Wiring aluminum boat

[TerryKing]

Originally Posted by Ike

(..snip..)So Do Not use the hull as a ground. It can be connect to the groundING system for protection from galvanic corrosion and stray currents. But not as a conductor.

Thanks, Peter, for clearing up a lot of things here.

The confusion over "GroundING Conductor" and "GrounDED Conductor" goes around and around in the Industrial Control and Home Wiring fields too.

Peter, what exactly is current practice in commercially-built metal hull boats?

Assuming there is a large Negative (Grounded Conductor) buss bar where all the many onboard loads terminate their negative wire, and also one (or more) Engine Blocks, WHERE does the BONDING conductor from Hull to "Common Negative/Common Ground" go? I would guess the single Negative Buss Bar.

BUT if the engine block has to be mechanically (and electrically) connected to the hull (Through drive train components), what is the best place for the BONDING conductor?

(This probably only makes a difference during engine cranking, when there is high current flowing thru the engine block)..

Oh, and where on a metal hull boat does the Negative BATTERY conductor go? Directly to the engine block, or to the common negative bus, with a large conductor to the engine block?

Oh, and what about multi-engine boats

I don't want to belabor this, but we're real close to a widely-applicable standard convention here...

BTW, thanks for all your hard work on the newboatbuilders website!

[Ike]

Well, I am a member of the Metal Boat Society so I lurk a lot on their forum and occasionally even chime in. http://www.metalboatsociety.org/ I gather from what I have read on their forum that the engine block is used as a common grounded and grounding point. The engine itself is generally isolated from the hull by using mounts that electrically isolate the engine from the engine beds.

The Negative battery conductor is not directly connected to the hull. It goes to the block or to a common negative bus bar. Then a green wire goes from the block to the hull.

Same for multi engine, but a cable connecting the engine blocks is required. This bonding of the engine blocks requires a cable as large as the cable from the battery to the starter. The reason for this is in case there is large current flow. It will carry that current with no difficulty. Without the bond it will fry all the electronics and electrically circuits on the engines. This is required in both the Federal regulations and ABYC.

And they argue about all of this a lot on the Metal Boat Society forum as well. There are people who believe that the hull should be isolated compleletly, that is no green wire for the DC circuits and no bonding of metal fittings. Both sides make valid points but in the long run I think the people who think it should be bonded will win. That's what all the various standards call for.

And thanks for the kudos. I keep working on my website. Keeps me out of bars and away from casinos. (What are you going to do when you're retired?)

[TerryKing]

Originally Posted by Ike

(..snip..) There are people who believe that the hull should be isolated completely, that is no green wire for the DC circuits and no bonding of metal fittings.

I don't think 'isolated completely' happens in a salt air / spray environment! Difference of potential is a Bad Thing, so bonding seems right...

[Ike]

I agree Terry. I was just trying to show that there are still differences of opinion on this.

[Ike]

I was jsut reading an article in Woodenboat Magazine #115 DEC 93. In it, Giffy Full says never bond!. He is of course talking about the chemical corrosion that occurs around metal fastners in wood boats, but in the article he extends that to all boats. Interesting article. "The Bonding Debate". So my point is this is not a new discussion and still goes on. I am on the ABYC electrical committee and they argue about it all the time.

[mydauphin]

Originally Posted by Frosty

You will never ever stop the hull from being grounded (negative).

The engine block is negative it has to be for oil pressure sw ,temp sw, starter. Even if you strap the engine straight to the batt the hull is neg.

(Oh but the engine is on rubber mountings) Ok throttle, stop pull cables. Or even the cooling water in the sea cock.

===================================================
Boats should never be used as a ground or conduit for electricity. Why, because in DC voltage electrons will transfer from one metal to other in a short order, and be trapped and escape and you will be left with a pile of scrap with not one electrons left....

Metal components of AL boats should not be bonded together because dissimilar metals will cause corrosion. ISOLATE AND ZINC

I have an AL boat, my engines are isolated, my sensors are isolated, my starters are air powered and there is rudder isolation between transmission and shafts. My controls are hydraulic and have no engine mounted alternators. My motor mounts are isolate and I have a Isolation transformer for AC to boat. So my engine is electrically neutral. And every electrical component of my boat is isolated from hull.

If this sounds like the rants of mad man, if you have an ALUMINUM boat you better be one or your boat will turn into ALKA-SELTZER.

[mydauphin]

AND MOST IMPORTANT....

NEVER CONNECT ANY PART OF DC AND AC TOGETHER....

Because some devices like chargers have been known to short in such a way to send some live AC thru DC ground and kill people in water or Boat that are AC ground according to ABYC.

[Ike]

And the beat goes on.........

[Mat-C]

Just posted a question here about this very topic....

And as I noted there, I am not exactly technically moned when it comes to onboard electrical systems... so please be gentle with me!
So, if we take an example boat - 30ft long. Aluminium with a single sterndrive.

The ground (black wire) will run from the battery(s) post to the engine block. There will also be a separate wire running to the negative side of the distribution panel. All devices - lighting, pumps etc - will have their negative wires run "back" to here.

The positive (red) wire is fused as close as possible to the battery, then runs to the postive side of the distribution panel and then to all the devices via the switches.

Is it that simple?... or do I have it wrong....?

What about stuff like fuel tanks... should they be grounded?

[Ike]

yes it's that simple. so far you have it right.

[Mat-C]

Thanks Ike!
So how does this differ from a vessel that is not aluminium?

[Ike]

It doesn't differ much. The problem with a metal vessel is you don't want the hull to become a conductor because that introduces stray currents into the water. This results in stray current corrosion and causes parts of your boat, and your neighbors boats to dissappear.

[CDK]

Whether you like it or not, the metal hull IS a conductor, even if you do your very best to isolate all on-board electrical circuits from it.
If the guy in the next berth with a grp hull has lousy wiring with a ground fault, his stern drive will create a voltage differential in the water around both boats. His boat will suffer little or no damage, but the metal hull quickly looses its zincs and the paint starts blistering because there is a voltage differential between the bow and the stern.

@Mat-C:
If the fuel tanks aren't already grounded by fuel lines or the tank element, they should be wired to ground. A common solution is a short wire between the filler neck and the tank. The fuel station attendant clamps his ground wire on a metal part of your boat and expects the fuel tank to be included in the circuit.
This applies to gasoline only, with diesel nothing can go wrong.

[Mat-C]

Ahhh... I see the debate that Ike eluded to when this thread was originally started hasn't abated!

It's certainly hard to imagine how you could possibly isolate a sterndrive &/or the engine it's connected to....
I know all the commercial (aluminium) vessels that I've been aboard have gone to great lengths to try to isolate things like stainless pipework from the aluminium.
Can't say I've ever seen a petrol pump with a ground clamp of any kind....
I gather the wire you refer to is to prevent a spark from igniting fuel vapours - but that's quite different from having the tank grounded to the dc negative.... isn't it...?

[CDK]

Originally Posted by Mat-C

I gather the wire you refer to is to prevent a spark from igniting fuel vapours - but that's quite different from having the tank grounded to the dc negative.... isn't it...?

That's what it's for, yes, but so is grounding metal objects in a boat. No matter how much effort you are prepared to put in, DC negative somewhere is in contact with the hull or finds a low resistance path. The fuel tank sensor normally has a sheet metal flange, internally connected to the negative terminal, so through at least one of the 6 or 8 screws the tank is also connected.

I personally think that creating a spark while filling a tank is next to impossible, but before I measured it myself I also would not have believed that the protective ground from a shore power socket could carry deadly voltages.