is not intended to be a sacrificial anode. The disk is an electrode. The reason for using bronze is precisely to PREVENT erosion of the metal disk by galvanic corrosion. To this disk a copper wire is connected. A number of other metal components of the boat are also electrically connected to the disk.
bassemir wrote:Q2: is the purpose of the disk important?
The purpose of the disk [or disc] is to establish a voltage potential that would typically be referred to as "ground" but since the boat is at sea, it is the potential of the sea. The disk works better in saltwater than in freshwater because saltwater is a better electrical conductor than very pure freshwater. The disk becomes part of an electrical circuit when the green wire is connected to the disc.
THE PURPOSE OF THE WIRE CONNECTED TO THE DISK
The wire connected to the disk becomes part of a circuit that connects to the metal fuel tank, the metal fuel inlet filler fitting, and the metal vent fitting. The purpose of this electrical circuit is to maintain all the elements of the fuel system that are conductive at the exact same voltage. This is VERY IMPORTANT. This circuit is the fuel tank bonding circuit
WHY THE FUEL TANK AND OTHER METAL COMPONENTS OF THE FUEL SYSTEM ARE BONDED TOGETHER
Gasoline fuel is an extremely good insulator of electrical current. When gasoline fuel is flowing from the fuel dispensing nozzle into the fuel filler hoses and into the tank, it is possible for an electrical charge (a "static" charge) to be created from the motion because the fuel itself is not conductive in any way. This is called the
TRIBOELECTRIC EFFECT. In order to prevent a build up of electrical charge, the metal components are joined together by very low resistance wire. This is why a 10-AWG wire is used. The wire has green insulation in order to identify it as a ground or bonding circuit.
WHY THE CIRCUIT IS ISOLATED
This circuit is never connected to any other electrical wiring in the boat. It remains isolated, and is only connected to the transom electrode. There should never be any current flowing on this circuit related to current flow from or to the boat battery. The only current flowing will be the discharge of any static electricity before it can build up any voltage difference between the conductive parts of the fuel system.
YOUR REMEDY TO REPAIR THE DEFECT YOU HAVE DISCOVERED
I recommend you reestablish the connection of the wire with green insulation to the bronze anode on the transom.
bassemir wrote:I see the wire going up the [rigging] tunnel towards the console, but I do not see it come out under the console.
That is normal. The green wire does not connect to any other electrical circuit in the boat. It only connects to the metal components of the fuel system: the filler inlet fitting, the vent fitting, the metal tank fuel tank, and the bronze disk on the transom.
SOME HISTORY
For many years all Boston Whaler boats that had below deck internal aluminum fuel tanks and associated fuel filler fitting and tank vent fittings were electrically connected together using a rather large 10-AWG copper wire with green insulation (or in some later years with yellow insulation). This practice continued into the 1990's, as evidenced by the appearance of the bronze anode on a 1991 model year boat. At some point--I do not know the exact epoch--Boston Whaler stopped installing the bronze transom electrode. After than, the fuel bonding circuit was connected to the battery negative because the battery negative would be connected to the outboard engines chassis, and the outboard engine chassis would be in contact with the sea via the exposed electrodes on the underwater portions of the outboard engine gear case and mounting bracket, which are, indeed, sacrificial anodes, but in the case of the fuel bonding circuit are just a substitute for the bronze electrode previously used.
There may have been some change in the recommendations of the American Boat and Yacht Council regarding the acceptable methods for bonding the fuel system metal components together and how that circuit would be connected to the sea which might have changed Boston Whaler's method for providing the fuel bonding circuit connection to the sea. I really have not researched this. Or, they might have decided to save money and eliminate the bronze anode and running an extra wire over the transom. I am sure that when the use of the overboard disk electrode ended, a Boston Whaler boat was still in full compliance with any USCG regulations or ABYC recommendations.
