How are boat batteries grounded?

[Navy Jr.]

Just a curious question. We have an aluminum boat with an outboard engine. Is the ground for the electrical system on the block of the outboard? Or is there a separate grounding block somewhere inside the boat? Or ?? Thanks. - Ken

 

[timalabim]

Re: How are boat batteries grounded?

Ultimately the ground is the - terminal on the battery.

There may be a common ground within the outboard block for the outboard electric connections, and a common ground in in a terminal block under the dash for dash components, but they would both eventually feed back to the - battery terminal.

 

[Beeched]

Re: How are boat batteries grounded?

One thing that you do NOT want to do!! Do not use the hull on an aluminum boat as the ground connection. If you do, it will set up electrolisys and the hull will begin pitting, then it can get eaten away. Be careful the hull is not part of the circuit.

I learned the hard way!

 

[Silvertip]

Re: How are boat batteries grounded?

Boat batteries are not grounded. The battery in the boat supplies the current requirements for all electrics on the boat. The negative terminal of the battery as previously stated is the central ground point for the entire boat (in a single battery system). The negative battery cable from the engine block runs to the negative terminal of the battery. The positive cable runst to the starter solenoid from the positive post on the battery. The engine electrical harness runs from the engine to the control box at the helm. This harness contains the circuits needed to run the trim, starter, choke/primer, ignition and the gauges. The second circuit is a pair of smaller (usually 10 gauge) wires that run from the battery to a fuse panel at the helm. All branch circuits (accessories) are fed from this panel which generally includes a ground bus. The ground bus is where the smaller black wire from the negative terminal of the battery is connected. So there may be three ground points in the boat. Battery, ground bus, and engine block. Siince the engine is bolted to the hull of the boat an aluminum hull would also be at ground potential but it is not recommended that accessories be grounded to the hull due to the questionable electrical contact and other corrosion possibilities.