Aluminum Boat Battery Wiring + or - ground

[Tanz]

I have a 20' welded aluminum boat with a single 150hp outboard. During the thief of my batteries someone also messed up the wiring for me. While looking for info about re-installing the battery switch, I came across an article by Don Casey:
?The negative side of the battery should be connected to the hull at a single point. All circuits on an aluminum boat must have a positive ground, meaning two wires connecting the appliance to the battery or distribution panel. The hull must never function as an electrical conductor. A single-point ground connection minimizes the likelihood of that occurring, but you must be vigilant to keep the wiring system in good order on an aluminum boat. Keep the copper cable terminal and the aluminum hull separated with a stainless steel washer to prevent galvanic action between the copper and the aluminum.?

Question: What is meant by -All circuits on an aluminum boat must have a positive ground, and what is the difference between a positive ground and negative ground.
Tanz

 

[Dunaruna]

Re: Aluminum Boat Battery Wiring + or - ground

The actual term 'positive ground' refers to an archaic practice of using the positive battery terminal as a common ground and switching the negative terminal. LUCAS was famous for doing this.

These days, ALL 12v circuits in cars and boats made in first world countries are negative ground systems, no exceptions (maybe some backwater POS Russian car maker uses positive ground, dunno).

Don Caseys' article could be easily mis-read. I think that he is using the term 'positive ground' to describe a good quality, individual ground.

The upshot is, the hull should not be used as a common ground but it should be bonded to the negative terminal of the battery (unless the motor is mounted on plastic or timber, it is already bonded to the hull). Each separate circuit should have a direct path to the negative terminal of the battery via wires, not hull.

 

[pvanv]

Re: Aluminum Boat Battery Wiring + or - ground

Yes, agreed. Casey could have worded the phrase better. He meant to say a Reliable ground -- not to be confused with the (+) side of the DC circuit.

It will be Negative Ground. Each device will be individually grounded -- NOT using the hull as a ground path, which invites corrosion.

 

[Wee Hooker]

Re: Aluminum Boat Battery Wiring + or - ground

Wow, have to agree. That's some awfully reckless wording for a technical artical regarding battery polarity. That should have NEVER made it through edit!

Still not even sure I agree that you should ground the hull either. If all your circuts are to/from battery/battery switch. I don't see the point (especially since your motor is grounded). Admittedly I'm new to electrical systems on aluminum boats ( but am getting ready to rig my 16' Mirrocraft soon.)

 

[Silvertip]

Re: Aluminum Boat Battery Wiring + or - ground

Yes the motor is grounded to the hull when it is bolted up. The idea is not that the hull "cannot have a ground", it "should not" have a bunch of separate ground points. In other words don't ground all of the electrical devices at different points on the hull. There should really be only three ground points. 1) Engine block, 2) Battery negative, and 3) the negative buss on the breaker/fuse panel. 4) if you count the hull.

 

[Wee Hooker]

Re: Aluminum Boat Battery Wiring + or - ground

Silvertip, I understand the motor is grounded to the hull (and water) and that all ground leads should return to the neg side of the battery (or battery switch). I'm not clear on whether your saying that the abovementioned practice of grounding the battery is acceptable or not. (By my way of thinking, that would cause a current path from that location and invite galvanic corrosion. i.e. I would guess that the battery should be isolated from any direct path to the hull.) Yes/no??

 

[Silvertip]

Re: Aluminum Boat Battery Wiring + or - ground

First -- there is no ground side of a battery switch so please lose that terminology. If you are thinking COM on the battery switch is ground, better have a fire extinguisher handy. I hate that term on those switches and the person that did it should be flogged. COM on a battery switch is really the single, +12V output of the switch. Every POS lead from every accessory on the boat,except for the bilge pump, should be connected to that terminal.

Now then -- lets consider grounds. Let's try and clarify the difference between "physical location" of ground points and "electrical paths". So here goes. A ground wire from any electrical device should NOT be "physically connected" to the hull of a tin boat. Those grounds should be connected to one of two points: 1) the negative buss on the fuse/breaker panel, or 2) the negative terminal of the battery. The negative terminal of the battery has only one attachment point and that is the engine block via the large gauge battery cable. Now then -- if you use and ohm meter and check for continuity between the negative terminal on the battery and the hull, between the negative buss on the fuse/breaker panel and the hull, or between the engine block and the hull you would indeed find continuity. That means "electrically" a path exists between these elements, but it occurs only through the engine mounting bolts which is not an especially good ground. Even though that "electrical" path exists, it is recommended that you NOT ground anything, including the battery DIRECTLY to the hull. To carry this just a little bit farther, boats typically have two basic wiring systems. 1) the engine harness going to the control box up front, and 2) the boat wiring harness that feeds the fuse/breaker panel. There are ground wires in both harnesses. The engine harness ground terminates at the engine block while the boat harness ground terminates at the negative terminal of the battery. Battery negative, the engine block, and the breaker panel ground buss are from an electrical standpoint, all the same since they are connected together by wire, not the boat hull. This was a long answer to a short question but I hope it helps you understand the grounding issue.

