Boat Wiring and Common Ground.

[jdmidwest]

I have gutted a Tracker Panfish boat and building back from scratch to Jet Boat 2.0.  I will be wiring it with all new wire.  One trolling battery and one start/accessory battery.  I am also converting my Crappie Pro from 12v trolling to 24v trolling motor also and came across this in the manual for the trolling motor.

Establishing a Common Ground
MotorGuide recommends isolating the trolling motor battery/batteries from the
main engine battery.
Electrolysis Issues – Using the engine starting battery as a source of power
for any trolling motor may cause electrolysis on metallic parts.
􀀹 If you have followed the battery wiring and installation instructions in
this manual and your boat continues to have electrolysis issues, you
will need to separate the trolling motor from any other boat electronics.
􀀹 Remove the engine starting battery from the wiring configuration of the
boat and isolate the power circuit for your trolling motor.
Establish a Common Ground: Common ground means the ground for
the main engine accessories and your trolling motor are connected to the
same negative ground terminal.
Not having a common ground can cause severe corrosion or electrolysis.
If left unchecked, damage may be caused to your trolling motor and boat.
Establishing a common ground connection will allow increased sensitivity
and improve detail on a sonar display.

I have a ground bus bar for new boat build.  Do I need to connect to each negative post of each battery to the bus bar?  This common ground and the Electrolysis issue is something I have never seen in the Aluminum boats, but sounds pretty nasty.  As far as I can tell, factory wiring does not seem to follow this rule that Motorguide recommends.  I do isolate the trolling battery to only trolling.

[fishinwrench]

Over engineering at it finest. 🙄 

For a 12v system in an aluminum boat a single Group 27-DP is all you need.   

No electrolysis issues or galvanic corrosion can occur since the TM is typically out of the water any time the outboard key switch is ON.  The rare occasion when you might idle across a cove with the TM down isn't going to amount to anything ever noticable.

To avoid distortion feedback on any dash or bow mounted sonar unit just route the 2 TM power cables ALONE along the port side of the boat, and route everything else (engine harness, sonar power and transducer cable, lights, bilge/livewell pumps, steering cable, ect.) along the starboard side.   

Avoid running any wires along the floor or under the flooring.....Keep them all up along the gunnels.  

This works fine even on narrow 36-42" wide aluminum boats. 

[jdmidwest]

So the galvanic action occurs when both batteries ground to water, both motors down?  My buddy does that alot in his boats.  What about kicker motors on bigger rigs, both hit the water some.

Main motor has the anode on the lower unit, troller has none that I have ever seen.  Does that come into play in this mix?

 

[fishinwrench]

As I understand it, the corrosion is a result of dissimilar metals sharing electrons via WATER.....which is a semi-conductor.  It can happen even if no battery(s) are onboard.    

In my time, dealing with boats everyday for going on 40 years, the only serious corrosion damage I've witnessed has been on boats/motors that are left in the water for extended periods of time, and left tied to metal frame docks with electrical circuits that are improperly grounded.  

[MrGiggles]

The hull on an aluminum boat is always going to be grounded to the starting battery via the outboard. Perhaps they want you to run a common ground as a path of least resistance. 

I've never done it. I prefer them to be totally isolated. If your outboard has a sturdy recoil, and you're able to use, you can use one battery. I wouldn't if electric start is all you have to crank it. 

[jdmidwest]

I will be running 2 battery systems.  3 on big boat, never tried to pull start the 50hp, but upgrading to 24v troller.

My trolling motors are isolated from the hull with the rubber spacers.  The more saline the water is has a difference in the electrolysis I think.  There was a thing in high school where we made a salt water battery reaction.

I have had interference with the sonar on the bigger boat, but I think it was cross talk between the transducers.  One was a bird and the other Lowrance.  I switched to Garmin and Lowrance and have clear pics.