 

[Wee Hooker]

Re: Aluminum Boat Battery Wiring + or - ground

Thanks, your clarification confirms my thoughts.
p.s. I get the whole common/ground/electrical path thing. I'm a mechanical engineer by degree/trade. I just avoid / routinely pass on my electical questions to those who know best.

 

[Tanz]

Re: Aluminum Boat Battery Wiring + or - ground

If the reasons for all the precautions in wiring an aluminum boat is to prevent accelerated corrosion, then I wonder how many unsuspecting aluminum boat owners are sitting on a potential time-bomb. One of the main reasons they bought them, me included, was because they were lead to believe their aluminum is virtually indestructible, will not rust and can last a lifetime. I wonder how long it would take for some of these expensive boats sitting in a salt-water slip to corrode to the point of no return and I would assume that a lot of that corrosion could also be in the form of pinholes throughout the hull. It seems that many people have difficulty grasping the grounding issue and treat their aluminum boat as though it was a metal car. There might be more than a few cheap aluminum boats for sale in a few years.

Tanz

 

[Silvertip]

Re: Aluminum Boat Battery Wiring + or - ground

Aluminum boats have been around since Hector was a pup so corrosion is not an issue. What is more of an issue (galvanic) is if the boat has grounding issues and is plugged into shore power or there is shore power at the dock.

 

[Tanz]

Re: Aluminum Boat Battery Wiring + or - ground

Yes, like expensive alumunim boats sitting in a salt-water slip

 

[Wee Hooker]

Re: Aluminum Boat Battery Wiring + or - ground

FWIW I had a buddy who bought a brand new 14' (98?) Lund fisherman. He had it dealer rigged with a finder and electric start honda. Within 3 years of mixed /fresh and SW use, the floor rivits were corroded through and popping loose. I figured it had something to do with his electrical system but he never got a straight answer (or satisfaction ) from Lund/dealership. ( One of the reasons i bought another brand when I went shopping.)

 

[Peter Eikenberry]

Re: Aluminum Boat Battery Wiring + or - ground

Silvertips explanation is the best, but I would break it down this way. Envision one simple circuit. A battery, a wire from the positive terminal (red for positive) to a switch, another red wire from the switch to a light socket. A light in the socket. Another wire (black for negative) from the light socket back to the negative terminal of the battery. When the switch is on current flows around the circuit. That's the basic circuit. But on a metal boat some people advocate a wire running from the negative terminal of the battery to the hull. Normally this wire does not carry any current. The only time it carries current is if there is ground fault or there are stray currents in the water around the boat.

I am not one of the advocates. I think that if there were a ground fault ( a positive wire touching a metal casing somewhere) then you would have current in the wire introducing current into the hull resulting in stray current corrosion, and causing galvanic corrosion of some part of the boat or engine. This happens to be very controversial and I have seen the ABYC electrical committee agrue about it for years.

Plus it would seem to me that on an outboard powered boat the metal of the engine is already in direct contact with the hull. The negative and positive from the battery go to the outboard, and inside the engine the negative is connected to the metal casing of the engine (thus also connected to the hull). So why a redundant wire connecting the negative to the hull?

On inboards, normal practice is to run the wire from the neg terminal to the engine block and the engine block becomes ground. So all grounds eventually go back to the engine block. What's different about the outboard engine being the ground? nothing electrically. So I woukd simply leave out the wire from the battery negative to the hull because it is redundant.

 

[Silvertip]

Re: Aluminum Boat Battery Wiring + or - ground

You missed the point. We are indicating that no boat manufacturer ties battery negative to the hull of the boat. It is individuals who don't understand the consequences that do that. The negative post on what I will call a recreational aluminum boat runs from the battery to the negative buss on the fuse/breaker panel. The large cable connects to the engine block. It is only when the engine is bolted to the transom that the ground to hull occurs (maybe) since the hull is normally painted. My pontoon for example has a full aluminum engine mount so the second the engine was bolted on a very good ground path was formed. My walleye boat however has a painted transom and while it also shows continuity between the hull and engine block, I would not assume that is always a good ground path. The ground from the engine block to the control box on the helm is necessary for operation of the various alarms, the tach, and trim controles. The hull harness feeds the console, instruments, and accessories. It is during installation of accessories that techs and boat owners that are electrically challenged tie accessory grounds to the hull.

 

[HVSTRINE]

Re: Aluminum Boat Battery Wiring + or - ground

The ground from the engine block to the control box on the helm is necessary for operation of the various alarms, the tach, and trim controles. The hull harness feeds the console, instruments, and accessories. It is during installation of accessories that techs and boat owners that are electrically challenged tie accessory grounds to the hull.

That pretty much says it all right there.

 

[sschefer]

Re: Aluminum Boat Battery Wiring + or - ground

I wish everyone would stop using the term grounds. Grounds are for use in a A/C environment where 55-62 times per second the line voltage swings (cycles) from negative to positive and back again... If you need more info there's plenty on the internet.

There is no such need in a closed loop battery environment where negative is always negative and positive is always positive.

1. Theory: Electrons flow from negative to positive.
2. To create a complete circuit you need to allow electrons to flow from negative to positive.

Hooking the negative side of the battery terminal to any portion of an aluminum boat, including the motor is doing nothing more than extending the negative terminal of the battery. When you use your aluminum boat hull as part of your electrical circuit, electrons will flow throught it and you will cause electrolysis.

If you isolate your motor from the hull with an insulator like non conductive rubber and paint the bolts that pass through the hull your motor will run fine and that nasty electrolysis problem at the transom will all but dissappear. The negative terminal of your battery should be connected to the motor at the designed engne connecting point.

All other load causing electrical devices should be connected in a complete circuit from negative to positive. When a switch is in the circuit, it should be placed on the positive side of the circuit.

If you extend the terminals of the battery to remote terminal blocks the wire should be of sufficient diameter to carry the load of all the devices connected to the terminal blocks. 14ga=15amps, 12ga=20amps, 10ga=30amps, 8ga=40amps and 6ga=50amps.

Does that clarify it better or did I just repeat a prior post somewhere.. Yeah I did.

 

[Peter Eikenberry]

Re: Aluminum Boat Battery Wiring + or - ground

In boat electrical systems, especially in ABYC, ISO, NFPA and other standards, the term grounded wire is commonly used to indicate the negative side of a two wire DC system. However, many boats now have a three wire electrical system on both AC and DC. The third wire is green and is called the GROUNDING wire as opposed to GROUNDED wire which is the negaive side of the DC system.

Silvertip, you're right, I went back and read that over again. I guess I was just really tired (look at the time I posted).

Oh yeah and while we are on the matter of terms, electrolysis is incorrect. It is galvanic corrosion, also called stray current corrosion. Electrolysis is actually the reverse of galvanic corrosion (or a means of removing unwanted hair LOL).

 

[Silvertip]

Re: Aluminum Boat Battery Wiring + or - ground

And when dealing with grounding issues down under (as in Australia for example) be prepared to deal with "earthing" in AC systems. How about we let this issue die. It's been nearly beaten to death anyway.

 

[sschefer]

Re: Aluminum Boat Battery Wiring + or - ground

Oh yeah and while we are on the matter of terms, electrolysis is incorrect. It is galvanic corrosion, also called stray current corrosion. Electrolysis is actually the reverse of galvanic corrosion (or a means of removing unwanted hair LOL).

Nope, not wrong, galvanic corrosion occurs between dissimilar metals. Although it is quite similar it is what's going on inside the battery not outside.
Michael Faraday, 1832, First law of electrolysis.

 

[pvanv]

Re: Aluminum Boat Battery Wiring + or - ground

In boat electrical systems, especially in ABYC, ISO, NFPA and other standards, the term grounded wire is commonly used to indicate the negative side of a two wire DC system. However, many boats now have a three wire electrical system on both AC and DC. The third wire is green and is called the GROUNDING wire as opposed to GROUNDED wire which is the negaive side of the DC system.

The Green wire is the BONDING wire. Separate issue entirely, and deals with corrosion of dissimilar metals (such as through-hulls) that are fastened to the hull below the waterline, and can include lightning bonding, such as in a sailboat's mast and rigging.

The DC Negative wire (used to always be Black, now ABYC prefers Yellow to avoid confusion with the AC hot side) is appropriately called the Ground (or for British types, Earth). Again, not to be confused with any of the AC wires, including the White AC Neutral or Green AC Ground.

As an EE and code enforcement officer, I feel these distinctions are important, but not necessarily germane to the accessory grounding thread. Maybe wiring standards should be a separate and/or sticky thread in this forum.